Abstract
The selection of the appropriate hemodynamic response function (HRF) for signal modeling in functional magnetic resonance imaging (fMRI) is important. Although the use of the boxcar-shaped hemodynamic response function (BHRF) and canonical hemodynamic response (CHRF) has gained increasing popularity in rodent fMRI studies, whether the selected HRF affects the results of rodent fMRI has not been fully elucidated. Here we investigated the signal change and t-statistic sensitivities of BHRF, CHRF, and impulse response function (IRF). The effect of HRF selection on different tasks was analyzed by using data collected from two groups of rats receiving either 3 mA whisker pad or 3 mA forepaw electrical stimulations (n = 10 for each group). Under whisker pad stimulation with large blood-oxygen-level dependent (BOLD) signal change (4.31 ± 0.42%), BHRF significantly underestimated signal changes (P < 0.001) and t-statistics (P < 0.001) compared with CHRF or IRF. CHRF and IRF did not provide significantly different t-statistics (P > 0.05). Under forepaw stimulation with small BOLD signal change (1.71 ± 0.34%), different HRFs provided insignificantly different t-statistics (P > 0.05). Therefore, the selected HRF can influence data analysis in rodent fMRI experiments with large BOLD responses but not in those with small BOLD responses.
Highlights
Functional magnetic resonance imaging was originally introduced in 1990
Robust functional magnetic resonance imaging (fMRI) activations in the contralateral side of the brain were detected in all rats under whisker pad or forepaw stimulation. fMRI signal time curves from the S1 of two representative rats under whisker pad stimulation or forepaw stimulation are shown in Figures 1A,B, respectively
We found that the choice of the hemodynamic response function (HRF) is crucial in the computation of activations in rat fMRI studies, especially in studies involving stimulations with large blood-oxygen-level dependent (BOLD) signal changes, such as whisker pad stimulation
Summary
Functional magnetic resonance imaging (fMRI) was originally introduced in 1990. It has been modified to enable investigations on different functional aspects of the brain. The most popular fMRI technique is blood-oxygen-level dependent (BOLD) contrast, which relies on local deoxyhemoglobin changes (Ogawa et al, 1990, 1992). Owing to its advantages of absent radiation burden and non-invasiveness, BOLD fMRI has become a pivotal method for understanding brain function and physiological conditions (Tsurugizawa et al, 2010; Rana et al, 2013; Wu et al, 2014; Nasrallah et al, 2015; Golestani et al, 2016). The applications of BOLD fMRI in animals such as rats, have recently received increased attention. The majority of rodent fMRI studies have been conducted by using electric stimulation to induce somatosensory stimulation and to estimate activations in the primary sensory cortex
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