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Abnormal Saccadic Intrusions with Alzheimer's Disease in Darkness
Kiyotaka Nakamagoe1, Shiori Yamada1, Rio Kawakami1
1Department of Neurology, Division of Clinical Medicine, Faculty of Medicine, University of Tsukuba, Tsukuba, Ibaraki, Japan.
Background:
Classified as saccadic intrusions, Square-Wave Jerks (SWJs) have been observed during Visual Fixation (VF) in Alzheimer's Disease (AD). However, the pathological significance of this phenomenon remains unclear.
Objective:
The present study analyzed the characteristics of SWJs in patients with AD with their eyes open in the dark without VF.
Methods:
Fifteen patients with AD and 15 healthy age- and sex-matched controls were investigated and compared. Saccadic intrusions with and without VF were detected as SWJs and measured using an electronystagmogram.
Results:
No significant difference in the frequency of SWJs was observed between control and AD groups with VF, but significantly more SWJs were observed in the AD group than in the control group in the absence of VF (p<0.01). In the control group, the frequency of SWJs was significantly higher with VF as compared to without VF. Conversely, the frequency in the AD group was significantly higher without VF. Furthermore, a directly proportional relationship was observed between the frequency of SWJs and higher-order function (R>0.55) in the AD group.
Conclusion:
SWJs without VF may have pathological significance in AD. In healthy individuals, SWJs are generated by VF and suppressed without VF. Conversely, in AD, SWJs are generated rather than suppressed in the absence of VF. These pathognomonic SWJs without VF also appear to be correlated with higher-order dysfunction, reflecting AD-related cortical damage. These findings suggest that pathological SWJs without VF observed in AD derive from cortical damage and may constitute an important marker of a higher-order function.