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 thereafter 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 depression 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, whenever serotonin activates a proteinkinase A. Besides carrying out a brief review on the matter, we support two different physiological explanations with regard to: (a) ion exchange process and the interstitial pH during habituation; and (b) the possibility of a sensitive presynaptic neuron interaction 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 postsynaptic onset responses. (C) 2000 Harcourt Publishers Ltd.