Motor cortical areas Flashcards
Which is lateral vs medial of SMA and PM
Premotor cortex is lateral area 6, SMA is medial area 6
How does GABA mediate cortical remapping
GABA inhibitory interneurons usually suppress local horizontal projectinos between different motor map areas… inhibiting these neurons allows remapping
How active is M1 in a rat running vs not runnning
M1 is less active during movement
What is the result of more direct connectinos from cortex to muscles in humans
eg corticospinal tract- increased dexterity, fine motor control
How much of motor control is ipsilateral
10%
What did Fritsch and Hitzgi find about M1
Stimulating different areas in the brain can cause twitching
What is motor control like in people with higher levels of GABA
More discrete finger representatinos, better behaviourally at distinguishing sensation in these fingers
Why are these species differences between mice and humans in M1 activation
Mice don’t need M1 for a lot of their movements, as most of their outputs come from other subcortical areas, only dexterous movements require mroe direct M1 connections
Why are these species differences between mice and humans in M1 activation
Mice don’t need M1 for a lot of their movements, as most of their outputs come from other subcortical areas, only dexterous movements require more direct M1 connections
How do different stimulatino parameters lead to different behaviour
Short stimulation- muscle twitches, joint rotation
Longer stimulation- complex movement eg reaching, likely because whole circuits are activated
M1 cortico-cortical inputs
Somatosensory cortex (cutaneous info), SMA and PM, rostral parietal cortex
M1 thalamic inputs
Dorsal columns via VPL, cerebellum via VL (proprioceptive info)
M1 pyramidal outputs
Pyramidal (corticospinal) tract neurons provide 40% of the fibres in the pyramidal tract
20% are monosynaptc to distal muscle motor neurons
M1 output to other brain areas
Corticocortical, putamen and intermediate cerebellum
M1 corticobulbar output
Projects to red nucleus, cranial nerve nuclei, brainstem reticular formation
How does M1 code force/muscle load
Using rate coding- increased firing forhigher load
What is Brodmann’s area 4
M1
What is PM divided into
PMd, prePMd, PMv
What form of coding does M1 use to code for movement
Populatino coding- the summed activity of selective neurons can be represented as a population vector,, indicating desired motor output
How does M1 code direction
M1 neurons are direction selective so act as vectors, allowing the use of a population vector to code movement direction
How do different M1 neurons signal movement differently
DIfferent or overlapping neuron populations may simultaneously signal kinematic movements (spatiotemporal info) and kinetic movements (force)- M1 may perform that transformations between the 2 representations
What is motor equivalence
The idea that different motor systems can perform the same action eg write with a pen
Suggests purposeful representations are represented abstractly in the brain, rather than as specific sets of muscle contractions
What is kinematic info
Position, velocity and acceleration of limbs, from muscle spindles
What is kinetic info
Forces generated by our body, Golgi tendons
What is inverse kinematic transformation
Determine joint trajectories to achieve eg a certain hand path, depenends on the arm’s kinematic properties eg length
What is inverse dynamic tranformation
Deetrmine the joint torques/muscle activity necessary to achieve joint trajectories, depends on the arm’s dynamic properties eg mass
What is an internal model
A neural circuit that computes transformations like estimating hand position from kinematic info
What are forward models
Represent the causal relatinoshpi between actions and their consequents, so predicts how a motor command will change the motor system’s state
What are inverse models
Calculate required motor outputs from sensory inputs that will produce a particular movement necessary for a desired sensory consequence
What is redundancy
The ability of motor systems to achieve a task in many different ways, plus the many different descending motor tracts
What are movement schemas
Stored neural representations of the simple spatiotemporal elements of a complex movement eg typing
What is feedforward control
Generated without regard to consequences or sensory feedback, open-loop, used to guide initial parts of movement
Strengths and weaknesses of feedforward control
Useful for rapid movements as there is no sensorimotor loop delay, errors can’t be corrected and will compound, can’t really work in complex systems
What is feedback control
Action is monitored-online and sensory signals used to correct errors, closed-loop
Strengths and weaknesses of feedback control
Necessary for complex movements, robust to neural noise and evironmental perturburations that can cause errors, delay
How does the brain alter movements commands in new kinematic and kinetic conditions
By adjusting internal models to maintain an appropriate relation between motor commands and motor outcome eg as body size changes
