1. Sensorimotor systems
Chapters 8

3. Three principles of sensorimotor function
hierarchical organization
Two other organizing characteristics?
motor output is guided by sensory input
The case of G.O. – darts champion
The exception?
learning changes the nature and locus of sensorimotor control

4. Posterior Parietal Association Cortex
Function: Integrates information on the position of parts of the body and external objects to direct voluntary movement and attention.
Sensory system inputs: visual, auditory and somatosensory.
Outputs: dorsolateral PFC, secondary motor cortex and frontal eye fields.

5. Inputs to Posterior Parietal Association Cortex
Dorsolateral PFC
Frontal eye
field
Auditory
cortex
Visual
cortex
Inputs to Posterior Parietal
Association Cortex

6. Outputs to Posterior Parietal Association Cortex
Dorsolateral PFC
Frontal eye
field
Auditory
cortex
Visual
cortex
Outputs to Posterior Parietal
Association Cortex

7. Damage to the Posterior Parietal Association Cortex
Can produce a variety of deficits
Perception and memory of spatial relationships
Reaching and grasping
Control of eye movements
Attention

8. Damage to the Posterior Parietal Association Cortex
Apraxia – a disorder of voluntary movement not attributable to a simple motor deficit (weakness or paralysis) or to a deficit in comprehension or motivation.
Results from unilateral damage to the left posterior parietal cortex.

9. Damage to the Posterior Parietal Association Cortex
Contralateral neglect – a disturbance in a patient’s ability to respond to stimuli on the side of the body contralateral to a brain lesion (not a simple sensory or motor deficit).
Often associated with large lesions of the right posterior parietal lobe.

10. Dorsolateral Prefrontal Cortex
Function: plays a role in the evaluation of external stimuli and initiation of voluntary responses to those stimuli.
Main input: posterior parietal cortex
Outputs: secondary motor cortex
primary motor cortex
frontal eye fields

11. Dorsolateral Prefrontal connectivity

12. Dorsolateral Prefrontal cortex
Neurons in this area respond to the characteristics of objects (e.g., color/shape), the location of objects or to both.
The activity of other neurons is related to the response itself.

13. Secondary motor cortex
Input: most from association cortex
Output: primary motor cortex
Two classic areas:
SMA
Premotor cortex

14. Secondary Motor Cortex
Current classifications suggest
At least 8 different areas
3 supplementary motor areas
SMA, preSMA &
supplementary eye field
2 premotor areas
PMd and PMv
3 cingulate motor areas
CMAr, CMAv & CMAd

15. Mirror neurons
Discovered in the ventral premotor cortex of the macaque (Rizzolatti et al., 2006)
Social cognition – knowledge of the perceptions, ideas and intentions of others

16. Secondary Motor Cortex
Subject of ongoing research
May be involved in programming movements in response to input from dorsolateral prefrontal cortex
Many premotor neurons are bimodal – responding to 2 different types of stimuli
(most common - somatosensory and visual)

17. Primary Motor Cortex Precentral gyrus of the frontal lobe
Major point of convergence of cortical sensorimotor signals
Major point of departure of signals from cortex
Somatotopic – more cortex devoted to body parts which make many movements

18. Motor homunculus

19. Primary Motor Cortex
Monkeys have two hand areas in each hemisphere, one receives feedback from receptors in skin.
Stereognosis – recognizing by touch – requires interplay of sensory and motor systems
Damage to primary motor cortex
Movement of independent body parts (e.g., 1 finger)
Astereognosia
Speed. accuracy and force of movement

20. Other sensorimotor structures outside of the hierarchy
(sometimes called extrapyramidal systems)
Cerebellum
Basal ganglia
both modulate and coordinate the activity of the pyramidal systems by interacting with different levels of the hierarchy.

21. Cerebellum 10% of brain mass, > 50% of its neurons
Converging signals from
primary and secondary motor cortex
brain stem motor nuclei (descending motor signals)
Somatosensory and vestibular systems (motor feedback)
Involved in motor learning, particularly sequences of movement
Damage to cerebellum – disrupts direction, force, velocity and amplitude of movements; causes tremor and disturbances of balance, gait, speech, eye movement and motor sequence learning .

22. Basal Ganglia A collection of nuclei
Part of neural loops that receive cortical input and send output back via the thalamus (cortical-basal ganglia-thalamo-cortical loops)
Modulate motor output and cognitive functions
Cognitive functions of the basal ganglia

23. Descending Motor Pathways
Two dorsolateral
Corticospinal
Corticorubrospinal
Two ventromedial
Cortico-brainstem-spinal tract
The corticospinal tracts are direct pathways

26. Dorsolateral Vs Ventromedial Motor Pathways
one direct tract, one that synapses in the brain stem
Terminate in one contralateral spinal segment
Distal muscles
Limb movements
Ventromedial
one direct tract, one that synapses in the brain stem
More diffuse
Bilateral innervation
Proximal muscles
Posture and whole body movement

27. Experiments by Lawrence and Kuypers (1968)
Experiment 1: bilateral transection of the
Dorsolateral (DL) corticospinal tract
Results:
monkeys could stand, walk and climb
difficulty reaching improved over time
could not move fingers independently of each other or release objects from their grasp.

28. Experiments by Lawrence and Kuypers (1968)
The same monkeys with DL corticospinal tract lesions received 1 of 2 additional lesions:
The other indirect DL tract was transected
Both ventromedial (VM) tracts were transected

29. Experiments by Lawrence and Kuypers (1968)
Experiment 2 Results:
The DL group could stand, walk and climb but limbs could only be used to ‘rake’ small objects of interest along the floor
VM group had severe postural abnormalities: great difficulty walking or sitting. Although they had some use of the arms they could not control their shoulders.

30. Experiments by Lawrence and Kuypers (1968)
Conclusions:
the VM tracts are involved in the control of posture and whole-body movements
the DL tracts control limb movements (only the direct tract controls independent movements of the digits.