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[0] Atallah HE, Lopez-Paniagua D, Rudy JW, O'Reilly RC, Separate neural substrates for skill learning and performance in the ventral and dorsal striatum.Nat Neurosci 10:1, 126-31 (2007 Jan)

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ref: Atallah-2007.01 tags: striatum skill motor learning VTA substantia nigra basal ganglia reinforcement learning date: 12-31-2011 18:59 gmt revision:3 [2] [1] [0] [head]

PMID-17187065[0] Separate neural substrates for skill learning and performance in the ventral and dorsal striatum.

  • good paper. via SCLin's blog. slightly confusing anatomical terminology.
  • tested in rats, which has a anatomically different basal ganglia system than primates.
  • Rats had to choose which driection in a Y maze based on olfactory cues. Normal rats figure it out in 60 trials.
  • ventral striatum (nucleus accumbens here in rats) connects to the ventral prefrontal cortices (for example, the orbitofrontal cortex)
    • in primates, includes the medial caudate, which has been shown in fMRI to respond to reward prediction error. Neural activity in the caudate is attenuated when a monkey reaches optimal performance.
  • dorsal parts of the striatum (according to web: caudate, putamen, globus pallidus in primates) connect to the dorsal prefrontal and motor cortices
    • (according to them:) this corresponds to the putamen in primates. Activity in the putamen reflects performance but not learning.
    • activity in the putamen is highest after successful learning & accurate performance.
  • used muscimol (GABAa agonist, silences neural activity) and AP-5 (blocks NMDA based plasticity), in each of the target areas.
  • dorsal striatum is involved in performance but not learning
    • Injection of muscimol during acquisition did not impair test performance
    • Injection of muscimol during test phase did impair performance
    • Injection of AP-5 during acquisition had no effect.
    • in acquisition sessions, muscimol blocked instrumental response (performance); but muscimol only has a small effect when it was injected after rats perfected the task.
      • Idea: consistent behavior creates a stimulus-response association in extrastriatal brain areas, e.g. cerebral cortex. That is, the basal ganglia is the reinforcement signal, the cortex learns the association due to feedback-driven behavior? Not part of the habit system, but make and important contribution to goal-directed behavior.
      • This is consistent with the observation that behavior is initially goal driven but is later habitual.
    • Actually, other studies show that plasticity in the dorsal striatum may be detrimental to instrumental learning.
    • The number of neurons that fire just before the execution of a response is larger in the putamen than the caudate.
  • ventral striatum is involved in learning and performance.
    • Injection of AP-5 or muscimol during acquisition (learning behavior) impairs test performance.
    • Injection of AP-5 during test performance has no effect , but muscimol impairs performance.
  • Their data support an actor-director-critic architecture of the striatum:
    • Actor = dorsal striatum; involved in performance, but not in learning them.
    • Director = ventral striatum; quote "it somehow learns the relevant task demands and directs the dorsal striatum to perform the appropriate action plans, but, crucially, it does not train the dorsal striatum"
      • ventrai striatum acts through the orbitofrontal cortex that mantains representations of task-reward contingencies.
      • ventral striatum might also select action selection through it's projections to the substantia nigra.
    • Critic = dopaminergic inputs from the ventral tegmental area and substantia nigra.