Near-infrared spectroscopy (NIRS) is a noninvasive technique for continuous monitoring of the amounts of total hemoglobin (total-Hb), oxygenated hemoglobin, (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb). The purpose of the present study was to demonstrate the utility of NIRS in functional imaging of the human visual cortex. A new NIRS imaging system enabled measurements from 24 scalp locations covering a 9 cm sq area. Topographic images were obtained from interpolations of the concentration changes between measurement points. Five healthy subjects between 25 and 49 years of age were investigated. After a resting baseline period of 50 s, the subjects were exposed to a visual stimulus for 20 s, followed by a 50 s resting period in a dimly lit, sound attenuating room. The visual stimulus was a circular, black and white, alternating checkerboard. In four of five subjects the visual cortex was the most activated area during visual stimulation. This is the first reported use of a NIRS-imaging system for assessing hemodynamic changes in the human visual cortex. The typical hemodynamic changes expected were observed; the total-Hb and oxy-Hb increased just after the start of stimulation and plateaued after 10 s of the stimulation period.
An automated analyzer for individual eye movements (EMs) has been developed that enables precise analyses of their incidence. Three new parameters for each EM are obtained: EM magnitude, the angle and speed of eyeball rotation, and the energy of each EM. All rapid eye movement (REM) sleep EMs from 40 nights of polysomnography for 20 healthy young men were analyzed. The mean frequency of eye movement (EM frequency) was 15.9 per minute. Compared to conventionally analyzed rapid eye movement (REM) density, EM frequency was more sensitive to differences among sleep cycles, nights, and individuals. The mean EM rotation was 6.27 +/- 0.021 degrees, the mean speed of rotation was 58.73 +/- 0.18 degrees/second, and mean energy was 525.85 +/- 3.82 degrees2/second. The distribution of changes in these new parameters differed from conventional measures across REM episodes. The conventional measures, REM episode duration, and REM density increased progressively in successive REM episodes in an ascent-to-right pattern. However, the new parameters peaked in the second, followed by relatively low values, producing an inverted V pattern. This discrepancy could indicate physiological mechanisms of EM that are not revealed in conventional measures of REM sleep intensity.
To visualize dreaming brain functions we studied hemodynamic changes in the visual cortex during the transition from non-rapid eye movement (NREM) to rapid eye movement (REM) sleep, using a 24-channel Near-Infrared Spectroscopy (NIRS) imaging method. Results were compared to the activation in visual cortex by visual stimulation during wakefulness. Subjects were four healthy males between 25 and 49 years of age. Five all-night polysomnographic and NIRS recordings were made. Increases in the oxygenated hemoglobin concentration in visual cortex were observed from nine of 14 REM periods. The activated areas were broader during REM sleep than during visual stimulation. These findings suggest that activation of visual cortex in REM sleep might represent dream-related brain activity.
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