Mental Rotation of the Neuronal Population Vector

TLDR

The study hypothesizes that solving the task requires creating and mentally rotating an imagined movement vector from the target light direction to the movement direction. A rhesus monkey performed arm movements counterclockwise from a target light while neuronal activity in motor cortex was recorded and the population vector was computed over successive time intervals during reaction time. The neuronal population vector rotated counterclockwise from light to movement at ~732°/s, providing direct neural evidence for the mental rotation hypothesis and demonstrating the vector’s utility for decoding cognitive operations.

Abstract

A rhesus monkey was trained to move its arm in a direction that was perpendicular to and counterclockwise from the direction of a target light that changed in position from trial to trial. Solution of this problem was hypothesized to involve the creation and mental rotation of an imagined movement vector from the direction of the light to the direction of the movement. This hypothesis was tested directly by recording the activity of cells in the motor cortex during performance of the task and computing the neuronal population vector in successive time intervals during the reaction time. The population vector rotated gradually counterclockwise from the direction of the light to the direction of the movement at an average rate of 732° per second. These results provide direct, neural evidence for the mental rotation hypothesis and indicate that the neuronal population vector is a useful tool for "reading out" and identifying cognitive operations of neuronal ensembles.