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Abstract:
Several optical studies have reported a brief initial increase of deoxyhemoglobin (1), which is consistent with an initial dip observed in the functional MRI (fMRI) signal, evoked by local neuronal activity. This effect is small and not always present (2), but it has stirred great interest because it may reflect a rapid increase of oxidative metabolism before increases in blood flow and, thus, may have a narrower spatial spread than the main positive hemodynamic response.
In a recent elegant and comprehensive study, Sirotin et al. (3) investigated the spatiotemporal specificity of intrinsic optical imaging signals at different wavelengths and for different chromophores.
