Nonlinear temporal dynamics of the cerebral blood flow response

The linearity of the cerebral perfusion response relative to stimulus durat ion is an important consideration in the characterization of the relationsh ip between regional cerebral blood flow (CBF), cerebral metabolism, and the blood oxygenation level dependent (BOLD) signal. It is also a critical com ponent in the design and analysis of functional neuroimaging studies. To st udy the linearity of the CBF response to different duration stimuli, the pe rfusion response in primary motor and visual cortices was measured during s timulation using an arterial spin labeling technique with magnetic resonanc e imaging (A IRI) that allows simultaneous measurement of CBF and BOLD chan ges. In each study, the perfusion response was measured for stimuli lasting 2, 6, and 18 sec. The CBF response was found in general to be nonlinearly related to stimulus duration, although the strength of nonlinearity varied between the motor and visual cortices. In contrast, the BOLD response was f ound to be strongly nonlinear in both regions studied, in agreement with pr evious findings. The observed nonlinearities are consistent with a model wi th a nonlinear step from stimulus to neural activity, a linear step from ne ural activity to CBF change, and a nonlinear step from CBF change to BOLD s ignal change. Hum. Brain Mapping 13:1-12, 2001. (C) 2001 Wiley-Liss, Inc.