CiteULike: awooga's abstract-model

Solving the Distal Reward Problem through Linkage of STDP and Dopamine Signaling.

Eugene M Izhikevich — 2007-01-17T21:02:55-00:00

Cereb Cortex (13 January 2007)

In Pavlovian and instrumental conditioning, reward typically comes seconds after reward-triggering actions, creating an explanatory conundrum known as "distal reward problem": How does the brain know what firing patterns of what neurons are responsible for the reward if 1) the patterns are no longer there when the reward arrives and 2) all neurons and synapses are active during the waiting period to the reward? Here, we show how the conundrum is resolved by a model network of cortical spiking neurons with spike-timing-dependent plasticity (STDP) modulated by dopamine (DA). Although STDP is triggered by nearly coincident firing patterns on a millisecond timescale, slow kinetics of subsequent synaptic plasticity is sensitive to changes in the extracellular DA concentration during the critical period of a few seconds. Random firings during the waiting period to the reward do not affect STDP and hence make the network insensitive to the ongoing activity-the key feature that distinguishes our approach from previous theoretical studies, which implicitly assume that the network be quiet during the waiting period or that the patterns be preserved until the reward arrives. This study emphasizes the importance of precise firing patterns in brain dynamics and suggests how a global diffusive reinforcement signal in the form of extracellular DA can selectively influence the right synapses at the right time.

Dopamine: generalization and bonuses

Sham Kakade — 2006-11-09T17:17:43-00:00

Neural Networks, Vol. 15, No. 4-6. ( 2002), pp. 549-559.

In the temporal difference model of primate dopamine neurons, their phasic activity reports a prediction error for future reward. This model is supported by a wealth of experimental data. However, in certain circumstances, the activity of the dopamine cells seems anomalous under the model, as they respond in particular ways to stimuli that are not obviously related to predictions of reward. In this paper, we address two important sets of anomalies, those having to do with generalization and novelty. Generalization responses are treated as the natural consequence of partial information; novelty responses are treated by the suggestion that dopamine cells multiplex information about reward bonuses, including exploration bonuses and shaping bonuses. We interpret this additional role for dopamine in terms of the mechanistic attentional and psychomotor effects of dopamine, having the computational role of guiding exploration.

Actor-critic models of the basal ganglia: new anatomical and computational perspectives

Daphna Joel — 2006-05-28T18:09:47-00:00

Neural Netw., Vol. 15, No. 4. (June 2002), pp. 535-547.

A computational model of the functional role of the ventral-striatal D2 receptor in the expression of previously acquired behaviors.

AJ Smith — 2005-03-16T15:50:59-00:00

Neural Comput, Vol. 17, No. 2. (February 2005), pp. 361-395.

The functional role of dopamine has attracted a great deal of interest ever since it was empirically discovered that dopamine-blocking drugs could be used to treat psychosis. Specifically, the D2 receptor and its expression in the ventral striatum have emerged as pivotal in our understanding of the complex role of the neuromodulator in schizophrenia, reward, and motivation. Our departure from the ubiquitous temporal difference (TD) model of dopamine neuron firing allows us to account for a range of experimental evidence suggesting that ventral striatal dopamine D2 receptor manipulation selectively modulates motivated behavior for distal versus proximal outcomes. Whether an internal model or the TD approach (or a mixture) is better suited to a comprehensive exposition of tonic and phasic dopamine will have important implications for our understanding of reward, motivation, schizophrenia, and impulsivity. We also use the model to help unite some of the leading cognitive hypotheses of dopamine function under a computational umbrella. We have used the model ourselves to stimulate and focus new rounds of experimental research.