Theoretical aspects of the neurobiological integration of memory

Whenever a peripheral structure like the visual system captures information , the input signal reverberates in circuits of neurons, which send it there after towards: (a) the motor system, triggering a specific response, evoked by a short-term memory mechanism; and (b) the hippocampus, to produce long -term potentiation or depression. Two different processes regulate short-term memory: (1) Homosynaptic depres sion that inhibits neurotransmitter release by means of a decrease in Ca+inflow, and an increase in calmodulin affinity for synaptic vesicles; and ( 2) Heterosynaptic facilitation that triggers neurotransmitter release, when ever serotonin activates a proteinkinase A. Besides carrying out a brief re view on the matter, we support two different physiological explanations wit h regard to: (a) ion exchange process and the interstitial pH during habitu ation; and (b) the possibility of a sensitive presynaptic neuron interactio n within the habituated reverberant circuit, to trigger dishabituation. We also propose the term 'time-mediated stimulatory action dependent' to name those serotonin receptors that may lead to a rapid or a delayed postsynapti c onset responses. (C) 2000 Harcourt Publishers Ltd.