Frontal Lobes & Hippocampus Flashcards Preview

Nervous System: Unit IV > Frontal Lobes & Hippocampus > Flashcards

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1

General function of prefrontal cortex

  • executive function
  • PFC can enhance or inhibit other neuronal networks
    • PFC is modulatory, not transmissive
  • "railroad switch operator" of the brain
  • frontal lobe damage:
    • leaves complex behavior intact
    • subject is unable to coordinate behavior in a task-appropriate way

2

"subdivisions" of prefrontal cortex

  • dorsolateral prefrontal cortex
  • ventromedial prefrontal cortex
  • anterior cingulate cortex

3

Inputs/outputs to DLPFC

  • inputs = somatosensory, visual, auditory cortical association areas
    • also involved in some basal ganglia-thalamocorical circuits
  • outputs = directed towards premotor cortex and somatosensory association cortices
    • may also reach brainstem

4

Consequences of lesion to DLPFC

  • lesions ==> inability to employ intentions (goals) to modualte attention
  • perseveration = inability to switch attention
  • environmental dependency = undue environmental cues necc. to complete a task

5

Inputs/Outputs to Ventromedial Prefrontal Cortex (aka "orbitofrontal")

  • inputs = prominent olfactory, gustatory, and visceral sensory info + strong input from amygdaloid complex and parahippocampal cortices
    • some info from association cortices also
    • involved in re-entrant basal ganglia thalamocortical circuits
  • outputs =
    • cholinergic cells @ basal forebrain
    • monoaminergic cells @ brainstem/hypothalamus
    • lateral/posterior hypothalamus (stress/autonomic control)
    • autonomic outputs to brainstem/spinal cord

6

Consequences of lesion to VMPFC

  • ==> characteristic performance on Iowa Gambling Task
    • loss of ability to estimate risk/reward of behaviors
    • loss of inhibition/aversion/stress associated with future prospect of negative outcome
  • e.g. Phineas Gage
  • ==> inadequate inhibition of aggression, sexual behavior, anxiety, and appetite

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Characteristics of Anterior Cingulate Cortex

  • reciprocal relationship w/autonomic and limbic structures
  • involved in attention (higher activity w/increased attentional demands)
  • stroke @ anterior cingulate ==> abulia = lack of will
    • patients can be completely akinetic and mute in some cases
    • ==> poor motivation, apathy, lack of will

9

General fxn of hippocampus

  • critical for formation of declarative memories
  • temporary involvement in memory
    • memories ==> neocortical stores via process of memory consolidation
  • acts as brain's "search engine" to retrieve memories ==> recall and planning
  • collaborates with several brain structures, esp. entorhinal cortex

10

Consequence of bilateral hippocampal damage

  • e.g. patient H.M. ==> loss of ability to form:
  • declarative memory
  • episodic memory
  • spatial memory
    • "place cells" @ hippocampus encode specific locations in environment

11

General structure of hippocampus

  • a) the dentate gyrus
  • b) the hippocampus (also known as Ammon’s Horn or cornu ammonis)
  • c) the subiculum = transition zone between the three layered hippocampus and the 6 layered entorhinal cortex. 

12

Major cells types w/in hippocampus

  • @ dentate = granule cells
  • @ hippocampus = pyramidal cells
    • CA3 field = close to dentate
    • CA2 field
    • CA2 field = merges w/subiculum
  • @ all layers = local circuiot neurons (interneurons)
    • inhibitory inputs to other cells

13

Major inputs to hippocampal formation

  • entorhinal cortex
    • "trisynaptic circuit"
      • entorhinal ==perforant path==> dentate gyrus ==mossy fibers==> CA3 field ==schaffer collaterals==> CA1 (OR some leave via fornix OR synapes on other CA3 neurons) ==> subiculum ==> entorhinal cortex ==> cortical association areas
  • septal nuclei

14

Role of sleep in memory consolidation

  • performance on learning/memory tasks improves following sleep
  • cortical and hippocampal neruons are synchronously activated during sleep
  • behavioral experiences are replayed @ neocortex and hippocampus during sleep session

15

Model of memory consolidation

  1. hippocampus rapidly and automatically acquires information
    • but has limited capacity ==> rapid forgetting
  2. info stored @ hippocampus becomse permentaly stored in cortex
  3. hippocampus plays critical role in genesis of cortical memories
  • memory remains @ hippocampus for ~ 1 week

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