Distinct Patterns of Overlapping Neural Representation Of Sensorimotor Variables in Primary and Associative Motor Areas: Insights from Chronic Intracortical Recordings in the Human Brain

Citation

Kadlec, Kelly (2025) Distinct Patterns of Overlapping Neural Representation Of Sensorimotor Variables in Primary and Associative Motor Areas: Insights from Chronic Intracortical Recordings in the Human Brain. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/e3x8-t812. https://resolver.caltech.edu/CaltechTHESIS:07292024-181336718

Abstract

Although many of the movements we make are produced without much conscious thought, motor control requires the coordination of multiple brain areas and several complex processes to occur as seamlessly as it does, two of which are primary motor cortex (MC) and posterior parietal cortex (PPC). Traditional views of the organization of these areas have mapped separate parts of the body, or effectors, onto separate areas of cortex. However, recent findings that show extensively overlapping representations of different effectors within small populations of neurons in both motor and posterior parietal cortices have reignited a debate over the organization of each area. The studies in this thesis aim to reconcile these conflicting records through a unique opportunity to directly compare between single neuron recordings in both areas in human participants chronically implanted with intracortical electrode arrays. The functional organization of these areas was investigated during movement of different parts of the body in different contexts. In the first study, I found that the entire body is represented within small patches of both MC and PPC, but with a clear emphasis on a single part of the body in MC. In PPC, although single neurons showed specialization for particular effectors, there were an equal number of neurons specialized for every effector resulting in an equal strength in representation of the population across effectors. In the second study, I investigated how spatial information was represented across different effectors. In particular, it has previously been reported that some areas within PPC represent location of an object in space relative to the position of one's eyes, or in an eye-centered coordinate frame, while other areas represent location in space as relative to the position of one's body, for example a hand-centered coordinate frame. We find that the population in PPC flexibly changes the coordinate frame it encodes the location of a visual target in from hand centered during a reach paradigm to eye-centered during a delayed saccade paradigm. In contrast to the multiple coordinate frames coded by the population in PPC, in MC the population predominantly encoded spatial location in hand-centered coordinates during reaches. The flexibility seen in the population results in PPC motivate the study of Chapter 4, where I explore these changing coordinate frames in more detail at the single neuron level. I found that the distinct coordinate frames are encoded by almost entirely separate sets of neurons, with very few neurons engaged in both task. Overall, these results show clearly distinct organization of motor variables within MC and PPC, and offer important insights into the possible functions of each region both within and beyond motor control. In addition, they highlight a need to continue exploring how neurons within a defined region respond beyond their traditionally associated functional roles.

Thesis Files