The Reward Factor in the Control of Action: A Neurophysiological Theory Johan Lauwereyns Victoria University of Wellington, New Zealand
How does the brain incorporate reward value in the control of action?
Studied in monkeys using saccadic eye movement tasks with asymmetrical reward schedule
Biased Saccade Task (BST)
Target position = unpredictable
Biased Saccade Task (BST) Reward association = known
Biased Saccade Task (BST)
No escape!
Biased Saccade Task (BST)
Saccade-related brain areas (macaque monkey) FEF: frontal eye field SEF: supplementary eye field LIP: area LIP of parietal cortex CD: caudate nucleus SNr: substantia nigra pars reticulata SC: superior colliculus Clbm: cerebellum SG: brainstem saccade generators
DA neuron responds to Reward & Reward Predictor
Signal Noise Neuronal activity Noise Signal +
Improved discrimination
Improved discrimination: Synergistic, multiplicative Sensory properties Non-linearly enhanced by reward Response = Input * Reward Gain Prefrontal cortex, parietal cortex Superior colliculus
General increase
General increase: Prospective, additive Bias in anticipatory activity Linearly enhances sensory activity Response = Input + Reward Bias Prefrontal cortex, basal ganglia Superior colliculus
Improved discrimination & General increase
Combination of both mechanisms Seen in all areas Loops between FC, BG and SC But most common in Superior Colliculus Response = (Input * Reward Gain) + Reward Bias On toward the oculomotor plant
Dopamine
Excitation
Dopamine Excitation Disinhibition
Synergistic, multiplicative Dopamine Excitation Disinhibition
Prospective, additive Synergistic, multiplicative Dopamine Excitation Disinhibition