Motor selection dynamics in FEF explain the reaction time variance of saccades to single targets.

Christopher K Hauser,Emilio Salinas,Terrence R Stanford,Dantong Zhu

doi:10.7554/elife.33456

Abstract

In studies of voluntary movement, a most elemental quantity is the reaction time (RT) between the onset of a visual stimulus and a saccade toward it. However, this RT demonstrates extremely high variability which, in spite of extensive research, remains unexplained. It is well established that, when a visual target appears, oculomotor activity gradually builds up until a critical level is reached, at which point a saccade is triggered. Here, based on computational work and single-neuron recordings from monkey frontal eye field (FEF), we show that this rise-to-threshold process starts from a dynamic initial state that already contains other incipient, internally driven motor plans, which compete with the target-driven activity to varying degrees. The ensuing conflict resolution process, which manifests in subtle covariations between baseline activity, build-up rate, and threshold, consists of fundamentally deterministic interactions, and explains the observed RT distributions while invoking only a small amount of intrinsic randomness.

Highlights

The reaction time (RT) represents the total time taken to perform all of the mental operations that may contribute to a particular action, such as stimulus detection, attention, working memory, or motor preparation
It involves four locations and variable block length. This task generates errors and a large spread in RT (Figure 2) under minimalistic sensory stimulation conditions. We exploit this to investigate how variance in saccadic performance relates to variance in frontal eye field (FEF) activity
We examined the responses of individual FEF neurons during correct saccades into the response field (RF), and found that their dependencies on RT could deviate quite substantially from those of the average population

Summary

Introduction

The reaction time (RT) represents the total time taken to perform all of the mental operations that may contribute to a particular action, such as stimulus detection, attention, working memory, or motor preparation. Differential measurements of RT may be used as a readout for changes in the (mean) time consumed by any one of the aforementioned operations, but a particular RT value is hard to interpret because it may be that not all of the operations involved are known, and those that are relevant may overlap in time to varying degrees. There is a firm mechanistic account that describes how saccades are triggered, but according to the present results, that account lacks a crucial ingredient — ongoing motor conflict — and assumes, incorrectly, that in response to the same stimulus, the fundamental reason why some saccades are triggered very quickly whereas others take much longer boils down to noise in the underlying neuronal activity

Methods

Results

Conclusion