25 Strategic Control over Oculomotor Reflexes Flashcards
Where is the frontal eye field region located?
Cortical region in the frontal lobe
State of the cortex and subcortex at birth?
Newborn is believed to have mature subcortical structures, but cerebral cortex is not fully developed.
Experiment: Fixation offset the effect in infants. What was the conclusion?
Results: compared to older infants, 1.5-month-olds show significantly slower responses on fixation overlap trials. This indicates that the fixation reflex was stronger in the 1.5 month year olds.
Conclusion: maturation of the cortex in older babies may have enabled them to exhibit better strategic control over the fixation reflex. More specifically maturation of cortico-subcortical pathways may underpin the shift from predominantly exogenously controlled orienting to increasing endogenous control
State of cortical pathways of infants 1-2 months old?
it is reflected in the natural orienting behaviour of infants.
At about 1-2 months of age infants often exhibit a prolonged periods of fixation with some apparent difficulty in looking away from fixated stimuli.
What is the postnatal development of the frontal lobe
the cerebral cortex is not fully mature at birth
immaturity of the frontal cortex contributes to the fact that newborns exhibit poverty of strategic behaviours, and instead are largely controlled by external stimuli.
When does frontal lobe become mature?
Frontal love development continues throughout childhood.
Given that the frontal loves do not fully develop until around 15 to 20 years of age, performance on tasks that require strategic control may continue to develop as well.
What is the anti-saccade test?
Not allowed to look at a stimulus. When something appears you can’t look it at and inhibit the natural response
a high percentage of reflexive eye movements suggests difficulty in imposing voluntary control over reflexive eye movements.
Abnormally slow correct reaction times would also suggest more of a struggle in imposing voluntary control over reflexive behaviour
Anti-Saccade Experiments in Children: Age-Related Performance on the Anti-Saccade Task
Experiment 1 (age 9 - 20)
Results: Moving from 9 year old’s to 15 year old’s there is a massive drop in errors. There was no statically difference between 15 and 20-year-olds’
Experiment 2 (age at least 5)
Results: Dramatic improvement in the performance of ages 5 and 15. 5-8 had the most errors
If the improvement in performing anti-saccades between the age of 5 and 15 years can be attributed to delayed maturation of the frontal love, then damage to the frontal lobe in adults should cause the poor performance to return.
Experiment: effects of a lesion involving the frontal eye field on anti-saccades. What was its conclusion?
Task: Anti-saccades
- FEF Group (lesion involved in frontal eye field)
- No FEF group: lesion spared the frontal eye field
- Control group: age-matched neurologically healthy
Results: Patients with unilateral frontal eye field (FEF) damage made abnormally frequent reflexive eye movements towards contralesional visual signals, but not ipsilesional visual signals.
Conclusion: This result supports the hypothesis that the FEF normally imposes inhibitory control over the ipsilesional oculomotor circuitry that generates reflex saccades.
Thus the selective deficit in inhibiting contralesional reflexive glances in patients with a unilateral lesion involving the FEF may reflect impaired modulating of activity in the ipsilesonal SC
The idea is if you knock out an eye field you lose the top-down control just in the damaged hemisphere.
Experiment on healthy aging. Comparing brains of 20 year old to 60 year old. Conclusions?
Considered above indicate that frontal love enables efficient voluntary control over visual orienting
the importance of the frontal loves in orchestrating reflexes was demonstrated in serval ways
- developmental processes in children contribute to the efficiency of strategic visual orientation
- damage involving the frontal cortex in adults can disrupt strategic visual orienting and allow uncontrolled reflexes behaviour to re-emerge
- The degenerative processes associated with aging cand disrupt strategic visual orienting and allow uncontrolled reflect behaviours to re-emerge in older adults.
Explain the Oculomotor System
Oculomotor behaviour is determined by cells in a number of brain areas at the subcortical and cortical levels;
Subcortical cells mediate more primitive reflexive oculomotor responses
Phylogenetically newer cortical cells impose control over primitive reflexes via projects to subcortical cells, facilitating them when advantageous and inhibiting them when disadvantages.
