Amygdala#Structure

File:Mouse Amygdala.pdf

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Thirteen nuclei{{Cite journal |last=Pabba |first=Mohan |date=2013-08-28 |title=Evolutionary development of the amygdaloid complex |journal=Frontiers in Neuroanatomy |language=English |volume=7 |page=27 |doi=10.3389/fnana.2013.00027 |doi-access=free |issn=1662-5129 |pmc=3755265 |pmid=24009561}} have been identified, each with their own subdivisions and distinct connections to the rest of the brain.{{cite journal | pmid=22806915 | date=2013 | last1=Bzdok | first1=D. | last2=Laird | first2=A. R. | last3=Zilles | first3=K. | last4=Fox | first4=P. T. | last5=Eickhoff | first5=S. B. | title=An investigation of the structural, connectional, and functional subspecialization in the human amygdala | journal=Human Brain Mapping | volume=34 | issue=12 | pages=3247–3266 | doi=10.1002/hbm.22138 | pmc=4801486 }} The chief nuclei are the basolateral complex, the central nucleus, the cortical nucleus, the medial nucleus, and the intercalated cell clusters. The cortical and medial nuclei connect with the olfactory system and hypothalamus. The central nucleus has extensive projections to the brainstem.

The basolateral complex can be further subdivided into the lateral, the basal, and the accessory basal nuclei.{{cite web|author=Ben Best|year=2004|title=The Amygdala and the Emotions|access-date=15 March 2007|url=http://www.benbest.com/science/anatmind/anatmd9.html| archive-url= https://web.archive.org/web/20070309132748/http://www.benbest.com/science/anatmind/anatmd9.html| archive-date= 9 March 2007 | url-status= live}}{{cite journal | vauthors = Solano-Castiella E, Anwander A, Lohmann G, Weiss M, Docherty C, Geyer S, Reimer E, Friederici AD, Turner R | title = Diffusion tensor imaging segments the human amygdala in vivo | journal = NeuroImage | volume = 49 | issue = 4 | pages = 2958–65 | date = February 2010 | pmid = 19931398 | doi = 10.1016/j.neuroimage.2009.11.027 | hdl = 11858/00-001M-0000-0010-ABE5-F | s2cid = 17137887 | hdl-access = free }} It has extensive connections with higher-order cortical areas in the prefrontal, temporal, insular cortices, and the hippocampus.{{cite book |last=McDonald |first=Alexander J. |title=Handbook of Behavioral Neuroscience |date=2020 |publisher=Elsevier |isbn=978-0-12-815134-1 |volume=26 |pages=1–38 |chapter=Functional neuroanatomy of the basolateral amygdala: Neurons, neurotransmitters, and circuits |doi=10.1016/b978-0-12-815134-1.00001-5 |pmc=8248694 |pmid=34220399}} The basolateral complex is surrounded by the intercalated cell net that is inhibitory and projects to a broad variety of areas in the basal forebrain, hypothalamus, and the amygdala.{{cite journal |last1=Stern |first1=Daniel B. |last2=Wilke |first2=Anna |last3=Root |first3=Cory M. |date=2023 |title=Anatomical Connectivity of the Intercalated Cells of the Amygdala |journal=eNeuro |volume=10 |issue=10 |pages=ENEURO.0238–23.2023 |doi=10.1523/ENEURO.0238-23.2023 |issn=2373-2822 |pmc=10576262 |pmid=37775310}}

The right and left portions of the amygdala have independent memory systems, but work together to store, encode, and interpret emotion.

The right hemisphere of the amygdala is associated with negative emotion.{{cite journal | vauthors = Barrett LF, Bliss-Moreau E, Duncan SL, Rauch SL, Wright CI | title = The amygdala and the experience of affect | journal = Social Cognitive and Affective Neuroscience | volume = 2 | issue = 2 | pages = 73–83 | date = June 2007 | pmid = 18392107 | pmc = 2288526 | doi = 10.1093/scan/nsl042 }}{{cite journal | vauthors = Berntson GG, Bechara A, Damasio H, Tranel D, Cacioppo JT | title = Amygdala contribution to selective dimensions of emotion | journal = Social Cognitive and Affective Neuroscience | volume = 2 | issue = 2 | pages = 123–9 | date = June 2007 | pmid = 18414599 | doi = 10.1093/scan/nsm008 | pmc = 2293306 }} It plays a role in the expression of fear and in the processing of fear-inducing stimuli. Fear conditioning, which occurs when a neutral stimulus acquires aversive properties, occurs within the right hemisphere. When an individual is presented with a conditioned, aversive stimulus, it is processed within the right amygdala, producing an unpleasant or fearful response. This emotional response conditions the individual to avoid fear-inducing stimuli and more importantly, to assess threats in the environment.

The right hemisphere is also linked to declarative memory, which consists of facts and information from previously experienced events and must be consciously recalled. It also plays a significant role in the retention of episodic memory. Episodic memory consists of the autobiographical aspects of memory, permitting recall of emotional and sensory experience of an event. This type of memory does not require conscious recall. The right amygdala plays a role in the association of time and places with emotional properties.Markowitsch, H. (1998). Differential contribution of right and left amygdala to affective information processing. IOS Press. 11(4), 233–244.

In one study, electrical stimulations of the right amygdala induced negative emotions, especially fear and sadness. In contrast, stimulation of the left amygdala was able to induce either pleasant (happiness) or unpleasant (fear, anxiety, sadness) emotions.{{cite journal |vauthors=Lanteaume L, Khalfa S, Régis J, Marquis P, Chauvel P, Bartolomei F |date=June 2007 |title=Emotion induction after direct intracerebral stimulations of human amygdala |journal=Cerebral Cortex |volume=17 |issue=6 |pages=1307–13 |doi=10.1093/cercor/bhl041 |pmid=16880223 |doi-access=}} Other evidence suggests that the left amygdala plays a role in the brain's reward system.{{cite book |title=The Human Amygdala |vauthors=Murray EA, Izquierdo A, Malkova L |publisher=Guilford Press |year=2009 |chapter=Amygdala function in positive reinforcement}}

{{See also|Neuroscience of sex differences}}

The amygdala is one of the best-understood brain regions with regard to differences between the sexes. The amygdala is larger in males than females, in children aged 7 to 11,{{cite journal|vauthors=Caviness VS, Kennedy DN, Richelme C, Rademacher J, Filipek PA|year=1996|title=The human brain age 7-11 years: a volumetric analysis based on magnetic resonance images|journal=Cerebral Cortex|volume=6|issue=5|pages=726–36|doi=10.1093/cercor/6.5.726|pmid=8921207|doi-access=}} adult humans,{{cite journal|vauthors=Goldstein JM, Seidman LJ, Horton NJ, Makris N, Kennedy DN, Caviness VS, Faraone SV, Tsuang MT|date=June 2001|title=Normal sexual dimorphism of the adult human brain assessed by in vivo magnetic resonance imaging|journal=Cerebral Cortex|volume=11|issue=6|pages=490–7|doi=10.1093/cercor/11.6.490|pmid=11375910|doi-access=free}} and adult rats.{{cite journal|vauthors=Hines M, Allen LS, Gorski RA|s2cid=171083|date=May 1992|title=Sex differences in subregions of the medial nucleus of the amygdala and the bed nucleus of the stria terminalis of the rat|journal=Brain Research|volume=579|issue=2|pages=321–6|doi=10.1016/0006-8993(92)90068-K|pmid=1352729}}

There is considerable growth within the first few years of structural development in both male and female amygdalae.{{cite journal | vauthors = Uematsu A, Matsui M, Tanaka C, Takahashi T, Noguchi K, Suzuki M, Nishijo H | title = Developmental trajectories of amygdala and hippocampus from infancy to early adulthood in healthy individuals | journal = PLOS ONE | volume = 7 | issue = 10 | pages = e46970 | year = 2012 | pmid = 23056545 | pmc = 3467280 | doi = 10.1371/journal.pone.0046970 | bibcode = 2012PLoSO...746970U | doi-access = free }} Within this early period, female limbic structures grow at a more rapid pace than the male ones. Amongst female subjects, the amygdala reaches its full growth potential approximately 1.5 years before the peak of male development. The structural development of the male amygdala occurs over a longer period than in women. Because of the early development of female amygdalae, they reach their growth potential sooner than males, whose amygdalae continue to develop. The larger relative size of the male amygdala may be attributed to this extended developmental period.

