NEUROMODULATION AND CORTICAL FUNCTION - MODELING THE PHYSIOLOGICAL-BASIS OF BEHAVIOR

Neuromodulators including acetycholine, norepinephrine, serotonin, dop amine and a range of peptides alter the processing characteristics of cortical networks through effects on excitatory and inhibitory synapti c transmission, on the adaptation of cortical pyramidal cells, on memb rane potential, on the rate of synaptic modification, and on other cor tical parameters. Computational models of self-organization and associ ative memory function in cortical structures such as the hippocampus, piriform cortex and neocortex provide a theoretical framework in which the role of these neuromodulatory effects can be analyzed. Neuromodul ators such as acetylcholine and norepinephrine appear to enhance the i nfluence of synapses from afferent fibers arising outside the cortex r elative to the synapses of intrinsic and association fibers arising fr om other cortical pyramidal cells. This provides a continuum between a predominant influence of external stimulation to a predominant influe nce of internal recall (extrinsic vs. intrinsic). Modulatory influence along this continuum may underlie effects described in terms of learn ing and memory, signal to noise ratio, and attention.