Spread deficits in initiation, speed and accuracy of horizontal and vertical automatic saccades in dementia with lewy bodies

Abstract

Background: Mosimann et al. (2005) reported prolongation of saccade latency of prosaccades in dementia with Lewy body (DLB). The goal of this study is to go further examining all parameters, such as rates of express latency, but also accuracy and velocity of saccades, and their variability.

Methods: We examined horizontal and vertical saccades in 10 healthy elderly subjects and 10 patients with DLB. Two tasks were used: the gap (fixation target extinguishes prior to target onset) and the overlap (fixation stays on after target onset). Eye movements were recorded with the Eyelink II eye tracker.

Results: The main findings were: (1) as for healthy, latencies were shorter in the gap than in the overlap task (a gap effect); (2) for both tasks latency of saccades was longer for DLB patients and for all directions; (3) express latency in the gap task was absent for large majority of DLB patients while such saccades occurred frequency for controls; (4) accuracy and peak velocity were lower in DLB patients; (5) variability of all parameters was abnormally high in DLB patients.

Conclusions: Abnormalities of all parameters, latency, accuracy and peak velocity reflect spread deficits in cortical-subcortical circuits involved in the triggering and execution of saccades.

Keywords: Lewy body; accuracy; latency; saccades; variability; velocity.

Figure 1

Experimental design. (A) Spatial arrangement. Five white luminous dots (angular size 0.2°) were presented on a black computer screen at 57 cm from the subject (required convergence 6°), one at the center of the screen; the others at an eccentricity of ±10° horizontally or vertically. (B,C) Temporal arrangement. Each trial started by lighting one central dot during approximately 1500–2000 ms. For the gap task, between the fixation offset and the target onset, there was a gap of 200 ms (B); for the overlap task, the fixation stays on 200 ms after the target onset (C). The target, one of the eccentric dots, appears for 1500 ms.

Figure 2

Typical recordings of horizontal saccade are obtained by averaging the position signal of the two eyes (LE + RE)/2 and their corresponding velocity traces for one healthy elderly and one DLB patient. The arrows “i” and “p” indicate the onset and the end of the primary saccade, respectively; the arrow “f” for the final eye position Figure 4. Examples of saccade latencies distribution with trials from some controls and DLB patients in the gap task. The mean values and the variability (standard deviation/mean latency) of saccade latency are presented in the box. All three DLB patients show abnormal long latency.

Figure 3

Group mean latency of saccades with standard error in gap and overlap tasks, for four directions in healthy elderly and DLB patients; longer latencies of saccades for DLB patients than for healthy elderly for each condition.

Figure 4

Examples of saccade latencies distribution with trials from some controls and DLB patients in the gap task. The mean values and the variability (standard deviation/mean latency) of saccade latency are presented in the box. All three DLB patients show abnormal long latency.

Figure 5

Group mean coefficient of variation (CV) in saccade latency in gap and overlap tasks, for each direction in healthy elderly and DLB patients. Variability is higher for DLB patients for all conditions.

Figure 6

Group mean gain of primary saccade and of the final eye position for each direction in healthy elderly and DLB patients; vertical lines are standard error; horizontal lines are gain at 1. Gain is lower for DLB patients for all directions.

Figure 7

Group mean coefficient of variation (CV) in the gain of the primary saccade and of the final eye position for each direction in healthy elderly and DLB patients; variability is higher for DLB patients for all directions.

Figure 8

Group mean value of peak velocity of primary saccade for each direction in healthy and DLB patients; vertical lines are standard error. Peak velocity is lower for DLB patients for all directions.

Figure 9

Group mean coefficient of variation (CV) in peak velocity of the primary saccade for each direction in healthy and DLB patients. Variability is higher for DLB patients for all directions.

Figure 10

Group mean peak velocity (with standard error) and its coefficient of variation for saccades of 9° to 11° for healthy and DLB patients; no significant difference of peak velocity between the two groups, yet, coefficient of variation is higher for DLB patients.

Figure 11

Distribution of latencies in the gap condition for healthy elderly (10) and the DLB subjects (10).