Hormonal factors may contribute to these sex-specific developmental differences. The amygdala is rich in androgen receptors—nuclear receptors that bind to testosterone. Androgen receptors play a role in the DNA binding that regulates gene expression. Though testosterone is present within the female hormonal systems, women have lower levels of testosterone than men. The abundance of testosterone in the male hormonal system may contribute to development. In addition, the grey matter volume on the amygdala is predicted by testosterone levels, which may also contribute to the increased mass of the male amygdala.

There are observable developmental differences between the right and left amygdala. The left amygdala reaches its developmental peak approximately 1.5–2 years prior to the right amygdala. Despite the early growth of the left amygdala, the right increases in volume for a longer period of time. The right amygdala is associated with response to fearful stimuli as well as face recognition. For the left amygdala, it is inferred that the early development of it functions to provide infants the ability to detect danger due to its reported responds predominantly to fearful events and faces.{{Cite journal |last=Hardee |first=Jillian E. |last2=Thompson |first2=James C. |last3=Puce |first3=Aina |date=2008-01-31 |title=The left amygdala knows fear: laterality in the amygdala response to fearful eyes |url=https://doi.org/10.1093/scan/nsn001 |journal=Social Cognitive and Affective Neuroscience |volume=3 |issue=1 |pages=47–54 |doi=10.1093/scan/nsn001 |issn=1749-5024|hdl=2022/22747 |hdl-access=free }}{{Cite journal |last=Phelps |first=Elizabeth A. |last2=O'Connor |first2=Kevin J. |last3=Gatenby |first3=J. Christopher |last4=Gore |first4=John C. |last5=Grillon |first5=Christian |last6=Davis |first6=Michael |date=2001 |title=Activation of the left amygdala to a cognitive representation of fear |url=https://doi.org/10.1038/86110 |journal=Nature Neuroscience |volume=4 |issue=4 |pages=437–441 |doi=10.1038/86110 |issn=1097-6256}} In childhood, the amygdala is found to react differently to same-sex versus opposite-sex individuals. This reactivity decreases until a person enters adolescence, where it increases dramatically at puberty.{{cite journal | vauthors = Telzer EH, Flannery J, Humphreys KL, Goff B, Gabard-Durman L, Gee DG, Tottenham N | title = "The Cooties Effect": Amygdala Reactivity to Opposite- versus Same-sex Faces Declines from Childhood to Adolescence | journal = Journal of Cognitive Neuroscience | volume = 27 | issue = 9 | pages = 1685–96 | date = September 2015 | pmid = 25848681 | pmc = 5723398 | doi = 10.1162/jocn_a_00813 }}

Other functional and structural differences between male and female amygdalae have been observed. Subjects' amygdala activation was observed when watching a horror film and subliminal stimuli. The results of the study showed a different lateralization of the amygdala in men and women. Enhanced memory for the film was related to enhanced activity of the left, but not the right, amygdala in women, whereas it was related to enhanced activity of the right, but not the left, amygdala in men.{{cite journal | vauthors = Cahill L, Haier RJ, White NS, Fallon J, Kilpatrick L, Lawrence C, Potkin SG, Alkire MT | display-authors = 6 | title = Sex-related difference in amygdala activity during emotionally influenced memory storage | journal = Neurobiology of Learning and Memory | volume = 75 | issue = 1 | pages = 1–9 | date = January 2001 | pmid = 11124043 | doi = 10.1006/nlme.2000.3999 | s2cid = 25492047 }} Similarly, a study of decision-making ability in patients with unilateral amygdala damage suggested that men with right (but not left) amygdala damage were more likely to be impaired in decision-making ability, while women with left (but not right) amygdala damage were more likely to be impaired in decision-making ability.{{cite journal | vauthors = Tranel D, Bechara A | title = Sex-related functional asymmetry of the amygdala: preliminary evidence using a case-matched lesion approach | journal = Neurocase | volume = 15 | issue = 3 | pages = 217–34 | date = June 2009 | pmid = 19308794 | pmc = 2829120 | doi = 10.1080/13554790902775492 }}{{cite journal | vauthors = Gupta R, Koscik TR, Bechara A, Tranel D | title = The amygdala and decision-making | journal = Neuropsychologia | volume = 49 | issue = 4 | pages = 760–6 | date = March 2011 | pmid = 20920513 | pmc = 3032808 | doi = 10.1016/j.neuropsychologia.2010.09.029 }} One study found evidence that, on average, women tend to retain stronger memories for emotional events than men.{{cite journal | vauthors = Hamann S | title = Sex differences in the responses of the human amygdala | journal = The Neuroscientist | volume = 11 | issue = 4 | pages = 288–93 | date = August 2005 | pmid = 16061516 | doi = 10.1177/1073858404271981 | s2cid = 15324475 }}

Variability in amygdala connectivity has been related to a variety of behaviors and outcomes such as fear recognition{{Cite journal |last1=McFadyen |first1=Jessica |year=2019 |title=An afferent white matter pathway from the pulvinar to the amygdala facilitates fear recognition |journal=eLife |volume=8 |doi=10.7554/eLife.40766 |pmc=6335057 |pmid=30648533 |doi-access=free}} and social network size.{{Cite journal |last1=Hampton |first1=WH |last2=Unger |first2=A |last3=Von Der Heide |first3=RJ |last4=Olson |first4=IR |year=2016 |title=Neural connections foster social connections: a diffusion-weighted imaging study of social networks |journal=Social Cognitive and Affective Neuroscience |volume=11 |issue=5 |pages=721–727 |doi=10.1093/scan/nsv153 |pmc=4847692 |pmid=26755769 |doi-access=free}} A simple view of the information processing through the amygdala follows as: the amygdala sends projections to the hypothalamus, septal nuclei and BNST (via the amygdalofugal tract), the dorsomedial thalamus (via the amygdalothalamic tract), the nuclei of the trigeminal nerve and the facial nerve, the ventral tegmental area, the locus coeruleus, and the laterodorsal tegmental nucleus.

