PSYC 427 Lecture Notes - Lecture 9: Cerebral Hemisphere, Central Sulcus, Premotor Cortex
14 May 2018
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PSYC 427 – LECTURE 9
SCHIEBER’S STUDIES
Schieber generated this distribution of neural activity in M1 of monkeys during individual finger movements
• Currents were injected into the brain and corresponding movement were studied
• One technique involved use of low currents to stimulate individual neurons allows mapping of the relationship between particular brain areas and
movements in peripheral body regions
• A more modern technique involves stimulations for longer periods of time, more closely matching natural or normal neural stimulation
o Higher-intensity currents result in not focal activity but current spread throughout an entire cell-network. This type of stimulation produces
coordinated behaviors, enabling visualization of how brain circuitry is recruited to produce these more complex movements.
PROCEDURE
Monkeys were trained to move each individual finger. Then, recording electrodes were placed in the contralateral hemisphere to record the discharge rate of cells as
the animal produced movements.
A: Upper panel shows surface features, including central sulcus and arcuate sulcus; Lower panel is a view from the frontal pole, showing the population of M1
neurons beneath the surface convexity (midline to left)
• Frontal pole: equivalent to looking at the monkey straight in the eye
B: Distribution of single neuron activity during 12 instructed finger/wrist movements (flexion/extension) in frontal pole orientation.
• Each recorded neuron is represented as a sphere colored according to instruction
o The white dots are the calibration bar
• Note that the colored spheres are at different depths. This is because they are aligned on lines that represent the electrode tracks, each with a different
penetration depth. When an activated neuron is encountered as penetration depth increases, it is encoded as a sphere.
• The radius shows change in discharge during movement
C: Each sphere represents maximum change in discharge frequency for that neuron for any of the 12 movements
• Lower panel shows centroids for each instructed movement
Note that spheres are different between the two states: relaxed and movement. Additionally, some neurons will fire for two different types of movement (response
is not mutually exclusive).
FINDINGS
Recordings showed that single M1 neurons are active with movements of different fingers.
• Neuronal populations that are maximally active for different finger movements overlap extensively.
The centroids shown lower panel C are calculated for each flexion and extension movement
• Centroid: center of mass for flexion and extension movements
o Measure of average location of neurons that are producing the movement for each finger
• Rather than shifting progressively across the field of active cortex for thumb through little finger and wrist movements, these centroids are all clustered
together in the center of the field.
o Very little indication that there is strict cortical organization in the motor cortex
• There is only a slight shift for movements of different digits or the wrist, reflecting the extensive overlap of the representations of different movements.
A: ICMS anesthetized owl monkey; M1 lies on surface of relatively lissencephalic cortex
B: ICMS awake stump-tailed monkey; 25f means digits 2-5 flexion; e=extension; a=add; b=abduction
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GRAZIANO’S INTERCORTICAL MICRO-STIMULATION STUDY
Stimulation involving low currents of short duration were used with the goal of mapping out movement of individual body parts
A: the dots represent simulation locations; the color represent locations at which movements can be elicited with micro-stimulation
• There is no order to this mapping.
• Forelimb representation appears to overlap substantially. Thus, there is fractured somatotopy.
B: flat map of the motor cortex (area 4); each label represents a response in finger muscles
• You get a variety of responses by stimulating throughout the anterior bank of the central sulcus and on the gyrus, involving both multiple and single digit
(finger) flexion/extension movements
• There is a pattern of interdigitation within the hand region of the primary motor cortex
Graziao’s icro-stimulation studies suggest that topographic representations of movement in M1 re organized in terms of ethologically relevant categories of
behavior.
Above is enlargement of the stimulation zone which extends from the central sulcus to the arcuate sulcus
• Patch of brain that is not just motor but also pre-motor
Prolonged micro-stimulation to the…
Arm region of the motor cortex brought the hand to central position, as if for visual inspection and object manipulation
o Central space: arms brought inwards and moved to front of body
• Face region produced hand-to-mouth movement and mouth opening
• Medial (trunk and leg) area resulted in climbing or leaping postures.
Reaching behavior involves simultaneous spreading of all fingers and arm-stretching outwards
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Behaviors do not seem to respect traditional cytoarchitectonic boundaries.
However, there is some organizations, with lower extremity movements being more medial and upper extremity movements more lateral.
Stimulation delivered on a timescale that more closely corresponds to the duration of volitional movements (hundreds of ms to s) results in movements that are
sequentially distributed across multiple joints and seemingly purposeful.
Above are two different stimulation locations at which movement can be elicited
• B: coordinated movements of the hand and mouth
• C: movements that bring the hand into central position (visual inspection and object manipulation)
The plus signs represent the limb start position, or where the current is turned on
The red dots represent the final location of the limb
Regardless of the position in which the animal starts out, the final position is determined by the locus of stimulation.
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