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 th e brain-stem reticular formation to widespread cerebral-cortical areas . Over the past decade, it has become clear that individual midline an d intralaminar nuclei each receive specific sets of afferents and proj ect to specific parts of the cerebral cortex and striatum. Moreover, t he targets of the thalamocortical and thalamostriatal projections of a given nucleus are interconnected through cortico-striatal projections . Therefore, the midline and intralaminar nuclei might have a dual rol e in cortico-subcortical interactions in the forebrain. Through distin ct sets of inputs to individual midline or intralaminar thalamic nucle i, these nuclei are in a position to interact selectively with particu lar, functionally segregated basal-ganglia-thalamocortical circuits. B y way of nonselective inputs, in particular from cholinergic brain-ste m nuclei, the midline and intralaminar nuclei might act in concert to modify the level of activity of the entire basal-ganglia-thalamocortic al system.