Proc. Natl. Acad. Sci. USA 109: 1731-1736, 2012.
Intracranial recording is an important diagnostic method routinely used in a number of neurological monitoring scenarios. In recent years, advancements in such recordings were extended to include unit activity of an ensemble of neurons. However, a detailed functional characterization of excitatory and inhibitory cells has not been attempted in human neocortex - particularly during the sleep state. Here, we report that such feature discrimination is possible from high-density recordings in the neocortex using 2-dimensional multielectrode arrays. Successful separation between RS neurons (regular or bursting cells) from fast-spiking (FS) cells resulted in well-defined clusters where each showed unique intrinsic firing properties. The high density of the array allowing recording from large number of cells (up to 90) helped us to identify apparent monosynaptic connections, which confirmed the excitatory and inhibitory nature of RS and FS cells, thus categorized as putative pyramidal and interneurons, respectively. Finally, we investigated the dynamics of correlations within each class. A marked exponential decay with distance was observed in the case of excitatory but not for inhibitory cells. While the amplitude of that decline was dependent on the timescale at which the correlations were computed, the spatial constant was not. Furthermore, this spatial constant is compatible with the typical size of human columnar organization. These findings provide a detailed characterization of neuronal activity, functional connectivity at the micro-circuit level and the interplay of excitation and inhibition in the human neocortex.