Behavioral Neuroscience, lecture on amygdala
Fear Conditioning
IV. Amygdala back to Afferent Pathways to Fear
A. Evolutionarily ancient heterogeneous structure
1. subcortical almond-shaped structure in the rostromedial temporal lobe
in front of the hippocampus
a. located just in front of the temporal horn of the lateral ventricle
and underneath the parahippocampal gyrus (uncus)
2. composed of 4 different functional systems
a. main olfactory + accessory olfactory
i. part of the "nose brain"
(1) heavily connected to the olfactory bulb
(2) expecially the cortical amygdala
b. autonomic
c. cortical
i. especially related to frontal and temporal lobes
3. diverged from struction with functions of both striatum and limbic system
a. consists of phylogenetically new and old divisions
i. multiple developmental origins
b. includes: amygdala and extended amygdala
i. BNST (bed nucleus of the stria terminalis)
c. also includes: striatum and nucleus accumbens
i. striatum - movement
ii. nucleus accumbens - reward, addiction,
motivation, salience
B. Nuclei of the Amygdala and extended Amygdala
1. functional systems of the amygdala are defined by their sensory input
a. have functionally specific outputs
b. specifically directional intra-amygdaloid circuitries
2. the Basolateral complex (BLA): frontotemporal amygdala
a. Lateral nucleus (LA) is the input region of the amygdala
i. from specific sensory regions of the thalamus
ii. sensory information rapidly transferred
to dorsolateral LA
(1) slower to the cortex
(2) produces primal emotional response
(3) preparation for higher cortex input
ii. cortico-amygdaloid pathways - Glutamatergic
iii. BLA complex receives highly processed
sensory information
(1) from prefrontal, temporal & insular cortices
b. reciprocal amygdalocortical pathways
i. to limbic, associational and
1o visual cortices
ii. Glutamatergic
c. BLA closely related to the cerebral cortex
i. histology, histochemistry and connections
are similar to cortex
d. BLA complex projects to the CeA
i. autonomic/somatic signs of fear
e. BLA projects to dorsal striatum and
the ventral striatum/nucleus accumbens
i. approach or avoidance
ii. N. accumbens - autonomic extended amygdala
continuum
(1) BLA involved in motivational
effects of emotion
(2) projects to BNST - autonomic fear, anxiety
f. projects to entorhinal cortex
i. indirectly to the dentate gyrus of the hippocampus
(1) via the perforant path
(2) influences LTP and hippocampal learning
(3) memory of emotional events
ii. medial BLA receives input from CA1
region of hippocampus
(1) and perirhinal cortex
(2) not sensory
g. BLA complex includes basal amygdala
i. basal amygdala: basolateral amygdala
(1) input from the hippocampus
ii. accessory basal nucleus: basomedial amygdala
(1) input from the frontal cortex
2. Cortical Amygdala (CoA)
a. surface of the amygdaloid body
adjacent to the temporal cortex and the MeA
b. 1o input to CoA from the olfactory bulb and olfactory cortex
i. olfactory amygdala
(1) also includes piriform cortex - CoA transition
and anterior amygdala
ii. also accessory olfactory amygdala (posteromedial part)
c. projects to the CeA
3. Medial Amygdala (MeA)
a. input from accessory olfactory
b. input from the hypothalamus
c. projects to the CeA
4. Central Amygdala (CeA)
a. output region of the amygdala
i. GABA projections
(1) connects to extended amygdala - BNST
ii. CRF projections
(1) connections to brainstem
(a) locus ceruleus, raphe
iii. Enkephalin projections
(1) to periaqueductal gray (PAG)
(2) CeA blocks pain via PAG Enk m-opiate-R
(a) also mediated by 5-HT
(3) CeA projections to PAG cause freezing
iv. projects via the stria terminalis
(1) BNST, PVN, nucleus accumbens?
v. projects via the ventral amygdalofugal pathway
(1) brainstem, dorsomedial thalamus,
cingulate gyrus, cortex
vi. not to the striatum
vii. to trigeminal facial motor nucleus
(1) facial expressions of fear
viii. to PnC
(1) enhances startle reflexes
b. CeA controls autonomic nervous system
i. via the PVN in the hypothalamus
ii. and the dorsal motor nucleus of the vagus
(1) HR, BP
c. dual autonomic - limbic association functions
d. input from the BLA, CoA, MeA
i. intra-amygdaloid association fibers
C. Intra-Amygdaloid circuitry
1. LA dorsal Þ LA medial and LA ventral
2. LAm Þ Basal and Accessory Basal and MeA
3. Accessory Basal Þ CeA
a. basal Þ CeA
b. MeA Þ CeA
4. CeA Þ amygdalofugal pathway
5. CeA Þ stria terminalis
D. Function of the Amygdala
1. detection of emotional events
a. production of appropriate responses
b. interpretation of emotional significance
of sensory stimuli
c. assigns emotional significance
d. sexually differentiated
e.generation of emotional aspects of dreams
2. facial recognition neurons
a. and produces facial expressions of fear
3. motivational significance
4. attention
5. regulation of the autonomic nervous system
6. perception of body movements
7. memory
a. especially fear memory
i. fear conditioning
