S timulus-modulated a pproach to s teady- s tate: A new paradigm for event-related fMRI

Functional MRI (fMRI) studies discard the initial volumes acquired during the approach of the magnetization to its steady-state value. Here, we leverage the substantially higher temporal signal-to-noise ratio (tSNR) of these initial volumes to increase the sensitivity of event-related fMRI experiments. To do this, we introduce Acquisition Free Periods (AFPs) that allow for the full recovery of the magnetization, followed by equal-length task or baseline acquisition blocks (AB) of fMRI volumes. An appropriately placed stimulus in the AFP produces a Blood Oxygenation-Level-Dependent (BOLD) response that peaks during the initial high tSNR phase of the AB, yielding an ∼50% reduction in the number of trials (relative to conventional fMRI) needed to achieve a given statistical threshold. The AFP allows flexibility for the presentation of auditory stimuli, uncontaminated recording of electrophysiological activity, physiological gating, as well as the ability to average aperiodic fMRI data using stimulus or response-locked signal acquisition.