Coupled spike activity in micropopulations of the cortex neurons

Abstract

Introduction: As it is known, in many CNS structures, neurons, which are spatially close to each other, form micropopulations. These neurons are characterized not only by neighboring spatial localization but also by the existence of close functional synaptic connections between members of such population. The phenomenon of association of cortical neurons in the so-called columns or rather similar groupings (barrels, etc.) is widely known. But the functional relations between members of such micro populations remain little studied. In our research we recorded rigid coupling of the impulse activity generated by two spatially close cortical neurons that were observed in many cases. Methods and Results: Using eight-channel metal microelectrodes (diameter of a separate channel 12 pm), we extracellularly recorded the impulse activity of 186 single neurons or their small groups (usually, pairs) localized in the motor cortex of rats anesthetized with ketamine. In 60 cases (32.3%), APs (action potentials) of two single neurons were generated in a parallel manner and demonstrated fixed time relations between each other. This is interpreted as being a result of excitation of two neighboring functionally connected (coupled) cells. These AP pairs could be recorded via one and the same or two neighboring microelectrode channels. Second AP in the pair was elicited exclusively in the case where an AP was preliminarily generated by another neuron, while APs of the latter in some cases could arrive independently. Therefore, “leading" and “accompanying” cells could be identified in such neuronal pairs. The coupling coefficient in the generation of APs by an accompanying unit with respect to APs generated by a leading cell was close to 100%, without dependence on the discharge frequency in the latter. Intervals between APs of two neurons in different coupled pairs varied from about 1.0 to 22-23 msec. In the case of minimum values of these interspike intervals, APs generated by coupled neurons overlapped each other; this resulted in the formation of spikes looking like “complex APs.” Within some time intervals, interspike intervals could increase, and such APs began to be decomposed. Conclusion: The above-described data are considered the electrophysiological proof of the existence of tight functional coupling between a significant part of cortical neurons spatially close to each other, i.e., members of a micro population, which was obtained in an in vivo experiment.