Effect of maintaining neck flexion on anti-saccade reaction time: an investigation using transcranial magnetic stimulation to the frontal oculomotor field

Abstract

BackgroundReaction time for anti-saccade, in which the gaze is directed to the position opposite to an illuminated target, shortens during maintenance of neck flexion. The present study applied transcranial magnetic stimulation (TMS) to the frontal oculomotor field, and investigated the effect of maintaining neck flexion on information processing time in the anti-saccade neural pathway before the frontal oculomotor field.MethodsThe reaction time was measured with the chin resting on a stand (‘chin-on’ condition) and with voluntary maintenance of neck flexion (‘chin-off’ condition) at 80% maximal neck flexion angle, with and without TMS. The TMS timing producing the longest prolongation of the reaction time was first roughly identified for 10 ms intervals from 0 to 180 ms after the target presentation. Thereafter, TMS timing was set finely at 2 ms intervals from −20 to +20 ms of the 10 ms step that produced the longest prolongation.ResultsThe reaction time without TMS was significantly shorter (21.9 ms) for the chin-off (235.9 ± 14.9 ms) than for the chin-on (257.5 ± 17.1 ms) condition. Furthermore, TMS timing producing maximal prolongation of the reaction time was significantly earlier (18.6 ms) for the chin-off than the chin-on condition. The ratio of the forward shift in TMS timing relative to the reduction in reaction time was 87.8%.ConclusionsWe confirmed that information processing time in the anti-saccade neural pathway before the frontal oculomotor field shortened while neck flexion was maintained, and that this reduction time accounted for approximately 88% of the shortening of reaction time.

Developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion position

“…We determined 80% of maximal neck flexion angle (neck flexion position) for each subject using a custom-made angular detector with the center point set at the acromion, while regulating the distance between the acromion and tragus. The set angle in the flexed position was defined as described by Fujiwara et al and Kunita and Fujiwara [ 28 , 31 ]. Head inclination angle was determined as the angle between the auriculo-infraorbital line and the gravitational line, and this was maintained at the same angle as the sitting posture to maintain constant sensory inputs from the vestibular organ.…”

“…These findings suggest that the shortening with maintaining neck flexion posture is attributable to an ascending brain activation system in tandem with increases in muscle afferent information [ 25 – 27 ]. The following changes in other physiological indices also support brain activation during neck flexion: 1) shortening of limb reaction times and latencies of visual, auditory and somatosensory evoked potentials [ 28 , 29 ]; 2) increased amplitudes of auditory evoked potentials and event-related potentials associated with motor preparation and cognition [ 28 – 30 ]; and 3) shortened latencies and increased amplitudes of motor evoked potentials evoked by transcranial magnetic stimulation [ 31 ].…”