Lecture 3&4 - Motor Systems Flashcards
motor system - the organization of actions: What does this field concern?
- a lot of msucles in the brain which need to be activated/deactivated in time to acheive what want to be done; execute an action
Levels of control of action (just the components names)
from lowest to highest level …
- spinal cord
- motor cortex (primary motor cortex (M1))
- pre-motor cortex (PMC), supplementary motor area (SMA)
- basal ganglia
- cerebellum
Reflexes (spinal cord)
spinal cord has neurons directly connected to the muscles; axon goes out of cell body into muslce, whenever AP goes down it releases vesicles at the synapse, neuro-muscular junction happens, releases neuotransmitters cause muscle twitch
-> see sensory neurons; working inverse; ex. finger produces action potential -> going up the arm to spinal cord -> back to finger which is moved (the brain is not involved, defintion of reflex)
Executing motor programs (motor cortex)
happens inside the brain, voluntary actions (planned movements), executing motor plans
initiation/stopping and planning of motor actions/sequences (PMC and SMA)
allows goal directed action planning, happens more towards frontal part of the brain
gating and control over action based on motivation, affective state (basal ganglia)
in subcortical part of the brain, for automatic movements/motivaltional control of movements/affective states playing a role there
-> also concerns inhibitation of certain actions
adjusting ongoing behavior, timing (cerebellum)
highly connected to motor system, backs up the control systems, timekeeper; comparing expected input with actual input
-> quick behavior changes can be done when there is mismatch -> requires quick adjustment of motor plan
lobes and major sulci
- central sulcus seperates frontal from parietal lobe
- sylvian/lateral fissure seperating parietal from from temporal lobe
- traverse fissure to half brain in top and bottom part
- longitudinal fissure to split brain in left and right side
hierarchies in the motor system (upper motor neurons)
- > motor cortex (primary and premotor, and supplementary); planning, initiating and directing voluntary movements
- primary motor neurons travel down the spinal cord to synapse onto local circuits (these control lower motor neurons directly; muscle contradiciton, operate with a level of (reflex) autonomy (ex. pain reflex))
- > brain stem centers; basic movement and postural control
- > basal ganglia; gatling proper initiation of movement
- > cerebellum; sensory motor coordination
central pattern generators
neuronal circuits able to produce rythmic motor patterns in the absence of sensory inputs (ex. wlaking)
hierarchies in the motor system (lower motor neurons)
- > have their cell body in spinal cord; movement provokes AP, cell becomes active, shift happens
- > direct control over muscle contractions
topology in the motor system
- spinal cord: medial to lateral
- primary motor cortex: motor homunculus
- voluntary movmement: maps in M1
Cortical motor neurons (M1)
- > directing/orchestrating voluntary movements
- > active before movement occurs/action is actually executed (signal takes time to travel down the spinal cord)
- can also generate complex, multi-joint movement
- are active in many movements (“borad tuning”), making it hard to predict direction/intensity of one single neuron
- > movements have to be specified with populations of neurons (combined output determines actual movement)
- > population movement vector
superior colliculus
area of brain stem directly controling eye movement (producing saccades; little eye jumps); the direction of eye movements is spatially organized
-> decoded population direction vectors precede movement (measuring the readiness potential (in premotor cortex); negative EEG deflection)
PMC (planning)
- > indicates future cues of movement (memory component; when signal is gone one remembers what to do)
- if this area is damaged there is a loss of motor awareness (person does not see own illness/inability)
- > initiation, termination, cued sequences; action/motor unit linked representations; “working memory for action”
supplementary MC
- > for planning movmements (not following a stimulus); precise planning, self-initiating
- neurons involved which define the position in sequence (irrespective of particular action required)
- > self-generated motor sequences/action plans; abstract representations; activity deterined by place in sequence
basal ganglia
- part of the limbic system
- made up of multiple nuclei (under cortex)
- facilitates movement; indirectly, different circuits promoting or inhibiting movement -> gating of motor output
- > output of basal ganglia affects thalamus
- precentral gyrus
- central sulcus
- lateral (sylvian) fissure
- on the side; on the border between frontal and parietal lobe
- on top; between frontal and parietal lobe
- bottom; between frontal and temporal lobe
- anterior
- posterior
- superior
- inferior
- in front of (front of head)
- behind (backside of head)
- above (on top of head)
- inferiro (below head, downside of head)
- rostal
- caudal
- dorsal
- ventral
- cutting brain in top and bottom part; going in front
- same as 1; going in the back
-> longitudinal axis of the forebrain - upper part in cut
- lower part in cut
; cutting from middle of the brain down the neck stem
-> longitudinal axis of the brainstem and spinal cord
- rostal
- caudal
- dorsal
- ventral
- cutting brain in top and bottom part; going in front
- same as 1; going in the back
-> longitudinal axis of the forebrain - upper part in cut (of brain)
- lower part in cut
; cutting from middle of the brain down the neck stem
-> longitudinal axis of the brainstem and spinal cord
insula
within the frontal lobe, on the border to the temporal lobe (seen by lateral view on the brain)
cerebellum (location)
under the occipital lobe (medial view on the brain)
