Lebid, S. and O'Neill, R. and Markham, C. and Ward, T. and Coyle, S
Multi-timescale measurements of brain responses in visual cortex
during functional stimulation using time-resolved spectroscopy.
SPIE Proceedings (5823-5827).
Studies of neurovascular coupling (hemodynamic changes and neuronal activation) in the visual cortex using a timedomain
single photon counting system have been undertaken. The system operates in near infrared (NIR) range of
spectrum and allows functional brain monitoring to be done non-invasively. The detection system employs a
photomultiplier and multi-channel scaler to detect and record emerging photons with sub-microsecond resolution (the
effective collection time per curve point is ~ 200 ns). Localisation of the visual evoked potentials in the brain was done
using knowledge obtained from electroencephalographic (EEG) studies and previous frequency-domain optical NIR
spectroscopic systems. The well-known approach of visual stimulation of the human brain, which consists of an
alternating black and white checkerboard pattern used previously for the EEG study of neural responses, is applied here.
The checkerboard pattern is synchronized with the multi-channel scaler system and allows the analysis of time variation
in back-scattered light, at different stimulation frequencies. Slow hemodynamic changes in the human brain due to Hb-
HbO2 changes in the blood flow were observed, which is evidence of the system’s capability to monitor these changes.
Monocular visual tests were undertaken and compared with those done with an EEG system. In some subjects a fast
optical response on a time scale commensurate with the neural activity associated with the visual cortex was detected.
Future work will concentrate on improved experimental protocols and apparatus to confirm the existence of this
important physiological signal.
||single photon counting; time-domain system; neurovascular signal; neuronal activation;
||Faculty of Science and Engineering > Electronic Engineering
Dr Tomas Ward
||17 Jun 2009 15:38
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