Effects of Stimulus Predictability and Interstimulus Gap on Saccades in Alzheimer’s Disease

Abstract

Objectives: Studies of saccadic eye movement impairment in Alzheimer’s disease (AD) have largely focused on simple reflexive eye movements and the antisaccade task. The effects of manipulating stimulus timing have been little studied. Methods: Fourteen patients with mild to severe AD and 11 age-matched controls were studied on the antisaccade task, while latencies on simultaneous, gap and predictable tasks were recorded from 11 patients and 11 controls. Dementia severity was assessed with the Mini-Mental State Examination. Results: As a group, patients’ latencies were significantly higher and more variable on the simultaneous and gap tasks. Predictable task performance was similar in mean but significantly more variable. Grossly anticipatory responses by patients were common on the predictable, simultaneous and gap tasks. Exclusion of these from subject means revealed that AD patients, when making target-driven saccades, demonstrated a gap effect of similar magnitude to normal subjects. Patients made significantly fewer correct antisaccades and significantly more reflexive errors not followed by a corrective antisaccade than did controls. Conclusions: The frequent presence of grossly anticipatory saccades may reflect dysfunction of fixation mechanisms possibly involving projections from frontal lobe to superior colliculus. The less frequently seen, marked prolongation of latency may reflect changes in posterior parietal mechanisms mediating reflexive saccade generation. The presence of the gap effect demonstrates a continued ability to benefit from externally controlled stimulus disengagement. Patients’ ability to make appropriately timed saccades to targets of known locations was particularly impaired, but the target sequence itself was at least grossly correctly learned. Larger studies may be able to identify clinically distinct populations of AD patients.

Medial Versus Lateral Frontal Lobe Contributions to Voluntary Saccade Control as Revealed by the Study of Patients with Frontal Lobe Degeneration

“…Our antisaccade results are similar to those reported for the frontal variant of FTLD (Meyniel et al, 2005). Consistent with other reports of antisaccade impairments in AD (Currie et al, 1991;Abel et al, 2002;Shafiq-Antonacci et al, 2003;Crawford et al, 2005), we found a strong correlation between antisaccade performance and general cognitive status as measured by MMSE score (Table 5). There was no correlation between MMSE score and antisaccade performance in FTLD.…”

Ocular motor abnormalities in neurodegenerative disorders

“…7 Furthermore, results from studies looking at the saccadic gain and velocity in AD are controversial; some studies found impairment, 8,14 whereas other studies did not. 9,15 intrusions during attempted fixation; 11 and (2) visual capture by the target in the antisaccadic paradigm, 14,[17][18][19] in which the subject has to suppress a reflexive saccade to a peripheral target and execute an endogenously driven saccade to an equal and opposite location. Interestingly, inhibition errors in the antisaccadic paradigm could be predicted by measures of dementia severity.…”

“…Interestingly, inhibition errors in the antisaccadic paradigm could be predicted by measures of dementia severity. 14,17,18,20 Antisaccades may provide not only a functional index of the dorsolateral prefrontal cortex, which is damaged in the later stages of AD, but also a tool for monitoring the progression of AD. 6 A more recent study 21 used an antisaccadic paradigm as a way of testing inhibitory control in AD patients.…”

The use of working memory for task prediction: What benefits accrue from different types of foreknowledge?

“…Predictive saccades have been studied in Alzheimer's disease, but the specific effects due to foreknowledge are not clear (Abel et al, 2002). Alcohol does not appear to impair the use of task-foreknowledge in predictive saccades (Wegner and Fahle, 1999).…”