More on Gnostic Units and Cortical Columns

This chapter returns to the subject of gnostic units discussed in Chapter 9, as well cortical columns, both of which form the building blocks of cortical function. Gnostic units are used to describe a neural assembly having knowledge (information). The chapter first expounds on gnostic units and how they relate to the concept/grandmother cells already discussed previously. It then goes on to consider the type of neural structure, which might correspond to a gnostic unit. At the simplest level, electrophysiological recordings have shown that a single neuron could be regarded as a gnostic unit. From here, the chapter conceives of a hierarchy of analyzers in the form of cortical columns. At the highest level will be the column(s) specific for a particular face or object—these cells will fire, and the face or object will be recognized by the conscious brain.

Real-time classification of experience-related ensemble spiking patterns for closed-loop applications

Communication in neural circuits across the cortex is thought to be mediated by spontaneous temporally organized patterns of population activity lasting ~50 –200 ms. Closed-loop manipulations have the unique power to reveal direct and causal links between such patterns and their contribution to cognition. Current brain–computer interfaces, however, are not designed to interpret multi-neuronal spiking patterns at the millisecond timescale. To bridge this gap, we developed a system for classifying ensemble patterns in a closed-loop setting and demonstrated its application in the online identification of hippocampal neuronal replay sequences in the rat. Our system decodes multi-neuronal patterns at 10 ms resolution, identifies within 50 ms experience-related patterns with over 70% sensitivity and specificity, and classifies their content with 95% accuracy. This technology scales to high-count electrode arrays and will help to shed new light on the contribution of internally generated neural activity to coordinated neural assembly interactions and cognition.