Faculty Collaboration Database

Modeling of region-specific fMRI BOLD neurovascular response functions in rat brain reveals residual differences that correlate with the differences in regional evoked potentials. Neuroimage 2008 Jun;41(2):525-34

Date

04/15/2008

Pubmed ID

18406628

Pubmed Central ID

PMC2483240

DOI

10.1016/j.neuroimage.2008.02.022

Scopus ID

2-s2.0-44149112299 (requires institutional sign-in at Scopus site)   45 Citations

Abstract

The response of the rat visual system to flashes of blue light has been studied by blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI). The BOLD temporal response is dependent on the number of flashes presented and demonstrates a refractory period that depends on flash frequency. Activated brain regions included the primary and secondary visual cortex, superior colliculus (SC), dorsal lateral geniculate (DLG), and lateral posterior nucleus (LP), which were found to exhibit differing temporal responses. To explain these differences, the BOLD neurovascular response function was modeled. A second-order differential equation was developed and solved numerically to arrive at region-specific response functions. Included in the model are the light input from the diode (duty cycle), a refractory period, a transient response following onset and cessation of stimulus, and a slow adjustment to changes in the average level of the signal. Constants in the differential equation were evaluated for each region by fitting the model to the experimental BOLD response from a single flash, and the equation was then solved for multiple flashes. The simulation mimics the major features of the data; however, remaining differences in the frequency dependence of the response between the cortical and subcortical regions were unexplained. We hypothesized that these discrepancies were due to regional-specific differences in neuronal response to flash frequency. To test this hypothesis, cortical visual evoked potentials (VEPs) were recorded using the same stimulation protocol as the fMRI. Cortical VEPs were more suppressed than subcortical VEPs as flash frequency increased, supporting our hypothesis. This is the first report that regional differences in neuronal activation to the same stimulus lead to differential BOLD activation.

Author List

Pawela CP, Hudetz AG, Ward BD, Schulte ML, Li R, Kao DS, Mauck MC, Cho YR, Neitz J, Hyde JS

Author

Christopher Pawela PhD Associate Professor in the Biomedical Engineering department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Animals
Brain
Brain Mapping
Evoked Potentials, Visual
Magnetic Resonance Imaging
Male
Models, Neurological
Photic Stimulation
Rats
Rats, Sprague-Dawley
Visual Pathways
Visual Perception