title: Motor-evoked potentials reveal a motor-cortical readout of evidence accumulation for sensorimotor decisions.
abstract: Many everyday activities require time-pressured sensorimotor decision making. Traditionally, perception, decision, and action processes were considered to occur in series, but this idea has been successfully challenged, particularly by neurophysiological work in animals. However, the generality of parallel processing requires further elucidation. Here, we investigate whether the accumulation of a decision can be observed intrahemispherically within human motor cortex. Participants categorized faces as male or female, with task difficulty manipulated using morphed stimuli. Transcranial magnetic stimulation, applied during the reaction-time interval, produced motor-evoked potentials (MEPs) in two hand muscles that were the major contributors when generating the required pinch/grip movements. Smoothing MEPs using a Gaussian kernel allowed us to recover a continuous time-varying MEP average, comparable to an EEG component, permitting precise localization of the time at which the motor plan for the responding muscle became dominant. We demonstrate decision-related activity in the motor cortex during this perceptual discrimination task, suggesting ongoing evidence accumulation within the motor system even for two independent actions represented within one hemisphere.
authors.affiliation: Department of Psychology, City University London, London, UK. Avhad@post.bgu.ac.il.|Department of Life Science, Ben-Gurion University, Be'er Sheva, Israel. Avhad@post.bgu.ac.il.
authors.forename: Aviad A
authors.initials: AA
authors.lastname: Hadar
authors.affiliation: Department of Psychology, City University London, London, UK.
authors.forename: Paula
authors.initials: P
authors.lastname: Rowe
authors.affiliation: Institute of Cognitive Neuroscience & Department of Psychology, University College London, London, UK.
authors.forename: Steven
authors.initials: S
authors.lastname: Di Costa
authors.affiliation: Department of Psychology, Middlesex University, London, UK.
authors.forename: Alexander
authors.initials: A
authors.lastname: Jones
authors.affiliation: Department of Psychology, City University London, London, UK.
authors.forename: Kielan
authors.initials: K
authors.lastname: Yarrow
mesh_terms: D000328:Adult; D003657:Decision Making / Q000502:physiology*; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor; D000066499:Facial Recognition / Q000502:physiology*; D005260:Female; D006225:Hand / Q000294:innervation / Q000502:physiology; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology; D011930:Reaction Time; D012815:Signal Processing, Computer-Assisted; D050781:Transcranial Magnetic Stimulation
keywords: Accumulation-to-bound models; Decision making; Face processing; MEP; Motor control; TMS