The motor system Flashcards
explain the behavioural appraoch to studying actions
A) Behavioural: Use video or electronic recording equipment -allows one to record the position of body parts in space and time
Can measure speed, accuracy and kinematics (velocity, acceleration, etc.)
Strengths: Allows us to systematically investigate the output of the action system
Weaknesses: Cannot tell us anything about the brain
evaluate and explain Muscle Physiology (electromyography)
Muscle Physiology (electromyography): can record activity of individual muscles or muscle fibers during action
Strengths: Allows an understanding of how muscles operate
Weaknesses: Also does not directly tell us anything about the brain
evaluate and explain Neurophysiology
Neurophysiology: Implant electrodes in brain and record activity of individual neurons
Can take a record of a number of neurons and measure their activity in real time
Strengths: Allows for excellent spatial and temporal resolution
Weaknesses: cannot examine more than a miniscule percentage of the neurons at any one time
monkeys aren’t humans
outline Neuroimaging
) Neuroimaging: Put a subject in a brain scanner and measure blood flow while they perform a task
More blood flow = more brain activity
Strengths: Allows for a direct measure of activity in the human brain
-has good spatial and fairly good temporal (at least for fMRI) resolution
Weaknesses: Many action processes take less than 2-4 seconds
-hard to make many movements in a scanner environment
Outline and evaluate Neuropsychology
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
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
Outline and Evaluate TMS
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
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
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!
Outline and evaluate Computational Modelling
Computational Modeling: devise mathematical models of how actions might be carried out by a set of neurons
Strengths: Approaches the question of brain function from a synthetic rather than analytical perspective
Weakness: Does not address how brain actually works
Outline and Evaluate event-related potentials
) Event-related potentials: record electrical activity from the scalp
Strengths: Very good temporal resolution
Weakness: Poor spatial resolution- what are you actually recording?
what are the two factors that effect The unfolding of movement kinematics
The unfolding of movement kinematics varies systematically with two factors:
1) the characteristics of the target
2) the relation between the target and the hand
E.g. grip aperture increases with increasing size ., grasping a fragile object leads to an extended deceleration phase Smaller targets lead to lower peak velocity and longer movement times
what information does reaching and grabbing rely on?
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
what info does percieving and action rely on
Milner & Goodale (1995) argued that perception and action rely on different parts of the brain
Perception and action said to use different visual information
what are the two visual streams
eyes --> LGN--> V1--> Dorsal(SPL) and ventral (IT) Ungerleider and Mishkin (1983) SPL deals with localization IT deals with identification Milner & Goodale (1995) SPL = action IT is perception
what is the differences between perception and actino
‘Perception’ involves identifying objects on the basis of
comparisons between what is seen and stored memories
‘Action’ involves moment-to-moment computations of a
target’s relation to the body
outline how perception and action rely on two different retina streams
A fast magnocellular (M) channel that relays information about motion and orientation
A slow parvocellular (P) channel that relays information about form and color
The ventral stream largely contains P type cells
The dorsal stream contains both M and P cells
Perception should be affected by such things as color and form that are coded in P cells
Action should be more sensitive to such things as motion and orientation that are coded in M cells
Brain activity in the ventral and dorsal stream should be associated with perception and action, respectively
what are the predictions made by perception Vs Action info
Contextual information (coded in the ventral stream) should affect perceptions but not actions
Thus, visual illusions should have small or null effects on actions
what study provides support for two stream theory?
Ebbinghaus Illusion and Grasping
Original study found smaller effect of illusion on PGA than on perceptions
Supported ‘two stream’ (perception/action) model
But:
Dozens of studies now on illusions and actions
and results are contriversial
name some critisicisms of the perception-action model
Plus: It is simple and straightforward
Plus: It accommodates a fair amount of behavioural and neurological data
Plus: It makes several predictions
Minus: It is too simple and too straightforward
Minus: It cannot explain the subtleties of much data
outline the planning-control model
Planning Vs. Control
Actions involve ‘planning’ and ‘on-line control’
Planning uses a motor program (a set of stored muscle commands called up from memory) to plan and initiate movement
On-line control uses visual and proprioceptive feedback to guide hand in flight
Planning-Control model of the visual brain
(Glover, 2004)
V1–> Perception (IT), Planning (IPL) and Control SPL
Planning tends to be slow (~250 msec) and involves much visual/cognitive information
-subject to some conscious influence
-involves a medial visual stream
On-line control is fast (~100 msec) and relies on simple information
- immune to conscious influence - involves the dorsal stream
what are the predictions ofthe planning-control model
Planning will be affected by cognitive factors such as illusions and semantics, on-line control will not
Activity related to planning and control will follow a inferior-superior gradient in the parietal lobes
what is the evidence for the 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
Outline 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
outline how Neurophysiology works
Recordings can be taken from the brain of the behaving macaque monkey
This involves placing electrodes in the brain and recording the activity of single cells
what have we learned about the frontal lobes? from Neurophysiology studies?
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
Activity in the frontal lobes follows a caudal-rostral gradient from planning to execution short-term planning(premotor) long-term planning (prefrontal) Execution (primary motor)
what have we learned about the Parietal lobes from neurophysiology
Parietal lobes:
Various regions of the parietal lobes can be associated with various actions
Reaching involves the caudal part of the superior parietal lobes (known as ‘parietal reach region’ or “PRR”)
Grasping involves the anterior intraparietal sulcus (AIP)
Eye movements involve the lateral intraparietal region (LIP)
Planning movements involves areas of the inferior parietal lobule (IPL)
On-line control involves areas of the superior parietal lobe (SPL) Activity in the parietal lobes is specific to specific actions Planning (IPL) On-line control (SPL) Grasping (anterior IPS) Reaching (posterior SPL) Eye movements (LIP
what have we learned from Neurophysiology about the basal ganglai and cerebellum
Basal ganglia are active both before and during a movement
Cerebellum seems linked with timing of actions and on-line adjustments
Basal ganglia and cerebellum also encode actions
Basal ganglia [subcortical] (planning and execution) Cerebellum (timing and on-line a adjustments
outline what has been found out from neurophysiology studies about mirror neurones
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
Ventral PMC (mirror neurons) STS (biological motion neurons)
outline what has been found about brain imaging of action
Brain imaging includes PET and fMRI
PET works by intravenuous injection of radioactive isotope that is taken up in the blood
fMRI works by measuring blood flow
PET studies showed action related to similar areas as found in monkey brain
i.e., frontal and parietal lobes, basal ganglia and cerebellum
PET studies showed action related to similar areas as found in monkey brain
i.e., frontal and parietal lobes, basal ganglia and cerebellum
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
Main difference is in IPL
why has the IPL changed in evolution?
According to planning-control model, one function of IPL in humans is tool use
This could explain why it has expanded so much
Suggests that other differences might exist and that therefore it is dangerous to assume that same structures in monkeys and humans have same functions
