Physiology 2130 Lecture Notes - Lecture 23: Functional Magnetic Resonance Imaging, Positron Emission Tomography, Supplementary Motor Area
1 May 2018
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Lecture 011: Motor Cortex
Techniques to Study the Motor Cortex
● Stimulation:
○ electrical, magnetic
○ epilepsy (results from abnormal firing of neurons, can spread)
● Lesion:
○ electrical, chemical, stroke (removing the blood supply), degeneration
● Recording
○ Single neurons
○ Evoked Potentials
○ EEG (ElectroEncephaloGraphy)
○ PET (Positron Emission Tomography)
■ Inject radioactive dye into the brain
■ Positrons emit from the active areas of the cortex (based on blood flow)
○ fMRI (Functional Magnetic Resonance Imaging)
● Specialized areas of cortex: somatosensory, visual, auditory, motor
○ Different areas of the brain for different functions
○ Combination of areas that may be interlinked with one another
Voluntary Movement Requires:
● Selection
● Planning
● Execution
○ Efferent axons from the motor cortex
● This occurs across multiple strictures in a distributed system that is in parallel and in
series
● These structures project directly to the motor cortex (just one link away, helps generate
movement)
○ Parietal cortex
○ Cerebellum
○ Basal ganglia (via the supplementary motor area cortex)
○ Premotor cortex
Define Motor Cortex
● Area of cortex from which low intensity electrical stimulation produces skeletal muscle
contractions which are contralateral for arm/leg
○ VERY LOW INTENSITY/THRESHOLD -> same stimulation will not generate
movement on another area of the cortex
● Located on the precentral gyrus
● Somatotopic organization
○ Distorted motor (homunculus)
○ Areas with more axons have more fine motor movement, neet more area in the
cortex
find more resources at oneclass.com
find more resources at oneclass.com
■ hand/fingers, face
● Evidence for somatotopic organization
○ March of epileptic seizures
■ Starts in the twitch of the fingers -> elbow -> shoulder -> face/leg
■ “March” of epilepsy in the order of the body
■ Must have a map of the body in the brain that the seizure is moving
across
○ Electrical stimulation
■ Animal experiments to find the motor cortex
■ Surgery of the motor cortex to treat epilepsy
■ Precise electrical stimulation of the precentral gyrus to map
somatosensory organization (by Penfield)
○ Lesions (Stroke)
■ Lose motor control in that area
○ Recordings of neural activity
■ Of someone flexing/extending toes
● Will see APs in the contralateral leg areas in the brain but none
in the areas for the arms (no correlation with leg movement)
Motor Representation
● What is represented?
○ Is it a representation of the
muscle or of the
movements
● Muscle Representation
○ Stimulation of a specific
neuron will generate a
specific muscle movement
○ Not the case
■ Widely dispersed
site of neurons within the same
somatosensory site that will all
project to a specific alpha neuron
● Bunch of finger cortical
neurons will all project to a
single alpha neuron of the
finger
■ A single cortical neuron can also
project to multiple motor neuron
● The muscle are usually in a
functional relationship
(contracts together)
■ Neither of these support a muscle
representation (single neuron to single muscle)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Epilepsy (results from abnormal firing of neurons, can spread) Electrical, chemical, stroke (removing the blood supply), degeneration. Positrons emit from the active areas of the cortex (based on blood flow) fmri (functional magnetic resonance imaging) Specialized areas of cortex: somatosensory, visual, auditory, motor. Different areas of the brain for different functions. Combination of areas that may be interlinked with one another. This occurs across multiple strictures in a distributed system that is in parallel and in series. These structures project directly to the motor cortex (just one link away, helps generate movement) Basal ganglia (via the supplementary motor area cortex) Area of cortex from which low intensity electrical stimulation produces skeletal muscle contractions which are contralateral for arm/leg. Very low intensity/threshold -> same stimulation will not generate movement on another area of the cortex. Areas with more axons have more fine motor movement, neet more area in the cortex.
