Figure 1.

Circuit diagrams illustrating (A) the synaptic relationships between key subcortical nuclei, and (B) the convergence in the striatum of learning signals from these nuclei. In both diagrams excitatory projections are green, inhibitory are red, and the neuromodulatory dopaminergic projection is in gray. (A) Putative subcortical loops are formed between the SC, rostral or caudal intralaminar nuclei, and through the basal ganglia to return to the SC. SNc, substantia nigra pars compacta; SNr/GPi, substantia nigra pars reticulata and globus pallidus internal segment. (B) Convergence onto striatal spiny projection neurons (labeled “S”) of a short-latency sensory signal from the SC, and a related short-latency dopaminergic signal from the SNc. When this conjunction is aligned with cortical input to spiny neurons, representing motor efferent copy, then the factors previously identified as necessary for potentiation of corticostriatal synapses are present (Reynolds and Wickens, 2002). CM/Pf, center median and parafascicular nuclei.