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Amygdala: What does it do?

Jacinta Robenstine

Amygdala - The Basics

· Link between fearful stimuli and fear expression · Fear conditioning · Highly adaptive for survival

http://thebrain.mcgill.ca/flash/a/a_04/a_04_cr/a_04_cr_peu/a_04_cr_peu.html

http://library.thinkquest.org/C0110291/images/brain1_large.gif

Structure

· 3 Main Groups · Basolateral

­ Cerebral cortex, prefrontal cortex

· Medial

­ Olfactory bulb

· Central and anterior

­ Brainstem, hypothalamus, other areas

http://thebrain.mcgill.ca/flash/i/i_04/i_04_cl/i_04_cl_peu/i_04_cl_peu.html

Physiological effects

Conditioned Fear

· Best Studied: Tone paired with fearinducing foot shock · Lateral nucleus, input from medial geniculate nucleus, auditory cortex · Induces LTP, necessary for formation of fear memories · Long Term Potentiation ­ increases sensitivity to stimulus

Early Phase LTP

· High frequency stimulus open glutamate channel hyperpolarization removes Mg++ from N-Methyl-D-aspartate (NMDA) influx of Ca++

Late Phase LTP

· Ca++ activates PKA MapK phosphorylation of CREB1 CREB1 overcomes repressor effects of CREB2 gene translation and protein synthesis more excitatory receptors formed

http://www.scholarpedia.org/article/Image:Amygdala_Figure_8.jpg

Amygdala & Norepinephrine

· In forming fear memories:

­ Connections with Locus coeruleus ­ Glutamates spillover onto receptor in noradrenergic terminal ­ NE release onto -adrenergic receptors on amygdala ­ -adrenergic G-protein coupled adenylate cyclase cAMP PKA MAPK ­ Maintenance of Late LTP

Amygdala & Norepinephrine

· Implicated in anxiety · Increased release into pre-frontal cortex · Pre-frontal cortex ­ assigning emotional significance

Amygdala and Serotonin

· Conditioned fear stimuli pathway · Central amygdala paraventricular nucleus of hypothalamus Release of corticosterone · Activate dorsal raphe increase 5-HT projections to amygdala · 5-HT inhibits glutamate activity in LA · Low serotonin anxiety disorders

Facial Memories

· Amygdala involved in facial recognition · Distinguish aggressive or fearful expressions · Amygdala and attention to eyes · Autism ­ limited eye contact, no facial adaptation in amygdala

Facial Recognition

· William syndrome ­ microdeletion on Chromosome 7 · No response to fearful faces, higher attention to happy, greater social anxiety

Urbach Wiethe Disease

· Lipid proteinosis, autosomal recessive · Cutaneous, mucosal, visceral deposits of glycoprotein material · Beaded eyelids, hoarseness from laryngeal deposits · Often calcifies amygdala

http://dermatology.cdlib.org/95/case_reports/lipoid/thappa.html

Urbach-Wiethe Disease

· Classic study ­ Adolphs et. al, 1995 · Not all lose ability to determine fear · Do lose ability to filter emotionally significant memories

Amygdala & Alzheimers

· -amyloid plaques and neurofibrillary tangle build-up in amygdala (Kile et. al 2009) · Klüver-Bucy Syndrome symptoms

Anxiety and Alcohol

(Pandey et al. 2003)

· Alcohol withdrawal causes anxiety · Decrease of Neuropeptide Y implicated · Only seen in Central amygdala

Left vs. Right Amygdala

· Left

­ Monitors gaze tracking and whiteness of eyes ­ More fear response viewed in fMRI imaging

· Right

­ Important in consolidating fear memories ­ NE antagonists inhibit long-term fear memory formation

References

· · · · · · · · · · R. Adolphs, D. Tranel, H. Damasio, and A.R. Damasio. (1995). Fear and the Human Amygdala. J. Neuroscience. 15: 5879-5891. Davis, M. (1997). Neurobiology of Fear Responses: The Role of the Amygdala. J. Neuropsychology. 9(3): 382-394. Haas, B.W.; Mills, D.; Yam, A.; Hoeft, F., Bellugi, U. and Reiss, A. (2009). Genetic Influences on Sociability: Heightened Amygdala Reactivity and Event-Related Responses to Postive Social Stimuli in Williams Syndrome. J. Neuroscience. 29(4): 1132-1139. Huang, Y. and Kandel, E.R. (1998) Postsynaptic Induction and PKA-dependent Expression of LTP in the Lateral Amygdala. Neuron. 21: 169-178. Huang, Y., Martin, K.C., and Kandel, E.R. (2000) Both Protein Kinase A and Mitogen-Activated Protein Kinase are Require in the Amygdala for the Macromolecular Synthesis Dependent Late Phase of the Long-Term Potentiation. J. Neuroscience. 20(17): 6317-6325. Hurlemann, R. et al. (2007). Amygdala Control of Emotion-Induced Forgetting and Remembering: Evidence from Urbach-Wiethe Disease. Neuropsychologia. 45: 877-884. Josselyn, S.A. et al. (2001). Long-term Memory is Facilitated by cAMP Response Element Binding Protein Overexpression in the Amygdala. J. Neuroscience. 21(7): 2404-2412. Kile, S.J et al. (2009). Alzheimer Abnormalities of the Amygdala with Kluver-Bucy Syndrome Symptoms. Arch Neurology. 66(1): 125-129. Lombardo, M.V., Chakrabarti, B. and Baron-Cohen, S. (2009). The Amygdala in Autism: Not Adapting to Faces? Am J Psychiatry. 166(4): 395-397. Pandey, S.C., Roy, A., and Zhang, H. (2003). The Decreased Phosphorylation of Cyclic Adenosine Monophosphate (cAMP) Response Element Binding (CREB) Protein in the Central Amygdala Acts as a Molecular Substrate for Anxiety Related to Ethanol Withdrawal in Rats. Alcohol Clin Exp Res. 27(3): 396-409. Wand, G. (2005). The Anxious Amygdala: CREB Signaling and Predisposition to Anxiety and Alcoholism. Journal of Clinical Investigation. 115(10): 2697-2699.

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