A neural mechanism of the generation of meaning in cognitive processes.

A neural mechanism for control of computational dynamics underlying the generation of meaning in cognitive processes is demonstrated. Meaning derives from recognition of connections between items in related conceptual classes of the neural representation in the brain. It is generated from a stimulated item in one conceptual class by an associative process in which linked items in related conceptual classes are activated in parallel. The complexity of the dynamics of this process varies between exploratory and direct retrieval modes. It is shown that the dynamics mode of the generation of meaning can be controlled by the neuronal adaptivity, i.e., the coupling strength between neuronal activity and excitability. Neuronal adaptivity in turn is controlled by neuromodulators in the brain. An autonomous regulation of the dynamics can be accomplished by an activity-dependent release of neuromodulators. The generation of a sequence of bifurcations from an initial exploratory phase to a final retrieval of appropriate item in each conceptual class is demonstrated. The time required for retrieval is shown also to depend on synaptic coupling strengths. The involvement of neuromodulatory systems in cognitive processes has long been observed but the underlying mechanisms not known. The present model describes a mechanism based on the primary effect observed of neuromodulators, viz. that on neuronal adaptivity, and is shown to be consistent with many neuroanatomical, neurophysiological and behavioural observations.