(10) Motor system Flashcards
What are the strengths to studying actions via behaviour?
Allows us to systematically investigate the output of the action system, how someone moves depending on target
What are the weaknesses of studying actions via behaviour?
Cannot tell us anything about the brain, only looks at output
How can you study actions behaviourally?
- 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.)
- Improvements in equipment, performance enhancing
How can you study actions via Muscle Physiology (electromyography)?
can record activity of individual muscles or muscle fibres during action
What are the strengths of studying actions via Muscle Physiology (electromyography)?
Allows an understanding of how muscles operate
What are the weaknesses of studying actions via Muscle Physiology (electromyography)?
does not directly tell us anything about the brain
How do you study actions via 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
What are the strengths of studying actions via Neurophysiology??
Allows for excellent spatial and temporal resolution, exactly where in the brain
What are the weaknesses of studying actions via Neurophysiology??
cannot examine more than a miniscule percentage of the neurons at any one time, 10 million neurons in the brain
How do you study actions via Neuroimaging?
Put a subject in a brain scanner and measure blood flow while they perform a task
- More blood flow = more brain activity
- When neurons fire they use energy - need glucose
What are the strengths of studying actions via Neuroimaging??
Allows for a direct measure of activity in the human brain -has good spatial and fairly good temporal (at least for fMRI) resolution
What are the weaknesses of studying actions via Neuroimaging??
Many action processes take less than 2-4 seconds
-Hard to make many movements in a scanner environment
How do you study actions via 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
What are the strengths of studying actions via Neuropsychology??
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, damage a certain area of the brain may effect behaviour: clear cause
What are the weaknesses of studying actions via Neuropsychology??
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
How do you study actions via 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
What are the strengths of studying actions via Transcranial Magnetic Stimulation (TMS)?
A lot more ethical than giving people brain damage -can more or less precisely define the area of disruption and the time of disruption
What are the weaknesses of studying actions via Transcranial Magnetic Stimulation (TMS)?
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, can’t test deep inside the brain
How do you study actions via Computational Modelling?
devise mathematical models of how actions might be carried out by a set of neurons
What are the strengths of studying actions via Computational Modelling?
Approaches the question of brain function from a synthetic rather than analytical perspective
What are the weaknesses of studying actions via Computational Modelling?
Does not address how brain actually works
How do you study actions via Event-related potentials?
record electrical activity from the scalp
What are the strengths of studying actions via Event-related potentials?
Very good temporal resolution
What are the weaknesses of studying actions via Event-related potentials?
Poor spatial resolution- what are you actually recording, large area
Movements of a particular type tend to be conducted in a very similar fashion from one instance to the next, for example…
-E.g., reaching and grasping have very consistent velocity/acceleration/hand shape profiles
-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
What information does reaching rely on?
Reaching relies on extrinsic object properties e.g., distance, position, velocity
What information does grasping rely on?
Grasping relies on intrinsic object properties e.g., size, shape, weight
What did Milner & Goodale (1995) argue?
argued that perception and action rely on different parts of the brain
- Perception and action said to use different visual information
- Two visual systems - sight and movements
What does perception involve?
‘Perception’ involves identifying objects on the basis of comparisons between what is seen and stored memories
What does action involve?
‘Action’ involves moment-to-moment computations of a target’s relation to the body, where objects are in relation to you
Input from the retina goes into two types of channels
- A fast magnocellular (M) channel that relays information about motion and orientation
- A slow parvocellular (P) channel that relays information about form and colour
-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
colour 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
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 are the strengths of the perception action model?
- It is simple and straightforward
- It accommodates a fair amount of behavioural and neurological data
- It makes several predictions
What are the weaknesses of the perception action model
- It is too simple and too straightforward
- It cannot explain the subtleties of much data
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 will be affected by cognitive factors such as
illusions and semantics, on-line control will not
Activity related to planning and control will follow an inferior-superior gradient in the
parietal lobes
Illusions do have larger effects early in a movement than
later
-Recordings can be taken from the brain of the behaving macaque monkey, which involves
placing electrodes in the brain and recording the activity of single cell
Prefrontal activity precedes an action by several hundred milliseconds, whereas Premotor activity precedes an action by
200-300 msec
What regions of the parietal lobes can be associated with reaching
Reaching involves the caudal part of the superior parietal lobes (known as ‘parietal reach region’ or “PRR”)
What regions of the parietal lobes can be associated with grasping
-Grasping involves the anterior intraparietal sulcus (AIP)
What regions of the parietal lobes can be associated with eye movements
-Eye movements involve the lateral intraparietal region (LIP)
What regions of the parietal lobes can be associated with planning movements
-Planning movements involves areas of the inferior parietal lobule (IPL)
What regions of the parietal lobes can be associated with on-line control
-On-line control involves areas of the superior parietal lobe (SPL)
Basal ganglia are active…
both before and during a movement
Cerebellum seems linked with…
timing of actions and on-line adjustments
Neurons in ventral premotor cortex appear to represent
actions
How does PET and fMRI measure action?
- PET works by intravenous injection of radioactive isotope that is taken up in the blood
- fMRI works by measuring blood flow
