Thalamic deactivation during early implicit sequence learning: a functional MRI study.

Previous research has implicated the striatum in implicit sequence learning. However, imaging findings have been inconsistent with regard to activity within the thalamus during performance of such tasks. Contemporary models of cortico-striato-thalamic circuitry suggest opposing influences on thalamic activity; suppression of thalamic activity is mediated by the indirect pathway and enhancement is mediated by the direct pathway. Using functional magnetic resonance imaging, we studied activity within human thalamus during early and late phases of an implicit sequence learning task known to reliably recruit the striatum. Significant deactivation (decreased signal relative to a baseline condition) was observed within the thalamus during early implicit learning. This finding is consistent with models of cortico-striato-thalamic function and specifically supports a profile of early 'thalamic gating' via the indirect pathway.