L11 Flashcards
why do we need Strategic Control over Oculomotor Reflexes
Oculomotor Reflexes are essential for survival BUT
• Voluntary control over the fixation reflex and reflexive eye movements is critical for effective strategic orienting
• The ability to control reflexive behaviours is critical for effective voluntary control.
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Humans rely on reflexive orientating to avoid danger but reflexive behaviours are not always advantageous
what is an example of this
Complex tasks such as driving require suppression of reflexive responses in favour of a more strategic volitional behaviour
Eg when you are dirving there are many things changing, you cant reflexively look at all of these things because then you would never be looking at the road but if you were about to crash then you do want them to work
describe the Cortex and Subcortex at Birth
• At birth, the newborn is believed to have mature subcortical structures, but cerebral cortex is not
fully developed.
at birth, the newborn is believed to have mature subcortical structures, but cerebral cortex is not
fully developed.
how can they test for this
using fixation offset and overlap trials (they would need to use a dynamic stimulis to get the babys attention)
Fixation Offset Effect in Infants used Groups of babies either 1.5, 3 or 6 months old
what did they find
Compared to the older
infants, 1.5-month-olds (youngest) showed
significantly slower responses on fixation overlap trials. This indicates that the fixation reflex was stronger in
the 1.5-month-olds.
• Conclusion: Maturation of the cortex in the older babies may have enabled
them to exhibit better strategic control
over the fixation reflex. More
specifically, maturation of corticosubcortical pathways may underpin
the shift from predominantly exogenously controlled orienting (in the 1.5-month-olds) to increasing endogenous control (in the older babies).
Describe the development of Cortico-Subcortical Pathways in Infants and how that relates to the fixation reflex
• The immaturity of cortical pathways is also reflected in the natural orienting behaviour of infants.
• At about 1-2 months of age, infants often exhibit prolonged periods of fixation with some
apparent difficulty in looking away from fixated stimuli.
therefore immaturity of corticospinal pathway leads to them getting stuck looking at an object and it is only when they start crying and they close their eyes is when they can disengage
describe postnatal Development of the Frontal Lobes
- Cerebral cortex is not fully mature at birth.
- Immaturity of the frontal cortex contributes to the fact that newborns exhibit a poverty of strategic behaviours, and instead are largely controlled by external stimuli.
describe how the Frontal Lobes mature and how this relates to strategic control
• Frontal lobe development continues throughout childhood.
• Given that the frontal lobes 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 a Anti-Saccade Task
Fixate on centre. When a stimulus appears in the periphery, move your eyes in the opposite direction as soon as you can. Then, return your eyes to centre.
what does the anti-saccade task require
• The anti-saccade task requires inhibition of a reflexive saccade, followed by execution of a
voluntary saccade.
how is preformance on the antisaccade task measured
• Performance on the anti-saccade task can be assessed both in terms of errors in the direction of
the saccade (i.e., erroneous reflexive eye movements) and reaction times (for correct responses only).
• 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.
what would you see when looking at performance on antisaccades of people aged between 9-15 years
Between the ages of 9 and 15 years, there was a rapid decrease in the frequency of direction errors (from 60% to 22%).
– Reaction times for correct anti-saccades also decreased between the ages of 9 and 15 years.
this decrease is even more dramatic when compeering 5-15 years
what do the results from antisaccade tasks from 5-15 year olds confirm
If the improvement in performing anti-saccades between the ages of 5 and 15 years can be
attributed to delayed maturation of the frontal lobes, then damage to the frontal lobes in adults
should cause the poor performance to return.
if you cant compleate an antisaccade what do ti mean
you have something wrong with the inhibitory control system
How might damage to the frontal eye field influence the ability to perform anti-saccades?
this was looked at in a study where they had a Lesion involved the frontal eye field (G1), Lesion spared the frontal eye field (G2) and a control group which they preformed an antisaccade task
what did this study find
Patients with unilateral
frontal eye field (FEF) damage made abnormally frequent reflexive eye movements toward
contralesional visual signals, but not ipsilesional visual signals.
• Conclusion: This result supports the hypothesis that the frountal eye feild 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 frontal eye field may reflect impaired modulation of activity in the ipsilesional
superior colliculus.
• We know that cortical projections are not fully developed at birth.
• And we know that damage to the cortex in adults can compromise some of the voluntary control
that we gained during postnatal development.
• Over the course of healthy aging, neurons die.
• What are the effects of the neurodegeneration that accompanies healthy aging?
things to think about
how can you tell the difference between a young brain and a old brain
Over the course of healthy aging, neurons die.
Consequently, the ventricles and Consequently, the ventricles and sulci expand.
older adults make more errors on antisaccade tasks and have a slower reaction time (but reaction time could also have to do with muscles)
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Together, the data considered in this lecture indicate that the frontal lobes enable efficient voluntary control over visual orienting.
what is the importance of the frontal lobes in orchestrating reflexes was demonstrated
(3 reasons)
– Developmental processes in children contribute to the efficiency of strategic visual orienting.
– Damage involving the frontal cortex in adults can disrupt strategic visual orienting and allow
uncontrolled reflexive behaviours to re-emerge.
– The degenerative processes associated with healthy aging can disrupt strategic visual
orienting and allow uncontrolled reflexive behaviours to re-emerge in older adults.
what is The Oculomotor System determined by
• 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 projections to
subcortical cells, facilitating them when advantageous and inhibiting them when
disadvantageous
