Addressing challenges of high spatial resolution, UHF field fMRI for group analysis of higher-order cognitive tasks; an inter-sensory task directing attention between visual and somatosensory domains

Abstract

Abstract:Functional MRI at ultra-high field (UHF, ≥7T) provides significant increases in BOLD contrast-to-noise ratio (CNR) compared with conventional field strength (3T), and has been exploited for reduced field-of-view, high spatial resolution mapping of primary sensory areas. Applying these high spatial resolution methods to investigate whole brain functional responses to higher-order cognitive tasks leads to a number of challenges, in particular how to perform robust group-level statistical analyses.This study addresses these challenges using an inter-sensory cognitive task which modulates top-down attention at graded levels between the visual and somatosensory domains. At the individual level, highly focal functional activation to the task and task difficulty (modulated by attention levels) were detectable due to the high CNR at UHF. However, to assess group level effects, both anatomical and functional variability must be considered during analysis. We demonstrate the importance of surface over volume normalization and the requirement of no spatial smoothing when assessing highly focal activity. Using novel group analysis on anatomically parcellated brain regions, we show that in higher cognitive areas (parietal and dorsal-lateral-prefrontal cortex) fMRI responses to graded attention levels were modulated quadratically, whilst in visual cortex and VIP, responses were modulated linearly. These group fMRI responses were not seen clearly using conventional second-level GLM analyses, illustrating the limitations of a conventional approach when investigating such focal responses in higher cognitive regions which are more anatomically variable. The approaches demonstrated here complement other advanced analysis methods such as multi-variate pattern analysis, allowing UHF to be fully exploited in cognitive neuroscience.

Two spatially distinct posterior alpha sources fulfill different functional roles in attention

“…Our EEG results are corroborated by a separate, high resolution fMRI study conducted by our group at ultra-high field (7T) on a sub-sample of the same subjects (7/10 participants also performed Experiment 1), using the same multi-modal task as in Experiment 1. This study (Aquino et al, 2018) also reveals two fMRI sources modulated by attention: i) quadratic BOLD-response modulations over parietal areas when contrasting attentional effort (100 vs. 60%) and ii) linear modulations over visual areas when contrasting the location of attention (100 vs. 100%). Due to the superior spatial resolution of fMRI, these results strongly suggest that the two alpha band sources measured with EEG are indeed distinct sources which need to be considered separately.…”