Problem 1 Flashcards
Extrastirate cortex is composed of … ?
2 segregated but interacting parallel processing streams
MT
Specialized for processing motion + depth
Traditional view of the action pathways?
Comprised of
- dorsal (where/how pathway)
vs
- ventral (what pathway)
Dorsal stream
Mediates navigation + the visual control of skilled actions directed at objects in the visual world
Ventral stream
Transforms visual inputs into representations that embody the enduring characteristics of objects + their spatial relationships
Dorsal stream lesions affect … ?
… 1. smooth pursuit eye movements
- Acura of goal directed arm movements
- speed discriminations
- complex mtotion perception
- Accruate encoding of visual space
Theory of independent visual-motor channels
Hypothesizes that reach-to-grasp movements require independent coding of different object properties
e.g. location, size, orientation etc
What does the newer view on action pathways consist ?
Dorsal stream should be subdivided into 2 sub circuits
Multiple parallel parieto-premotor circuits
They refer to the parallel running dorsal and ventral subcircuits/pathways in the dorsal system
–> dorso-dorsal + ventro-dorsal pathway
AND: maintain segregation until frontal cortex
What is the function of the dorso-dorsal pathway ?
Grasp-system
Controlling ones actions while they are on-going (“online”)
–> e.g. grasping something based on current visual info
What is the function of the ventral-dorsal pathway ?
Use-system
- Space perception
- Maintaining knowledge of particular skilled actions
associated with familiar objects - Action understanding
- -> recognizing + understanding the actions that were made by other
The dorsal + ventral streams clearly make up 2 relatively separate circuits.
Does that mean that the anatomical segregation between the 2 is absolute ?
No.
There is clear evidence of cross-talk between the streams
–> most connections from the V stream reach the ventral part of the D stream
THUS: VD stream constitutes an interface btw the ventral + dorsal streams of visual info processing
How do the sub streams thus interact ?
They both process the same set of visual attributes but for different behavioral goals
–> everyday actions require precise coordination between the systems
Lesions to the dorso-dorsal stream lead to … ?
Optic ataxia, where patients lose the ability to complete visually guided reaching tasks
–> reaching + grasping a target object with your hand arm/targeted arm movement
Lesions to the ventro-dorsal stream lead to … ?
Ideomotor/Limb Apraxia
- Deficits in object -related actions, meaning difficulty performing a motor task
- Especially without direct visual control, despite intact sensory, motor + language functions
The left lateralized system is crucial in making … ?
… correct inferences about the function of an object from its structure
–> tool use - knowing a calculator can do maths
Bilateral system
Specialized for online actions directed at currently visible stimuli on the basis of their structure
–> primarily subserved by a dorso-dorsal system
Left-lateralized system
Devoted to skilled, functional object-related actions
–> mediated by inferior venture-dorsal stream
e.g. tool use
Respondent behavior
Responding to an external stimulus
e.g. food is presented, eat it
Operant behavior
Operating on the environment by being or not being rewarded
e.g. dog coming up voluntarily - then getting a scratch on the back
Difference between respondent vs operant behavior ?
Respondent
–> externally triggered behavior
Operant
–> self-initiated behavior
How does operant behavior (self-initiated) show on a neuronal level ?
Neurons in
- Supplementary motor cortex (SMA + pre SMA)
- Lateral pre motor cortex
–> most crucial + firing in SMA, CMA - lateral does not have a big effect
It has been established that the same areas become activated when movement is externally triggered as when self-initiated.
How come ?
Activation in these areas are not confined to self initiated movements
BUT: activation in the pre SMA + SMA starts earlier when the movements is operant (
The role of the ACC in behavioral responding ?
It has cells that fire when an action is NOT followed by the expected reward
–> so an alternative action must be performed on the next trial
BUT: do not fire if there is an external cure that specifies the shift in responding
