Sensorimotor Dysfunction

Question 1

Even “simple” behaviours are mediated by how many parts of the brain?

Answer 1

• MANY
• EX: a tennis player receiving a serve - involves premotor cortex, amygdala, etc.

Question 2

Sensation, movement planning, and execution are always WHAT? What do they rely on?

Answer 2

• Always intertwined
• Large reliance on feedback

Question 3

Sensory feedback

Answer 3

Our sensory systems monitor the body’s responses -> feed that information BACK to sensorimotor circuits, so they can take it into account and build on it

Question 4

Examples of sensory feedback

Answer 4

• Ballistic movements (e.g. swatting)
• Reflexes (e.g. yanking hand away)

Question 5

Hieararchical organization of the motor system:

Answer 5

1. Association cortex
2. Secondary motor cortex
3. Primary motor cortex
4. Brainstem motor nuclei
5. Spinal motor circuits

AKA, movement going from a plan -> actual production (sending plan down brain, brainstem, spine, and out towards the body via motor neurons)
* First levels: “chop an onion”
* Middle levels: reach hand toward onion (refining movement)
* Final levels: extending arm and opening hand (specific motor sequence)

Question 6

Hieararchical organization of the motor system: IN PARALLEL, 2 structures:

Answer 6

• Basal ganglia
• Cerebellum
• Responsible for managing these movements and modifying them as we go (to make sure sequence is good)

Question 7

During the hierarchical organization of the motor system, how is information being received?

Answer 7

• ALL THE TIME: real time, “online” sensory feedback

Question 8

What is the role of the lower HOMS levels in this real time, sensory feedback?

Answer 8

• Lower levels of the HOMS have sensorimotor programs
• Once active, these programs can operate without higher control (first learning how to ride a bike - you’re thinking about it a lot, but over time these processes become automatic)

Question 9

Why should our motor system be flexible?

Answer 9

• Living in a complex, world, reflexes just aren’t enough
• Can see this in the principle of motor equivalence: there;s more than one way to carry out a movement (EX: writing with left hand, right hand, foot - all produce similar letters despite different approaches)

Question 10

BREAKING DOWN HOMS

Question 11

In reference to association cortex:

Answer 11

Involves…
* Posterior parietal association cortex
* Dorsolateral prefrontal association cortex

Question 12

Posterior parietal association cortex

In reference to association cortex:

Answer 12

• Integrates information about the current position of body parts with information about external objects you may act upon
• Receives inputs/raw information from all systems (visual, auditory…) to make a plan of action
• Stimulation can make the patient feel like they’re performing an action

Question 13

Posterior parietal association cortex DAMAGE

In reference to association cortex:

Answer 13

• Contralateral neglect: dysfunction of attention
• Apraxia: impaired voluntary movement (associated with left hemisphere damage - symptoms are bilateral)

Apraxic errors particularly for:
* Imitation of gestures
* Performance of gestures on command
* Use of tools and objects in unusual contexts

Question 14

Dorsolateral prefrontal cortex (dlPFC)

In reference to association cortex:

Answer 14

• Involved in evaluation of external stimuli and the initiation of voluntary reactions (decide and react: phone is ringing, do I walk over and pick it up?)
• Gets this initial information from the posterior parietal association cortex
• Some of the first neurons fire here when anticipating a motor movement -> decision to act may begin here
• Also involved in cognition (e.g. problem solving, math…)

Question 15

What changes with movement practice?

Answer 15

• As a movement is practiced, effort goes away or there’s less activity
• People start response chunking - sequence treated as a unit (opposed to a bunch of different things, when first learning how to do something)
• Shifting control to lower levels

Question 16

In reference to secondary motor cortex:

Answer 16

• 8 areas of secondary motor cortex (premotor, supplemental, cingulate)
• ALL receive information from the association cortex and send them on to primary motor cortex
• Produce and guide complex movements in space

Question 17

Mirror neurons

In reference to secondary motor cortex:

Answer 17

• In ventral promotor cortex and other locations
• Have the property of firing both when you carry out an action and when you see that same action being done by the same individual
• Potentially related to the theory of the mind, empathy
• Most ebidence is from monkeys as single-neuron resolution is needed

Question 18

In reference to primary motor cortex (M1):

+ lesion effects

Answer 18

• Somatotopically organized (PENFIELD = stimulation experiments)

Lesion effects: show less dysfunction than you may think
* disrupted ability to move one body part independently of others
* may produce astereognosia
* may reduce speed, acuracy, and force of movements

Question 19

Cerebellum

Basal Ganglia + Cerebellum

Answer 19

Receives inputs from:
* primary and motor cortex
* Information about descending motor signals from the brain stem nuclei
* Feedback from motor responses via the somatosensory and vestibular systems

ALLOWS US TO COMPARE intended movements to actual movements
Critical for sequencing and timing of movement

Question 20

Cerebellar Damage

Basal Ganglia + Cerebellum

Answer 20

Many possible effects:
* Loss of ability to precisely control the direction, force, velocity, and amplitude of movements (ataxia/dysmetria) - affecting gait, eye movements
* Loss of ability to adapt patterns of motor output to changing conditions
* Impairments in learning new motor sequences + others

Question 21

Basal Ganglia

Basal Ganglia + Cerebellum

Answer 21

• Like cerebellum, modulate motor output
• DON’T contribute to sending information to spinal cord - rather, all activity is receiving information IN the brain and sending information IN the brain

ALSO:
* critical to habit formation
* many cognitive roles
* promotes skill learning

Question 22

2 pathways in the Basal Ganglia

Basal Ganglia + Cerebellum

Answer 22

• Two pathways in balance involving cortex, basal ganglia, and thalamus
• At rest, BG inhbit the motor/premotor areas = no movement (STOP pathway)
• To activate motor cortex, we must inhibit the inhibition (dishinhibition) via dopamine signalling from the substantia nigra (GO pathway)

Question 23

Dysfunction within the 2 Basal Ganglia pathways

Basal Ganglia + Cerebellum

Answer 23

Parkinson’s disease:
* Most dopaminergic neurons of the substantia nigra die (thus, less GO)
* Results in diminished movement, particularly movement initiation
* Initial symptoms: stiffness, resting tremor (during inactivity)
* later symptoms: muscular rigidity, slow movement, “mask-like” face, pain, depression

Question 24

Treatment for Parkinson’s

Dysfunction within the 2 Basal Ganglia pathways

Answer 24

• L-Dopa (dopamine precursor)
• Deep brain stimulation of substantia nigra

Question 25

Huntington's Disease ## Footnote Dysfunction within the 2 Basal Ganglia pathways

Answer 25

* Affect neurons across the brain, particularly striatum * **Decreases tonic inhibition** (STOP) leading to ***excessive movement*** * Rare and highly genetically determined * No strong treatment options