Motor Intention

What is motor control?

Generate and execute movement, therefore it is essential to understand how the brain plans and controlled skilled actions

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What are motor representations?

Internal programmes, which correspond to the desired result of movment. Voluntary movements are initiated to accomplish as specific goal

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How are motor representations refined?

By learning. Even though motor learning is acquired primarily through practice, skilled performers are often unable to express what they have learned 'implicit' learning

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What do motor representations inform?

The nervous system how to respond to patterns of sensory information through feedback control and feedforward control

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What is feedback control?

Sensory signals are used to act on the limb, least efficient and always corrected too late

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What is feedforward anticipatory control?

(most efficient and main, proactive strategies based on experience e.g. make a prediction of how to do a movement and what it will look like after years of practice)

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In order to understand how our motor system works what can we use?

Functional imaging

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To what?

Look at how brain damage affects action planning/execution.

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For example?

Parkinsons disease, which affects the basal ganglia producing slowing of movement, whereas damage to the cerebellum makes movements jerky

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What are the two major descending pathways?

Pyramidal and Extrapyramidal

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What is the Pyramidal tract?

Cortex to spinal cord, pathway for voluntary/ skilled tasks

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Where do most of the fibres originate?

Primary motor cortex, cross to contralateral side at the medulla oblongata (Control body in a contralateral way)

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10% remain in the ipsilateral fibres in healthy people, not completely understood why we have to do this, what happens in patients who contralateral fibres are impaired/

the ipsilateral fibres are useful in order to support control

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What are the extrapyramidal pathways?

rubrospinal (limb movements), vestibulospinal (posture and balance movements), tectospinal (capture and avoidance movements, mediates reflex postural movements of the head in response to visual and auditory stimuli), reticulospinal (startle and escap

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Therefore what is this pathway used for?

less skilled movement

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Where does this pathway originate?

Brain stem

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How are movements controlled?

Ipsilateral way

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Why is this system called extrapyramidal?

distinguish it from the tracts of the motor cortex that reach their targets by traveling the pyramids of the medulla

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What is the Primary motor cortex?

Located anterior to the central sulcus, projections to the spinal cord

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What happens when the primary motor cortex is damaged?

Weakness or loss of voluntary movement contralateral side

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What other areas are in motor organisation or planning?

Movement can still occur but if there's an impairment in M1 then movement is completely impaired

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What is the motor homonculus?

• Representation of the body in M1. The areas assigned to body parts are proportional to the complexity of the movements they can perform (Penfield – electrostimulation of parts of the cortex in patients with epilepsy)

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For example?

size of brain area corresponds to how complex movement is e.g. big area involved in hand and finger movements because they’re complex

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Lipert et al (1998)

Stroke Patients: The motor cortex was spatially mapped using focal transcranial magnetic stimulation (TMS) before and after 2 weeks of constraint-induced movement therapy (CI)

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What happened after CI therapy?

motor performance improved substantially in all patients. There was also an increase of motor output area size and motor evoked potential amplitudes, indicating enhanced neuronal excitability in the damaged hemisphere for the target muscles

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Therefore even in chronic stroke patients what?

reduced motor cortex representations of an affected body part can be enlarged and increased in level of excitability by an effective rehabilitation procedure

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Nudo et al (1996)

• Monkeys either had to use their fingers (difficult) or whole hand (easy) to get food from hole

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What happened in the finger monkets?

Their motor representation of their fingers changed in the brain (Plasticity)

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Functional mapping for pre- vs post-training shows what?

An expansion of the digit span representation and a shrinkage of the wrist/forearm representation

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Nitsche et al (2003)

• Transcranially applied weak direct currents are capable of modulating motor cortical excitability in the human. Anodal stimulation enhances excitability, cathodal stimulation diminishes it.

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What does cortical excitability do?

Cortical excitability changes accompany motor learning. Weak direct currents are capable of improving implicit motor learning in the human

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What happened during a performance of a serial reaction time task?

the primary motor cortex, premotor, or prefrontal cortices were stimulated contralaterally to the performing hand

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What did anodal stimulation of the primary motor cortex result?

increased performance, whereas stimulation of the remaining cortices had no effect. They conclude that the primary motor cortex is involved in the acquisition and early consolidation phase of implicit motor learning

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What are the premotor areas?

Anterior and projections to M1, Projections into pyramidal tract

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What are the two distinct sub regions with own somatopic map?

lateral premotor,  Supplementary motor area (SMA)  SMA proper – strong connections to motor system  Pre-SMA – strong connections to frontal areas, more involved in cognitive processes

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What does damage result in?

Planning deficits e.g. difficulties make compound and complex movements such as sequencing and coordination as compared to simple movements

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What are lateral premotor systems?

controls movements guided by sensory cues (externally-guided movements) e.g. have to respond to a cue

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What is the medial premotor system?

controls movements through internal motivation (internally- or self-guided movements) e.g. self-paced

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What happens if lesions of medial premotor system interferes with internal control of movements?