The basolateral amygdala projects to the nucleus accumbens, including the medial shell.{{cite journal | vauthors = Lalumiere RT | title = Optogenetic dissection of amygdala functioning | journal = Frontiers in Behavioral Neuroscience | volume = 8 | pages = 107 | date = 2014 | pmid = 24723867 | pmc = 3972463 | doi = 10.3389/fnbeh.2014.00107 | doi-access = free }}{{cite journal | vauthors = Nieh EH, Kim SY, Namburi P, Tye KM | title = Optogenetic dissection of neural circuits underlying emotional valence and motivated behaviors | journal = Brain Research | volume = 1511 | pages = 73–92 | date = May 2013 | pmid = 23142759 | pmc = 4099056 | doi = 10.1016/j.brainres.2012.11.001 }}{{Cite journal |last1=Kamali |first1=A. |last2=Sair |first2=H. I. |last3=Blitz |first3=A. M. |last4=Riascos |first4=R. F. |last5=Mirbagheri |first5=S. |last6=Keser |first6=Z. |last7=Hasan |first7=K. M. |date=2016 |title=Revealing the ventral amygdalofugal pathway of the human limbic system using high spatial resolution diffusion tensor tractography |journal=Brain Structure & Function |volume=221 |issue=7 |pages=3561–3569 |doi=10.1007/s00429-015-1119-3 |pmid=26454651 |s2cid=253982337}}{{Cite journal |pmid=29607550 |date=2018 |last1=Kamali |first1=A. |last2=Riascos |first2=R. F. |last3=Pillai |first3=J. J. |last4=Sair |first4=H. I. |last5=Patel |first5=R. |last6=Nelson |first6=F. M. |last7=Lincoln |first7=J. A. |last8=Tandon |first8=N. |last9=Mirbagheri |first9=S. |last10=Rabiei |first10=P. |last11=Keser |first11=Z. |last12=Hasan |first12=K. M. |title=Mapping the trajectory of the amygdalothalamic tract in the human brain |journal=Journal of Neuroscience Research |volume=96 |issue=7 |pages=1176–1185 |doi=10.1002/jnr.24235 |s2cid=4565237 }}{{Cite journal |pmid=37148369 |date=2023 |last1=Kamali |first1=A. |last2=Milosavljevic |first2=S. |last3=Gandhi |first3=A. |last4=Lano |first4=K. R. |last5=Shobeiri |first5=P. |last6=Sherbaf |first6=F. G. |last7=Sair |first7=H. I. |last8=Riascos |first8=R. F. |last9=Hasan |first9=K. M. |title=The Cortico-Limbo-Thalamo-Cortical Circuits: An Update to the Original Papez Circuit of the Human Limbic System |journal=Brain Topography |volume=36 |issue=3 |pages=371–389 |doi=10.1007/s10548-023-00955-y |pmc=10164017 }} Glutamatergic neurons in the basolateral amygdala send projections to the nucleus accumbens shell and core. Activation of these projections drive motivational salience. The ability of these projections to drives incentive salience is dependent upon dopamine receptor D1. The endocannabinoid system that produces lipoid neuromodulators has its specific receptors (CB1) found in amygdalae.{{Cite journal |last=Calabrò |first=Rocco S. |last2=Cacciola |first2=Alberto |last3=Bruschetta |first3=Daniele |last4=Milardi |first4=Demetrio |last5=Quattrini |first5=Fabrizio |last6=Sciarrone |first6=Francesca |last7=la Rosa |first7=Gianluca |last8=Bramanti |first8=Placido |last9=Anastasi |first9=Giuseppe |date=2019-09-30 |title=Neuroanatomy and function of human sexual behavior: A neglected or unknown issue? |url=https://doi.org/10.1002/brb3.1389 |journal=Brain and Behavior |volume=9 |issue=12 |doi=10.1002/brb3.1389 |issn=2162-3279|pmc=6908863 }}

File:Gray 718-amygdala.png section of brain through intermediate mass of third ventricle. Amygdala is shown in purple.]]

The medial nucleus is involved in the sense of smell and pheromone-processing. It receives input from the olfactory bulb and olfactory cortex.{{cite book |last=Carlson |first=Neil | name-list-style = vanc |title=Physiology of behavior|url=https://archive.org/details/physiologybehavi00carl_811 |url-access=limited |date=12 January 2012|publisher=Pearson|isbn=978-0205239399|page=[https://archive.org/details/physiologybehavi00carl_811/page/n356 336]}} The lateral amygdalae, which send impulses to the rest of the basolateral complexes and to the centromedial nuclei, receive input from the sensory systems. The centromedial nuclei are the main outputs for the basolateral complexes, and are involved in emotional arousal in rats and cats.{{cite journal | vauthors = Groshek F, Kerfoot E, McKenna V, Polackwich AS, Gallagher M, Holland PC | title = Amygdala central nucleus function is necessary for learning, but not expression, of conditioned auditory orienting | journal = Behavioral Neuroscience | volume = 119 | issue = 1 | pages = 202–12 | date = February 2005 | pmid = 15727525 | pmc = 1255918 | doi = 10.1037/0735-7044.119.1.202 }}

{{Main |Emotion and memory}}

In complex vertebrates, including humans, the amygdalae perform primary roles in the formation and storage of memories associated with emotional events. Research indicates that, during fear conditioning, sensory stimuli reach the basolateral complexes of the amygdalae, particularly the lateral nuclei, where they form associations with memories of the stimuli. The association between stimuli and the aversive events they predict may be mediated by long-term potentiation,{{cite journal | vauthors = Maren S | title = Long-term potentiation in the amygdala: a mechanism for emotional learning and memory | journal = Trends in Neurosciences | volume = 22 | issue = 12 | pages = 561–7 | date = December 1999 | pmid = 10542437 | doi = 10.1016/S0166-2236(99)01465-4 | hdl = 2027.42/56238 | s2cid = 18787168 | url = https://deepblue.lib.umich.edu/bitstream/2027.42/56238/1/marenTINS99.pdf | hdl-access = free }}{{cite journal | vauthors = Blair HT, Schafe GE, Bauer EP, Rodrigues SM, LeDoux JE | title = Synaptic plasticity in the lateral amygdala: a cellular hypothesis of fear conditioning | journal = Learning & Memory | volume = 8 | issue = 5 | pages = 229–42 | year = 2001 | pmid = 11584069 | doi = 10.1101/lm.30901 | doi-access = free }} a sustained enhancement of signaling between affected neurons.{{cite journal | vauthors = Ressler K, Davis M | title = Genetics of childhood disorders: L. Learning and memory, part 3: fear conditioning | journal = Journal of the American Academy of Child and Adolescent Psychiatry | volume = 42 | issue = 5 | pages = 612–5 | date = May 2003 | pmid = 12707566 | doi = 10.1097/01.CHI.0000046835.90931.32 }} There have been studies that show that damage to the amygdala can interfere with memory that is strengthened by emotion. One study examined a patient with bilateral degeneration of the amygdala. He was told a violent story accompanied by matching pictures and was observed based on how much he could recall from the story. The patient had less recollection of the story than patients with functional amygdala, showing that the amygdala has a strong connection with emotional learning.{{cite book|last=Carlson|first=Neil R. | name-list-style = vanc |title=Physiology of Behavior|url=https://archive.org/details/physiologybehavi00carl_811|url-access=limited|date=12 January 2012|publisher=Pearson|isbn=978-0205239399|page=[https://archive.org/details/physiologybehavi00carl_811/page/n384 364]}}

Emotional memories are thought to be stored in synapses throughout the brain. Fear memories, for example, are considered to be stored in the neuronal connections from the lateral nuclei to the central nucleus of the amygdalae and the bed nuclei of the stria terminalis (part of the extended amygdala). These connections are not the sole site of fear memories given that the nuclei of the amygdala receive and send information to other brain regions that are important for memory such as the hippocampus. Some sensory neurons project their axon terminals to the central nucleus.{{cite book|last=Carlson|first=Neil R. | name-list-style = vanc |title=Physiology of Behavior|url=https://archive.org/details/physiologybehavi00carl_811|url-access=limited|date=12 January 2012|publisher=Pearson|isbn=978-0205239399|page=[https://archive.org/details/physiologybehavi00carl_811/page/n473 453]}} The central nuclei are involved in the genesis of many fear responses such as defensive behavior (freezing or escape responses), autonomic nervous system responses (changes in blood pressure and heart rate/tachycardia), neuroendocrine responses (stress-hormone release), etc. Damage to the amygdalae impairs both the acquisition and expression of Pavlovian fear conditioning, a form of classical conditioning of emotional responses. Accumulating evidence has suggested that multiple neuromodulators acting in the amygdala regulates the formation of emotional memories.{{cite journal | vauthors = Uematsu A, Tan BZ, Ycu EA, Cuevas JS, Koivumaa J, Junyent F, Kremer EJ, Witten IB, Deisseroth K, Johansen JP | display-authors = 6 | title = Modular organization of the brainstem noradrenaline system coordinates opposing learning states | journal = Nature Neuroscience | volume = 20 | issue = 11 | pages = 1602–1611 | date = November 2017 | pmid = 28920933 | doi = 10.1038/nn.4642 | s2cid = 34732905 }}{{cite journal | vauthors = Tang W, Kochubey O, Kintscher M, Schneggenburger R | title = A VTA to basal amygdala dopamine projection contributes to signal salient somatosensory events during fear learning | journal = The Journal of Neuroscience | pages = JN–RM–1796-19 | date = April 2020 | volume = 40 | issue = 20 | pmid = 32277045 | doi = 10.1523/JNEUROSCI.1796-19.2020 | pmc = 7219297 }}{{cite journal | vauthors = Fadok JP, Dickerson TM, Palmiter RD | title = Dopamine is necessary for cue-dependent fear conditioning | journal = The Journal of Neuroscience | volume = 29 | issue = 36 | pages = 11089–97 | date = September 2009 | pmid = 19741115 | pmc = 2759996 | doi = 10.1523/JNEUROSCI.1616-09.2009 }}

