The flow of thought and the flow of substance in the brain

Many neuroactive substances undergo cytoplasmic transport along the axons and dendrites of cerebral neurons, and the expression of their activities is determined by the time occupied by their transport. Such substances include cyclic nucleotides which are formed postsynaptically as mediators by several neurotransmitters including catecholamines, and which are capable of acting at numerous postsynaptic sites during their subsequent intracellular translocation. Temporally patterned changes in cell-firing tendency during some seconds or minutes following brief stimuli are attributed to movement of such compound, as is also the subjective sense of a flow of thought. Descriptions are appraised which indicate that components experienced as part of a stream of thought can be initiated by drive-inducing catecholaminergic systems acting through cyclic nucleotides, thus affording endogenous signals that contribute to electrophysiological matching processes in perception and recall. Roles for satiety mechanisms involving opioid peptides are also assessed.