THE MOTOR CORTEX
The motor cortex contains areas for planning movement, as well as executing it.
Motor cortex makes decisions about what movements to make.
The motor cortex encodes sensory information.
The motor cortex selects voluntary actions, as well as executes them.
There isn’t one motor cortex- there are several.
The motor cortex has a map of our body.
1. Perception of a stimulus
2. Recognition
3. Deciding on the action
The motor cortex consists of separate regions:
- Primary motor cortex (M1)
- Premotor cortex (Dorsal- PMdc, Ventral- PMvc)
- Supplementary motor complex (Supplementary Motor area- SMA, Pre SMA)
Descending Pathways of Cortex
Cortico- and rubrospinal: skilled mvts, correction of spinal cord commands.
Reticulospinal: activation of SC stereotyped actions (e.g. stepping), posture.
Vestibulospinal: antigravity activity.
The motor cortex works by controlling four descending pathways. Two of these, the rubrospinal and
the corticospinal are involved in very finely controlled movements like writing. Another one, the
vestibulospinal pathway, controls our ability to stay standing despite the effects of gravity. The final one,
the reticulospinal pathway, is involved in maintaining our posture.
Primary Motor Cortex
= It is somatotopically organized.
= Dorsomedial regions distal parts of the
body
= Ventromedial regions proximal parts of
the body
= Not proportional to body part size or area.
= It has internal concentric organization.
= Arm motor map has
concentric
organisation.
= Distal in. middle,
proximal outside.
= Stimulation of several sites same movement.
= M1 neurones encode force and direction of movement. Monkey trained to move
lever against weight. Opposing load, increased activity. Assisting load, decreased
activity.
= The firing rate of a neurone in the primary cortex is proportional to the force of the
movement.
, = M1 uses population encoding. Each neurone has a preferred direction, but also responds (less) to other
directions. So you have to look at the population as a whole.
= M1 codes the movement and sends the projection down to cortex, forming pyramids, to spinal
cord. Cerebral peduncle in midbrain. Enters the pyramids in the medulla. Travels in Lateral
columns in spinal cord. Synapses onto interneurons and motor neurones in Ventral Horn.
= Most descending interneurons, synapse directly. They mediate the spinal cord reflexes. (small
proportion connects directly- only in humans).
= M1 is remapped in training. Motor map changes on training. Movements part of “trained”
tasks increased in area.
= Rate of firing in M1 neurones determines which direction and how strong a movement will
be.
= The presupplementary area is anterior to the supplementary area.
= When you learn a fine motor skill, M1 neurones change the spinal neurones they connect to.
= If you damage a very small area in M1, the patient would lose fine control of one set of
muscles.
= Lesion of the corticospinal tracts would result in more clumsy movements.
Parietal & Premotor Cortex
= Premotor cortex encode motor rule. Shown delayed match-to-
sample task. Separates perceptual and motor information.
= PM activity corresponds to motor rule, not command or
perceptual information.
= Premotor cortex more involved with planning. Instructed delay
tasks separates motor from planning. Not entirely separated in
PM cortex but more planning than motor.
= It shows how much a neurone is involve din planning a
movement compared to how much it is involved in executing the
movement or processing visual cues.
= Premotor neurones encode choices of responses. In reaction time
task, firing ramps up when waiting. In delay task, ramping only
when movement intended.
= Some premotor neurones encode observed actions of others.
Neurons fire when performing action. Also fire when monkey sees
another monkey doing the same action and when they see a human
doing it.
= Different parietal/premotor circuits for reaching and grasping.
= Reaching superior and dorsal parietal cortex. Reciprocal
connections with premotor cortex.
= Grasping ventral, inferior parietal cortex. Connections with F5.
= M1 is involved in how strong the muscle moves, which direction to
move.
= M1 is being told by the premotor cortex what the sequence should be, which groups of muscle should
contrac.t Premotor cortex is able to do that because its talking to the parietal cortex, dorsal part is
telling about sensory information, kind of movement.
= Plans an individual movement and works with M1 to turn that into a force and direction command to
be sent to spinal motor networks.
