Lecture 9 - Motor system Flashcards
How do you study action
Behavioural: Use video or electronic recording equipment - allows one to record the position of body parts in space and time (speed, accuracy and kinematics)
Muscle Physiology (electromyography): can record activity of individual muscles or muscle fibers during action
Neurophysiology: Implant electrodes in brain and record activity of individual neurons
Matrix of electrodes connecting each to individual neurones -> measure activity
Neuroimaging: Put a subject in a brain scanner and measure blood flow while they perform a task
More blood flow = more brain activity
Blood flow = using sugar = active
Red= more active
Neuropsychology: examine the consequences of brain damage in humans or animals
If damage to one area is linked to a behavioural deficit, then can infer that area is necessary for that function
Transcranial Magnetic Stimulation (TMS): temporarily disrupt brain activity in healthy humans (or animals) using a high-powered magnetic coil
-as with neuropsychology, infer function from effects of TMS
Current through the scalp
Figure eight looking coil -> focuses the magnetic feild to this
Disrupts the area of the brain specific in the reagion the coil is placed
Computational Modeling: devise mathematical models of how actions might be carried out by a set of neurons
Event-related potentials: record electrical activity from the scalp
Strengths and weaknesses of behavioural study
Strengths: Allows us to systematically investigate the output of the action system
Weaknesses: Cannot tell us anything about the brain
Strengths and weaknesses of muscle physiology
Strengths: Allows an understanding of how muscles operate
Weaknesses: Also does not directly tell us anything about the brain
Strengths and weaknesses of neurophysiology
Strengths: Allows for excellent spatial and temporal resolution
Know exactly where neurones are
In real time, as it is happening -> within ms
Weaknesses: cannot examine more than a miniscule percentage of the neurons at any one time
Trying to infer from monkey information despite the fact they different -> can infer due to similarities
Strengths and weaknesses of neuroimaging
Strengths: Allows for a direct measure of activity in the human brain
-has good spatial and fairly good temporal (at least for fMRI) resolution
Whole picture
Can look at human brain within mm of where activity
Weaknesses: Many action processes take less than 2-4 seconds
-hard to make many movements in a scanner environment
Indirect measure of activity
Unable to measure components of movement
Not natural enviroment -> is the brain activity due to cramped enviroment (ethological validity)
Strengths and weaknesses of neuropsychology
III. How do you study actions?
Strengths: Allows one to examine consequences of (in humans) naturally-occurring brain damage
-can be used to show what areas are most important for a particular function
Weaknesses: Cannot (in humans and often not in animals) place lesions where you want them and the size you want them
-lesions often have effects on neurons far from the lesion site
Area, though active, may not actually be used in movement (may just be receiving information to other parts or receiving)
Strengths and weaknesses of TMS
III. How do you study actions?
Strengths: A lot more ethical than giving people brain damage
-can more or less precisely define the area of disruption and the time of disruption
No lasting effects
Weaknesses: not all areas can be tested, must be on the surface of the brain
-must be very careful not to give the participant a seizure!
Cannot study brain stem (away from surface)
Epilepsy predisposition -> stimulation -> seazure
Strengths and weaknesses of computational modeling
Strengths: Approaches the question of brain function from a synthetic rather than analytical perspective
Weakness: Does not address how brain actually works
Strengths and weaknesses of event-related potential
Strengths: Very good temporal resolution
Weakness: Poor spatial resolution- what are you actually recording?
