Saccade Profiles Across Tasks After Childhood Hemispherectomy

Saccades and smooth pursuit are supported by overlapping, bilateral brain networks including the brainstem and cortex (McDowell et al., 2008, Coiner et al., 2019, Sharpe, 2008, Lencer et al., 2008). Previous studies of patients, following lesions or hemispherectomies, reported both contralesional, as well as task-dependent ipsilesional, saccade deficits, and ipsilesional pursuit deficits (Troost et al., 1972, Herter et al., 2007, Sharpe et al., 1979, Morrow et al., 1993 & 1995, Thurston et al., 1988). Systematic studies of saccade function in hemispherectomy patients across task contexts are relatively lacking. We previously quantified the ‘catch-up’ saccade main sequence during sinusoidal pursuit in childhood hemispherectomy patients and found increased eye speeds relative to controls, especially ipsilesionally. Here, we compare saccade profiles during sinusoidal pursuit to profiles during visually-guided saccades in an overlapping set of childhood hemispherectomy patients (n = 12; surgery age: < 1 month-10 years, test age: 5-32 years) and similarly-aged controls (n = 14, test age: 6-32 years). We recorded eye movements using an EyeLink 1000 Plus while participants performed visually-guided saccades, with six possible directions containing a horizontal component (0°, 45°, 135°, 180°, 225°, 315°). We compared the latency, amplitude, and peak speed of the first saccade on each trial, and examined the main sequence, in patients and controls. We found that patient saccades had significantly longer latencies, shorter amplitudes, and slower speeds than controls, especially toward their contralesional blind field (p < 0.05). The main sequence slope was significantly reduced for patients in both visual fields relative to controls, indicating slower speeds across amplitudes (non-overlapping confidence intervals). This result contrasts with the increased main sequence slopes seen for catch-up saccades in similar patients relative to controls during pursuit. Future analyses will compare saccade and pursuit performance within-participants to elucidate how disrupted oculomotor networks affect saccade function across task contexts.