Topic 6: Brain Control of Human Movement Flashcards
3 stages of movement control
- Determines what needs to be done (Prefrontal Cortex): Identifies the goal of the movement and best strategy to accomplish goal
- Plans the specific movement (Motor cortex): Specific sequences of muscle activations and patterns required to do the movement
- Execute the plan (Spinal Cord): Activation of the motor neurons to do the movement and make minor adjustments
- Also have input from cerebellum and basal ganglia at stage 2
Prefrontal Cortex
- Highest in the chain of command and the greatest complexity
- Identifies a goal and determines what needs to be done to accomplish this
- Highly connected with sensory cortex
Executive Function
- Higher cognitive processes for planning, organizing, and controlling thoughts, speech, and behaviour
- Involves a wide-range of skills
Executive Functions involvement in movement
- Goal-directed actions
- Organizing
- Planning
- Directing: send info to next processing system - Attention
- Multitasking: allocating effectively among tasks performed simultaneously
- Response inhibition: respond effectively with distractions/irrelevant information
Executive Function and aging
EXECUTIVE FUNCTION DECLINES WITH AGE
- Lesions in white matter
- loss of grey matter
- loss of dendritic branching
CHANGES ARE HIGHLY VARIABLE
- Decline can be minimal in health adults
- Influenced by things like lifestyle, education, genetics
AGING RELATED DELINES IN:
- overall processing speed
- problem solving ability (Goal-directed actions)
- Controlling attentional resources (Attention)
Changes in gait parameters with age
- Decrease in gait speed and step length
- Increase in step time and variability in these parameters
- Reduced executive function may be an important driver of these changes
- healthy older adults may have little to no change
Executive Function and Gait
GAIT IS A COMPLEX MOTOR TASK THAT USES EXECUTIVE FUNCTION
- not fully managed by CPGs
- EF needed to plan, organize, and direct movements
- Often must also divide attention to other tasks
EF ALLOWS EFFECTIVE DIVISIONS OF ATTENTION BETWEEN GAIT AND OTHER TASKS (multitasking)
Area 6 involvement in the planning of movement
- Creates movement plans and holds them until ready to execute (Active just before movement occurs)
- Plans must be highly integrated with sensory information
- Details of coding taking place remains unclear
Premotor area involvement in planning of movement
Selection of best motor plans based on current sensory information
Supplementary Motor Area in planning of movement
- More Complex motor sequences often with bilateral connections
- May be more internally driven (remembering sequences)
Measuring the planning of movement
Instruction stimulus
- Red light where movement will need to be
- PMA neuron begins firing
Trigger Stimulus
- Blue light tell it to act
- PMA neuron stops firing soon after the action is made
Mirror Neurons
Exist in the PMA
- Respond when movement is imagined or watched
- Each cell has very specific movement preference
May be part of an extensive brain system for understanding actions and intentions of others
Primary motor cortex involvement in movement planning
- Transforms the motor plan into specific movement patterns
- Motor map masks the deeper complexity
- Very different from lower motor neurons
- Complex and overlapping neurons work together to control specific movements
- Coding related to direction and force of movement
Premotor lesions
AREA 6
- Difficulty choosing the correct or appropriate sequence of muscle actions needed to accomplish a goal
Primary motor region lesions
AREA 4
- While the appropriate action may be taken, there is difficulty in the execution of the task
- Weakness, lack of coordination, or even complete paralysis
The coding of movement in the Primary Motor Cortex
- Movement direction is encoded by the collective activity of neurons
- Many neurons are active for every movement
- activity of each cell represents a single vote
- direction of movement is based on a tally and averaging of votes
Direction vector vs population vector
DV: a single cells vector vote
- Each cell has a preferred direction
PV: a tally of all cells vector vote
How would you train neural decoding AI algorithm?
Data must have inputs
- Brain-computer interface
- Signals from neurons in brain
- EEG and/or fNIRs, implants
Data must have outputs
- Know of the resulting movement related to the record electrical signal
Needs lots of data
Flaws with recording only cerebral cortex activity in neural decoding algorithms
- Missing sensory feedback
- maybe missing out on complete information from loops
- artificial movements lack smoothness
Basal Ganglia
Group of Subcortical nuclei which supports the selection and initiation of willed movements, while preventing unwanted movements
- Input received from many areas of the cortex
- Loop with major input into area 6 (premotor)
What are the 4 main nuclei in the basal ganglia?
