Comparing fMRI responses measured at 3 versus 7 Tesla across human cortex, striatum, and brainstem

Abstract

Significant progress has been made in ultra-high field functional magnetic resonance imaging (fMRI) at 7 Tesla (T). While fMRI at 7 T promises a general increase in sensitivity compared to lower field strengths, the benefits may be most pronounced for specific applications. The current study aimed to evaluate the relative benefit of 7 T over 3 T fMRI for the assessment of task-evoked fMRI responses in different brain regions. We compared the amplitude of task-evoked responses between 3 T and 7 T measured from the same human participants. Participants performed a challenging random dot motion discrimination task with delayed monetary feedback, which animal physiology has linked to several cortical and subcortical structures including extrastriate (dorsal) visual cortical areas, the striatum, and the brainstem including dopaminergic midbrain nuclei. We quantified the evoked fMRI responses in each of these brain regions during the decision interval and the post-feedback interval of the task, and compared them between brain regions and field strengths. The dependence of response amplitudes on field strength during the decision interval differed between cortical, striatal, and brainstem regions, with a generally bigger 7 T vs. 3 T benefit in subcortical (in particular brainstem) structures. We also found stronger differential responses during easy than hard decisions at 7 T for the dopaminergic nuclei, possibly reflecting reward expectation. Our results demonstrate the potential of 7 T fMRI for illuminating the contribution of small brainstem nuclei to the orchestration of cognitive computations in the human brain. HighlightsO_LIWe compared 7 T to 3 T fMRI during perceptual decision-making under uncertainty. C_LIO_LIDifferences between 7 T and 3 T evoked responses and tSNR varied across the brain. C_LIO_LIEvoked responses in dopaminergic brainstem nuclei were bigger at 7 T than 3 T. C_LIO_LIThe responses of dopaminergic nuclei are consistent with reward expectation. C_LIO_LIResults highlight the potential of 7 T fMRI for imaging small brainstem nuclei. C_LI