PROBLEM 1. PERCEPTION AND MOTOR BEHAVIOR
Chapter 9: Organization of Motor
System
Motor system
1. Motor cortex
2. Basal ganglia
3. Cerebellum
4. Brainstem
5. Motor neurons
The Neocortex: Initiating Movement
1. Posterior cortex: specifies movement goals and sends sensory info (vision, touch, hearing) to frontal regions
through multiple routes
i. Direct: prompt M1 to execute relatively automatic movements
For simple movement goals: premotor and motor cortex make the action
ii. Indirect: movements requiring conscious control, pass through temporal and frontal cortex
For movements that require planning: prefrontal/ temporal
decision pre-motor/motor execute
2. Prefrontal cortex: creates plans for movements and passes them to
the premotor and motor cortex
3. Premotor cortex: movement repertoire, recognizes others’
movements and selects similar or different actions
4. Supplementary motor cortex: dorsal to premotor area
5. Primary motor cortex (M1):elementary movements -execution
A. Homunculus
i. Disproportionate relative sizes of body parts (broader regions-
smaller representation, small fine movement regions-larger
representation)
ii. The arrangement of body parts is different from that of the real
body
B. Natural Movement Categories
Each region- Three types of organization: the body part to be moved, the spatial direction location and the
movement’s function
Dorsal premotor (PMC): whole body movements e.g. climbing, Ventral premotor (SMA) hand-movements
to mouth, Ventral Motor Cortex (M1): reaching to grasp,
Graziano consistent with Penfield: whole-body moves =premotor cortex & discrete moves = motor cortex
Visual–Parietal–Motor Connections
Visual cortex identifies the spatial location and shape of the target
Parietal cortex identifies the body part that will contact the object
Motor cortex in turn represents the elements required to move the arm to the target and shape to grasp
Movements (e.g. grasp) may not be directed only from cortex but from brainstem or spinal cord
, PROBLEM 1. PERCEPTION AND MOTOR BEHAVIOR
The Movement Lexicon
Skilled movements that are encoded as basic movement patterns called and modified when necessary
Evidence supporting the movement lexicon/repertoire of movement categories:
1. Similar ways that different people perform skilled movements e.g. pincer grip (thumb and another finger)
2. Most primate species use this same grip pattern
3. Lesions of motor cortex around the thumb region weak in the other fingers and in the arm
Monkey studies:
A. Premotor cortex and the primary motor cortex share a common movement lexicon and that the repertoire available to the
premotor cortex is more complex (responsible for complex movements)
Monkeys w/ PMC lesions were not able to do complementary movements together
Conclusion: premotor cortex greater role in organization of whole body movements than M1 (responsible for specific
acts) basic movements of M1 can extent to other actions through learning
B. Neurons of the motor cortex participate in planning, initiating, executing, increasing the force of the movement and specify
the movement direction
C. Movements are not produced by a single cell but by the coordinated activity of cell populations
Monkeys moving a lever in different directions, they found that each neuron is maximally active when the monkey moves
its arm in a particular direction
Mirroring Movement
Recording motor cortex in social interactions: neurons in premotor area
discharge when monkey makes a movement but also discharge in much the
same way when the monkey observes the same movement
Mirror system neurons: encode the goal of an action-target, more important
than details of the actions required
o Core mirror system: ventral premotor (PMC), motor cortex, and inferior
parietal cortex broadly tuned, respond to wide range of actions used in
obtaining a goal
o Distributed mirror neuron system: SMA, SPL, Broca’s responds to
movements with no goal present
Functions: self-action, imagine movements, understand actions of others by internal replication of the
movements
Relation w/disorers: absence of empathy mirror system dysfunction
The Brainstem: Motor control
Responsible for whole body-movement control, emotional behavior, movements used in eating and drinking,
posture, grooming etc.
Basal ganglia and movement force
Basal ganglia: subcortical nuclei in the forebrain
1. Connect the motor cortex with the midbrain
2. Connect the sensory regions of the neocortex with the motor cortex
3. Responsible for movement modulation
Caudate & putamen & Globus pallidus = Striatum
Substantia nigra: pigmented cells of the midbrain
Globus pallidus, internal & external
Input to basal ganglia from:
1. All areas neocortex and limbic cortex, including the motor cortex, project to the basal ganglia.
2. The Nigrostriatal dopamine pathway extends into the basal ganglia from the substantia nigra
Possible disorders:
o Mainly involuntary hyperkinetic movements
Dyskinesia: unwanted choreiform movements, result by caudate putamen cells are damage
Huntington’s: genetic disorder that destroys caudate putamen involuntary and exaggerated movements
Hyperkinetic symptoms: caudate putamen damage, unwanted tics and vocalizations found in Tourette’s
