Sensorimotor Control of Behavior: Movement Lecture 9

Motor Systems n Functions l movement l posture & balance l communication n Guided by sensory systems l internal representation of world & self l detect changes in environment external & internal ~

Movement & Muscles n Movement occurs at joints n Contraction & relaxation of of opposing muscles l agonists prime movers l antagonists counterbalance agonists decelerate movement ~

Dorsal Ventral Alpha Motor neurons + Upper Motor Neurons

Movement & Muscles n Movement control more than contraction & relaxation l Accurately time control of many muscles l Make postural adjustment during movement l Adjust for mechanical properties of joints & muscles inertia, changing positions ~

3 Classes of Movement n Voluntary l complex actions reading, writing, playing piano l purposeful, goal-oriented l learned improve with practice ~

3 Classes of Movement n Reflexes l involuntary, rapid, stereotyped eye-blink, coughing, knee jerk l graded control by eliciting stimulus ~

3 Classes of Movement n Rhythmic motor patterns l combines voluntary & reflexive acts chewing, walking, running l initiation & termination voluntary l once initiated, repetitive & reflexive ~

Organization of Motor Control n Hierarchical & Parallel n Parallel l pathways active simultaneously l e.g. moving arm 1. muscles producing movement 2. postural adjustments during movement n Recovery of function after lesion l overlapping functions ~

Hierarchical Control of Movement n 3 levels of control l Cortex l Brainstem l Spinal cord (SC) n Division of responsibility l higher levels: general commands l spinal cord: complex & specific n Each receives sensory input l relevant to levels function ~

Hierarchical Control of Movement n Association cortices & Basal Ganglia l strategy : goals & planning l based on integration of sensory info n Motor cortex & cerebellum l tactics: activation of motor programs n Spinal cord execution: activates  motor neurons l reflexes l rhythmic pattern generators ~

Sensorimotor Cortical System n Integration of sensory information and directed movements n Anatomy n Descending spinal tracts l Lateral pathway Pyramidal Motor System l Ventromedial pathway l Extrapyramidal pathway ~

Cortical Anatomy n S1 - postcentral gyrus n PPC - Posterior Parietal Cortex n M1 - Precentral Gyrus l Frontal Lobe somatotopic organization n M2 - Secondary Motor Cortex SMA - Supplementary Motor Area PM - Premotor Cortex

M1 SMA S1 PM PPC

The Descending Spinal Tracts

Brain to Spinal Cord n Upper motor neurons communication with lower (  ) motor neurons n Lateral pathway l direct cortical control n Ventromedial pathway l brain stem control ~

The Lateral Pathway n Voluntary movement l distal limbs l 2 tracts n Corticospinal tract about 1 million axons n Rubrospinal tract small part of pathway ~

Dorsal Ventral Spinal Cord: Lateral Pathway Corticospinal tract Rubrospinal tract

Corticospinal tract n Motor cortex ---> spinal cord l uninterrupted axon l 2/3 of axons from motor cortex l 1/3 from somatosensory cortex n Decussates at medulla n Contralateral control movement ~

The Rubrospinal Tract n Motor Cortex ---> red nucleus n Red nucleus ---> spinal cord l inputs from motor cortex l bigger role in other mammalian species ~

Lateral Pathway Damage n Lesion both tracts l no independent movement of distal limbs l voluntary movements slow & less accurate n Corticospinal only l same deficits l recovery over several months l compensation by rubrospinal tract ~

The Ventromedial Pathway n Neurons originate in brainstem n Vestibulospinal & tectospinal tracts l head & posture posture l orienting responses n Pontine & medullary reticulospinal tracts l originate in reticular formation l trunk & antigravity leg muscles l tracts are antagonistic ~

Dorsal Ventral Spinal Cord: Ventromedial Pathway Tectospinal tract Pontine Reticulospinal tract Medullary Reticulospinal tract Vestibulospinal tract

Major Descending Spinal Tracts Motor Cortex Spinal cord Red Nucleus Reticular Nuclei Superior Colliculus vestibular nuclei Ventromedial Lateral

Primary Motor Cortex n Somatotopic organization l neurons have preferred direction of movement n Motor homunculus ~ Cortical Control of Movement

M1: Coding Movement n Movement for limbs n Neuron most active l Preferred direction but active at 45  from preferred n How is direction determined? l Populations of M1 neurons l Net activity of neurons with different preferred directions l vectors ~

M1: Coding Movement n Implications 1. Most M1 active for every movement 2. Activity of each neuron 1 “vote” 3. direction determined by averaging all votes ~

Motor Association Cortex n Motor area other than M1 l secondary motor cortex (M2) n Premotor & Supplemental Motor Areas n Active during preparation for movement l Planning of movements n Stimulation - complex movements l motor programs ~

Supplementary Motor Area - SMA n Primarily midline cortex n Inputs from … l PPC l S1 n Bilateral output to M1 l to distal limbs ~

Premotor Area - PMA n Anterior to M1 n Input l primarily from PPC l reciprocal connections with SMA n Outputs to M1 l then proximal limbs ~

M1S1 PMA SMA Spinal cord PPC

Planning Movements n Targeting vs trigger stimulus recording activity of neurons n active when movement planned l for specific direction n Different populations of neurons active l during planning (targeting) l & execution (trigger stimulus) n PM active before movement ~

n Simple finger flexion l only M1 activation

n Sequence of complex finger movements l M1 + SMA activation ~

n Mental rehearsal of finger movements l only SMA activation ~

Sensorimotor Integration n Perceptual development n Active interaction required l environmental feedback important n Held & Hein (1950s) l kittens passively moved l depth perception deficits & related responses, blinking, looming ~

Sensorimotor Integration n Sensory inputs guide movement l visual, auditory, tactile location of objects in space l Proprioceptive & vestibular position of our body n Critical for planning & refining movements ~

Generation of Rhythmic Motor Patterns

Central Pattern Generators n Half-center Model l alternating activity in flexor & extensor n Step-cycle has 2 phases l swing phase foot off ground & flexing forward l stance phase foot planted & leg extending n Each limb has own pattern generator ~

Half-center Model   + + Tonic input Flexor Extensor

Rhythmic Patterns: Sensory Feedback n Not necessary for locomotion l but slower, less coordinated n Stumble correction reaction l during swing phase l tactile stimulus on dorsal foot ---> flexion n Reflex reversal l override during extension l flexion would cause collapse ~

Goal-directed Locomotion n Requires intact supraspinal systems n Coordination of antigravity muscles Brainstem motor nuclei n modulation of contraction strength Reticulo-, rubro-, corticospinal n Balance Vestibulospinal tract (Ventromedial) n Also cortical & subcortical areas ~