The effects of neck flexion on cerebral potentials evoked by visual, auditory and somatosensory stimuli and focal brain blood flow in related sensory cortices

Abstract

BackgroundA flexed neck posture leads to non-specific activation of the brain. Sensory evoked cerebral potentials and focal brain blood flow have been used to evaluate the activation of the sensory cortex. We investigated the effects of a flexed neck posture on the cerebral potentials evoked by visual, auditory and somatosensory stimuli and focal brain blood flow in the related sensory cortices.MethodsTwelve healthy young adults received right visual hemi-field, binaural auditory and left median nerve stimuli while sitting with the neck in a resting and flexed (20° flexion) position. Sensory evoked potentials were recorded from the right occipital region, Cz in accordance with the international 10–20 system, and 2 cm posterior from C4, during visual, auditory and somatosensory stimulations. The oxidative-hemoglobin concentration was measured in the respective sensory cortex using near-infrared spectroscopy.ResultsLatencies of the late component of all sensory evoked potentials significantly shortened, and the amplitude of auditory evoked potentials increased when the neck was in a flexed position. Oxidative-hemoglobin concentrations in the left and right visual cortices were higher during visual stimulation in the flexed neck position. The left visual cortex is responsible for receiving the visual information. In addition, oxidative-hemoglobin concentrations in the bilateral auditory cortex during auditory stimulation, and in the right somatosensory cortex during somatosensory stimulation, were higher in the flexed neck position.ConclusionsVisual, auditory and somatosensory pathways were activated by neck flexion. The sensory cortices were selectively activated, reflecting the modalities in sensory projection to the cerebral cortex and inter-hemispheric connections.

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

“…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 ].…”

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

“…Maintaining the neck flexion position, which constitutes a part of this dynamic posture, leads to non-specific activation of the brain. This results in: 1) shortened limb and saccade reaction times [ 2 - 5 ]; 2) reduced latencies of visual, auditory, and somatosensory evoked potentials, and increased amplitudes of auditory evoked potentials [ 6 , 7 ]; 3) increased oxy-hemoglobin concentration, taken as an index of cerebral blood flow, in the visual, auditory, and somatosensory areas [ 6 ]; 4) increased amplitudes of the event-related potentials associated with motor preparation and cognition [ 3 , 8 ]; and 5) shortened latencies and increased amplitudes of motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation (TMS) [ 9 ].…”