In learning dynamic tasks, where inverse models must be updated, which modality seems most important
Proprioception
How are the muscles of the HAND VS ARM mapped in M1
Neurons controlling the muscles of the digits/hand are concentrated around the central zone, but different digits are distributed widely, while neurons controlling more proximal arm muscles are in a horseshoe-shaped ring around the central core
What does SMA receive input from
Reciprocal cnonectinos with M1 and PM, somatosensory cortex and rostral parietal cortex, prefrontal cortex
What does PM receive input from
Reciprocal connections with M1, SMA, and progressively more caudal/medial/lateral parts of the parietal cortex, prefrontal cortex
What is the pyramidal tract
Projects from layer V in precentral (M1, SMA, PM) and parietal motor regions, to subcortical areas and the spinal cord
Many pyramidal tract axons decussate and form the CST
How does M1 affect reflex and pattern-generating circuits
Many CST axons from M1 and premotor areas terminate on spinal interneurons that are components of these circuits, exerting descending control
Result of M1 lesinos in humans
Muscle weakness, imprecise and slow movement, discoordinatino of multi-joint movements, paralysis
Result of PMd and SMA lesions in humans
Impact ability to learn and recall sensorimotor mappings eg visuomotor rotations, temporal movement sequences
Result of PMv lesions in humans
Prevent ability to use visual info about an object to shape the hand to grasp it
What is the timing of M1 firing
M1 neurons fire just before (50-150ms) and during movement, suggesting they initiate movement/muscle contraction
What is the organisation of M1 neurons
Cell bodies and apical dendrites form radially oriented columns
Neurons form orientation columns or columns of prefered body part, and tend to cluster in small groups with similar muscle fields
What is the organisation of thalamocortical and corticortical axons in M1
The terminal arbors of thalamocortical and corticocortical axons form localised columns/bands
How do population codes code continuous movement
The pattern of neural activit distributed across eg the arm’s motor map varies continuously in time during complex arm movements, signalling moment-to-moment details of desired movement
What is the force-control hypothesis
The motor system controls a movement by planning and controlling its causal dynamic forces or muscle activity
What is the position-control hypothesis
The motor system signals the desired endpoints and equilibrium configurations (posture where external forces=internal forces) of the arm and body
How is movement encoded at the periphery by the motor cortex in position-control hypothesis
Inverse-kinematic and inverse-dynamic transformatinos occur implicitly at local spinal cord circuits and in the motor periphery
How does M1 use local spinal cord circuits and the motor periphery in the position-control hypothesis
A descending signal specifies a referent configuration that exploits spinal reflex circuits and tone, changing muscle activity and creating an imbalance between external and internal force, that causes arm movement until equilibrium is restored
What do M1 neurons use sensory input from proprioceptors or cutaneous mechanoreceptors for
Feedback control of ongoing movements, feed-forward control of intended movements, teaching signal during motor learning
How does sensory input to M1 allow feed-forward control
Sensory input allows continuous pretuning of the pattern of activity in the motor map and spinal motor apparatus, as a function of the limb’s motor state before movement-> correct motor motor command for the desired movement
What is the result of learning on connectinos between neurons in the motor map
Learning eg an arm mvoement leads to increased synaptic strength of local horizontal connections between different parts of the arm motor map
What does motor learning theory suggest about learning
Learning involves feedback-error learning and supervised learning
Motor learning theory- what is feedback-error learning
Sensory feedback about an erorr guides correction for immediate perturbation, via compensating for expected perturburation
Motor learning theory- what is supervised learning
Adaption of internal models eg internal inverse model uses error signals to learn the motor command that will produced a desired movement by compensating for the expected perturburation, neurons are retuned
Where are the neural circuits constituting internal forward and inverse models
M1, PM, cerebellum, superior parietal cortex
Is the M1 motor map static?
No- it has a dynamic adaptive map that generates the motor commands needed to accomplish desired actions under different conditions
What happens in PM during preparation for a movement
Many PM cells show directionally tuned activity changes that signal the direction of impending movement
What can PM activity encode durnig the planning stage
Abstract representatinos of motor output, what the arm must do to produce these movements, higher-order aspects such as an action’s goal or expected reward
During a monkey exploration task, when do parietal neuron discharge?
