Cerebral Haemoglobin Oxygenation during Sustained Visual Stimulation-A Near-Infrared Spectroscopy Study
Using near-infrared spectroscopy, we investigated the time-course of the concentrations of oxygenated haemoglobin, [oxy-Hb], and deoxygenated haemoglobin, [deoxy-Hb], in the occipital cortex of healthy human adults during sustained visual stimulation. Within a few seconds after stimulation (by coloured dodecahedron), we observed a decrease in [deoxy-Hb], peaking after 13 s ('initial undershoot'). In the subsequent 1-2 min, in seven out of ten subjects, [deoxy-Hb] gradually returned to a plateau closer to the baseline level. After cessation of stimulation, there was a 'post-stimulus overshoot' in [deoxy-Hb]. There was a statistically significant correlation between the size of the 'initial undershoot' and the 'post-stimulus overshoot'. The concentration of oxyhaemoglobin increased upon functional activation. However, in the mean across all subjects there was no 'initial overshoot'. After approximately 19 s it reached a plateau and remained constantly elevated throughout the activation period. After cessation of activation there was a 'post-stimulus undershoot' of oxyhaemoglobin. It is important to consider the time-course of haemoglobin oxygenation when interpreting functional activation data, especially those data obtained with oxygenation-sensitive methods, such as BOLD-contrast fMRI.
Philosophical Transactions of the Royal Society of London Series B
- Pub Date:
- June 1997