The Hippocampus and Anxiety Flashcards
Where is the human hippocampus located?
In medial temporal lobe
Which procedure did patient HM have and what was its effect?
Bilateral medial temporal lobectomy
Caused anterograde amnesia - no memory of new events
Which type of memory is the hippocampus required for?
Episodic
Where are grid cells found?
Medial entorhinal cortex
What does the argument that there is no difference between the dorsal and ventral hippocampus suggest?
Both encode space
vHPC cells encode place on larger scale - larger place fields
How does the medial entorhinal cortex support the idea that there is no difference between the roles of the vHPC and dHPC?
mEC is major input to HPC
Gradient of grid cell field scales along DV axis - small at dorsal end, large at ventral end
mEC DV axis directly maps onto HPC DV axis
What is the basic hippocampal circuit?
Dentate gyrus to CA3 to CA1
How do anatomical connections of vHPC and dHPC differ?
vHPC has strong reciprocal connections with amygdala
vHPC projects to PFC, BNST, subcortical regions associated with HPA axis
Visuospatial input from primary sensory cortex to dorsal 2/3 of HPC - but olfactory input along whole DV axis
How do molecular markers differ along the DV HPC axis?
More calretinin+ mossy cells in vHPC
Higher density of DAergic, NAergic, serotonergic terminals in vHPC
How do HPC lesions affect contextual fear conditioning acquisition and expression?
vHPC lesion - blocks acquisition and expression
dHPC lesion - no effect
How do HPC lesions affect intrinsic fear response (without learning)?
vHPC lesion - faster to enter anxiogenic environments (e.g. light, exposed), increased social interaction, decreased hyponeophagia (faster to eat in novel environments), smaller rise in plasma corticosterone levels after confinement - reduced anxiety
dHPC lesion - no/lower effects
How do HPC lesions affect activity levels and what is a possible explanation for this?
dHPC lesion - hyperactivity
vHPC lesion - no effect
Tendency to move more in novel environments - could be dHPC lesion failure to recognise location - causes increased novelty response
How do amygdala lesions affect intrinsic fear response (without learning)?
No effect on elevated plus maze/successive alley test
Decreased social interaction
Hyponeophagia
Define fear
Phasic response to explicit cues - often conditioned - intense, short-lived - can lead to later anxiety
Define anxiety
Tonic response to diffuse aversive cues - often unconditioned - prolonged, moderate
Which brain area is key for fear?
Amygdala
Which brain area is key for anxiety?
vHPC
Which brain areas are required for Pavlovian fear conditioning?
Amygdala
Which brain areas are required for contextual fear conditioning?
Amygdala and hippocampus
What is the role of the lateral nucleus and the effect of its damage on fear conditioning?
Impairs conditioning to a stimulus (Pavlovian) - contextual fear conditioning intact
Sensory input to amygdala via lateral nucleus - damage prevents making association
What is the role of the basolateral nucleus and the effect of its damage on fear conditioning?
Impairs contextual fear conditioning - conditioning to a stimulus (Pavlovian) intact
vHPC (CA1 and subiculum) project to basolateral nucleus
What is the role of the central nucleus and the effect of its damage on fear conditioning?
Impairs conditioning to a stimulus (Pavlovian) and contextual fear conditioning
Output to motor systems - damage impairs fear expression (e.g. increased BP, freezing)
What is the evidence for LTP-dependent changes in the firing of lateral nucleus cells in fear conditioning?
Block VGCC and NMDARs in lateral nucleus - impairs fear conditioning
Block protein synthesis and PKA in lateral nucleus - impairs fear conditioning
