Asymmetry of Cerebral Blood Flow Velocity Response to Color Processing and Hemodynamic Changes during -6 Degrees 24-hour Head-down Bed Rest in Men

Njemanze, P.C. Asymmetry of cerebral blood flow velocity response to color processing and hemodynamic changes during -6 degrees 24-hour head-down bed rest in men. J. Grav. Physiol. 12(2):??-??, 2005. Color stimulation may evoke significant cerebral responses that may be altered by head-down bed rest (HDR). Eight men were examined in supine horizontal position, with 30 deg head-up (Pre-HDR), and exposed to 24-hours (H) of -6 deg HDR, and then returned (Post-HDR). Transcranial Doppler (TCD) ultrasonography was used to monitor mean flow velocity (MFV) and pulsatility index (PI), in the right and left middle cerebral arteries (MCAs) simultaneously during stimulations. Heart rate (HR) was monitored. Data collection TIMES were at Pre-HDR, 6H-HDR, 24H-HDR, and Post-HDR respectively. The STIMULATIONS included black, white, blue, yellow, and red. The laterality index (LI) for each color was calculated as side-to-side difference in MFV relative to black. Subjects were right lateralized for colors at Pre-HDR, but left lateralized at 6H-, 24Hand Post-HDR. LI showed main effect of TIMES (p < 0.0004), but not STIMULATIONS (p > 0.05). MFV showed main effect of TIMES (p < 0.0001) and STIMULATIONS (p < 0.0001). There was a TIMES x STIMULATIONS x MCAs interaction (p < 0.0001). At Pre-HDR, MFV responses for blue vs yellow (p = 0.05), and white vs black (p < 0.05), were significant, but not during and after HDR. PI and HR decreased at 6H-HDR, 24H-HDR and Post-HDR (p < 0.05). HDR altered color processing and opponent mechanisms for blue vs yellow, and white vs black axes of color space. HDR was associated with left lateralization, decreased pulsatility and heart rate.