Lecture 24- Voluntary Eye Movements

Question 1

What are voluntary eye movements? What are they referred to as?

Answer 1

-eye movements that depend more on voluntary (i.e., self-initiated) behaviour.
-Voluntary eye movements are often referred to as endogenous because they are initiated internally.

Question 2

Does a visual stimulus have to be present for endogenous/ voluntary eye movements to occur?

Answer 2

• Endogenous eye movements can be generated even in the absence of any visual stimulus.

Question 3

What experiment can be used to show the involvement of the cortex in voluntary eye movements?

Answer 3

An experiment looking at the effects of TMS over cortex on saccadic eye movements

Question 4

What specific areas of cortex where investigated using TMS for their involvement in generating voluntary eye movements?

Answer 4

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).

Question 5

In the TSM study what was the difference between an endogenous and exogenous task?

Answer 5

-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.

Question 6

What method was used in the TSM study?

Answer 6

Method: Each “go signal” was presented with a TMS pulse.

-The TMS coil was placed over either superior
prefrontal cortex (anterior) or the superior parietal lobule (posterior).

-The ‘X’ marks the position that stimulated
movement in the contralateral hand.

Question 7

What were the results of the TMS study for the endogenous saccade task?

Answer 7

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.

Question 8

What were the results of the TMS study for the exogenous saccade task?

Answer 8

Results for exogenous saccade task: Neither
TMS over the SPFC nor TMS over the SPL
affected the latencies of exogenous saccades
(i.e., exogenous saccades were not affected).

Question 9

What was the conclusion from the TMS study?

Answer 9

Conclusion: The delay in contralateral
endogenous saccades associated with TMS
over the superior prefrontal cortex (SPFC)
was hypothesized to be a consequence of
disrupting the normal operation of the
frontal eye field (FEF; the connections from
the FEF to subcortical oculomotor regions
are diagrammed on the next page).

Question 10

What is a limitation with the TMS study?

Answer 10

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.

Question 11

What pathways occur for subcortical and cortical control of eye movements?

Answer 11

• 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 12

Where is the frontal eye field?

Answer 12

Located at the intersection of the superior frontal sulcus and the precentral gyrus

Question 13

Who were the participants in the ‘Effects of a lesion involving the frontal eye field on voluntary saccades’ experiment?

Answer 13

Participants:
– Group 1: Lesion involved the frontal eye field
– Group 2: Lesion spared the frontal eye field

Question 14

What was the task of participants in the ‘Effects of a lesion involving the frontal eye field on voluntary saccades’ experiment?

Answer 14

Task: Move your eyes to the left or right in response to a central arrowhead.

Question 15

What were the results from the ‘Effects of a lesion involving the frontal eye field on voluntary saccades’ experiment?

Answer 15

For patients with a FEF lesion, voluntary saccades directed toward the
contralesional hemifield were delayed.

Question 16

What is the conclusion from the ‘Effects of a lesion involving the frontal eye field on voluntary saccades’ experiment?

Answer 16

The delayed contralateral
endogenous saccades associated with damage to the frontal eye field (FEF)
indicate that the FEF is normally involved
in generating voluntary saccades.

Question 17

How does the ‘Effects of a lesion involving the frontal eye field on voluntary saccades’ experiment support previous findings to do with voluntary eye movements?

Answer 17

*This result supports the hypothesis that the delayed contralateral endogenous
saccades caused by TMS over the superior prefrontal cortex were a consequence of disrupting the normal
operation of the frontal eye field (see previous experiment).

Question 18

Is there difference in the underlying circuitry between reflective and voluntary eye movements?

Answer 18

Yes.
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.

Question 19

What feels easier: reflective or endogenous eye movements? Why might this be?

Answer 19

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