Dopamine

• Dopamine


  The 'pleasure chemical'
• Parkinsons Disease

  • Gradual loss of dopamine neurons in the nigrostriatal pathway
  • No cure currently
  • Primarily a motor disorder - bradykinesia (slowed movement), akinesia (impairment of voluntary movement) and tremor
  • 1980s/90s - found deficits in executive control functions in PD - eg. Planning, working memory, attentional set-shifting
• How does dopamine influence cognitive control?

  • Dopamine might play different roles depending on the site of action
  • D1 receptors are more prevalent in the PFC - function linked to stability of representations
  • D2 receptors are more prevalent in the striatum - function linked to flexible behavior
  • Dopamine might achieve a balance of stability and flexibility by exerting different effects on striatal and PFC activation
• Van Schouwenberg et al. (2010)

  • Gating role for basal ganglia in cognition - flexible updating of current goal states into PFC
• Evidence consistent with a dual role for dopamine in maintaining stability of responding (PFC) and enabling flexible switching (striatum)
• Perhaps dopaminergic signaling in the striatum can account for individual differences in traits (e.g. impulsivity) that are risk factors for ADHD
• Colour of fixation cross instructed subjects to encode faces or scenes

  1. Trials were either switch (attend to different stimulus than the previous trial) or nonswitch (attend to the same stimulus as previous trial)

  2. Cools et al examined effects of bromocriptine (D2 receptor antagonist) on switching behaviour and neural activation in the striatum
• Complex emotions


  • Combinations of basic emotions
  • May be socially or culturally learned
  • Requires cognitive processing
  • E.g. regret (also grief, jealousy)
• Basic emotions


  • Unique characteristics
  • Developed through evolution
  • Reflected in facial expressions
  • Relatively automatically generated
  • E.g. Fear, sadness, happiness, anger, disgust, suprise
• The Amygdala plays a key role in fear

  • Translates threatening stimuli into a behavioural response not in the conscious experience of fear
• Learning, Emotion and the amygdala: Fear Conditioning

  1. Tone alone (CS) – No response

  2. Shock + Tone – Startle (UR)

  3. Tone alone – Startle (CR)

  4. Shock alone (US) – Normal startle (UR)
• Extinction


  1. Tone alone – startle (CR)

  2. Tone alone –startle (CR)

  3. Tone alone – No startle
• Quirk et al (1995) - As a result of fear conditioning, tone-evoked firing rate of cells in LA increased in 1/4 of the cells studied
• Role of the amygdala in fear conditioning

  • Amygala lesions block fear learning
  • Rats with amygdala lesions do not learn to associate the noise (CS) with the shock (US) to produce a fear response (CR)
  • LeDoux (1996)
• Feinstein et al. (2013)

  • Patients inhaled CO2 – method of inducing panic
  • Measured rates of panic attacks and subjective fear/panic
  • Findings:
  • Intact fearful response to CO2 inhalation in patients missing both amygdalae - patients can experience fear
  • Amygdala isn't necessary for the conscious experience of fear
• Bechara et al. (1995) studied 3 patients – one with amygdala lesion, one with hippocampal lesion, one with damage to both structures


  Findings:

  • Amygdala damage = impaired SCR to the CS but intact factual learning
  • hippocampus damage = normal SCR to the CS but impaired factual learning
  • Amygdala & hippocampus damage = impaired SCR to CS and impaired factual learning
• LeDoux - 2 emotion systems

  • High road = Slow, Conscious experience, Full sensory analysis of threat
  • Low road = Fast, uncinscious, immediate response
• Role of straitum & dopamine:

  • Striatum plays a key role in executive function
  • Parkinson’s Disease = deficit in cog lexibility suggesting a role for striatal dopamine
  • Effects of dopamine on executive function may depend on site of action
  • Striatum – Cognitive flexibility
  • PFC – Cognitive stability
• Brozoski (1979)


  Dopamine depletion in the PFC of monkeys causes a deficit in spatial working memory nearly as severe as complete ablation (removal)