ABSTRACT
The cerebral cortex is a highly interconnected network of neurons in which the activity of each cell is necessarily related to the combined activity in the neurons that are afferent to it. Due to the presence of reciprocal connections between cortical areas and between the cortex and the thalamus, re-entrant activity through chains of neurons is likely to occur. Certain pathways through the network may be favored by preferred synaptic interactions between the neural elements as a consequence of developmental and/or learning processes. In cell assemblies interconnected in this way, some ordered, and precise (in the order of few ms) interspike interval relationships referred to as ‘spatio-temporal firing patterns’, may recur within spike trains of individual neurons, and across spike trains recorded from different neurons. If functional correlates of spatio-temporal neural coding exist, one would expect that whenever the same information is presented, the same temporal pattern of firing would be observed. Electrical stimulation with complex stimuli that include amplitude and frequency modulation revealed remarkable invariance in the firing times of the tested neurons in vitro and indicated a high degree of reliability of their response (Bryant & Segundo, 1976; Mainen & Sejnowski, 1995). Experimental evidence exists that correlated firing between single neurons recorded simultaneously in the primate frontal cortex may evolve within tens of milliseconds in systematic relation to behavioral events without modulation of the firing rates (Vaadia et al., 1995). Precise firing sequences have been described in relation to particular temporal relationships to stimuli (Villa
& Abeles, 1990), or movement (Abeles et al., 1993), or differentially during the delay period of a delayed response task (Prut et al., 1998; Villa & Fuster, 1992; Villa et al., 1999b).
