Cortical spike multiplexing using gamma frequency latencies

Abstract

One of the fundamental problems in understanding the brain, in particular the cerebral cortex, is that we only have a partial understanding of the basic communication protocols that underlie signal transmission. This makes it difficult to interpret the significance of particular phenomena such as basic firing patterns and oscillations at different frequencies. There are, of course, useful models. Motivated by single-cell recording technology, Poisson statistics of cortical action potentials have long been a basic component in models of signal representation in the cortex. However, it is increasingly difficult to integrate Poisson spiking with spike timing signals in the gamma frequency spectrum. A potential way forward is being sparked by new technologies that allow the exploration of very low-level communication strategies. Specifically, the voltage potential of a cells soma now can be recorded with very high fidelity in vivo, allowing correlation of its fine structure to be correlated with behaviors. To interpret this data, we have developed a unified model (gamma spike multiplexing, or GSM) wherein a cells somatic gamma frequencies can modulate the generation of action potentials. Such spikes can be seen as the basis for a general-purpose method of modulating fast communication in cortical networks. In particular, the model has several important advantages over traditional formalisms: 1) It allows multiple, independent processes to run in parallel, greatly increasing the processing capability of the cortex 2) Its processing speed is 102 to 103 times faster than population coding methods 3) Its processes are not bound to specific locations, but migrate across cortical cells as a function of time, facilitating the maintenance of cortical cell calibration.