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OIS and MRI measurements: towards a biophysical model of the relationship between neural activity and the BOLD signal

John Mayhew et al

Sheffield University , UK

The long term research objective is to build a ‘forward’ biophysical model that can be used to develop the ‘inverse’ analysis methodologies needed for the understanding of the hemodynamic response to neural activation. A description of our current model linking neural activity to the hemodynamic response will given. Data from high resolution optical imaging of barrel cortex will be presented. The other major focus of the presentation will be to describe research evaluating biophysical models of the BOLD signal.


Optical imaging spectroscopy (OIS) data of the hemodynamic response to activation of rat barrel cortex, captured concurrently will fMRI and cbv-MRI data, is used to evaluate the MGH (Davis, Hoge) model of BOLD signal commonly used in neuroimaging studies to estimate activation induced changes in CMRO 2. In our experiments, the OIS measured changes in blood volume and saturation are input to a MCS-model to predict the fMRI measurements which are compared with the measured BOLD signals. The MCS-model incorporates methods for incorporating both IV and EV contributions from mixtures of vessels and parenchyma. The results of the study suggest that the assumptions underlying the MGH model (also the Obata-Buxton model), namely that the blood volume changes are mainly venous and that the BOLD signal derives mainly from changes in the venous concentration of Hbr are, if not totally incorrect, inadequate to account for our measured data. In contrast theYablonskiy-Haacke model of the extravascular contribution (for TEs >40s) is supported by both the measured MRI data and the MCS predictions.


The research is funded by awards from the NIH, MRC and the EPSRC.