Voluntary Movement II. 1. Primary motor cortex: how are movement - PDF document

Voluntary Movement II. 1. Primary motor cortex: how are movement parameters coded Cortical representation of • Distal movements • CM neurons. movements and • Population coding. 2. Premotor areas higher order features of parameters. movement • Supplementary motor area: Sequences • Lateral dorsal premotor area: sensorimotor transformations • Lateral ventral premotor area: grasping Claude Ghez, M.D. 3. Experience modifies representations Corticospinal neurons (PTN) code direction and force Target muscles can be identified by “spike triggered averaging” CM neurons: divergence CM neurons to distal muscles have small “muscle fields” (1-4 muscles) CM neurons to proximal muscles have large (6+) “muscle fields” Single corticospinal axons diverge to terminate CM neurons code for force exerted in several motor nuclei Phasic-tonic type (59%) 50 Unit (Hz) 0 ECU Tonic firing frequency (Hz) EDC ECRL Torque Tonic type (28%) 50 Unit (Hz) 0 ECU EDC ECRL Static torque (x10 5 dyne/cm) Torque 1

Section of pyramidal tracts in monkeys produces loss of independent “individuated” digit control CM neurons are preferentially recruited for tasks requiring topographical precision Intact (normal) After section of corticospinal fibers CM neuron EMG of muscle Precision grip Power grip Neurons in proximal motor cortex regions Movement direction can be coded precisely by the are broadly tuned for direction population responses of broadly tuned neurons “Self initiated”voluntary movement are preceded by premotor activation: Primary motor cortex receives direct input from 5 premotor areas early evidence from evoked potentials These premotor areas also project to the spinal cord 2

Planning movement sequence without moving activates SMA Activation of motor areas depend different on First neuroimaging data behavioral context Repeated simple finger flexion Repeating sequence finger-thumb apposition Supplementary Motor cortex Sensory cortex motor area Primary motor cortex Lateral premotor area Supplementary motor area 1st key touch 1st key touch 1st key touch Visual Cue Mental rehearsal of finger sequence Learned Sequence Separate pathways convey visual inputs to premotor areas Supplementary motor area neurons code movements in for reaching and grasping specific context of movement sequence. Primary Motor Cell fires with pull followed by turn but not followed by pull Reaching Grasping Cell fires with turn followed by pull and push but not just with pull Instructed delay task: coding of “preparatory set” for directed reach Neurons in ventral premotor area (PMv) code for by dorso-lateral premotor neurons hand configuration of grasp Instruction: Left Instruction: Right Contralateral movement Ipsilateral movement LED= trigger signal Precision grip Panel= instruction signal Rec. Ventral PM Power grip Instruction Trigger Instruction Trigger stimulus stimulus stimulus stimulus 3

“Mirror neurons” in PMv represent types of movement Practice and learning of finger sequence can alter independent of its actualization: motor vocabulary motor representations in primary motor cortex Damage to local region of motor cortex induces Motor practice can alter functionality and motor mapping change in representation of nearby areas In motor cortex Post infarct with Preinfarct Rehabilitative therapy Elbow & shoulder Infarct Infarct Infarct Infarct Digit Digit, wrist & forearm No response Wrist & forearm Proximal 4