24 Cortical Control over Movement of the Eyes

Question 1

What are endogenous movements?

Answer 1

Voluntary eye movements

can be generated in the absence of any stimulus.

Question 2

Experiment: Effects of TMS over cortex on saccadic eye movements. Conclusion?

Answer 2

The contribution of the superior prefrontal cortex (SPFC_ and the superior parietal lobule (SPLP in generating voluntary and visually guided saccades were invested using 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.

Conclusion: the delay in contralateral endogenous saccades associated with TMS over the superior prefrontal cortex (SPFC) was hypothesised to be a consequence of disrupting the normal operation of the frontal eyefield

However considering we do not know exactly where the magnetic field of TMS coil was directed nad other regions of frontal cortex could contribute to oculomotor behaviour.

Question 2

Experiment: Effects of TMS over cortex on saccadic eye movements. Conclusion?

Answer 2

The contribution of the superior prefrontal cortex (SPFC_ and the superior parietal lobule (SPLP in generating voluntary and visually guided saccades were invested using 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.

Conclusion: the delay in contralateral endogenous saccades associated with TMS over the superior prefrontal cortex (SPFC) was hypothesised to be a consequence of disrupting the normal operation of the frontal eye field

However, considering we do not know exactly where the magnetic field of the TMS coil was directed and other regions of the frontal cortex could contribute to oculomotor behaviour.

Question 3

Brain features involved inb Subcortical and cortical control of eye movements

Answer 3

the superior colliculus (SC) which receives information directly from the retina projects down to the saccade generators (SG) in the brain stem.
The frontal eye field (FEF) which receives visual information indirectly, also projects down to the SG in the brain stem.

Question 4

Experiment: Effects of a lesion involving the frontal eye field on voluntary saccades. The task is to move your eyes to the left or right in response to the central arrowhead. Conclusion?

Answer 4

Results: Patients with FEF lesion voluntary saccade directed towards the contralesional hemifield were delayed.

Conclsuion: the delayed contralengenous saccades associated with damage to the drontal eye field (FEF indicate that the FEF is normally involved in generating voluntary saccades.

Supporting the hypothesis that the delay contralateral endogenous saccades caused by TMS over the superior prefrontal cortex consequence of disrupting the normal operation in the frontal eyefield

Question 5

Notes on exogenous vs endogenous eye movements

Answer 5

A comparison of reflective versus voluntary saccades demonstrates dissociation in the underlying neural circuitry involved.
Reflective eye movements depend more on subcortical structures and voluntary eye movements depend more on cortical structures

Question 6

Do exogenous or endogenous eye movements happen quicker?

Answer 6

exogenous
Considerations of the connections between reflexive versus voluntary eye movements help explain why reflective eye movements are generated significantly faster than voluntary ones.

Question 7

Do exogenous or endogenous eye movements require more neural connections?

Answer 7

endogenous
Reflective eye movements require fewer neural connections (fewer processes required)