This can lead to automatisms in which movements are triggered automatically by external stimuli e.g. sees an apple and cannot help but eat it

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What are the external guidance of actions?

PMC is part of an external loop (generating a tapping sequence from cues

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What are the internal guidance of actions?

SMA is part of an internal loop (generating a tapping sequence from memory), connections to basal ganglia and to pre-frontal cortex, also very controlled by pre-frontal areas, conscious movement

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What does the external loop dominate in?

Visually guided movements

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When does the internal loop dominate?

During self guided movements. Switch between circuits during course of learning

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Mushiake et al (1991)

Measured single cell recording whilst tapping visually or internally cue sequence in primates

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What was found?

No difference in single cell recording for M1, M1 shows similar activity, PMC/SMA is more active during visual/internal cueing

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Premotor vs primary motor cortex: repetitive TMS - Gerloff et al (1998)

Tapping task: finger sequences of varying complexity, rTMS to either SMA or contralateral M1 after first key press for 2 seconds

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What happened at both M1 and SMA?

TMS at M1: immediate effect on performance, impairs it, “my hand got stuck” • TMS at SMA: impairment occurs later, “I forgot where I was in the sequence”

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Hari et al, 1998

The ventral premotor cortex of monkeys contains a specific set of neurons that discharge both when the monkey performs hand actions and when it observes another individual making a similar action (“mirror neurons”).

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What does this system then do?

matches action observation and execution might play an important role in action imitation and action understanding

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Fadiga et al, 1995 Evidence in humans?

responses recorded from the hand muscles significantly increase when the subject observes another individual making hand or arm actions

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What is the posterior parietal cortex for?

Damage can cause apraxia and deficits in directing attention and visually guided reaching

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What is apraxia?

Loss of the ability to execute skilled movement

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What is ideomotor apraxia?

inability to copy movements or make gestures such as using a tool or waving goodbye. This includes inability to demonstrate tool-use by pantomime whereas actual tool-use is less affected

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What is ideational apraxia?

inability to coordinate activities that include sequential movements, such as dressing, eating

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How do the hemispheres communicate?

several fibre tracts, allowing the exchange of information.

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What are the three main places that the hemispheres connect?

Anterior commissure: connects the middle and inferior temporal gyri of the hemispheres  Posterior commissure: connects midbrain and diencephalon structures  Corpus callosum: connects various regions from both hemispheres

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What are the homotopic areas of the corpus callosum?

connecting areas in corresponding locations (mostly association areas) e.g. left pre-motor area connected to left pre-motor area

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What are the heterotopic areas of the Corpus callosum?

to different areas (generally mirror within hemisphere connections, but are less extensive) e.g. left pre-motor cortex, connected to the right primary motor cortex

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What happened in split-brain patients?

Visuospatial ability is driven by the right hemisphere. Copying is possible with left hand, but not with right hand, because left hand is controlled by the same hemisphere as visuospatial ability

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What happened to people born without a corpus callosum?

Can perform some tasks that split-brain people fail to perform (plasticity) • Often enlarged anterior commissure which also connects the two hemispheres

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What is Anarchic hand syndrome?

unintended but purposeful and autonomous movements of the upper limb. Patients seem to be controlled by their environment. Patients acknowledge the hand as theirs, although they are frustrated by its unintended actions

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Object representations activated inappropriately, what happens?

The sight of an object is enough to elicit the movement even though this does not fit with the patient’s current goals

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Patient is aware of his intention to move and of the movement having occured however not aware of?

Not aware of initiated the movement

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Alien hand syndrome?

unintended but purposeful and autonomous movements of the upper limbs and exploratory reflexes. Patients with alien hand syndrome tend to dissociate themselves from the hand and its actions, say the hand doesn’t belong to them

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Desmurget and Sirigu, 2012

• Alien hand syndrome: activity in M1, no voluntary planning of the ppt (Desmurget & Sirigu, 2012) – voluntary movements show activity in M1, SMA and PMC

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Sala (1998)

anarchic hand is linked with anterior lesions of the corpus callosum and the supplementary motor area contralateral to the wayward hand.

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Beaumont et al, 1996)

Alien hand, which has been reported after posterior lesions of the corpus callosum, probably encroaching upon the parietal cortex, should be thought of as a partial hemisomatognosia.

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Unilateral what?

Loss of the knowledge or sense of one's own body and bodily condition

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What is motor intention?