The amygdalae are also involved in appetitive (positive) conditioning. It seems that distinct neurons respond to positive and negative stimuli, but there is no clustering of these distinct neurons into clear anatomical nuclei.{{cite journal | vauthors = Paton JJ, Belova MA, Morrison SE, Salzman CD | title = The primate amygdala represents the positive and negative value of visual stimuli during learning | journal = Nature | volume = 439 | issue = 7078 | pages = 865–70 | date = February 2006 | pmid = 16482160 | pmc = 2396495 | doi = 10.1038/nature04490 | bibcode = 2006Natur.439..865P }}{{cite journal | vauthors = Redondo RL, Kim J, Arons AL, Ramirez S, Liu X, Tonegawa S | title = Bidirectional switch of the valence associated with a hippocampal contextual memory engram | journal = Nature | volume = 513 | issue = 7518 | pages = 426–30 | date = September 2014 | pmid = 25162525 | pmc = 4169316 | doi = 10.1038/nature13725 | bibcode = 2014Natur.513..426R }} However, lesions of the central nucleus in the amygdala have been shown to reduce appetitive learning in rats. Lesions of the basolateral regions do not exhibit the same effect.{{cite journal | vauthors = Parkinson JA, Robbins TW, Everitt BJ | title = Dissociable roles of the central and basolateral amygdala in appetitive emotional learning | journal = The European Journal of Neuroscience | volume = 12 | issue = 1 | pages = 405–13 | date = January 2000 | pmid = 10651899 | doi = 10.1046/j.1460-9568.2000.00960.x | s2cid = 25351636 }} Research like this indicates that different nuclei within the amygdala have different functions in appetitive conditioning.{{cite journal | vauthors = Balleine BW, Killcross S | s2cid = 14958970 | title = Parallel incentive processing: an integrated view of amygdala function | journal = Trends in Neurosciences | volume = 29 | issue = 5 | pages = 272–9 | date = May 2006 | pmid = 16545468 | doi = 10.1016/j.tins.2006.03.002 }}{{cite journal | vauthors = Killcross S, Robbins TW, Everitt BJ | s2cid = 205028225 | title = Different types of fear-conditioned behaviour mediated by separate nuclei within amygdala | journal = Nature | volume = 388 | issue = 6640 | pages = 377–80 | date = July 1997 | pmid = 9237754 | doi = 10.1038/41097 | bibcode = 1997Natur.388..377K }} Nevertheless, researchers found an example of appetitive emotional learning showing an important role for the basolateral amygdala: The naïve female mice are innately attracted to non-volatile pheromones contained in male-soiled bedding, but not by the male-derived volatiles, become attractive if associated with non-volatile attractive pheromones, which act as unconditioned stimulus in a case of Pavlovian associative learning.{{cite journal | vauthors = Moncho-Bogani J, Lanuza E, Hernández A, Novejarque A, Martínez-García F | title = Attractive properties of sexual pheromones in mice: innate or learned? | journal = Physiology & Behavior | volume = 77 | issue = 1 | pages = 167–76 | date = September 2002 | pmid = 12213516 | doi = 10.1016/s0031-9384(02)00842-9 | s2cid = 10583550 }} In the vomeronasal, olfactory, and emotional systems, Fos (gene family) proteins show that non-volatile pheromones stimulate the vomeronasal system, whereas air-borne volatiles activate only the olfactory system. Thus, the acquired preference for male-derived volatiles reveals an olfactory-vomeronasal associative learning. Moreover, the reward system is differentially activated by the primary pheromones and secondarily attractive odorants. Exploring the primary attractive pheromone activates the basolateral amygdala and the shell of nucleus accumbens but neither the ventral tegmental area nor the orbitofrontal cortex. In contrast, exploring the secondarily attractive male-derived odorants involves activation of a circuit that includes the basolateral amygdala, prefrontal cortex, and ventral tegmental area. Therefore, the basolateral amygdala stands out as the key center for vomeronasal-olfactory associative learning.{{cite journal | vauthors = Moncho-Bogani J, Martinez-Garcia F, Novejarque A, Lanuza E | title = Attraction to sexual pheromones and associated odorants in female mice involves activation of the reward system and basolateral amygdala | journal = The European Journal of Neuroscience | volume = 21 | issue = 8 | pages = 2186–98 | date = April 2005 | pmid = 15869515 | doi = 10.1111/j.1460-9568.2005.04036.x | s2cid = 17056127 }}

The amygdala is also involved in the modulation of memory consolidation. Following any learning event, the long-term memory for the event is not formed instantaneously. Rather, information regarding the event is slowly assimilated into long-term (potentially lifelong) storage over time, possibly via long-term potentiation. Recent studies suggest that the amygdala regulates memory consolidation in other brain regions. Also, fear conditioning, a type of memory that is impaired following amygdala damage, is mediated in part by long-term potentiation. During the consolidation period, the memory can be modulated. In particular, it appears that emotional arousal following the learning event influences the strength of the subsequent memory for that event. Greater emotional arousal following a learning event enhances a person's retention of that event. Experiments have shown that administration of stress hormones to mice immediately after they learn something enhances their retention when they are tested two days later."Researchers Prove A Single Memory Is Processed in Three Separate Parts of the Brain" {{cite web |url=https://www.sciencedaily.com/releases/2006/02/060202182107.htm |title=Researchers Prove a Single Memory is Processed in Three Separate Parts of the Brain |access-date=2018-02-28 |url-status=live |archive-url=https://web.archive.org/web/20170912055423/https://www.sciencedaily.com/releases/2006/02/060202182107.htm |archive-date=12 September 2017}}

The amygdala, especially the basolateral nuclei, are involved in mediating the effects of emotional arousal on the strength of the memory for the event, as shown by many laboratories including that of James McGaugh. These laboratories have trained animals on a variety of learning tasks and found that drugs injected into the amygdala after training affect the animals' subsequent retention of the task. These tasks include basic classical conditioning tasks such as inhibitory avoidance, where a rat learns to associate a mild footshock with a particular compartment of an apparatus, and more complex tasks such as spatial or cued water maze, where a rat learns to swim to a platform to escape the water. If a drug that activates the amygdalae is injected into the amygdalae, the animals had better memory for the training in the task.{{cite journal | vauthors = Ferry B, Roozendaal B, McGaugh JL | s2cid = 36848472 | title = Role of norepinephrine in mediating stress hormone regulation of long-term memory storage: a critical involvement of the amygdala | journal = Biological Psychiatry | volume = 46 | issue = 9 | pages = 1140–52 | date = November 1999 | pmid = 10560021 | doi = 10.1016/S0006-3223(99)00157-2 }}

