Cortico-striatal plasticity for action-outcome learning using spike timing dependent eligibility

We recently proposed that short-latency, sensory-evoked dopamine release is critical for learning action-outcome causality [1]. If an action causes an unexpected outcome associated with a phasic visual event, there will be a phasic burst of dopamine in the striatum. Subsequent reinforcement of the striatal response to the cortical representation of the action then makes the selection of the action (and its outcome) more likely; i.e. there is "repetition biasing" of action selection. This, in turn, facilitates associative learning of the action-outcome pairing elsewhere in the brain. Here, we present a model of cortico-striatal plasticity in medium spiny neurons (MSNs) that could form the basis for a quantitative account of action-outcome learning in basal ganglia.

When phasic dopamine is elicited by the causal action, it induced a rapid increase in MSN response that would be the foundation for inducing repetition bias of action selection. Further, the MSN has become receptive to the action request through synaptic pattern matching (Fig 1b top panel). Subsequent trials induce more selective synaptic patterning (reduced response at trial 1200). Dopamine dips (caused by assigning a noxious value to the outcome) induce a reduction in response. We conclude that the recently discovered complex dopamine-receptor dependent forms of STDP [2] can lead to cortico-striatal plasticity that can support action-outcome learning.