INVESTIGATING THE HIERARCHY OF SUBDIVISIONS IN PRIMARY MOTOR CORTEX, AND BETWEEN PRIMARY MOTOR AND SOMATOSENSORY CORTICES DURING NATURALISTIC BEHAVIORS

A popular framework to help comprehend the complicated connections and interactions between cortical areas is to place them in a so-called cortical hierarchy [1]. To do so is helpful not only to describe interactions between cortical areas and their neural processing, but also to make predictions. For example, one would expect a cortical area that is higher in the hierarchy to have more complex, or abstract, receptive or projection fields. Indeed, this functional difference in cortical areas is a defining characteristic of cortical hierarchies. Another defining characteristic are different patterns of laminar connections: ascending projections terminate on middle cortical layers, and descending projections terminate onto high and low cortical layers, avoiding the middle layers [2]. Thus, cortical hierarchies, in this dissertation, are defined by the functional properties of responses, and the neuroanatomical underpinnings of laminar connectivity. Here, I propose using spike-field coherence to measure the interactions between individual neurons in one cortical area and populations of neurons in another to validate the hierarchical structure between cortical areas. First I will show that these anatomically intertwined areas are synchronized in a low frequency band, and that this coherence is not symmetrical. I expect that rM1-cM1 spike-field coherence will precede cM1-rM1 spike-field coherence, and likewise that M1-S1 spike-field coherence will precede S1-M1 coherence. Additionally, I will provide support that coherence is a functional mechanism that is meaningful above and beyond either spikes or local fields. Finally, I will place these cortical areas in a somatomotor hierarchy, and discuss their evolutionary origins and roles in motor control.