Amygdala activity at the time of encoding information correlates with retention for that information. However, this correlation depends on the relative "emotionalness" of the information. More emotionally arousing information increases amygdalar activity, and that activity correlates with retention. Amygdala neurons show various types of oscillation during emotional arousal, such as theta activity. These synchronized neuronal events could promote synaptic plasticity (which is involved in memory retention) by increasing interactions between neocortical storage sites and temporal lobe structures involved in declarative memory.{{cite journal |vauthors=Paré D, Collins DR, Pelletier JG |date=July 2002 |title=Amygdala oscillations and the consolidation of emotional memories |journal=Trends in Cognitive Sciences |volume=6 |issue=7 |pages=306–314 |doi=10.1016/S1364-6613(02)01924-1 |pmid=12110364 |s2cid=10421580}}

In rats, DNA damage was found to increase in the amygdala immediately after exposure to stress.{{cite journal |vauthors=Consiglio AR, Ramos AL, Henriques JA, Picada JN |s2cid=38959073 |title=DNA brain damage after stress in rats |journal=Prog. Neuropsychopharmacol. Biol. Psychiatry |volume=34 |issue=4 |pages=652–6 |date=May 2010 |pmid=20226828 |doi=10.1016/j.pnpbp.2010.03.004 |doi-access=free }} Stress was induced by 30 minutes of restraint or by forced swimming. By seven days after exposure to these stresses, increased DNA damage was no longer detectable in the amygdala, probably because of DNA repair.

Buddhist monks who do compassion meditation have been shown to modulate their amygdala, along with their temporoparietal junction and insula, during their practice.{{cite web | title = Cultivating compassion: Neuroscientific and behavioral approaches | first = Richard J. | last = Davidson | name-list-style = vanc | url = http://ccare.stanford.edu/node/25 |access-date=2010-07-04 |url-status=dead |archive-url=https://web.archive.org/web/20100714174906/http://ccare.stanford.edu/node/25 |archive-date=14 July 2010}} In an fMRI study, more intensive insula activity was found in expert meditators than in novices.{{cite journal | vauthors = Lutz A, Brefczynski-Lewis J, Johnstone T, Davidson RJ | title = Regulation of the neural circuitry of emotion by compassion meditation: effects of meditative expertise | journal = PLOS ONE | volume = 3 | issue = 3 | pages = e1897 | date = March 2008 | pmid = 18365029 | pmc = 2267490 | doi = 10.1371/journal.pone.0001897 | veditors = Baune B | bibcode = 2008PLoSO...3.1897L | doi-access = free }}

File:Rorschach blot 03.jpg blot 03]]

Research using Rorschach test blot 03 finds that the number of unique responses to this random figure links to larger sized amygdalae. The researchers note, "Since previous reports have indicated that unique responses were observed at higher frequency in the artistic population than in the nonartistic normal population, this positive correlation suggests that amygdalar enlargement in the normal population might be related to creative mental activity."{{cite journal | vauthors = Asari T, Konishi S, Jimura K, Chikazoe J, Nakamura N, Miyashita Y | s2cid = 30109156 | title = Amygdalar enlargement associated with unique perception | journal = Cortex; A Journal Devoted to the Study of the Nervous System and Behavior | volume = 46 | issue = 1 | pages = 94–9 | date = January 2010 | pmid = 18922517 | doi = 10.1016/j.cortex.2008.08.001 }}

Early research on primates provided explanations as to the functions of the amygdala, as well as a basis for further research. As early as 1888, rhesus monkeys with a lesioned temporal cortex (including the amygdala) were observed to have significant social and emotional deficits.{{cite journal | vauthors = Brown S, Shafer E | year =1888| title = An investigation into the functions of the occipital and temporal lobes of the monkey's brain| journal =Philosophical Transactions of the Royal Society B | volume =179 | pages =303–327| doi = 10.1098/rstb.1888.0011| doi-access =free}} Heinrich Klüver and Paul Bucy later expanded upon this same observation by showing that large lesions to the anterior temporal lobe produced noticeable changes, including overreaction to all objects, hypoemotionality, loss of fear, hypersexuality, and hyperorality, a condition in which inappropriate objects are placed in the mouth. Some monkeys also displayed an inability to recognize familiar objects and would approach animate and inanimate objects indiscriminately, exhibiting a loss of fear towards the experimenters. This behavioral disorder was later named Klüver–Bucy syndrome accordingly,{{cite journal | vauthors = Klüver H, Bucy PC | title = Preliminary analysis of functions of the temporal lobes in monkeys | journal = Archives of Neurology and Psychiatry| volume = 9 | issue = 4 | pages = 606–20 | year = 1939 | doi = 10.1001/archneurpsyc.1939.02270240017001 }} and later research proved it was specifically due to amygdala lesions. Monkey mothers who had amygdala damage showed a reduction in maternal behaviors towards their infants, often physically abusing or neglecting them.{{cite journal | vauthors = Bucher K, Myers RE, Southwick C | title = Anterior temporal cortex and maternal behavior in monkey | journal = Neurology | volume = 20 | issue = 4 | pages = 415 | date = April 1970 | pmid = 4998075 | doi = 10.1212/wnl.20.4.402 | s2cid = 219204628 }} In 1981, researchers found that selective radio frequency lesions of the whole amygdala caused Klüver–Bucy syndrome.{{cite journal | vauthors = Aggleton JP, Passingham RE | title = Syndrome produced by lesions of the amygdala in monkeys (Macaca mulatta) | journal = Journal of Comparative and Physiological Psychology | volume = 95 | issue = 6 | pages = 961–77 | date = December 1981 | pmid = 7320283 | doi = 10.1037/h0077848 }}

Increased activity in the amygdala following compassion-oriented meditation may contribute to social connectedness.{{cite journal | vauthors = Hutcherson CA, Seppala EM, Gross JJ | title = Loving-kindness meditation increases social connectedness | journal = Emotion | volume = 8 | issue = 5 | pages = 720–4 | date = October 2008 | pmid = 18837623 | doi = 10.1037/a0013237 }} Similarly, the structural white matter connectivity to other brain regions is also associated with social network size. The amygdala is also thought to be a determinant of the level of a person's emotional intelligence. It is particularly hypothesized that larger amygdalae allow for greater emotional intelligence, enabling greater societal integration and cooperation with others.{{cite book |title=The Human Amygdala |vauthors=Buchanan TW, Tranel D, Adolphs R |publisher=Guilford |year=2009 |isbn=978-1-60623-033-6 |veditors=Whalen PJ, Phelps EA |location=New York |pages=289–318 |chapter=The Human Amygdala in Social Function |chapter-url=https://books.google.com/books?id=275mEq72pkUC&pg=PA289}}

