Sensorimotor systemsSensorimotor systems

Chapters 8Chapters 8

Three principles of sensorimotor Three principles of sensorimotor functionfunction

hierarchical organizationhierarchical organizationTwo other organizing characteristics?Two other organizing characteristics?

motor output is guided by sensory inputmotor output is guided by sensory inputThe case of G.O. – darts championThe case of G.O. – darts championThe exception?The exception?

learning changes the nature and locus of learning changes the nature and locus of sensorimotor controlsensorimotor control

Posterior Parietal Association CortexPosterior Parietal Association Cortex

Function: Integrates information on the Function: Integrates information on the position of parts of the body and external position of parts of the body and external objects to direct voluntary movement and objects to direct voluntary movement and attention.attention.

Sensory system inputs: visual, auditory and Sensory system inputs: visual, auditory and somatosensory.somatosensory.

Outputs: dorsolateral PFC, secondary motor Outputs: dorsolateral PFC, secondary motor cortex and frontal eye fields.cortex and frontal eye fields.

Frontal eye field

Dorsolateral PFC

Visualcortex

Auditorycortex

Inputs to Posterior ParietalInputs to Posterior ParietalAssociation CortexAssociation Cortex

Frontal eye field

Dorsolateral PFC

Visualcortex

Auditorycortex

Outputs to Posterior ParietalOutputs to Posterior ParietalAssociation CortexAssociation Cortex

Damage to the Posterior Parietal Damage to the Posterior Parietal Association CortexAssociation Cortex

Can produce a variety of deficitsCan produce a variety of deficitsPerception and memory of spatial Perception and memory of spatial

relationshipsrelationshipsReaching and graspingReaching and graspingControl of eye movementsControl of eye movementsAttentionAttention

Damage to the Posterior Parietal Damage to the Posterior Parietal Association CortexAssociation Cortex

Apraxia – a disorder of voluntary movement Apraxia – a disorder of voluntary movement not attributable to a simple motor deficit not attributable to a simple motor deficit (weakness or paralysis) or to a deficit in (weakness or paralysis) or to a deficit in comprehension or motivation.comprehension or motivation.

Results from unilateral damage to the left Results from unilateral damage to the left posterior parietal cortex.posterior parietal cortex.

Damage to the Posterior Parietal Damage to the Posterior Parietal Association CortexAssociation Cortex

Contralateral neglect – a disturbance in a Contralateral neglect – a disturbance in a patient’s ability to respond to stimuli on the patient’s ability to respond to stimuli on the side of the body contralateral to a brain side of the body contralateral to a brain lesion (not a simple sensory or motor lesion (not a simple sensory or motor deficit).deficit).

Often associated with large lesions of the Often associated with large lesions of the right posterior parietal lobe.right posterior parietal lobe.

Dorsolateral Prefrontal CortexDorsolateral Prefrontal Cortex

Function: plays a role in the evaluation of Function: plays a role in the evaluation of external stimuli and initiation of voluntary external stimuli and initiation of voluntary responses to those stimuli.responses to those stimuli.

Main input: posterior parietal cortexMain input: posterior parietal cortex

Outputs: Outputs: secondary motor cortexsecondary motor cortex

primary motor cortexprimary motor cortex

frontal eye fieldsfrontal eye fields

Dorsolateral Prefrontal connectivityDorsolateral Prefrontal connectivity

Dorsolateral Prefrontal cortexDorsolateral Prefrontal cortex

Neurons in this area respond to the Neurons in this area respond to the characteristics of objects (e.g., characteristics of objects (e.g., color/shape), the location of objects or to color/shape), the location of objects or to both. both.

The activity of other neurons is related to the The activity of other neurons is related to the response itself.response itself.

Secondary motor cortexSecondary motor cortex

Input: most from association cortexInput: most from association cortex

Output: primary motor cortexOutput: primary motor cortex

Two classic areas:Two classic areas:

1)1) SMASMA

2)2) Premotor cortexPremotor cortex

Secondary Motor CortexSecondary Motor Cortex

Current classifications suggestCurrent classifications suggestAt least At least 88 different areas different areas

33 supplementary motor areas supplementary motor areas SMA, preSMA & SMA, preSMA & supplementary eye fieldsupplementary eye field

2 premotor areas 2 premotor areas PMd and PMvPMd and PMv

3 cingulate motor areas3 cingulate motor areasCMAr, CMAv & CMAdCMAr, CMAv & CMAd

Mirror neuronsMirror neuronsDiscovered in the ventral premotor cortex Discovered in the ventral premotor cortex

of the macaque (Rizzolatti et al., 2006)of the macaque (Rizzolatti et al., 2006)Social cognition Social cognition – knowledge of the – knowledge of the

perceptions, ideas and intentions of othersperceptions, ideas and intentions of othershttp://video.pbs.org/video/1615173073/

Secondary Motor CortexSecondary Motor Cortex

Subject of ongoing researchSubject of ongoing researchMay be involved in programming May be involved in programming

movements in response to input from movements in response to input from dorsolateral prefrontal cortexdorsolateral prefrontal cortex

