Fast cerebral functional signal in the 100-ms range detected in the visual cortex by frequency-domain near-infrared spectrophotometry.
Brain activity is associated with physiological changes, which alter the optical properties of the tissue in the near-infrared part of the spectrum. Two major types of optical signals following functional brain activation can be distinguished: a slow signal due to hemodynamic changes and a fast signal, which is directly related to neuronal activity. The fast signal is small and therefore difficult to detect. We used a specially noise-optimized frequency-domain near-infrared spectrometer with a pi-sensor, which was expected to be particularly sensitive to deeper tissue layers, to investigate the human visual cortex during visual stimulation generated by a checkerboard. We were able to detect significant fast signals in single light bundles, but not in pi-signals. The fast signals were mostly collocated with strong slow hemodynamic signals, but showed a higher degree of localization than the latter. The latencies of 40 +/- 16 ms of the fast signals were similar between locations. Our results also indicate that the brain responds differently to a single and double (forth and back) reversal of the checkerboard, with a stronger reaction upon the double reversal.
Laboratory for Fluorescence Dynamics, Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA. martin.wolf@alumni.ethz.ch
Martin
M
Wolf
Ursula
U
Wolf
Jee H
JH
Choi
Vladislav
V
Toronov
L Adelina
LA
Paunescu
Antonios
A
Michalos
Enrico
E
Gratton
D000328:Adult; D000465:Algorithms; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D010775:Photic Stimulation; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D014793:Visual Cortex / Q000033:anatomy & histology / Q000502:physiology*