During eye, arm or hanf movements- neurons discharge strongly during reaching to grasp, or manipulating an object, but are much less active during general arm movements
What is the dorsal stream’s role
Extracting sensory info about the world andbody to plan and guide movements- the ‘how’ pathway
What is the neural component of space
There are many spatial maps each related to a different motor effector, each adapted to its specific needs and created through environmental interaction, some in the parietal cortex and other in the frontal cortex
Evidence for there being lots of different motor maps each related to a specific motor effectors
Parietal cortex is arranged as a sereis of areas working in parallel, near space is encoded in different areas to those that represent far space, functinoal properties of the spatial neurons vary depending on the body part controlled
In monkeys, where are peripersonal space representations located?
Inferior parietal cortex and interconnected parts of the PMv
What stimuli do neurons in F4 in PMv respond to, suggesting its involved in constructing peripersonal space
All neurons respond to somatosensory inputs, especially tactile stimuli on the upper body
Half also respond to visual stimuli, and some to auditory stimunli
What about the topography of F4 PMv neurons suggests they’re involved in constructing a peripersonal spatial map
The modality-specific receptive fields lie in register, and their visual receptive fields move in response to body movement rather than looking direction, suggesting they’re anchored to specific body parts
What do neurons in the F4 PMv discharge in correlation with
Movements, mostly of the arm/wrist/neck/face, and towards different body parts or close objects
What is the main role of the PM
Choosing and planning movements
How does the superior parietal lobe create a body schema to guide arm movements
Superior parietla lobe neurons integrate info on joint and limb segment position with respect to the body
When do neurons of the superior parietal lobe fire, suggesting they’re involved in body schema
Many discharge during combined movements of multiple joints, assumption of specific postures, or movements of the limbs and body
What do more posterior sectors of the superior parietal cortex do
Receive input from V2 and V3, integrate this with copies of outgoing motor commands and proprioceptive info to signal the target of reaching via a forward internal model
What do PMd neurons do in reaching movements
Reach-related neurons fire to represent the intended direction of reaching, independent of gaze or the arm that will perform it
What are affordances
When we see an object, our visual system identifies the parts of it that allow for efficient manipulation of it and afford specific opportunities for action
What does the inferior parietal cortex do
Receives input from the dorsal stream, giving it the visual info to code object affordances
Neurons respond preferentially to objects of specific shapes that each require a specific grip shape, linking an object’s affordances to motor actions
What does F5 in PMv receive input from
Reciprocally connected with the inferior parietal cortex and secondary somatosensory areas
What representations does F5 in PMv contain
Overlapping representations of hand and mouth movements
What special neurons are in F5 in PMv
Canonical neurons- discharge identically when an animal grasps OR sees an object, suggesting they signal how to interact with an object
What does F5 in PMv firing correlate with
A motor act’s goal, independent of what effector is grasping
Different neurons are selective for grip type, allowing us to link object affordances consistently with appropriate motor actions
What does the SMA contain a map of
The entirety of contralateral body movements, but the map is not as detailed as in M1
How do the stimulus requirements of the SMA differ
SMA requires strong stimulus currents, evokes complex actions like postural adjustment or stepping
What suggests that SMA is involved in conditional control of vountary behaviour
Subthreshhold stimulation can evoke the urge to move, SMC lesions produce problems initiating or suppressing inappropriate movement
How is the SMA presumably involved in contextual control of behaviour
Involved in selecting and executing/inhibiting actions appropriate on the basis of internal and external cues, situating actions in a movement sequence or social context
What is motor imagery
When humans are asked to imagine performing a certain motor act, the premotor and parietal cortex become active- signifies preparation to act dissociated from execution
What is the direct matching hypothesis
Observing the actions of others activates the motor circuits responsible for similar motor actions by the observer (mirror neurons)
Where are mirror neurons especially prominent
PMv, specifically F5
What does the mirror mechanism seem to be important for
Uderstanding the actions of other through linking the observed actions of others to our own stored knowledge of the nature/motives/consequences of our own corresponding actions
