Frontal Lobes and Hippocampus Flashcards
Describe the result of bilateral hippocampal dysfunction
- pt HM
- cannot form new memories (anterograde amnesia)
- hippocampus needed for memory of facts and events (declarative or episodic memory)
- (HM could learn new skills, procedures, games etc)
- problems w/ spatial memory (declarative memory concerned with locations)
Describe the result of bilateral hippocampal dysfunction
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Explain the apparent importance of sleep in hippocampal-dependent memory consolidation
- information is originally encoded and registered, memory of these new stimuli becomes retained in both the hippocampus and cortical regions
- Information originally stored in the hippocampus becomes permanently stored in the cortex and independent of the hippocampus.
- initial hippocampus dependent stage (1 week)
- hippocampus has ltd storage space
- Coordinated replay during SWS between hippocampus and cortex makes memories independent of hipp.
- During sleep, both hippocampal and neocortical neurons (for example in the visual cortex) have a tendency to be activated in a temporal sequence similar to the sequence seen during behavior.
Explain the apparent importance of sleep in hippocampal-dependent memory consolidation
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Divisions of frontal lobes
primary motor cortex
premotor cotex
prefrontal cortex (receives input from mediodorsal nucleus of thalamus; sometimes includes anterior cingulate cortex)
PFC function
=executive function:
-enhance/inhibit motor, sensory func, and interoceptive (emotional control) stimuli
how does enhancement/inhibition occur?
- short term: modulation of “effective connectivity”
- long term: modulation of synaptic strengths
PFC acts as “switch operator” for train tracks
modulatory rather than transmissive role
PFC division
DLPFC– representation, planning and selection of goal directed behaviors
VMPFC (orbitofrontal or orbitomedial PFC)– assessing positive and negative valence of stimuli and computes gains/losses of potential actions
anterior cingulate cortex (medial surface)– detects conflicts b/t current attn and goal, promotes action toward a goal.
have projections thru striatal-pallidal-thalamocortical loops
DLPFC inputs, outputs, lesions*
inputs: somatosensory, visual and auditory cortical association areas in the parietal, occipital and temporal lobes. Included in basal ganglia-thalamocortical circuits.
DLPFC is modulated by cholinergic and monoaminergic inputs from basal forebrain and brainstem
outputs: directed towards the premotor cortex, as well as to the somatosensory association cortices, from which it also receives info. Also: may reach brainstem structures like the deep layers of the superior colliculus, the midbrain tegmentum, and part of the PAG
Lesions: inability to employ intention (goals) to modulate attention (task at hand)
- Fail to switch attention–>perseveration
- environmental dependency (need external cues to complete goals.)
Ventromedial (or orbitofrontal) PFC input, output, lesion*
input: somatosensory, visual and auditory association areas, lesser extent than the DLFPC; olfactory, gustatory and visceral sources are much more prominent
- basal amygdaloid complex and the parahippocampal cortices
- is involved in re-entrant basal ganglia-thalamocortical circuits that involve parts of the basal ganglia innervated by the hippocampus and amygdala and limbic associational cortices.
outputs:
- cholinergic and monoaminergic innervation of widespread cortical and subcortical regions of the forebrain
- further projects to the lateral and posterior hypothalamus, where it interconnects with stress and autonomic centers
LESIONS:
- on Iowa Gambling Task: keep drawing from “bad decks”, even though they’re losing; no stress responses to impending punishment
- impaired ability to estimate risk/reward assoc w/ certain behaviors
- phineas gage
- inadequate inhibition of aggression, sexual behavior, anxiety, and appetitive functions
Frontal subcortical circuits
DLPFC–> caudate–>GPi–>MD thalamus back to DLPFC
VMPFC–>nuc accumbens–> GPi–> MD thalamus back to VMPFC
ACC–>caudate/nuc accumbens–>GPi–>MD thalamus and back to ACC
Frontal subcortical circuits
DLPFC–> caudate–>GPi–>MD thalamus back to DLPFC
VMPFC–>nuc accumbens–> GPi–> MD thalamus back to VMPFC
ACC–>caudate/nuc accumbens–>GPi–>MD thalamus and back to ACC
grid cells
- neurons found not in the hippocampus but in the entorhinal cortex, the principal input structure to the hippocampus
- spatial firing fields all at equal distances from their neighbors
- dynamic computation of self-position
grid cells
- neurons found not in the hippocampus but in the entorhinal cortex, the principal input structure to the hippocampus
- spatial firing fields all at equal distances from their neighbors,
What does high-freq stim of hippocampal input fibers lead to?
- long-lasting enhancement of transmission efficacy at downstream synapses (LTP)
- Hebbian
Subdivision of hippocampus
“CA fields”
CA3 field is adjacent to the dentate and extends through the opening or hilus of the dentate gyrus; a short CA2 field follows; and a more extensive CA1 field merges with the subiculum