The motor cortex contains areas for planning movement, as well as executing it.
Motor cortex makes decisions about what movements to make.
The motor cortex encodes sensory information.
The motor cortex selects voluntary actions, as well as executes them.
There isn’t one motor cortex- there are several.
The motor cortex has a map of our body.
1. Perception of a stimulus
2. Recognition
3. Deciding on the action
The motor cortex consists of separate regions:
- Primary motor cortex (M1)
- Premotor cortex (Dorsal- PMdc, Ventral- PMvc)
- Supplementary motor complex (Supplementary Motor area- SMA, Pre SMA)
Descending Pathways of Cortex
Cortico- and rubrospinal: skilled mvts, correction of spinal cord commands.
Reticulospinal: activation of SC stereotyped actions (e.g. stepping), posture.
Vestibulospinal: antigravity activity.
The motor cortex works by controlling four descending pathways. Two of these, the rubrospinal and
the corticospinal are involved in very finely controlled movements like writing. Another one, the
vestibulospinal pathway, controls our ability to stay standing despite the effects of gravity. The final one,
the reticulospinal pathway, is involved in maintaining our posture.
Primary Motor Cortex
= It is somatotopically organized.
= Dorsomedial regions distal parts of the
body
= Ventromedial regions proximal parts of
the body
= Not proportional to body part size or area.
= It has internal concentric organization.
= Arm motor map has
concentric
organisation.
= Distal in. middle,
proximal outside.
= Stimulation of several sites same movement.
= M1 neurones encode force and direction of movement. Monkey trained to move
lever against weight. Opposing load, increased activity. Assisting load, decreased
activity.
= The firing rate of a neurone in the primary cortex is proportional to the force of the
movement.
, = M1 uses population encoding. Each neurone has a preferred direction, but also responds (less) to other
directions. So you have to look at the population as a whole.
= M1 codes the movement and sends the projection down to cortex, forming pyramids, to spinal
cord. Cerebral peduncle in midbrain. Enters the pyramids in the medulla. Travels in Lateral
columns in spinal cord. Synapses onto interneurons and motor neurones in Ventral Horn.
= Most descending interneurons, synapse directly. They mediate the spinal cord reflexes. (small
proportion connects directly- only in humans).
= M1 is remapped in training. Motor map changes on training. Movements part of “trained”
tasks increased in area.
= Rate of firing in M1 neurones determines which direction and how strong a movement will
be.
= The presupplementary area is anterior to the supplementary area.
= When you learn a fine motor skill, M1 neurones change the spinal neurones they connect to.
= If you damage a very small area in M1, the patient would lose fine control of one set of
muscles.
= Lesion of the corticospinal tracts would result in more clumsy movements.
Parietal & Premotor Cortex
= Premotor cortex encode motor rule. Shown delayed match-to-
sample task. Separates perceptual and motor information.
= PM activity corresponds to motor rule, not command or
perceptual information.
= Premotor cortex more involved with planning. Instructed delay
tasks separates motor from planning. Not entirely separated in
PM cortex but more planning than motor.
= It shows how much a neurone is involve din planning a
movement compared to how much it is involved in executing the
movement or processing visual cues.
= Premotor neurones encode choices of responses. In reaction time
task, firing ramps up when waiting. In delay task, ramping only
when movement intended.
= Some premotor neurones encode observed actions of others.
Neurons fire when performing action. Also fire when monkey sees
another monkey doing the same action and when they see a human
doing it.
= Different parietal/premotor circuits for reaching and grasping.
= Reaching superior and dorsal parietal cortex. Reciprocal
connections with premotor cortex.
= Grasping ventral, inferior parietal cortex. Connections with F5.
= M1 is involved in how strong the muscle moves, which direction to
move.
= M1 is being told by the premotor cortex what the sequence should be, which groups of muscle should
contrac.t Premotor cortex is able to do that because its talking to the parietal cortex, dorsal part is
telling about sensory information, kind of movement.
= Plans an individual movement and works with M1 to turn that into a force and direction command to
be sent to spinal motor networks.
