Motor cortex

3 processes involved in movement?

• planning

• execution

• feedback

Main cerebral areas involved in human motor system/

• motor cortex

• supplementary motor area

• premotor cortex

• posterior parietal cortex

• (primary somatosensory cortex)

What are the 4 types of evidence to show that there are 4 cortical motor regions?

• neurons increasae firing rate before movements and specific features of activity reflect specific movement features

• neurons send their axons to terminate in motor centres of the brainstem and spinal cord

• electrical stim of these areas elicits movement

• neurons send their axons to connect most densely with other motor areas

Does size and shape of motor areas vary across species?

yes

What are Brodmann’s areas?

52 regions of the cerebral cortex defined by its cytoarchitexture numbered by Brodmann in early 1900s

What are areasa 4 and 6?

M1 and PMC/SMA

How does laminar organisation work?

each layer has differing/specific functions depending on the cell types contained within and how they interact

What are layers 2 and 4 like?

• have a receptive role due to presence of many afferent fibre synapses within laminae

What did Sherrington do?

research on motor control and refelxes revealing how neural circuits coordinate movement

What did Penfield do?

cortical stimulation in awake patietns which mapped out specific motor functions to distinct regions of the primary motor cortex

Why are new versions of motor homunculus better?

refined because we have better techniques aka smaller microelectrode arrays and more advanced work with patients in surgery

What did Roux and Durand 2017 do?

How does the primarymotor cortex control voluntary movement (cellular)?

• large corticospinal neurons project from large pyramidal neurons (Betz neurons) in cortical layer V to lower motor neurons

• either excites them monosynaptically or branch and excite local inhibitory neurons

• generates the antagonistic muscle contraction patterns important for coordinated working of muscles

What are the different experimental techniques used to investigate the motor cortex?

• TMS

• fMRI

• EEG

How does a TMS work?

• TMS coil applies magnetic stimulation over M1, indirectly activating upper motor neurons by generating perpendicular magnetic field

• motor neurons descend down spinal cord where activate lower motor neurons connect to muscles

• potential recorded via EMG over target muscle

How does an fMRI work?

• measures the small changes in blood flow that occur with brain activity

• blood oxygen level dependent (BOLD) signal

• indirect with good spatial but bad temporal

What did Gordon et al, 2023 show?

• task fMRI activations during a movement task including movement of toes, ankles, hands, eyelids, tongue and swallowing

• see neat mapping of area

• asked to move or asked to plan movement and when plan see the inter coordinated movement regions light up more

What did Lacourse et al, 2005 do?

?

Common example of plasticity work?

• experience dependent plasticity

• eg remove whisker from a rodent

What did Donoghue and Sanes, 1997 do?

• cortical microstimulation in rats

• they mapped the regions of M1 that normally elicit movement to the forelimb, facial whiskers and muscles around the eye

• they then cut the motor nerve which innervated the muscles of the snout and whiskers

• observed that regions of M1 which used to evoke whisker movements were now specialised to forelimb or eye movements

• suggests malleableness of motor map could be basis of learning og fine motor skills

What did Walther 2009 do?

What do Merzenich et al, 1984 do?

What did Makin and Krakauer 2023 do?

What did Evarts 1968 do?

What does M1 neurons firing 5-100msec before the onset of movement tell us?

rather than firing as the result og musscle activity, these neurons are involved in relaying motor commands to the motor neurons that eventually cause the appropriate muscles to contract

What do M1 neurons encode?

• force of movement

• direction of movement

  • selective for a particular direction, discharge rates relative

• extent of movement

  • firing of some correlated with the distance of a movement

• speed of movement

  • firing rate correlate with movement speed profile

  • info about movement speed contained in spike trains of these neurons

What did Georgopoulos et al, 1982 do?

• trained monkeys to move a joystick towards a light

• cells in M1 fired most vigorously to their preferred direction yet still fired for differing angles just at a lesser intensity

• encoded through collecctive activity of a population of neurons - direction of movement determined mosst common response registered

• plot responses in tuning curve shows discharge rates before onset of movement

What did Evarts et al, 1968 do?

• single neuron recordings in monkeys for encoding of force

• firing rate of M1 neurons correlated with force used in movement when moving a lever upregulating when the weight increased

3 areas connected to?

• basal ganglia

• cerebellum

• thalamus

What does the basal ganglia do?

• set of subcortical nuclei that coordinate movement indirectly in set of loops

• receive input from cortex and return to cortex via thalamus

• loss of dopaminergic cells in the substantia nigra of the BG can lead to Parkinsons

What does the cerebellum do?

• highly folded and contains half of all brain neurons

• important for adaptation and error signalling

What does Martin et al, 1996 do?

• Throw darts at a target

• Put on prism glasses

• Big errors in throwing then gradually get better

• Then reverse effect and adapt

• Cerebellum signals that you've made an error - updates motor command

• Damage shows that adaptability is diminished

What does the thalamus do?

• main relay station of the brain

• located between motor areas of the cerebral cortex and two subcortical networks - BG and cerebellum