L10 Flashcards
voluntary eye movement is controlled by the cortical part of vision
therefore voluntary eye movements are often referred to as
endogenous because they are initiated internally.
• Endogenous eye movements can be generated even in the absence of any visual stimulus.
what is the difference between exogenous and endogenous
Endogenous eye movements can be generated even in the absence of any visual stimulus.
Exogenous are reflexive in nature and are initiated because of external changes
what is an example of an Endogenous Eye Movement Task
• Task: Fixate on centre until an arrowhead Task: Fixate on centre until an arrowhead
appears at centre, then move your eyes in
the direction that the arrowhead points.
• After each response, return your eyes to
centre and wait for the next arrowhead
what is an example of an Exogenous Eye Movement Task
• Task: Fixate on centre until an asterisk Task: Fixate on centre until an asterisk
appears in the periphery, then move your
eyes to the asterisk.
• After each response, return your eyes to
centre and wait for the next asterisk centre and wait for the next asterisk.
will the exogenous or endogenous eye movement task be easier
Reflexive eye movement task will be easier as this is the natural response (you don’t have to think/less connections)
will also be faster
what is Smooth pursuit
Smooth pursuit is when you are traccing something with your eyes
The contributions of the superior prefrontal
cortex (SPFC) and the superior parietal lobule
(SPL) in generating voluntary and visually
guided saccades were investigated using
transcranial magnetic stimulation (TMS).
• Endogenous Task: Move your eyes to the left
or right in response to a central arrowhead.
• Exogenous Task: Move your eyes to a
peripheral asterisk when it appears.
Each “go signal” was presented with
a TMS pulse.
The TMS coil was placed over either superior
prefrontal cortex or the
superior parietal lobule
what did the results show
Results for endogenous saccade task: When
TMS was applied over the SPFC, endogenous
saccades directed toward the contralateral
hemifield were delayed.
TMS over the SPL did
not affect the latencies of endogenous saccades.
• exogenous saccades were not affected
therefore these indicates that the frontal lobe is important for voluntary control of sys movement
what caused the delay in contralateral
endogenous saccades associated with TMS
over the superior prefrontal cortex (SPFC)
it is hypothesized to be a consequence of
disrupting the normal operation of the
frontal eye field
• However, considering that we do not know
exactly where the magnetic field of the TMS coil was directed and other regions of frontal cortex
located near the FEF contribute to oculomotor behaviour, we cannot be certain that the TMS pulse
disrupted activity in the FEF.
TMS causes a transient lesion (stops the thing from working how it is supposed to)
k
describe Subcortical and Cortical Control of Eye Movements
subcortical control
• The superior colliculus (SC), which receives information directly
from the retina, projects down to the saccade generators (SG) in
the brain stem. = direct control
cortical control
• The frontal eye field (FEF), which receives visual information
indirectly, also projects down to the SG in the brain stem. = indirect control
in a previous study delay in contralateral
endogenous saccades was hypothesised to be caused because of disruption in the frontal eye field. how can we test to see if this is true
Participants= Lesion involved the frontal eye field (G1) and group 2 = Lesion but the frontal eye field is speared
participants were then asked to move their eyes to the left or right in response to a central
arrowhead. (testing voluntary control)
Participants= Lesion involved the frontal eye field (G1) and group 2 = Lesion but the frontal eye field is speared
participants were then asked to move their eyes to the left or right in response to a central
arrowhead. (testing voluntary control)
what would a study like this find
For patients with a frontal eye field lesion, voluntary saccades directed toward the contralesional hemifield were delayed compeered to group 2.
therefore the delayed contralateral
endogenous saccades are associated with
damage to the frontal eye field and indicate that the frontal eye field is normally involved in generating voluntary saccades
what is involved in generating voluntary saccades
the frontal eye field
Exogenous vs. Endogenous Eye Movements
• Comparisons of reflexive versus voluntary saccades demonstrated dissociations in the underlying neural circuitry involved.
• Reflexive eye movements depend more on subcortical structures and voluntary eye movements
depend more on cortical structures.
• When you tried the tasks, you might have noticed that it felt a lot easier to execute reflexive eye
movements than endogenous eye movements.
• Consideration of the connections for reflexive versus voluntary eye movements helps explain why reflexive eye movements are generated significantly faster than voluntary eye movements.
• Reflexive eye movements require fewer neural connections (less processing is required) compared
to voluntary eye movements.
