Cognitive Neuroscience Week 5
Cognitive Neuroscience Week 5 PSYC 3122
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This 15 page Class Notes was uploaded by Freddi Marsillo on Thursday September 29, 2016. The Class Notes belongs to PSYC 3122 at George Washington University taught by Dr. Shomstein in Fall 2016. Since its upload, it has received 9 views. For similar materials see Cognitive Neuroscience in Psychology at George Washington University.
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Date Created: 09/29/16
Cognitive Neuroscience Week 5 9/29/16 9:48 PM Motor System • Cortex & subcortical (cerebellum & basal ganglia) • Spinal cord o Cortical o Subcortical • To muscles o Effectors: proximal and distal Muscle Signals • Paired agonist and antagonist • Released via acetylcholine • Innervations from own stretch spindles and also spinal cord • Excitatory to one, inhibitory to other Knee Reflex: Stretch Sensory signal ▯ stretch receptor ▯ alpha motor ▯ contract quadriceps Cortex Cortico-spinal tract • Motor neurons from motor cortex • Premotor cortex • Supplementary motor cortex Organization • Topographic • Importance of effectors and precision of movement • Cross body (decussate) at medulla/spinal cord juncture • Hierarchical arrangement o Abstract cortex regulates o Simple reflex at bottom Hierarchy: Cortex and Periphery Sherrington • Cut input from cortex (efferent) • Reflexes exaggerated • Animals still move • Cut sensory root (afferent): no longer move • Sensory feedback crucial Brown • Actually, sensory is not necessary • Humans with neuropathies can still make movements o Although they do make errors and if complex, they are not coordinated • Central pattern generators o Hierarchy ▯ Cortex simply activates pattern generator neurons: command into movement ▯ Postural adjustments Motor Representation Hierarchical sequences • Chunks • Seems non-cognitive, as we cannot verbalize it • Independent of particular muscle group o Several distributed anatomical structures Directional tuning of motor cells • Georgopolous: neurons like particular directions of action Direction of movement (M1 cells) Population Vector Summed activity over all neurons = population vector Population Vector: Action or Intention? ▯ Intention! Motor Planning vs. Execution Hierarchical ideas • Primary and somatosensory activated for simple movements • More complex motor planning: supplementary motor area (SMA) and prefrontal cortex • When you are imagining yourself making these movements: only SMA is activated, because you are not actually making the movement – no muscles are being stretched or flex (abstract motor plan) Evidence from TMS study • You interfere with actual execution of movement o Over motor cortex: movement halted or wrong key pressed o Over SMA: delayed movement Movement occurs when M1 cells fire (nothing else activates movement) Internal vs. External Guidance Internal guidance • “Muscle memory” – you just know what to do • SMA is the major contributor (along with prefrontal cortex) to internal guidance External guidance • You have to see something in order to know what to do with it (for example, you need to read a sign to know where to go) • Premotor cortex (PMC) (visually-guided) is the major contributor to external guidance Internal vs. External Guidance Effects of Learning • New sequences: lateral premotor and prefrontal cortex (the red areas = brain regions that are activated when you are just learning a new task) • Previously learned sequences: activate SMA and hippocampus (the blue areas = the brain regions that activate after you’ve already learned) o Hippocampus is activated because it is involved with memory Summary • Parallel circuits • Parietal, PMC (and cerebellar) ▯ spatially directed or guided movement, dominate in early acquisition • SMA (and basal ganglia) ▯ when skill is learned and driven by internal representation Functional Analysis ▯ and produce movement Movement Disorders Hemiplegia • Damage in M1 (Example: with damage in left side of M1, it is impossible to move right side of body – reflexes are still there because they do not engage the motor cortex) • Loss of voluntary movement • Reflexes return (but they are hyper, exaggerated – this shows how the cortex, when not damaged, can inhibit muscles so that they do not move accidentally; when you remove the cortex, you remove the inhibition) o Therefore, increased spasticity (increased muscle tone; muscles are overly active) Apraxia (left hemi, parietal) • Loss of motor skill (not muscle related; they have the muscular capability) o They can describe the steps they need to take to carry out an action, but cannot physically carry out that action ▯ Ideomotor – knows sequence but cannot implement ▯ Ideational – disrupted knowledge of action Alien hand syndrome • SMA • Inability to inhibit o E.g. sees a cup, has to pick it up • Movements are complex o Distributed process involving many neural regions Cerebellum Vestibulocerebellum • Balance, VOR, etc. • Spinocerebellum o Sensory info from spinal cord o Also from auditory/visual ▯ Polysensory o Output to spinal cord and motor cortex • Neocerebellum o Has inputs from all the regions spinocerebellum has o Innervated by cerebral cortex and goes back to the thalamus; integrating a lot of info that comes from the motor and sensory systems and brings it back to spinal cord and back to the motor cortex o Newest part of cerebellum Cerebellar Lesions Vestibulocerebellum • Damage to this area affects balance Damage to the spinocerebellum • Affects having smooth control of action o Especially axial muscles (body and trunk) o Alcohol • Hypermetria o Good initiation of movement but it’s clumsy, irregular, erratic (like a drunk person) • Neocerebellum o Similar to spinocerebellum but with prolonged initiation (planning role) – difficult to start the movement Cerebellar Atrophy – ataxia Cerebellar function • Not clear – it receives a LOT of inputs • Timing hypothesis (think of cerebellum as a conductor; tells each muscle when to start and when to stop) – controls the timing of activation of particular muscles Basal Ganglia • Input to basal ganglia is excitatory; output to basal ganglia is inhibitory • Movement initiation o Function of basal ganglia is to inhibit unwanted movements and to facilitate wanted movements • Inhibition keeps motor system in check, while motor plan is emerging • As specific motor plan is derived, inhibitory signal is decreased for selected neurons Basal Ganglia: Disorders Parkinson’s (damage in the substantia niagra) • Bradykinesia – slowness in execution (initiation) of movements • Hypokinesia – reduction in voluntary movements (hypo = not enough) Huntington’s chorea (striatum) • Clumsiness, balance problems, increase in involuntary movements o Not restricted to the motor system, general dementia Fluorodopa – radioactive tracer • Uptake at the striatum Summary 9/29/16 9:48 PM 9/29/16 9:48 PM
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