Many premotor neurons are bimodal – Many premotor neurons are bimodal – responding to 2 different types of stimuliresponding to 2 different types of stimuli

(most common - somatosensory and visual)(most common - somatosensory and visual)

Primary Motor CortexPrimary Motor Cortex

Precentral gyrus of the frontal lobePrecentral gyrus of the frontal lobe Major point of convergence of cortical Major point of convergence of cortical

sensorimotor signalssensorimotor signals Major point of departure of signals from cortexMajor point of departure of signals from cortex Somatotopic – more cortex devoted to body Somatotopic – more cortex devoted to body

parts which make many movementsparts which make many movements

Motor Motor homunculushomunculus

Primary Motor CortexPrimary Motor Cortex

Monkeys have two hand areas in each Monkeys have two hand areas in each hemisphere, one receives feedback from hemisphere, one receives feedback from receptors in skin.receptors in skin.

StereognosisStereognosis – recognizing by touch – requires – recognizing by touch – requires interplay of sensory and motor systemsinterplay of sensory and motor systems

Damage to primary motor cortexDamage to primary motor cortex Movement of independent body parts (e.g., 1 finger)Movement of independent body parts (e.g., 1 finger) AstereognosiaAstereognosia Speed. accuracy and force of movementSpeed. accuracy and force of movement

Other sensorimotor structures Other sensorimotor structures outside of the hierarchyoutside of the hierarchy

(sometimes called extrapyramidal systems)(sometimes called extrapyramidal systems)CerebellumCerebellumBasal gangliaBasal ganglia

both modulate and coordinate the activity of both modulate and coordinate the activity of the pyramidal systems by interacting with the pyramidal systems by interacting with different levels of the hierarchy. different levels of the hierarchy.

CerebellumCerebellum

10% of brain mass, > 50% of its neurons10% of brain mass, > 50% of its neurons Converging signals fromConverging signals from

primary and secondary motor cortexprimary and secondary motor cortex brain stem motor nuclei (descending motor signals)brain stem motor nuclei (descending motor signals) Somatosensory and vestibular systems (motor Somatosensory and vestibular systems (motor

feedback)feedback) Involved in motor learning, particularly sequences Involved in motor learning, particularly sequences

of movementof movement Damage to cerebellum – disrupts direction, force, velocity Damage to cerebellum – disrupts direction, force, velocity

and amplitude of movements; causes tremor and and amplitude of movements; causes tremor and disturbances of balance, gait, speech, eye movement and disturbances of balance, gait, speech, eye movement and motor sequence learning .motor sequence learning .

Basal Ganglia Basal Ganglia

A collection of nucleiA collection of nucleiPart of neural loops that receive cortical Part of neural loops that receive cortical

input and send output back via the input and send output back via the thalamus (cortical-basal ganglia-thalamo-thalamus (cortical-basal ganglia-thalamo-cortical loops)cortical loops)

Modulate motor output and cognitive Modulate motor output and cognitive functionsfunctions

Cognitive functions of the basal gangliaCognitive functions of the basal ganglia

Descending Motor PathwaysDescending Motor Pathways

Two dorsolateralTwo dorsolateral Corticospinal Corticospinal CorticorubrospinalCorticorubrospinal

Two ventromedialTwo ventromedial CorticospinalCorticospinal Cortico-brainstem-spinal tractCortico-brainstem-spinal tract

The corticospinal tracts are direct pathwaysThe corticospinal tracts are direct pathways

Dorsolateral Vs Ventromedial Motor Dorsolateral Vs Ventromedial Motor PathwaysPathways

VentromedialVentromedial one direct tract, one one direct tract, one

that synapses in the that synapses in the brain stembrain stem

More diffuseMore diffuse Bilateral innervationBilateral innervation Proximal musclesProximal muscles Posture and whole Posture and whole

body movementbody movement

DorsolateralDorsolateral one direct tract, one one direct tract, one

that synapses in the that synapses in the brain stembrain stem

Terminate in one Terminate in one contralateral spinal contralateral spinal segmentsegment

Distal musclesDistal muscles Limb movementsLimb movements

Experiments by Lawrence and Experiments by Lawrence and Kuypers (1968)Kuypers (1968)

Experiment 1: bilateral transection of theDorsolateral (DL) corticospinal tractResults: 1) monkeys could stand, walk and climb 2) difficulty reaching improved over time3) could not move fingers independently of

each other or release objects from their grasp.

Experiments by Lawrence and Experiments by Lawrence and Kuypers (1968)Kuypers (1968)

Experiment 2:

The same monkeys with DL corticospinal tract lesions received 1 of 2 additional lesions:

1) The other indirect DL tract was transected2) Both ventromedial (VM) tracts were

transected

Experiments by Lawrence and Experiments by Lawrence and Kuypers (1968)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.

Experiments by Lawrence and Experiments by Lawrence and Kuypers (1968)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.