Amygdala volume correlates positively with both the size (the number of contacts a person has) and the complexity (the number of different groups to which a person belongs) of social networks.{{cite journal | vauthors = Bickart KC, Wright CI, Dautoff RJ, Dickerson BC, Barrett LF | title = Amygdala volume and social network size in humans | journal = Nature Neuroscience | volume = 14 | issue = 2 | pages = 163–4 | date = February 2011 | pmid = 21186358 | pmc = 3079404 | doi = 10.1038/nn.2724 }}{{Cite magazine|url=https://healthland.time.com/2010/12/28/how-to-win-friends-have-a-big-amygdala/?xid=rss-topstories|title=How to Win Friends: Have a Big Amygdala?|magazine=Time|first=Maia|last=Szalavitz | name-list-style = vanc |date=28 December 2010|access-date=30 December 2010|url-status=live|archive-url=https://web.archive.org/web/20110717061203/http://healthland.time.com/2010/12/28/how-to-win-friends-have-a-big-amygdala/?xid=rss-topstories|archive-date=17 July 2011}} Individuals with larger amygdalae had larger and more complex social networks. The amygdala is responsible for facial recognition and allows others to respond appropriately to different emotional expressions.Lynn Ladel, Oxford University Press. "[https://books.google.com/books?id=A2s963AzymYC&q=human+amygdala+function%2F&pg=PA106 Cognitive Neuroscience of Emotion]." 9 October 2014. 1 July 2019. They were also better able to make accurate social judgments about other persons' faces.{{cite journal | vauthors = Bzdok D, Langner R, Caspers S, Kurth F, Habel U, Zilles K, Laird A, Eickhoff SB | title = ALE meta-analysis on facial judgments of trustworthiness and attractiveness | journal = Brain Structure & Function | volume = 215 | issue = 3–4 | pages = 209–23 | date = January 2011 | pmid = 20978908 | pmc = 4020344 | doi = 10.1007/s00429-010-0287-4 }} The amygdala's role in the analysis of social situations stems specifically from its ability to identify and process changes in facial features. It does not, however, process the direction of the gaze of the person being perceived.{{cite journal | vauthors = Mormann F, Niediek J, Tudusciuc O, Quesada CM, Coenen VA, Elger CE, Adolphs R | title = Neurons in the human amygdala encode face identity, but not gaze direction | journal = Nature Neuroscience | volume = 18 | issue = 11 | pages = 1568–70 | date = November 2015 | pmid = 26479589 | pmc = 4624486 | doi = 10.1038/nn.4139 }}{{cite journal | vauthors = Huijgen J, Dinkelacker V, Lachat F, Yahia-Cherif L, El Karoui I, Lemaréchal JD, Adam C, Hugueville L, George N | title = Amygdala processing of social cues from faces: an intracrebral EEG study | journal = Social Cognitive and Affective Neuroscience | volume = 10 | issue = 11 | pages = 1568–76 | date = November 2015 | pmid = 25964498 | doi = 10.1093/scan/nsv048 | pmc = 4631154 }}

The amygdala processes reactions to violations concerning personal space. These reactions are absent in persons in whom the amygdala is damaged bilaterally.{{cite journal | vauthors = Kennedy DP, Gläscher J, Tyszka JM, Adolphs R | title = Personal space regulation by the human amygdala | journal = Nature Neuroscience | volume = 12 | issue = 10 | pages = 1226–7 | date = October 2009 | pmid = 19718035 | pmc = 2753689 | doi = 10.1038/nn.2381 }} Furthermore, the amygdala is found to be activated in fMRI when people observe that others are physically close to them, such as when a person being scanned knows that an experimenter is standing immediately next to the scanner, versus standing at a distance.{{cite web |url-status=dead |first1=Kimberly |last1=Brown |website=Manifest Yourself |url=http://www.manifestyourself.com/event-sweat-city-sequel/ |title=Event: Sweat in the City: The Sequel! |archive-url=https://web.archive.org/web/20190329230852/https://www.manifestyourself.com/event-sweat-city-sequel/ |archive-date=29 March 2019 |date= 9 October 2014 }} Animal studies have shown that stimulating the amygdala appears to increase both sexual and aggressive behavior. Likewise, studies using brain lesions have shown that harm to the amygdala may produce the opposite effect. Thus, it appears that this part of the brain may play a role in the display and modulation of aggression.{{cite web |url=http://www.saylor.org/site/wp-content/uploads/2011/01/TLBrink_PSYCH04.pdf |title=Unit 4: The Nervous System |pages=61 |first1=T.L. |last1=Brink |date=2008 |work=Psychology: A Student Friendly Approach |access-date=2016-02-07 |url-status=live |archive-url=https://web.archive.org/web/20160303205950/http://www.saylor.org/site/wp-content/uploads/2011/01/TLBrink_PSYCH04.pdf |archive-date=3 March 2016}}

Recent studies have suggested possible correlations between brain structure, including differences in hemispheric ratios and connection patterns in the amygdala, and sexual orientation. Homosexual men tend to exhibit more feminine patterns in the amygdala than heterosexual males do, just as homosexual women tend to show more masculine patterns in the amygdala than heterosexual females do. It was observed that amygdala connections were more widespread from the left amygdala in homosexual males, as is also found in heterosexual females. Amygdala connections were more widespread from the right amygdala in homosexual females, as in heterosexual males.{{cite journal |vauthors=Swaab DF |date=July 2008 |title=Sexual orientation and its basis in brain structure and function |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=105 |issue=30 |pages=10273–4 |bibcode=2008PNAS..10510273S |doi=10.1073/pnas.0805542105 |pmc=2492513 |pmid=18653758 |doi-access=free}}{{cite journal |vauthors=Swaab DF |date=September 2007 |title=Sexual differentiation of the brain and behavior |journal=Best Practice & Research. Clinical Endocrinology & Metabolism |volume=21 |issue=3 |pages=431–44 |doi=10.1016/j.beem.2007.04.003 |pmid=17875490}}

The amygdala appears to play a role in binge drinking, being damaged by repeated episodes of intoxication and withdrawal.{{cite journal | vauthors = Stephens DN, Duka T | title = Review. Cognitive and emotional consequences of binge drinking: role of amygdala and prefrontal cortex | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 363 | issue = 1507 | pages = 3169–79 | date = October 2008 | pmid = 18640918 | pmc = 2607328 | doi = 10.1098/rstb.2008.0097 }}{{cite journal|vauthors=Marinkovic K, Oscar-Berman M, Urban T, O'Reilly CE, Howard JA, Sawyer K, Harris GJ|date=November 2009|title=Alcoholism and dampened temporal limbic activation to emotional faces|journal=Alcoholism: Clinical and Experimental Research|volume=33|issue=11|pages=1880–92|doi=10.1111/j.1530-0277.2009.01026.x|pmc=3543694|pmid=19673745}} Protein kinase C-epsilon in the amygdala is important for regulating behavioral responses to morphine and ethanol and controlling anxiety-like behavior. The protein is involved in controlling the function of other proteins and plays a role in the development of the ability to consume a large amount of ethanol.{{cite journal|vauthors=Newton PM, Ron D|date=June 2007|title=Protein kinase C and alcohol addiction|journal=Pharmacological Research|volume=55|issue=6|pages=570–7|doi=10.1016/j.phrs.2007.04.008|pmid=17566760}}{{cite journal|vauthors=Lesscher HM, Wallace MJ, Zeng L, Wang V, Deitchman JK, McMahon T, Messing RO, Newton PM|date=July 2009|title=Amygdala protein kinase C epsilon controls alcohol consumption|journal=Genes, Brain and Behavior|volume=8|issue=5|pages=493–9|doi=10.1111/j.1601-183X.2009.00485.x|pmc=2714877|pmid=19243450}} The duration of chronic alcohol consumption and abstinence may affect dynamic brain network adaptations. When excessive drinking occurs, the amygdala is affected through behavioral changes and reduces the brain's plasticity. Often, when binge drinking or alcoholism occurs, the amygdala is affected and leads to behavior damage. These behavioral damages can be lack of control, inability to conduct oneself in a mature manner, irritability and aggressive behavior, anxiety, depression, personality disorders, excessive drug intake, bipolar disorder, confusion, higher tolerance levels, and inappropriate sexual behaviors with others and self.{{Cite journal|last1=Stephens|first1=David N|last2=Duka|first2=Theodora|date=2008-10-12|title=Cognitive and emotional consequences of binge drinking: role of amygdala and prefrontal cortex|journal=Philosophical Transactions of the Royal Society B: Biological Sciences|volume=363|issue=1507|pages=3169–3179|doi=10.1098/rstb.2008.0097|issn=0962-8436|pmc=2607328|pmid=18640918}}

