Isolating bold fMRI correlates of interhemispheric visual processing: A comparison of parametric and exploratory analysis techniques

Blood-oxygen level-dependent (BOLD) functional MRI is currently used to measure the haemodynamic response in gray matter regions of the brain, but activity in these regions is thought to represent only the input signal to a neuron. It is also important to measure the output and the connectivity of neural activation (in white matter), but the BOLD contrast in this respect suffers from very low SNR and activation has proven difficult to detect. This study has measured the BOLD response as subjects attend to a block paradigm visual stimulus that forces activation to cross or not to cross the white matter region known as the corpus callosum. Two approaches to data analysis (parametric mapping and exploratory data analysis) have been employed and we have found a greater BOLD response during 'crossed' rather than 'uncrossed' stimulus in a region that includes the corpus callosum, with a confidence of p = 0.05. Further, it has been shown that exploratory data analysis detects this activity to a higher significance level and its results are consistent with known physiology.