• Intention is a fundamental feature of willed action and relies on a cascade of neural processes • Conscious intention is not a cause but rather a consequence of motor preparation

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Libet, 1985

• Ppt wearing EEG, watching a clock, what time on the clock did they have the conscious intention to move and then make the movement

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Intention to act?

about 250 ms before movement onset

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Activity before this intention?

before you know you want to move consciously, your brain is preparing to move, Brain activity: 1s or more before onset of movement

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Desmurget and Sirigu (2012)

• Unconscious phase of motor preparation in the parietal cortex – inferior parietal lobule (IPL) • Conscious intention around -250 ms due to increase of neural activity within IPL during early phase of preparation. Wanting to move

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What happens during final 250 ms

the action is planned. Inhibitory control prevents early release of action (by medial frontal areas, MPA). Urge to move • 2 brain areas involved: parietal and mesiofrontal areas involved in the later stages

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What are the two areas involved?

Parietal and Mesiofrontal areas involved in later stages

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Parietal invovlement

Subjects report the time they become aware of their intention to move, stimulation generates conscious motor intentions, stimulating the parietal areas, have the conscious intention to move

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What do they have to wait until?

release of motor command to access subjective experience of motor intention, no preparatory activity

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Mesiofrontal involvement ?

 Stimulation produces feeling of urge to move (Fried et al., 1991)  Lesions to SMA and pre-SMA can produce automatic execution of actions in response to environmental triggers, lack inhibitory process

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In a first event related fMRI experiment what did they find?

Preparing to move according to arbitary visuo motor associations relies not only on parieto frontal circuitry, but also on portions of the posterior superior temporal sulcus

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What happened in the second imaging experiment?

They further defined the relative contributions of these parietal, premotor, and temporal areas to the preparatory process and their involvement in motor representations.

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What did they conclude?

posterior parietal cortex is interested in evaluating the potential motor significance of sensory stimuli, irrespectively of the likelihood of providing a response (“motor intention”)

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Preparatory activity in frontal premotor regions appears to be a function of what?

probability of a subsequent movement. Finally, on the basis of the present and published data, we suggest that posterior temporal cortex might be involved in the extraction of contextual and intentional cues during goal-oriented behaviour

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Andersen and Buneo (2002)

One of the functions of the posterior parietal cortex (PPC) is the forming of intentions, that is, high-level cognitive plans for movement

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There is a map of what?

intentions within the PPC, with different sub regions dedicated to the planning of eye movements, reaching movements, and grasping movements

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These areas appear to be specialized for the multisensory integration and what?

coordinate trans-formations required to convert sensory input to motor output

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In several sub regions of the PPC?

these operations are facilitated by the use of a common distributed space representation that is independent of both sensory input and motor output

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What are also evidence in the PPC?

Attention and learning effects

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Anderson and Buneo (2002) PPC in paralysed patients

recording the activity of PPC neurons, interpreting the movement intentions of the subject with computer algorithms, and using these predictions of the subject’s intentions to operate external devices such as a robot limb or a computer

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Preliminary investigations in healthy monkeys estimated what?

estimate the number of parietal cells needed to operate such a prosthesis (Meeker et al., 2001, Shenoy et al., 1999b

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Recently found what?

monkeys can use this intended movement activity to position a cursor on a computer screen just by thinking about a reach movement, without actually generating a reach (Meeker et al., 2005)

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This result was obtained without what?

extensive training and strongly suggests that they are in fact tapping into the highly abstract neural signals that represent the earliest plans for movement

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Parietal cortex is also involved in what?

changes in movement plans (synder et al, 2000)

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what did they find?

strong modulation of activity when movement plans were changed without changes in the locus of attention

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What did this result suggest?

Parietal cortex, which has been postulated to play a role in shifting attention, may also play a role in changing movement intentions

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What did they do in Macaque monkeys?

they planned a saccade (red flash) or reach (green flash) to the flash location. In some trials, a second flash 750 ms later could change the motor plan but never shifted attention.

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When did the second flashes occur?

In the same location as the preceding first flash

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Roland et al, 1980

More complex, more brain areas involved • Simple flexion performed with right index finger = motor cortex and somatic sensory cortex • Movement sequence imagined with fingers of right hand = SMA, planning

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When was movement sequence performed?

fingers of right hand (common bed side test, involves lots of areas, gives idea of motor skills and pre-fontal skills)

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What happened in the SMA, inferior prefrontal cortex?

both left and right hemisphere and motor cortex and somatic sensory cortex of left hemisphere

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What is importance of coordination?

Important for a lot of movements we conduct in everyday life, Coordination is more than the sum of components

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For example?

“rub your stomach and pat your head at the same time” – very complicated because the processing signals from both hemispheres interfere with each other

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How do you do this?

Can do this spatially e.g. draw line with one hand and circle with another, interference (Franz, 1997)

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Coordination in split brain patients?

When they have to do asymmetrical movements (different movements with each hand), there’s an advantage but when they have to do the same thing with both hands they struggle

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Motor Intention

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