Muscle and Movement Representations in the Primary Motor Cortex

• Published in: Science (American Association for the Advancement of Science) 1999-09, Vol.285 (5436), p.2136-2139
• Main Authors: Kakei, Shinji, Hoffman, Donna S., Strick, Peter L.
• Format: Article
• Language: English
• Subjects: Anatomical correlates of behavior; Animals; Arm; Arm - physiology; Behavioral psychophysiology; Biological and medical sciences; Biomechanical Phenomena; Brain; Carpus, Animal; Coding; Coordinate systems; Electromyography; Fingers; Forearm; Forearm - physiology; Fundamental and applied biological sciences. Psychology; Haplorhini; Human mechanics; Joints; Mechanics (Physics); Monkeys & apes; Motor ability; Motor cortex; Motor Cortex - physiology; Movement - physiology; Muscle Contraction; Muscle, Skeletal - physiology; Muscular system; Neurons; Neurons - physiology; Neuroscience; Posture; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Shoulder - physiology; Space life sciences; Wrist; Wrist - physiology; Wrist joint; Wrist Joint - physiology
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.285.5436.2136

What aspects of movement are represented in the primary motor cortex (M1): relatively low-level parameters like muscle force, or more abstract parameters like handpath? To examine this issue, the activity of neurons in M1 was recorded in a monkey trained to perform a task that dissociates three major variables of wrist movement: muscle activity, direction of movement at the wrist joint, and direction of movement in space. A substantial group of neurons in M1 (28 out of 88) displayed changes in activity that were muscle-like. Unexpectedly, an even larger group of neurons in M1 (44 out of 88) displayed changes in activity that were related to the direction of wrist movement in space independent of the pattern of muscle activity that generated the movement. Thus, both "muscles" and "movements" appear to be strongly represented in M1.