Figure 6. Modeling alertness fluctuations in fMRI analysis impacts statistical inference of task-evoked activation.

General linear model analyses of responses to event-related auditory task. For each subject, beta maps were calculated for event-related responses to the auditory stimuli, resulting in group-level t-statistics (voxelwise one-sample t-test) for (A) a model that includes regressors only for the task stimuli; (B) a model that includes task regressors along with the fMRI alertness index as a covariate; and (C) a model that includes task regressors along with the EEG alertness index as a covariate.

Figure 6—figure supplement 1. Comparison between event-related task response and vigilance template.

General linear model analysis of the event-related task responses (A) was accompanied by negative BOLD signal changes in a number of cortical regions, resembling the pattern of correlations with an EEG index of alertness (B).