CHARACTERIZING THE RELATIONSHIP BETWEEN BOLD CONTRAST AND REGIONAL CEREBRAL BLOOD-FLOW MEASUREMENTS BY VARYING THE STIMULUS-PRESENTATION RATE

This paper investigates the relationship between the blood oxygenation level dependent (BOLD) contrast effect and regional cerebral blood fl ow using the techniques of functional MRI (fMRI) and positron emission tomography (PET). A passive listening paradigm with parametric variat ion in word presentation rate was used to investigate the rate depende ncy of both BOLD contrast fMRI and (H2O)-O-15 PET in primary auditory cortex. We attempted to equate the stimulus presentation acoustic envi ronments by using prerecorded echoplanar imaging sounds during the PET paradigm. We show that there is a linear relationship between word pr esentation rate and cerebral blood flow in primary auditory cortex, wh ereas the relationship between BOLD contrast and stimulus presentation rate is highly nonlinear, showing a saturable effect. Two possible ex planations for our results are discussed: a nonlinearity in the relati onship between BOLD contrast and deoxyhemoglobin concentration or a no nlinear rate dependency of the physiological mechanisms causing change s in deoxyhemoglobin concentration. (C) 1997 Academic Press.