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AJNR - American Journal of Neuroradiology

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Effect of Stage 1 Sleep on Auditory Cortex During Pure Tone Stimulation: Evaluation by Functional Magnetic Resonance Imaging with Simultaneous EEG Monitoring

Hisashi Tanaka^a, Norihiko Fujita^a, Mayako Takanashi^c, Norio Hirabuki^a, Hideaki Yoshimura^a, Kazuo Abe^b and Hironobu Nakamura^a

^a Department of Radiology, Osaka University Medical School, Osaka, Japan
^b Department of Neurology, Osaka University Medical School, Osaka, Japan
^c Department of Neurology, Osaka Prefectural Hospital, Osaka, Japan

View larger version (25K): [in a new window]   FIG 1. Timing of auditory stimulation, functional MR imaging, and EEG measurements. Black vertical bars indicate echo-planar imaging measurements of 16 sections within 1.9 seconds followed by a noise-free and EEG measurement period of 10.1 seconds. Auditory stimulus was alternated with the baseline every 36 seconds. Acquisition time was 30–40 minutes, or 153–194 image acquisitions.

View larger version (61K): [in a new window]   FIG 2. Regions of interest in one subject. The region of interest were chosen so as to include the transverse temporal gyrus and its adjacent sulci in five contiguous sections.

View larger version (15K): [in a new window]   FIG 3. Evaluation of the effect of habituation. Percentage signal intensity changes during the first and second half of the measurements are shown. Panels A and B correspond to the right and left hemispheres, respectively. Two-factor factorial ANOVA demonstrated the effect of the timing of data acquisition was not significant, which implied that the effect of habituation measured with this method was insignificant. On the other hand, the effect of state of consciousness was found to be significant.

View larger version (15K): [in a new window]   FIG 4. Percentage signal intensity change in the transverse temporal gyri. A significant effect of state of consciousness was revealed by two-way repeated-measure ANOVA. The Tukey-Kramer post hoc test showed that the percentage signal intensity change during stage 1 sleep was significantly smaller than during wakefulness. The overall effect of the hemisphere was not significant.

View larger version (54K): [in a new window]   FIG 5. Positively or negatively correlated pixels (t >3.5; cluster > = 4 pixels; corrected P value < .05) during wakefulness and stage 1 sleep in one subject. Clusters of positively correlated pixels are seen in the bilateral transverse temporal gyri during wakefulness. No cluster is found during the other conditions.

View larger version (20K): [in a new window]   FIG 6. Number of activated pixels in the transverse temporal gyrus. A significant effect of state of consciousness was revealed by two-way repeated-measure ANOVA. The Tukey-Kramer post hoc test showed the number of positively correlated pixels during wakefulness was significantly larger than that under other conditions. The overall effect of the hemisphere was not significant.