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. 2012 Dec 3;31(1):31.
doi: 10.1186/1880-6805-31-31.

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

Katsuo Fujiwara  1 , Kenji Kunita, Naoe Kiyota, Aida Mammadova, Mariko Irei
Affiliations

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

Katsuo Fujiwara et al. J Physiol Anthropol. .

Abstract

Background: A 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.

Methods: Twelve 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.

Results: Latencies 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.

Conclusions: Visual, 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.

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Figures

Figure 1
Figure 1
Pictures showing experimental setup for simultaneous recordings of auditory evoked potentials and oxidative-hemoglobin concentration in the auditory cortex. (A) Resting neck position. (B) Flexed neck position.
Figure 2
Figure 2
Schematics indicating the arrangement of optical probes for measurement of oxidative-hemoglobin concentration. Light and dark circles indicate light-emitter and -detector probes, respectively. (A) Visual cortex; (B) auditory cortex; (C) somatosensory cortex.
Figure 3
Figure 3
Schematic indicating the experimental protocol. Each set consisted of at least 70 s rest, 15 s preparatory sensory stimuli and 30 s sensory stimuli. For the flexed neck target position, the flexed position was adopted after 10 s of preparatory sensory stimulation. The set was repeated as necessary.
Figure 4
Figure 4
Grand averaged waveforms of visual (A), auditory (B) and somatosensory (C) evoked potential in resting (upper) and flexed (lower) neck positions. Thick lines are grand averaged waveforms. Dashed lines indicate ±1 SD of a grand averaged waveform. The analyzed components of each evoked potential are labeled. AEP: auditory evoked potentials; SEP: somatosensory evoked potentials; VEP: visual evoked potentials.
Figure 5
Figure 5
Latency of each component (left panel) and peak-to-peak amplitude of neighboring components (right panel) of visual (A), auditory (B) and somatosensory (C) evoked potentials in resting (open circles) and flexed (closed circles) neck position. Values represent mean. Error bars represent SD. Asterisk indicate a significant (P < 0.05) difference between neck positions.
Figure 6
Figure 6
Oxidative-hemoglobin (oxy-Hb) concentration during right hemi-field visual stimulation. (A) Mean and standard deviation of oxy-Hb in resting (open circles) and flexed (closed circles) neck positions. Plus signs (+) indicate oxy-Hb concentration significantly greater than zero in the resting neck position. Asterisks indicate a significant difference in oxy-Hb concentration between neck positions. (B) A schematic indicating the arrangement of optical probes for measurement of oxy-Hb concentration in the visual cortex. Small circles indicate that oxy-Hb concentration was significantly greater than zero at that channel in the resting neck position. Large circles indicate there was a significant difference in oxy-Hb concentration between neck positions at that channel. oxy-Hb: oxidative-hemoglobin.
Figure 7
Figure 7
Oxidative-hemoglobin (oxy-Hb) concentration during auditory stimulation. (A) Mean and standard deviation of oxy-Hb in resting (open circles) and flexed (closed circles) neck positions. Plus signs (+) indicate oxy-Hb concentration significantly greater than zero in the resting neck position. Asterisks indicate a significant difference in oxy-Hb concentration between neck positions. (B) A schematic indicating the arrangement of optical probes for measurement of oxy-Hb concentration in each hemisphere of the auditory cortex. Small circles indicate that oxy-Hb concentration was significantly greater than zero at that channel in the resting neck position. Large circles indicate there was a significant difference in oxy-Hb concentration between neck positions at that channel. oxy-Hb: oxidative-hemoglobin.
Figure 8
Figure 8
Oxidative-hemoglobin (oxy-Hb) concentration during somatosensory stimulation. (A) Mean and standard deviation of oxy-Hb in resting (open circles) and flexed (closed circles) neck positions. Plus signs (+) indicate oxy-Hb concentration significantly greater than zero in the resting neck position. Asterisks indicate a significant difference in oxy-Hb concentration between neck positions. (B) A schematic indicating the arrangement of optical probes for measurement of oxy-Hb concentration in each hemisphere of the somatosensory cortex. Small circles indicate that oxy-Hb concentration was significantly greater than zero at that channel in the resting neck position. Large circles indicate there was a significant difference in oxy-Hb concentration between neck positions at that channel. oxy-Hb: oxidative-hemoglobin.
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