- Striatum (caudate nucleus and putamen)
- Globus pallidus (internal and external)
- Subthalamic Nucleus
- Substantia Nigra
Direct pathway of the basal ganglia
Helps to select motor plans and facilitates movement
- Striatum receives excitatory input from the cerebral cortex and substantia nigra
- Striatum sends inhibitory signal to Globus pallidus internal
- Causes less inhibition of Globus pallidus internal on thalamus
- Thalamus sends excitatory signal to area 6 facilitating movement
The indirect pathway of the basal ganglia
Helps suppress competing or inappropriate motor plans - inhibits movement
- Excitatory signals sent from cortex to striatum
- Striatum inhibits the globus pallidus external
- less inhibition from the globus pallidus external leading to excitatory signals from the subthalamic nucleus to the globus pallidus internal
- causes greater inhibition from globus pallidus to thalamus
- thalamus sends inhibitory signals to area 6 to suppress inappropriate movements
Parkinson’s Disease as a disease of the direct pathway
- Difficulty stimulating wanted movement
- Reduced direct pathway release of thalamus inhibition
- arises from loss of dopaminergic neurons acting on the striatum in the direct pathway
- Hypokinetic disorder (reduced voluntary moto activity), Bradykinesia (slowness of movement), akinesia (lack of movement)
Huntington’s disease as a disorder of the indirect pathway
- Difficulty suppressing unwanted movements
- Reduced indirect pathway = reduction thalamus inhibition
- Arises from a loss of striatum neurons acting on the globus pallidus external in the indirect pathway
- Hyperkinetic (excessive involuntary motor activity), Chorea (spontaneous and uncontrollable movements)
- Rare genetic disorder
- Symptoms arise in 30s or 40s
-Neuron loss will also occur in other areas of the cerebral cortex, leading to: dementia, personality changes, and death about 20 years after diagnosis
Cortico-Cerebellar Loop
Proper execution of planned, voluntary, multijoint movements
- Necessary to fine tune the sequences of muscle contractions
- Made up of:
1. Cortico-ponto-cerebellar pathway
2. Within the Cerebral cortex
3. Cerebello-thalamo-cortical pathway
Cortico-ponto-cerebellar pathway
- sensory and motor cortex axons form massive projection on pons
- Pontine nuclei relay information to cerebellar cortex
Within the cerebellar cortex in the cortico-cerebellar loop
Granule Cells
- Most numerus cells in cerebellum
- Excitatory output on purkinje cells
Purkinje Cells
- Largest cells in cerebellum
- receive thousands of synaptic inputs
- inhibitory output to deep cerebellar nuclei
Deep Cerebellar Nuclei
- Excitatory or inhibitory output to thalamus
Cerebello-thalamo-cortical pathway
- Deep Cerebellar nuclei relay to thalamus
- VL relays information back to M1 (area 4) - last chance tuning
Cerebellar Lesions
Can cause Ataxia: uncoordinated and inaccurate movements
- Dysmetria: Overshoot or undershoot target
- Dyssynergia: decomposition of synergistic multijoint movements
What are the two major groups of descending spinal tract pathways
Lateral motor pathways
- Commands voluntary movement
Ventromedial motor pathways
- Posture and reflex movements
Corticospinal Tract (CST)
Primary pathway for voluntary motor control (neck to feet - one of the largest and longest pathways)
-Pyramidal cells arising from the motor cortex (M1, but also premotor and other areas)
- Can be divided into lateral and anterior
Lateral CST
- Controls Limbs
- 90% of CST axons
- Decussate in medullary pyramids
- Control proximal/distal muscles
Anterior CST
- Controls trunk, neck, shoulders (axial muscles)
- 10% of CST axons
- Decussate within spinal cord
Rubrospinal Tract
Much Smaller than the CST
- Originates at the red nucleus
- Receives input form cortex
- Function greatly reduced in humans
Lateral pathways Lesions
The effects of experimental corticospinal lesions
- Deficit in motor control of limbs
- Recovery if rubrospinal tracts is intact
- subsequent rubrospinal lesion reverses recovery
strokes effecting motor cortex or corticospinal tract
- Paralysis on contralateral side
- some recovery over time
