Moving through the brain [electronic resource] : a study of movement preparation in the oculomotor and reach systems

Movement preparation allows the rapid and accurate execution of voluntary move- ments, and can be influenced by factors that may change from moment to moment, such as attention and differences in stimulus properties. Consequently, movement preparation unfolds differently across many repetitions of the same movement. Averaging neural responses across many repetitions is necessary to interpret single-cell recordings, but diminishes our ability to characterize the dynamics of the underlying process. A central question in neuroscience, and also of fundamental clinical importance, is to understand how these plans develop in the brain. Several research groups are starting to build prosthetic devices that are controlled directly by neural activity in motor areas of the brain (Nicolelis, 2001; Donoghue, 2002; Musallam et al., 2004; Schwartz, 2004; Santhanam et al., 2006; Hochberg et al., 2006; Mulliken et al., 2008; Andersen et al., 2010), but the extent to which these can be developed may hinge critically upon our understanding of the neural basis of motor preparation. Simultaneous recording from populations of neurons allows dynamics of movement preparation to be estimated on single trials. Our goal is to characterize these dynamics, to gain insight into the process underlying movement preparation. Here, we recorded peri-saccadic activity from ensembles of neurons in an oculomotor area, prearcuate cortex, in two monkeys. While monkeys performed visually-guided eye movements, we measured firing rates of a population of neurons using a 96-electrode array. We studied (1) the responses from a heterogeneous population of prearcuate cortex neurons involved in decision-making and movement preparation, (2) the relationship between saccade initiation times and responses from the neural population, and (3) how these responses compared to those recorded in PMd, a cortical area involved in arm movements. The array data from prearcuate allowed us to compare responses from individual neurons with previous findings, but also allowed us to analyze the population dynamics of movement planning, by using techniques applied to the reach system. We found that ensemble responses from diverse populations of prearcuate neurons (1) can be visualized as trajectories moving through a low-dimensional neural state space, (2) reflect visual, decision-, and movement-related aspects of the task, and (3) correlate with a monkey's reaction time on a trial-by-trial basis. Further, the single-trial relationship between ensemble activity in prearcuate cortex and saccadic reaction times was qualitatively and quantitatively very similar to the relationship between ensemble activity in PMd and corresponding reach reaction times. This framework for analyzing neural population activity and dynamics should permit new extensions of single-neuron-level models, and may offer further insight into general mechanisms of movement preparation across motor systems.

Keywords: Neurosciences.
Advisor: Newsome William T. primary advisor. Thesis advisor
Shenoy Krishna V. (Krishna Vaughn) primary advisor. Thesis advisor
Moore Tirin
Wandell Brian A. advisor. Thesis advisor