Feelings of anxiety start with an environmental stimulus that provokes stress. This can include various smells, sights, and internal sensations that result in anxiety. The amygdala reacts to this stimuli by preparing to either stand and fight or to turn and run. This response is triggered by the release of adrenaline into the bloodstream; the amygdala sends signals to the paraventricular nucleus of the hypothalamus for the initiation of the HPA axis response.{{Cite journal |last=Dedovic |first=Katarina |last2=Duchesne |first2=Annie |last3=Andrews |first3=Julie |last4=Engert |first4=Veronika |last5=Pruessner |first5=Jens C. |date=2009 |title=The brain and the stress axis: The neural correlates of cortisol regulation in response to stress |url=https://doi.org/10.1016/j.neuroimage.2009.05.074 |journal=NeuroImage |volume=47 |issue=3 |pages=864–871 |doi=10.1016/j.neuroimage.2009.05.074 |issn=1053-8119}} Consequently, blood sugar rises, becoming immediately available to the muscles for quick energy. Shaking may occur in an attempt to return blood to the rest of the body. Long-term changes in amygdala neurons may also increase anxiety after long-term or traumatic stress, led by the action of stress-related hormones within the amygdala.{{cite journal |last1=Mitra |first1=Rupshi |last2=Sapolsky |first2=Robert |year=2008 |title=Acute corticosterone treatment is sufficient to induce anxiety and amygdaloid dendritic hypertrophy |journal=Proc Natl Acad Sci U S A |volume=105 |issue=14 |pages=5573–8 |bibcode=2008PNAS..105.5573M |doi=10.1073/pnas.0705615105 |pmc=2291109 |pmid=18391224 |doi-access=free}} On the flip side, blocking the action of stress hormones in the amygdala reduces anxiety.{{cite journal |last1=Mitra |first1=Rupshi |last2=Sapolsky |first2=Robert |year=2010 |title=Expression of chimeric estrogen-glucocorticoid-receptor in the amygdala reduces anxiety |journal=Brain Res |volume=1342 |issue=1 |pages=33–8 |doi=10.1016/j.brainres.2010.03.092 |pmid=2038147 |s2cid=26769079}} There may also be a link between the amygdala and anxiety.{{cite journal | vauthors = Ziabreva I, Poeggel G, Schnabel R, Braun K | title = Separation-induced receptor changes in the hippocampus and amygdala of Octodon degus: influence of maternal vocalizations | journal = The Journal of Neuroscience | volume = 23 | issue = 12 | pages = 5329–36 | date = June 2003 | pmid = 12832558 | pmc = 6741186 | doi = 10.1523/JNEUROSCI.23-12-05329.2003 }} In particular, there is a higher prevalence of females that are affected by anxiety disorders.

The central nucleus of the amygdala has direct correlations to the hypothalamus and brainstem—areas directly related to fear and anxiety. (The central nucleus have high densities of opiate receptors.{{Cite journal |last=Davis |first=Michael |date=1992 |title=The Role of the Amygdala in Fear and Anxiety |url=https://emotion.wisc.edu/wp-content/uploads/sites/1353/2021/03/Davis-The-Role-of-the-Amygdala-in-Fear-and-Anxiety-1992-Annual-Review-of-Neuroscience.pdf?utm_source=chatgpt.com |journal=Annual Reviews |volume=15 |issue=353-75}}) This connection is evident from studies of animals that have undergone amygdalae removal.{{Cite news |last=Bhanoo |first=Sindya N. |date=2010-12-16 |title=Humans, Like Animals, Behave Fearlessly Without the Amygdala |url=https://www.nytimes.com/2010/12/21/science/21obbrain.html |access-date=2025-02-15 |work=The New York Times |language=en-US |issn=0362-4331}} Such studies suggest that animals lacking an amygdala have less fear expression. In an experiment, degu pups were removed from their mother but allowed to hear her call. In response, the males produced increased serotonin receptors in the amygdala but females lost them. This led to the males being less affected by the stressful situation.

The clusters of the amygdala are activated when an individual expresses feelings of fear or aggression. This occurs because the amygdala is the primary structure of the brain responsible for fight-or-flight response. Anxiety and panic attacks can occur when the amygdala senses environmental stressors that stimulate fight-or-flight response.{{Cite journal |last=Coplan |first=Jeremy D |last2=Lydiard |first2=R.Bruce |date=1998 |title=Brain circuits in panic disorder |url=https://doi.org/10.1016/s0006-3223(98)00300-x |journal=Biological Psychiatry |volume=44 |issue=12 |pages=1264–1276 |doi=10.1016/s0006-3223(98)00300-x |issn=0006-3223|doi-access=free }}{{Cite journal |last=Gorman |first=Jack M. |last2=Kent |first2=Justine M. |last3=Sullivan |first3=Gregory M. |last4=Coplan |first4=Jeremy D. |date=2000-04-01 |title=Neuroanatomical Hypothesis of Panic Disorder, Revised |url=https://psychiatryonline.org/doi/10.1176/appi.ajp.157.4.493 |journal=American Journal of Psychiatry |language=en |volume=157 |issue=4 |pages=493–505 |doi=10.1176/appi.ajp.157.4.493 |issn=0002-953X}} The amygdala is involved in the expression of conditioned fear. Conditioned fear is the framework used to explain the behavior produced when an originally neutral stimulus is consistently paired with a stimulus that evokes fear. Fear is measured by changes in autonomic activity including increased heart rate, increased blood pressure, as well as in simple reflexes such as flinching or blinking.{{Cite journal |last=Sehlström |first=Malcolm |last2=Ljungberg |first2=Jessica K. |last3=Claeson |first3=Anna-Sara |last4=Nyström |first4=Markus B. T. |date=2022 |title=The relation of neuroticism to physiological and behavioral stress responses induced by auditory startle |url=https://pubmed.ncbi.nlm.nih.gov/35403836 |journal=Brain and Behavior |volume=12 |issue=5 |pages=e2554 |doi=10.1002/brb3.2554 |issn=2162-3279 |pmc=9120885 |pmid=35403836}} Studies in 2004 and 2006 showed that normal subjects exposed to images of frightened faces or faces of people from another race will show increased activity of the amygdala, even if that exposure is subliminal.{{cite journal |vauthors=Williams LM, Liddell BJ, Kemp AH, Bryant RA, Meares RA, Peduto AS, Gordon E |date=August 2006 |title=Amygdala-prefrontal dissociation of subliminal and supraliminal fear |journal=Human Brain Mapping |volume=27 |issue=8 |pages=652–61 |doi=10.1002/hbm.20208 |pmc=6871444 |pmid=16281289}}{{cite journal |vauthors=Cunningham WA, Johnson MK, Raye CL, Chris Gatenby J, Gore JC, Banaji MR |date=December 2004 |title=Separable neural components in the processing of black and white faces |url=http://nrs.harvard.edu/urn-3:HUL.InstRepos:12164714 |journal=Psychological Science |volume=15 |issue=12 |pages=806–13 |doi=10.1111/j.0956-7976.2004.00760.x |pmid=15563325 |s2cid=82916}} [https://www.sciencedaily.com/releases/2004/12/041208231237.htm Lay summary] available from Science Daily. However, the amygdala is not necessary for the processing of fear-related stimuli, since persons in whom it is bilaterally damaged show rapid reactions to fearful faces, even in the absence of a functional amygdala.{{cite journal |vauthors=Tsuchiya N, Moradi F, Felsen C, Yamazaki M, Adolphs R |date=October 2009 |title=Intact rapid detection of fearful faces in the absence of the amygdala |journal=Nature Neuroscience |volume=12 |issue=10 |pages=1224–5 |doi=10.1038/nn.2380 |pmc=2756300 |pmid=19718036}}

