The nucleus basalis magnocellularis Meynert (NbmM) complex--a central integrator of coded "limbic signals" linked to neocortical modular operation? A proposed (heuristic) model of function.

Since the discovery of the NbmM as an afferent cholinergic projection system supplying the entire cortical mantle, its morphological organization has been extensively investigated. Applying the principle of convergence and divergence--an important principle of the integrative function of the CNS discerned by Sherrington a long time ago--the topistic organization of this projection could enable the system to exert a high degree of integrative influence on cortical neuronal activity. Candidates for putative regulatory afferents to the NbmM in the main seem to originate within structures linked to the limbic system. With the main centres of this system--ventral tegmental area, mediodorsal thalamus, basolateral amygdala, limbic compartment of striatum, hippocampal formation, paralimbic cortex--the NbmM seems to be interconnected bidirectionally by feedforward and feedback connections. With this central position within the limbic circuitries the NbmM complex--regarded as a morpho-functional entity--could play a key role, in both (i) the filtering and selection of "limbic signals" carrying coded information from the CNS-external (objective-surrounding) and CNS-internal (cognitive-emotional) world, and in (ii) the processing and transmission of these informations together with sequential integration into circuitries of neocortical processing. On the basis of the modular operation of the neocortex a speculative model of action of the NbmM complex is proposed which explains its possible role as an important central integrator in cognitive brain function.