Frontal Lobes & Hippocampus

Question 1

General function of prefrontal cortex

Answer 1

• 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

Question 2

“subdivisions” of prefrontal cortex

Answer 2

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

Question 3

Inputs/outputs to DLPFC

Answer 3

• 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

Question 4

Consequences of lesion to DLPFC

Answer 4

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

Question 5

Inputs/Outputs to Ventromedial Prefrontal Cortex (aka “orbitofrontal”)

Answer 5

• 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

Question 6

Consequences of lesion to VMPFC

Answer 6

• ==> 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

Question 8

Characteristics of Anterior Cingulate Cortex

Answer 8

• 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

Question 9

General fxn of hippocampus

Answer 9

• 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

Question 10

Consequence of bilateral hippocampal damage

Answer 10

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

Question 11

General structure of hippocampus

Answer 11

• 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.

Question 12

Major cells types w/in hippocampus

Answer 12

• @ 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

Question 13

Major inputs to hippocampal formation

Answer 13

• 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

Question 14

Role of sleep in memory consolidation

Answer 14

• 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

Question 15

Model of memory consolidation

Answer 15

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