11Voluntary MovementsLu Chen, Ph.D.MCB, UC Berkeley2Cortical areas involved in voluntary movement• Primary motor cortex (M1, also called Brodmann’s area 4)area 6}46Primary motor cortexPremotorareaanteriorposteriorSupplementary motor cortex•Premotorcortex• Supplementary motor cortex23How are these motor areas discovered?• Discovered in 1870 by Fritsch and Hitzig - electrical stimulation of different parts of the frontal lobe produces movements of muscles. - low stimulation, simple movement, opposite side,primary motor cortex- high stimulation, complex movement, bilaterally,premotor and supplementary motor cortexDR. EDUARD HITZIGDR. GYSTAV.T. FRITSCH4A somatotopic map of human motor cortexTopographicalMuscle groups control fine movements have bigger areas of representation - distal muscles•1930s-1950s, Canadian neurosurgeon Wilder Penfield used this methods to map the cortex of neurosurgical patients –orderly map of the body on the cortex, thesomatotopic organization of the cortex.35Corticospinal tract influence spinal motor neurons through direct and indirect connectionsCorticalspinal tractAgonist muscleAntagonist muscleContribute to multi-jointed movements such as reaching and walking6Fine control of the digits requires primary motor cortex47The lateral premotor areas contribute to the selection of action and to sensorimotor transformationsInstruction stimulus onTrigger stimulus onInstruction stimulus Trigger stimulus onReady… Set… Go!8Supplementary motor cortex are activated during complex and imagined movementsSupplementary motor area59M1 neuron controls movement Neuron discharge starts several hundred millisecond before movement.Discharge frequency changed systematically in temporal relation to either flexion or extension. Evarts group, 196810Direct relationship between the firing rate of motor cortical neurons and force generation611Georgopoulos et al., 1982Different cells have different preferred movement directions.Individual M1 neuron fire preferentially in connection with movement in certain direction.90o0o180o270o12Direction of movement is encoded in the motor cortex by the pattern of activity in an entire population of cellsM1 cortical neurons with different preferred directions are all active during movement in a particular direction. The entirety of this activity results in a population vector that closely matches that of the direction of movement.713Direction vectors and population vectors90o0o180o270o0oDirection of movementFiring rate of M1 neuron(Hz)Firing rate of M1 neuron(Hz)90o180o0o270oDirection of movementup rightCell 1Cell 2left downMovement directionrightupDirection vector for cell 1Direction vector for cell 2Population vector for cell 1 and 2++Each neuron’s activity contributes one vector. Direction: preferred direction of the neuronAmplitude: firing rate of the