Spectroscopic analysis of changes in remitted illumination: The response to increased neural activity in brain

Imaging of neural activation has been used to produce maps of functional ar chitecture and metabolic activity. There is some uncertainty associated wit h the sources underlying the intrinsic signals. It has been reported that f ollowing increased neural activity there was little increased oxygen consum ption (similar to 5%), although glucose consumption increased by similar to 50%. The research we describe uses a modification of the Beer-Lambert Law called path-length scaling analysis (PLSA) to analyze the spectra of the he modynamic and metabolic responses to vibrissal stimulation in rat somatosen sory cortex. The results of the PLSA algorithm were compared with those obt ained using a linear spectrographic analysis method (we refer to this as LM CA). There are differences in the results of the analysis depending on whic h of the two algorithms (PLSA or LMCA) is used. Using the LMCA algorithm, w e obtain results showing an increase in the volume of Hbr at similar to 2 s , following onset of stimulation but no complementary decrease in oxygenate d haemoglobin (HbO(2)). These results are similar to a previous report. In contrast, after using the PLSA algorithm, the time series of the chromophor e changes shows no evidence for an increase in the volume of deoxygenated h aemoglobin (Hbr). However, after further analysis of the time series from t he PLSA using general linear models (GLM) to remove contributions from low frequency baseline oscillations, both the HbO(2) and Hbr times series of th e response to stimulation were found to be biphasic with an early decrease in saturation peaking similar to 1 s after onset of stimulation followed by a larger increase in saturation peaking at similar to 3 s. Finally, follow ing the PLSA-then-GLM analysis procedure, we do not find convincing evidenc e for an increase in cytochrome oxidation following stimulation, though we demonstrate the PLSA algorithm to be capable of disassociating changes in c ytochrome oxidation state from changes in hemoglobin oxygenation. (C) 1999 Academic Press.