With advances in neuroimaging technology such as MRI, neuroscientists have made significant findings concerning the amygdala in the human brain. A variety of data shows the amygdala has a substantial role in mental states, and is related to many psychological disorders. Some studies have shown children with anxiety disorders tend to have a smaller left amygdala. In the majority of the cases, there was an association between an increase in the size of the left amygdala with the use of SSRIs (antidepressant medication) or psychotherapy. The left amygdala has been linked to social anxiety disorder, obsessive and compulsive disorders, and post-traumatic stress disorder (PTSD), as well as more broadly to separation and generalized anxiety disorder.{{cite journal |last1=Arehart-Treichel |first1=Joan |name-list-style=vanc |year=2005 |title=Changes in Children's Amygdala Seen After Anxiety Treatment |journal=Psychiatric News |volume=40 |issue=9 |page=37 |doi=10.1176/pn.40.9.00400037 |issn=0033-2704}} Multiple studies have found that the amygdalae may be responsible for the emotional reactions of PTSD patients. One study in particular found that when PTSD patients are shown pictures of faces with fearful expressions, their amygdalae tended to have a higher activation than someone without PTSD.{{cite book |last=Carlson |first=Neil R. |url=https://archive.org/details/physiologybehavi00carl_811 |title=Physiology of Behavior |date=12 January 2012 |publisher=Pearson |isbn=978-0205239399 |page=[https://archive.org/details/physiologybehavi00carl_811/page/n628 608] |url-access=limited |name-list-style=vanc}}

In 2006, researchers observed hyperactivity in the amygdala when patients were shown threatening faces or confronted with frightening situations. Patients with severe social phobia showed a correlation with increased response in the amygdala.{{cite journal |vauthors=Phan KL, Fitzgerald DA, Nathan PJ, Tancer ME |date=March 2006 |title=Association between amygdala hyperactivity to harsh faces and severity of social anxiety in generalized social phobia |journal=Biological Psychiatry |volume=59 |issue=5 |pages=424–9 |doi=10.1016/j.biopsych.2005.08.012 |pmid=16256956 |s2cid=34105191}} [https://www.sciencedaily.com/releases/2006/01/060118205940.htm Lay summary] available from Science Daily. Individuals with psychopathy show reduced autonomic responses to instructed fear cues than otherwise healthy individuals.{{cite journal |vauthors=Blair RJ |date=August 2008 |title=The amygdala and ventromedial prefrontal cortex: functional contributions and dysfunction in psychopathy |journal=Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences |volume=363 |issue=1503 |pages=2557–65 |doi=10.1098/rstb.2008.0027 |pmc=2606709 |pmid=18434283}} Similarly, depressed patients showed exaggerated left amygdala activity when interpreting emotions for all faces, and especially for fearful faces. This hyperactivity was normalized when patients were administered antidepressant medication.{{cite journal |vauthors=Sheline YI, Barch DM, Donnelly JM, Ollinger JM, Snyder AZ, Mintun MA |date=November 2001 |title=Increased amygdala response to masked emotional faces in depressed subjects resolves with antidepressant treatment: an fMRI study |journal=Biological Psychiatry |volume=50 |issue=9 |pages=651–8 |doi=10.1016/S0006-3223(01)01263-X |pmid=11704071 |s2cid=8927264}}

In a 2003 study, subjects with borderline personality disorder showed significantly greater left amygdala activity than normal control subjects. Some borderline patients even had difficulties classifying neutral faces or saw them as threatening.{{cite journal |display-authors=8 |vauthors=Donegan NH, Sanislow CA, Blumberg HP, Fulbright RK, Lacadie C, Skudlarski P, Gore JC, Olson IR, McGlashan TH, Wexler BE |date=December 2003 |title=Amygdala hyperreactivity in borderline personality disorder: implications for emotional dysregulation |url=https://wesscholar.wesleyan.edu/cgi/viewcontent.cgi?article=1193&context=div3facpubs |journal=Biological Psychiatry |volume=54 |issue=11 |pages=1284–93 |doi=10.1016/S0006-3223(03)00636-X |pmid=14643096 |s2cid=7493725}} The amygdala has been observed to respond differently in people with bipolar disorder. Amygdala dysfunction during face emotion processing is well-documented in bipolar disorder. Individuals with bipolar disorder showed greater amygdala activity (especially the amygdala/medial-prefrontal-cortex circuit).{{cite journal |vauthors=Thomas LA, Kim P, Bones BL, Hinton KE, Milch HS, Reynolds RC, Adleman NE, Marsh AA, Blair RJ, Pine DS, Leibenluft E |date=January 2013 |title=Elevated amygdala responses to emotional faces in youths with chronic irritability or bipolar disorder |journal=NeuroImage: Clinical |volume=2 |issue=2 |pages=637–645 |doi=10.1016/j.nicl.2013.04.007 |pmc=3746996 |pmid=23977455}}{{cite journal |vauthors=Keener MT, Fournier JC, Mullin BC, Kronhaus D, Perlman SB, LaBarbara E, Almeida JC, Phillips ML |date=September 2012 |title=Dissociable patterns of medial prefrontal and amygdala activity to face identity versus emotion in bipolar disorder |journal=Psychological Medicine |volume=42 |issue=9 |pages=1913–24 |doi=10.1017/S0033291711002935 |pmc=3685204 |pmid=22273442}} For people with manic bipolar I disorder, a decreased negative functional connectivity between the orbitofrontal cortex and the amygdala was also observed.{{Cite journal |last=Foland |first=Lara C. |last2=Altshuler |first2=Lori L. |last3=Bookheimer |first3=Susan Y. |last4=Eisenberger |first4=Naomi |last5=Townsend |first5=Jennifer |last6=Thompson |first6=Paul M. |date=2008 |title=Evidence for deficient modulation of amygdala response by prefrontal cortex in bipolar mania |url=https://doi.org/10.1016/j.pscychresns.2007.04.007 |journal=Psychiatry Research: Neuroimaging |volume=162 |issue=1 |pages=27–37 |doi=10.1016/j.pscychresns.2007.04.007 |issn=0925-4927|pmc=2410029 }} A 2003 study found that adult and adolescent bipolar patients tended to have considerably smaller amygdala volumes and somewhat smaller hippocampal volumes.{{cite journal |vauthors=Blumberg HP, Kaufman J, Martin A, Whiteman R, Zhang JH, Gore JC, Charney DS, Krystal JH, Peterson BS |date=December 2003 |title=Amygdala and hippocampal volumes in adolescents and adults with bipolar disorder |journal=Archives of General Psychiatry |volume=60 |issue=12 |pages=1201–8 |doi=10.1001/archpsyc.60.12.1201 |pmid=14662552 |doi-access=}} Many studies have also focused on the connections between the amygdala and autism.{{cite journal |vauthors=Schultz RT |year=2005 |title=Developmental deficits in social perception in autism: the role of the amygdala and fusiform face area |journal=International Journal of Developmental Neuroscience |volume=23 |issue=2–3 |pages=125–41 |doi=10.1016/j.ijdevneu.2004.12.012 |pmid=15749240 |s2cid=17078137}}

• Accessory olfactory cortical areas
• Amygdala hijack
• BELBIC
• Intercalated cells of the amygdala
• List of regions in the human brain
• Triune brain
• Amygdalotomy
• Amygdalohippocampectomy
• S.M. (patient)

{{reflist}}

• {{cite journal | vauthors = LeDoux JE | year = 2008 | title = Amygdala | journal = Scholarpedia | volume = 3 | issue = 4| page = 2698 | doi = 10.4249/scholarpedia.2698 | bibcode = 2008SchpJ...3.2698L | doi-access = free }}

{{wiktionary}}

{{commons category|Amygdala}}

• {{BrainMaps|amygdala}}

{{limbic system}}

{{Olfactory system}}

{{Authority control}}