UMass Amherst KIN 460 - 15-Motor cortex (20 pages)

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15-Motor cortex



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15-Motor cortex

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Pages:
20
School:
University of Massachusetts Amherst
Course:
Kin 460 - Motor Control
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Motor Cortex Overall organization of neural structures that control movement Questions What is the function of the motor cortex in motor control Does the primary motor cortex encode for muscle or for movement How does the motor cortex encode precise movement patterns such as reaching movements What motor functions are lost when the motor cortex is damaged The primary motor cortex and the premotor area Movement coordination and planning Movement execution More monosynaptic connections to alpha MNs controlling upper limbs Questions What is the function of the motor cortex in motor control How does the motor cortex encode for muscle or for movement How does the motor cortex encode precise movement patterns such as reaching movements What motor functions are lost when the motor cortex is damaged Motor cortex functional organization Somatotopic organization of the contralateral body motor maps Large areas reflect larger number of neurons needed for fine motor control fingers face mouth What do motor maps represent Evidence from cortical electrical stimulation studies Motor cortex contains a spatial map of the contralateral body Direct pathway to brainstem and spinal cord low current stimulation to motor cortex activates different muscles low threshold monosynaptic connection Each muscle can be activated by stimulating many widely dispersed sites 2 3 mm of the motor cortex Movements are encoded instead of muscles Muscle field axons from motor cortex terminate on sets of spinal motor neurons that innervate different muscles Representation of different muscles overlap on the motor cortex Allows coordinated activation of multiple muscle groups across multiple joints to perform behaviorally useful actions What do motor maps represent Example arm hand control Sites controlling an individual muscle are not located together but are distributed over a wide area of motor cortex Intracortical microstimulation was used to identify sites in monkey primary motor cortex at which low threshold stimulation evoked electromyographic activity indicating monosynaptic connections in a shoulder abduction muscle middle head of deltoid muscle and a wrist extensor muscle extensor carpi radialis ECR Topographic maps of the identified sites reveal overlap between shoulder and wrist representations From Humphrey DR Tanji J 1991 In DR Humphrey HJ Freund eds Motor Control Concepts and Issues pp 413 443 New York Wiley Questions What is the function of the motor cortex in motor control Does the motor cortex encode for muscle or for movement How does the motor cortex encode precise movement patterns such as reaching movements What motor functions are lost when the motor cortex is damaged Direction of arm movements is predicted by a neuronal population vector Neuronal population vector Concurrent discharge of a large population of upper motor neurons prior to movements determines movement direction Discharge of individual upper motor neurons cannot specify arm movement direction broadly tuned to direction Same site in motor cortex same UMN population can encode different movement parameters trajectory final position etc Example cortical recording during visually guided reaching movements of arm hand in monkey next slides Directional tuning of an upper motor neuron in the primary motor cortex Part 1 Monkey is trained to move a joystick in the direction indicated by a light Directional tuning of an upper motor neuron in the primary motor cortex Part 2 Single neuron activity recorded during arm movements in each direction Zero movement onset Short black lines action potential Yellow zone Increased activity for 90 225 movements Blue zone decreased activity for 45 315 movements Directional tuning of an upper motor neuron in the primary motor cortex Part 3 Plot showing that the neuron s preferred direction neuron s discharge rate was greatest before movements in a particular direction Directional tuning of an upper motor neuron in the primary motor cortex Part 4 Black lines discharge rates of individual upper motor neurons prior to each direction of movement Red arrows population vector defined by combining the responses of all the neurons movement direction encoded by simultaneous activity of entire population Questions What is the function of the motor cortex in motor control Does the primary motor cortex encode for muscle or for movement How does the motor cortex encode precise movement patterns such as reaching movements What motor functions are lost when the motor cortex is damaged Overview of descending motor control Cortical damage Cortical damage stroke Cerebral Palsy CP Spasticity Increased response to muscle rate of stretch velocity Lack of inhibition to spinal cord Abnormal reflexes Babinsky Loss of fine control Figure 17 16 The Babinski sign A monkey that controls a robot with its thoughts http www ted com talks miguel nicolelis a monkey that co ntrols a robot with its thoughts no really html


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