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The adaptation of saccadic eye movements to environmental changes occurring throughout life is a good model of motor learning and motor memory. Numerous studies have analyzed the behavioral properties and neural substrate of oculomotor learning in short-term saccadic adaptation protocols, but to our knowledge, none have tested the persistence of the oculomotor memory. In the present study, the double-step target protocol was used in five human subjects to adaptively decrease the amplitude of reactive saccades triggered by a horizontally-stepping visual target. We tested the amplitude of visually guided saccades just before and at different times (up to 19 days) after the adaptation session. The results revealed that immediately after the adaptation session, saccade amplitude was significantly reduced by 22% on average. Although progressively recovering over days, this change in saccade gain was still statistically significant on days 1 and 5, with an average retention rate of 36% and 19%, respectively. On day 11, saccade amplitude no longer differed from the pre-adaptation value. Adaptation was more effective and more resistant to recovery for leftward saccades than for rightward ones. Lastly, modifications of saccade gain related to adaptation were accompanied by a decrease of both saccade duration and peak velocity. A control experiment indicated that all these findings were specifically related to the adaptation protocol, and further revealed that no change in the main sequence relationships could be specifically related to adaptation. We conclude that in humans, the modifications of saccade amplitude that quickly develop during a double-step target adaptation protocol can remain in memory for a much longer period of time, reflecting enduring plastic changes in the brain. (Contains 7 figures.)

Sensorimotor adaptation is fundamental to maintain accurate saccadic eye movements for optimal perception and interaction with the environment throughout life. We previously showed that adaptation mechanisms for reactive (externally-triggered) saccades (RS) are in place early during development (Lemoine-Lardennois et al., 2016). Nevertheless, this cannot be automatically extended to voluntary (internally-guided) saccades (VS). Indeed, adaptation mechanisms are partially separate for RS and VS in adults (Pélisson et al., 2010), and brain regions involved in VS adaptation also show late maturation (e.g., Lenroot & Gieed, 2006). Here we adapted our previous protocol to elicit VS, without verbal instruction, in toddlers (age < 3.5 years) and adults, using an overlap procedure. To prompt a decision, two identical peripheral stimuli appeared simultaneously at 10° eccentricity from a fixation point (140 trials). During the saccade toward the target, it systematically stepped in the direction opposite to the saccade to induce an adaptive decrease in saccade amplitude. Preliminary results showed that toddlers were able to select and direct their gaze toward one target without any explicit task instruction. Analysis of baseline performance revealed longer saccade latency (M = 415ms, SD = 112ms) and lower accuracy (M = 9.2°, SD = 0.4°) in toddlers compared to adults (M = 205ms, SD = 111ms; M = 9.6°, SD = 0.6°). Crucially, both adult and toddler groups exhibited an adaptive decrease in saccade amplitude, with similar amount of adaptation. Overall, our results suggest that the neural mechanisms underlying VS adaptation are in place early during development. [ABSTRACT FROM AUTHOR]

Adults with attention-deficit/hyperactivity disorder (ADHD) often display executive function impairments, particularly in inhibitory control. The antisaccade task, which measures inhibitory control, requires one to suppress an automatic prosaccade toward a salient visual stimulus and voluntarily make an antisaccade in the opposite direction. ADHD patients not only have longer saccadic reaction times, but also make more direction errors (i.e., a prosaccade was executed toward the stimulus) during antisaccade trials. These deficits may stem from pathology in several brain areas that are important for executive control. Using functional MRI with a rapid event-related design, adults with combined subtype of ADHD (coexistence of attention and hyperactivity problems), who abstained from taking stimulant medication 20 h prior to experiment onset, and age-match controls performed pro- and antisaccade trials that were interleaved with pro- and anti-catch trials (i.e., instruction was presented but no target appeared, requiring no response). This method allowed us to examine brain activation patterns when participants either prepared (during instruction) or executed (after target appearance) correct pro or antisaccades. Behaviorally, ADHD adults displayed several antisaccade deficits, including longer and more variable reaction times and more direction errors, but saccade metrics (i.e., duration, velocity, and amplitude) were normal. When preparing to execute an antisaccade, ADHD adults showed less activation in frontal, supplementary, and parietal eye fields, compared to controls. However, activation in these areas was normal in the ADHD group during the execution of a correct antisaccade. Interestingly, unlike controls, adults with ADHD produced greater activation than controls in dorsolateral prefrontal cortex during antisaccade execution, perhaps as part of compensatory mechanisms to optimize antisaccade production. Overall, these data suggest that the saccade deficits observed in adults with ADHD do not result from an inability to execute a correct antisaccade but rather the failure to properly prepare (i.e., form the appropriate task set) for the antisaccade trial. The data support the view that the executive impairments, including inhibitory control, in ADHD adults are related to poor response preparation.