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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.
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