Hand reaching
Velocity, acceleration and grip aperture graphs
Slow as movement begins, quick to reach the object but slows again for accuracy of reaching target correctly
Hand begins to move -> peak acceleration -> through stopping -> peak deceleration -> hand reaches target (stops)
Hand begins to move -> peak grip aperture -> reduces slightly to reach target
Brain to adapt by knowing the size of the object -> very sensitive changes to movement
Hit vs. grab
Brain makes distinction between hit or grab the object -> effect characteristics for either power or precision
Reaching vs. grasping
Reaching vs. Grasping
Reaching (arm) and grasping (hand) rely on different information:
Reaching relies on extrinsic object properties
e.g., distance, position, velocity
Grasping relies on intrinsic object properties
e.g., size, shape, weight
If you think object full and actually empty you over compensate the weight of the object and lift more than meant to
Perception-action model
Milner & Goodale (1995)
Perception and action rely on different parts of the brain
Perception and action use different visual information
Perception - identifying objects based on comparisons between seen and stored
Action - identifying target’s relation to the body
Retina input ->
Fast magnocellular (M) channel -> motion and orientation (dorsal stream)
Slow parvocellular (P) channel -> form and color (Ventral and dorsal stream)
Critiquing the perception-action model
Critiquing the perception-action model Plus Simple and straightforward Accommodates a fair amount of behavioural and neurological data Several predictions
Minus
Too simple and straightforward
Cannot explain the subtleties of much data
Planning vs. control model
Actions involve ‘planning’ and ‘on-line control’
Planning - motor program (stored muscle commands from memory) -> plan and initiate movement
On-line control - visual and proprioceptive feedback -> guide hand in flight
Planning = slow, involves much visual/cognitive information -> conscious influence, medial visual stream
On-line control = fast, relies on simple information -> no conscious influence, dorsal stream
Neurophysiology
Recordings can be taken from the brain of the behaving macaque monkey
Placing electrodes in the brain and recording the activity of single cells
Frontal lobes
Prefrontal activity precedes an action by several hundred milliseconds
Premotor activity precedes an action by 200-300 msec
Primary motor activity goes on throughout the action
Findings from Neurophysiology
Activity in the frontal lobes follows a caudal-rostral
gradient from planning to execution
Parietal lobes
Various regions of the parietal lobes can be associated with various actions
Reaching -> parietal reach region (PRR)
Grasping -> anterior intraparietal sulcus (AIP)
Eye movements -> lateral intraparietal region (LIP)
Planning movements -> areas of the inferior parietal lobule (IPL)
On-line control -> areas of the superior parietal lobe (SPL)
Findings from Neurophysiology
Activity in the parietal lobes is specific to specific actions
Basal ganglia and cerebellum
Basal ganglia are active both before and during a movement
Cerebellum seems linked with timing of actions and on-line adjustments
Findings from Neurophysiology
Basal ganglia and cerebellum also encode actions
Mirror neurons and biological motion neurons
Neurons in ventral premotor cortex appear to represent actions
These neurons respond both to the action carried out by the monkey and a similar action carried out by the experimenter
Neurons in superior temporal sulcus appear to code biological motion
Neurons in ventral PMC appear to represent actions, those in
Superior temporal sulcus appear to encode biological motion
Brain imaging of action
PET -> intravenuous injection of radioactive isotope that is taken up in the blood
fMRI -> measuring blood flow
PET studies showed action related to similar areas as found in monkey brain
In frontal lobes, same basic caudal-rostral gradient is found as for monkeys
In parietal lobes story is more complicated, because of evolutionary changes
In humans, the parietal lobes are greatly expanded as compared to macaques
Predictions of planning- action model
Perception -> color and form (P cells)
Action -> motion and orientation (M cells)
Brain activity in the ventral and dorsal stream -> perception and action
Context (ventral stream) -> perceptions but not actions-> visual illusions have small/ null effects on actions
Evidence for the planning- action model
Milner & Goodale (1995)
Original study found smaller effect of illusion on PGA than on perceptions -> supports
Predictions of planning- control model
Planning = cognitive factors effect (illusions and semantics)
Planning and control activity -> follows inferior-superior gradient in the parietal lobes
Evidence for a planning-control model
Illusions do have larger effects early in a movement than later
Words can affect the early portions of an action, but not the later portions
Language and planning vs. control
‘large-object’ words led to a larger grip aperture early in a movement than ‘small-object’ words but effect dissipates to zero during execution APPLE GRAPE PEAR PILL JAR PEA
