Biomedical subjects

R Sayres

Publications and source records attributed to R Sayres.

2 recordsLinked to original sources

PubMed2004

Effect of sodium valproate on neuromagnetic responses to chromatic flicker: implication for photosensitivity.

The effect of oral administration of sodium valproate in normal subjects was evaluated using whole-scalp magnetoencephalography, with results compared to the effect of sodium valproate in photosensitive children. Neuromagnetic responses to 10 Hz equiluminant red-green and red-blue flicker were measured before and after 5 days of sodium valproate administration. For the red-green flicker, relative power spectra at the stimulus frequency (10 Hz) were attenuated with medication in most brain regions. However, for the red-blue flicker, the 10-Hz power in the occipital region was enhanced with medication, while it was reduced in other regions. These results qualitatively resembled those in photosensitive children. The present findings suggest that (1) combinational chromatic sensitivity can be a critical factor for cortical excitability, that (2) the effect of sodium valproate is qualitatively similar in normal and photosensitive subjects, and that (3) the effect of sodium valproate on cortical excitability is not simply to suppress the stimulus-synchronized occipital activity, but rather to inhibit the spread of cortical activity from the occipital region to other regions.

Adolescent↗

PubMed2001

Pupillary response to chromatic flicker.

There is significant evidence for higher-level cortical control of pupillary responses to visual stimuli, suggesting that factors other than luminance changes may induce a pupillary response. In the present study, the pupillary responses to equiluminant flickering stimuli in a range of 3-13 Hz were examined. Flicker stimuli included color-black (luminance-modulated) and color-color (hue-modulated) flicker. Equiluminance was determined both by objective luminance measures as well as by subjective, perceptual equiluminance for each subject. For both objectively and subjectively equiluminant flicker, significant, sustained pupillary constrictions were recorded. The magnitude of these responses was sensitive to both color and frequency parameters; red-blue color-paired flicker consistently produced the strongest constrictions. These responses occurred even when the flicker was of a lower luminance, both physically and perceptually, than a preceding nonflickering color, indicating that chromatic rather than luminance-sensitive mechanisms are involved in this response. Interestingly, the color- and frequency-sensitivity of constriction parallels those of flickers which maximally stimulate photosensitive epileptic patients, raising the possibility that chromatic response may be a factor in photosensitivity.

Adolescent↗