Background and PurposeThe present study was designed to examine the effects of color stimulation on cerebral blood mean flow velocity (MFV) in men and women.MethodsThe study included 16 (8 men and 8 women) right-handed healthy subjects. The MFV was recorded simultaneously in both right and left middle cerebral arteries in Dark and white Light conditions, and during color (Blue, Yellow and Red) stimulations, and was analyzed using functional transcranial Doppler spectroscopy (fTCDS) technique.ResultsColor processing occurred within cortico-subcortical circuits. In men, wavelength-differencing of Yellow/Blue pairs occurred within the right hemisphere by processes of cortical long-term depression (CLTD) and subcortical long-term potentiation (SLTP). Conversely, in women, frequency-differencing of Blue/Yellow pairs occurred within the left hemisphere by processes of cortical long-term potentiation (CLTP) and subcortical long-term depression (SLTD). In both genders, there was luminance effect in the left hemisphere, while in men it was along an axis opposite (orthogonal) to that of chromatic effect, in women, it was parallel.ConclusionGender-related differences in color processing demonstrated a right hemisphere cognitive style for wavelength-differencing in men, and a left hemisphere cognitive style for frequency-differencing in women. There are potential applications of fTCDS technique, for stroke rehabilitation and monitoring of drug effects.

Facial processing was studied in 16 (eight men and eight women) right-handed healthy participants using a new functional transcranial Doppler technique called functional transcranial Doppler spectroscopy (fTCDS). MFV was recorded simultaneously in both right and left middle cerebral arteries in dark condition and during visual processing of object and facial tasks. fTCDS used Fourier analysis of mean flow velocity (MFV) time series to derive spectral density estimates that correlate with expected mental activity. Men were right lateralised for object and facial perception, while women were left lateralised for facial tasks but showed a right tendency or no lateralisation for object perception. For facial perception, men used a category-specific process-mapping system for right cognitive style, but women used same for the left.

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The present study evaluated cerebral lateralization during RavenÕs progressive matrices (RPM) paradigm in female and male subjects. Bilateral simultaneous transcranial Doppler (TCD) ultrasound was used to measure mean blood flow velocities (MBFV) in the right and left middle cerebral arteries (MCAs) in 24 (15 females and 9 males) right-handed normal subjects. The female subjects used a left hemisphere strategy, while males used a right hemisphere strategy to successfully solve RPM tasks. This implies that general intelligence is associated with neural systems within one hemisphere that are accessible to a variety of cognitive processes.

Eight normal subjects were examined in dark, light and color conditions. Mean cerebral blood flow velocity (MBFV) were recorded almost simultaneously from their posterior cerebral arteries (PCA) using transcranial Doppler (TCD) ultrasound. The side-to-side difference was significant during the dark (p = 0.0159) and color stimulation (p = 0.0001) but not in light condition. This side-to-side difference in MBFV was used to characterize lateralization of color perception. This showed that the right PCA was always greater than the left during the presentation of color stimuli. Primary psychological colors (blue, yellow, red and green) induced greater lateralization as compared with color resulting from a mixed blue-green wavelength. This suggests that the right visual cortex is selectively sensitive to wavelengths.

Simultaneous color contrast and color constancy are memory processes associated with color vision, however, the gender-related differences of 'physiologic color space' remains unknown. Color processing was studied in 16 (8 men and 8 women) right-handed healthy subjects using functional transcranial Doppler (fTCD) technique. Mean flow velocity (MFV) was recorded in both right (RMCA) and left (LMCA) middle cerebral arteries in dark and white light conditions, and during color (blue and yellow) stimulations. The data was plotted in a 3D quadratic curve fit to derive a 'physiologic color space' showing the effects of luminance and chromatic contrasts. In men, wavelength-differencing of opponent pairs (yellow-blue) was adjudged by changes in the RMCA MFV for Yellow plotted on the Y-axis, and the RMCA MFV for Blue plotted on the X-axis. In women, frequency-differencing for opponent pairs (blue-yellow) was adjudged by changes in the LMCA MFV for Yellow plotted on the Y-axis, and the LMCA MFV for Blue plotted on the X-axis. The luminance effect on the LMCA MFV in response to white light with the highest luminous flux, was plotted on the (Z - axis), in both men and women. The 3D-color space for women was a mirror-image of that for men, and showed enhanced color constancy. The exponential function model was applied to the data in men, while the logarithmic function model was applied to the data in women. Color space determination may be useful in the study of color memory, adaptive neuroplasticity, cognitive impairment in stroke and neurodegenerative diseases.

Background: This study was designed to determine the minimal mean flow velocity and pressure-flow relation necessary to preserve human consciousness.Methods: Passive upright tilt provocation was used in conjunction with transcranial Doppler in 80 patients with a history of syncope of unknown etiology. Cerebral blood flow velocity, blood pressure, and heart rate were monitored noninvasively.Results: Forty patients remained asymptomatic, and the rest had clinically induced true syncope or premonitory symptoms. In the asymptomatic group, there was a 23±16% (p=0.000) drop in mean flow velocity, but no significant changes in systolic and diastolic blood pressures. In the symptomatic patients, there was a 58+14% (/>=0.000) drop in mean flow velocity, 37±23% (p=0.000) fall in systolic pressure, and 31 ±20% (p=0.000) fall in diastolic pressure. In 80% of symptomatic patients, the critical lower limit of mean flow velocity was at -50% of resting baseline while patients were lying supine. The symptomatic group had lower mean flow velocity and blood pressure responses as compared with the asymptomatic group. The slope and intercept values of the pressure (y axis) to flow velocity (or axis) regression curves indicate a greater degree of impaired autoregulation in the symptomatic group (y=0.529x-6.11, ^=0.108, p=0.038) as compared with the asymptomatic (y=0.317 x+0.966, ^=0.14,^=0.017).Conclusions: The critical lower limit of cerebral perfusion lies at 50% below baseline supine mean flow velocity. (Stroke 1992;23:1743-1747 KEY WORDS • autoregulation • blood flow velocity • hypotension • ultrasonics

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