OFC

• Orbitofrontal cortex (OFC)


  Region involved in decision making
• Striatum


  Region involved in executive function
• Dopamine


  The 'pleasure chemical'
• 'Cold' cognition


  Regions in lateral/medial PFC (DLPFC, VLPFC, ACC) are doing something different from the orbitofrontal cortex (OFC)
• 'Hot' cognition


  Role of the Orbitofrontal Cortex in Cognitive Control
• Problems with reversal learning hypothesis of OFC function:

  • Monkeys with OFC lesions do not always show reversal learning deficit.
• Recent perspectives on OFC function

  • Serves as an 'accountant', converting info about outcomes to 'common neural currency' on which to base choices
  • May account for the role OFC plays in generation of complex emotions
• Striatum (basal ganglia)


  Region involved in executive function
• Dopamine (DA)


  A neurotransmitter (chemical released by neurons to transmit an electrical signal between one neuron and another)
• Dopamine (DA)


  • Produced by dopaminergic neurons in the ventral tegmental area (VTA) and substantia nigra (SN) in the midbrain
  • D1 receptors much more abundant in PFC
  • D2 receptors more abundant in striatum
  • Dopaminergic signalling occurs via several different pathways.
• Dopamine (DA) functionRole of DA in addiction is well established

  • Modern theories emphasise learning and motivation over pleasure ('hedonic impact' of rewards)
  • Drugs of abuse enhance DA function by acting on midbrain neurons to increase extracellular concentrations of DA transiently
  • DA neurons encode reward prediction error - discrepancy between expected and gained reward (Schultz, 1998)
  • Prediction errors play a key role in the development of addiction
• Brozoski (1979) – dopamine depletion in the PFC of monkeys causes a deficit in spatial working memory nearly as severe as complete ablation (removal)
• Parkinson's Disease


  • Gradual loss of dopamine neurons in the nigrostriatal pathway.
  • Primarily a motor disorder
  • Currently no cure
  • Studies in the 1980s/90s found deficits in executive control functions in PD
• How does dopamine influence cognitive control?

  • Dopamine might play different roles depending on the site of action
  • D1 receptors = prevalent in the PFC – stability of representations
  • D2 receptors =prevalent in the striatum – flexible behavior
  • Dopamine might balance stability and flexibility by exerting different effects on striatal and PFC activation.
• Summary – role of striatum and dopamine in executive function

  • Striatum plays a key role in executive function
  • Parkinson's Disease involves a deficit in cognitive flexibility suggesting a role for striatal dopamine
  • Effects of dopamine on executive function may depend on site of action

  Striatum – Cognitive flexibility

  PFC – Cognitive stability
• Bechara et al (1994)

  • IOWA gambling task

  Findings :

  • Controls avoided risky decks – chose ones with overall profit
  • Patients w lesions to OFC preferred risky decks
• Bechara (1996)

  • Skin conductance

  Findings:

  • SCRs = relatively equal in all ppts
  • Anticipatory SRCs = reduced in patients with OFC lesions