Specific thalamus nuclei have, each, a limited and well-defined target area in the cerebral cortex from where they receive a well-defined and characteristic return flow of nerve signals. Most thalamus nuclei are included.
Nonspecific thalamus nuclei have round-trip connections with large overlapping areas of the cerebral cortex. The nonspecific thalamus nuclei receive mixed signal inputs from the basal ganglia, brainstem (especially from formatio reticularis), cerebellum and spinal cord.
They are considered to interact with the cerebral cortex during sleep and awakening, as well as in connection with pain-triggered emotions and directed attention.
The core group includes the intralaminar and anterior thalamus nuclei.