Representations of population activity during sensorimotor transformation for visually guided eye movements* Eve C. Ayara,c,d, Michelle R. Heusserb,d, Neeraj J. Gandhia,b,c,d Department of Neuroscience, bDepartment of Bioengineering, c Center for Neuroscience (CNUP), d Center for Neural Basis of Cognition (CNBC)
a
Eve Ayar is a junior Neuroscience student. She is interested in investigating patterns of population activity during sensorimotor integration. After graduation, she plans to pursue a Ph.D. in Neural Computation. Eve Ayar
Michelle Heusser is a Ph.D. candidate in Bioengineering at the University of Pittsburgh. Her research in the Gandhi lab focuses on the time course of neural population activity in the superior colliculus and its relationship to motor behavior. Michelle R. Heusser
Neeraj (Raj) Gandhi, Ph.D.
Neeraj (Raj) Gandhi, Ph.D. is Professor and Graduate Program Director in the Department of Bioengineering. He also developed the Professional Masters program focused on neural engineering. His research focuses on understanding neural communication during sensation, action, and cognition.
Significance Statement
Sensorimotor transformation is a process that humans perform over 100,000 times a day—for example, when we look at or reach for objects of interest. Many areas of the brain register a sensory stimulus and convert the stimulus-related information into an appropriate motor output. Deficits in sensory and/or motor processes are implicated in a number of neurological disorders such as Parkinson’s Disease [1]. We are interested in how the context of visual behavioral tasks impacts patterns of population activity during sensorimotor transformation.
Category: Computational Research
Keywords: saccade, dimensionality reduction, eye movement, sensorimotor Abbreviations: superior colliculus (SC), peristimulus time histogram (PSTH) *
Reviewers’ Choice
Ingenium 2021
Abstract
For visually guided eye movements known as saccades, neurons in the superior colliculus in the midbrain emit a volley of action potentials to register a visual (sensory) stimulus, and they also discharge another high frequency burst of spikes to move the line of sight. We investigated the representations of sensory- and motor-related population activity during two paradigms, the delayed saccade and gap tasks. The two tasks differ in instructing the time to initiate the eye movement, permitting different temporal evolutions of the sensorimotor transformation. Dimensionality reduction methods were used to visualize the pattern of activity of recorded neurons and determine if the population responses in both tasks exhibit similar visual and motor patterns despite differences in event timing and cognitive context. Preliminary analyses suggest that the visual patterns explored during the delay and gap tasks largely overlap, while patterns of motor activity present differences, leading us to believe that downstream structures may differentiate signal processing between behavioral tasks.
1. Introduction
Consider a monkey in a tree searching for a banana. If he sees something yellow appear in his visual field, he will look at it. Simply put, this is the process of sensorimotor transformation: the brain registers a sensory input (e.g., banana) and then converts it to a motor output (e.g., the act of looking at or reaching for the banana). The superior colliculus (SC) is a structure in the brain that is integral in this process because it contains both visual and motor related signals that rapidly redirect the visual axis. We want to understand how sensorimotor transformation occurs in different tasks. If the context of a behavioral task matters, we expect to see differences in SC neural activity patterns because the signals involved in sensorimotor transformation will be processed differently. To characterize different representations of population activity, neural activity patterns were analyzed across two conditions: the delayed saccade task and gap task (Figure 1). The delayed saccade task requires the animal to volitionally withhold movement generation until a later point in time. This condition separates the visual and motor bursts in time. The gap saccade task, in contrast, requires the animal to react immediately. Thus, the movement can happen as soon as visual signals are processed. In this condition, the visual and motor neural bursts can temporally overlap and may even merge into a single burst. For both tasks, we care about activity at two key time points in a trial, 1) estimated visual burst time and 2) saccade onset, indicated by the lines in Figure 1. These key points occur in both tasks but have different timelines because one task has an imposed delay, and the other does not. In this project, we focus on the similarities and differences between visual and motor bursts under the two conditions in a low-dimensional state space, with the goal of determining whether there is a different pattern of population activity relayed to downstream areas. 7
