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Motor Control (The Motor Brain (Cortical Lobes
Occipital Lobe - vision
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Motor Control
The Motor Brain
What We Know About the Brain?
- Cytoarchitecture - study of neurons with microscopes
- Physiological Studies - study of AP and synaptic transmissions
- Neuroimaging - fMRI, PET, EEG
- Peripheral NS - NS not in bone
- Central NS - NS in brain and Spine
- Weighs ~1500g
- 2 hems connected by corpus collosum
Anatomical Terms
- Ipsilateral - on same side as...
- Contralateral - opposite side as...
- Cortical - within cerebral cortex
- Sub cortical - underneath cerebral cortex
What is in our Head?
- Grey Matter - cerebral cortex, cerebellum and subcortical (cell bodies of neurons)
- White Matter - myelinated fibre tracts
- Association Fibres - connect one part of brain to other
- Commissural fibres - connects left side to right
- Projection fibres - connects spinal cord and brain stem to cerebral cortex
- Structural tissue - Meninges (covering brain)
Skin
Skull
Dura matter
Arachnoid
Pia matter
4.Ventricles - fluid filled pockets (cerebral spinal fluid)
Divisions of the Brain
Midbrain:
- Cerebellum - 'little brain', balance and co-ord
- PONS and reticular formation - complex reflexes, breathing and BP, wakefulness and sleep
- Tectum - contains superior and inferior collicus, orientating behaviour (old 'visual system')
Forebrain (diencephalon):
- Thalamus - sensory info, arousal and sleep, learning
- Hypothalamus
Forebrains (Telencephalon):
- Cerebral Cortex
- Subcortical
Cortical Lobes
- Occipital Lobe - vision
- Parietal Lobe - process info
- Temporal Lobe - Memory
- Frontal Lobe - Movement
Main Cortical Motor Areas
- Primary Motor Cortex (M1) - Movements, somatotopic organisation, in precentral gyrus
- Dorsal Premotor area (PMd) - selection of response
- Ventral premotor area - perception and control of goal-directed actions
- Supplementary motor area (SMA) - internally guided movement sequences
- Pre-supplementary motor-area (pre-SMA)- Learning of movements
How do we move?
- Fibre tracts descend from corticol and subcortical regions through spinal cord
- Alpha motor neurons connect spinal cord to muscles
Tract Lesions - Larence and Kuypers (1968)
- Showed lesions to corticolspinal tract lead to immediate paralysis
Findings:
- Never recovered independent finger movement
- Cerebellum - Feedback from motor responses, involved in timing and motor learning
- Spinocerebellum - co-ord of voluntary movements
- Cerebrocerebellum - planning and control of voluntary movement
- Vestibulocerebellum - needed for balance, co-ord of eye movement
Perception and Action
Anatomy? Frogs' visual system (Ingle,1973)
- Unilateral removal of frogs tectum leads to regrowth towards ipsilateral tectum
- Frogs 'see' stationary objects as barriers
- Mirror symmetrical orientating behaviour (catch fly wrong)
Ungerleider and Mishkin, 1982
- Object discrimination task - impaired by lesions to ventral stream (temporal lobe)
- Landmark task - impaired by lesions of dorsal stream (posterior parietal cortex)
What vs Where
- Dorsal/where stream - spatial processing
- Ventral/what stream - object processing (colours, size, shape)
Patient DF - agnosia
- Can still 'see' (colour, orientation etc.), but can't read, recognise objects e.g. faces or shapes
Goode and Milner, 1992
- Dorsal visual pathways guide action
- Ventral visual pathways guid perception
AKA perception-action model
Findings:
- If goal is perception for perception sake, then impaired
- If goal is controlling movement = not impaired
How to measure visually guided actions?
- Grasping
- Grip aperture - distance between thumb and forefinger increases until 70% through reach
- Peak grip aperture decreases/increases with object size
Dorsal Stream Damage - Optic Ataxia
- Damage to left parietal lobe
- Affects visually guided actions e.g. orientation of hands
- Can discriminate between objects
- Patient RV couldn't do posting task
Types of Mirror Neurons
- Specific actions - particular grasp on a small object
- Specific action endpoint - goal of grasping an object, regardless of how it's achieved
- Specific abstract modality - independent goal
Molenburgh et al, 2011
- Observed sig activation clusters in early visual cortex and cerebellum
- Stronger activation of action observation network when watching something you're good at
Novelty
- High activation for novel actions (Liew et al, 2013)
Evidence from TMS:
- MEP scale correlates with observed action to muscle
Losing Touch - peripheral deafferentation - Patient IW
- Lost proprioception (knowledge of static limb position)and impaired sense of touch
- Poor weight discrimination with eyes closed, fine with eyes open
Iriki, Tanaka and Iwamura (1996)
- Found that neurons fired when in peripersonal space
- Tools become part of body
Disorders of Body Representation
- Damage to right parietal lobe
- Asomatognosia - loss of awareness of limbs
- Somatoparaphrenia - denial of ownership of limb
- Supernumeracy phantom limb - extra limb
- Body integrity limb disorder - amputate healthy limbs
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Motor Control
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Brain Scans
Structural Methods
- Computed Tomography - CAT scan
- Related to x-ray absorption = more absorption in high density areas
- Magnetic resonance imaging - how different tissues response to magnetic fields:
- no radiation
- Better spatial resolution
What to look out for when using MRI
- Neurological Convention - left side on left, right on right
- Radiological Convention -other way round
- Brain Space normalisation
Functional
- Electrophysiological:
- Single-cell recordings - electrode placed in our near neuron
- Event related potential - electrode placed on skull
- Measures number of AP
- non - invasive
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Positron Emission Tomography (PET)
- Measure local blood flow
- Radioactive tracer injected into blood, 30s to peak
- Good Spatial resolution
Functional Magnetic Resonance Imaging (fMRI)
- measures concentration of deoxyhemoglobin in blood
- No radiation
- BOLD (Blood Oxygen Level Dependant contrast) - change response over time is called hemoglobindynamic response function
- peaks 6-8s, limiting temporal resolution
Trasncranial Magnetic Stimulation (TMS)
- Brief, powerful pulses of electromagnetic stimulation
- Multiple rapid pulse to induce virtual lesion (rTMS)
Advantages:
- Temporary
- Reversible
- Targets region of interest
Disadvantages:
- Can't be used in all populations
- Uncomfortable
- Hard to stimulate some regions