Does a bimodal distribution of preferred directions to hand movements in visuo-parietal areas reflect a genuine motor response?
Creators: name: Essink, Simon
name: Ito, Junji
name: Riehle, Alexa
name: Brochier, Thomas
name: Grün, Sonja
Publisher: name: Forschungzentrum Jülich
Year: 2022

description: INM-IBI Retreat, Juelich, Germany, 18 Oct 2022 - 19 Oct 2022
description: Decades of intense research established that neurons in the monkey motor cortex are tuned to handmovement direction with a cosine-like function that can be characterized by a preferred direction[1]. Although preferred directions were assumed to be uniformly distributed at the population level,more recent analyses showed that these preferred directions are bimodally distributed if hand move-ments are constrained to a horizontal work area [2,3]. In electrophysiological recordings in macaquemonkeys via multiple Utah electrode arrays during a visually guided motor task that is constrainedto the horizontal plane [4], we reproduced this result for the motor cortex and expand the analysisto visual area V2 and parietal areas DP and 7A.Macaque monkeys had been trained to perform a visually guided sequential reaching task while theirarm was in a robotic exoskeleton system (KINARM Exoskeleton Laboratory, BKIN Technologies).Both eye movements and hand movements were recorded along with extracellular potentials from224 channels across visual (V1, V2), parietal (DP, 7a) and motor (M1/PMd) areas. After spike sorting,we relate spiking activity per single unit with the instantaneous hand movement direction throughreverse correlation [5]. From this, we extract the preferred hand movement direction by fitting avon Mises tuning model [6]. The resulting distributions of preferred directions per area were testedfor bimodality using the Rayleigh r statistic.We confirmed the bimodality of preferred directions of hand movement-related responses (peaksat ~109 and ~309 degrees) for neurons recorded in the motor cortex. Surprisingly, we observedthe same tendencies in visual area V2 and in the parietal areas DP and 7A and checked for thestatistical significance of the results. Subsequently, we investigated whether the observations in ourexperiment are a genuine expression of the hand movement or rather arise in response to the visualstimuli toward which the monkeys moved their hands. The responses to hand movement directionsin area V2 can be explained by the receptive field locations of the recorded neurons and the visualstimuli arising during the task. In the parietal areas, however, we tend to exclude visual stimuli asconfounding signals, hinting at the presence of a genuine motor signal in parietal areas.References:[1] Georgopoulos, A., Kalaska, J., Caminiti, R. &amp; Massey, J. On the relations between the directionof two-dimensional arm movements and cell discharge in primate motor cortex. J. Neurosci. 2,1527–1537 (1982).[2] Scott, S. H., Gribble, P. L., Graham, K. M. &amp; Cabel, D. W. Dissociation between hand motion andpopulation vectors from neural activity in motor cortex. Nature 413, 161–165 (2001).[3] Lillicrap, T. P. &amp; Scott, S. H. Preference Distributions of Primary Motor Cortex Neurons ReflectControl Solutions Optimized for Limb Biomechanics. Neuron 77, 168–179 (2013).[4] de Haan, M. J., Brochier, T., Grün, S., Riehle, A. &amp; Barthélemy, F. V. Real-time visuomotor be-havior and electrophysiology recording setup for use with humans and monkeys. Journal of Neuro-physiology 120, 539–552 (2018).Page 136INM IBI Retreat 2022 / Book of Abstracts[5] Eggermont, J. J., Johannesma, P. M. &amp; Aertsen, A. M. Reverse-correlation methods in auditoryresearch. Q Rev Biophys 16, 341–414 (1983).[6] Amirikian, B. &amp; Georgopulos, A. P. Directional tuning profiles of motor cortical cells. Neuro-science Research 36, 73–79 (2000).