The specificity of the ‘nonspecific’ midline and intralaminar thalamic nuclei

The midline and intralaminar thalamic nuclei have long been considered to be a ‘nonspecific’ nuclear complex that relays the activity of the brain-stem reticular formation to widespread cerebral-cortical areas. Over the past decade, it has become clear that individual midline and intralaminar nuclei each receive specific sets of afferents and project to specific parts of the cerebral cortex and striatum. Moreover, the targets of the thalamocortical and thalamostriatal projections of a given nucleus are interconnected through corticostriatal projections. Therefore, the midline and intralaminar nuclei might have a dual role in corticosubcortical interactions in the forebrain. Through distinct sets of inputs to individual midline or intralaminar thalamic nuclei, these nuclei are in a position to interact selectively with particular, functionally segregated basal-ganglia-thalamocortical circuits. By way of nonselective inputs, in particular from cholinergic brain-stem nuclei, the midline and intralaminar nuclei might act in concert to modify the level of activity of the entire basal-ganglia-thalamocortical system.