Physical model for the spectroscopic analysis of cortical intrinsic optical signals

We used Monte Carlo simulations and the diffusion approximation to estimate correction terms for the analysis of reflectance spectra of cortical intri nsic optical signals. These corrections depend on scattering and absorption properties, i.e. they are dependent on assumptions on the tissue blood con tent and oxygen saturation. The analysis was applied to reflectance spectra acquired during whisker barrel stimulation in the rat where attenuation sp ectra were converted to changes in oxygenated and deoxygenated haemoglobin concentration. The description of the experimental data as judged by the re sidual and sensitivity to variations of wavelength was considerably improve d when the correction terms were included. Inclusion of the correction does have a considerable impact on the time course of deoxyhaemoglobin concentr ation changes. In contrast to the calculation without correction terms, the re is no indication for an early increase in deoxyhaemoglobin ('early dip') . This finding might further current interpretation of the coupling between neuronal activation and oxygen extraction and supply.