Neocortex
rational or thinking brain
-> on top of the brain
Neocortex
rational or thinking brain (inhibitry control)
-> on top of the brain
repetilian brain
instrinctual or dinosaur brain
-> on top of the brain part going down the neck
lateral and medial view (distinguish)
Lateral is from the side; medial is towards the midline
limbic system
- a series of cortical structures surrounding the boundary between the cerebral hemispheres and the brainstem
OR
a group of subcortical structures (such as the hypothalamus, the hippocampus, and the amygdala) of the brain that are concerned especially with emotion and motivation
direct pathway (basal ganglia)
promotes movement (disinhibition of thalamus)
indirect pathway (basal ganglia)
inhibits movement (extra step - disinhibition of subthalamic nucleaus, inhibits thalamus)
basal ganglia in motor learning
especially active when learning new motor skills; mapping of intentions and motor plans need to be discovered (right neurons to fire need to be found (announced))
striatum (basal ganglia)
- nucleus caudatus
- putamen
- > activated when cortex has intention to move (having negative effect) on palidus
globus pallidus (basal ganglia)
- interna and externa
- > inhibited from striatum, therwith inhibits thalamus
- > causes thalamus to become more active, causing movement in cortex again, double negativity, supression tonic inhibition
substantia nigra (basal ganglia)
- compacta and reticulata
- > parses reticulata, tonically active
subthalamic nucleus (basal ganglia)
major part of the subthalamus
Cerebellum
- densely connected to cortex
- connetced to spinal cord and vestibular system (remaining good posture)
- giving densed in- and output
- adjusts behaviors while those are executed
- > error correction; producing smooth movements (dental nucleous (deep structure) outputs back to motor cortex; for final movement adjustments)
Cerebellum
- densely connected to cortex
- connetced to spinal cord and vestibular system (remaining good posture)
- giving densed in- and output
- adjusts behaviors while those are executed
-> error correction; producing smooth movements (dental nucleous (deep structure) outputs back to motor cortex; for final movement adjustments)
(does not store memory but stores capacity to compare in- and output)
cerebellum and cognition
- always active (the more errors to correct, the more active)
- > more automated skills need less cerebellum
- also corrects cognition errors; going beyond motor learning
Hippocampus
in brain stem; for declarative consious memories such as facts
subcortical motor disease
- M1; paralysis, unable to move certain body parts
- PMC: deficiency in cue-based sequencing behavior
- SMA: deficiency in self-generated sequences
- subcortical area: changes in goal-directedness/smoothness of motro behavior (ex. Parkinson, Huntingtons, Tourette)
subcortical motor disease
- M1; paralysis, unable to move certain body parts
- PMC: deficiency in cue-based sequencing behavior
- SMA: deficiency in self-generated sequences
- subcortical motor area: changes in goal-directedness/smoothness of motro behavior (ex. Parkinson, Huntingtons, Tourette)
Parkinson (disease) - what is it?
neurodegenerative disease, problems with movements, problem in substantia nigra (cells dying off, cannot be retained), no dopamine production anymore (needed neurotransmitter for movement) - cannot be cured by just giving dopamine, since this cannot cross the BBB
- > reduction of dopamine input from substantia nigra to striatum, less dissinhibition in direct pathway, overactive inidirect pathway, effect on thalamus in motor cortex slower, resulting in less movement
- > brain can accommodate for dopamine loss to a certain extend (neuroplasticity)
components of Parkinson
- Tremors: involuntary movement in resting state
- akinesia: reduced reflexes
- cogwheel rigidity: start/stop movement
- distributed posture: postural impairment
- cognitive slowing: slowed down thinking process
Where is dopamine produced?
midbrain, basal ganglia
Role of dopamine in learning
- reinforcement learning/learning from (un)expected outcomes (expectation meeting the output?)
- teaching signal (reward-prediciton-error)
- > matching memory on what has been done to incoming reward
Rescorla-Wagner learning rule (prediction errors)
strongest learning when outcome is of greates surprise (biggest trigger)
(outcome - expectation = prediction error)
-> when outcome and expectation macth the prediciton error is zero and no updating of the associations need to be done
-> paying attention to changes (updating policy)
(beta as learning rate; usually higher learning rate at the beginning)
-> dopamine acts as prediciton error signal
dopamine as PE signal
- unexpected reward occurs, firing rate increases
- cue predicts reward fully, firing rate increases
- outcome lower than expected, firing rate decreases
nucleaus accumbens
reward system in the brain
-> dopamine as motivational center of the brain
Treating Parkinson
- L-Dopa: can cross BBB, targets unspecificially
- deep brain stimulation: more specific, strenghten/decrease indirect pathway (can stop tremors)
Huntington (disease) - what is it?
neurons dying in the brain, inhibitory cells in caudate nucleus, loss of controlled movements, thoughts and emotions, herritable disease
- > problem with indirect pathway (cells of striatum, caudate nucleus, affected (inhibitory cells))
- > hyperactive indirect pathway, reduced inhibtion of thalamus, excessive activation of motor cortex
Huntington - disease expressions (forms)
- Tourette (involuntary, repetitive movements)
- > echolalia (speech repetition)
- > coprolalia (offensive speech)
- > can be treated with dopamine recpetor antagonist - tardive dyskinesia (repetitive muscle contradictions)
- > occurs by people taking antipsychotic medication
BCI
brain computer interface
-> encoding brain activity from any user
