Addressing challenges of high spatial resolution UHF fMRI for group analysis of higher‐order cognitive tasks: An inter‐sensory task directing attention between visual and somatosensory domains

Abstract

Functional MRI at ultra‐high field (UHF, ≥7 T) provides significant increases in BOLD contrast‐to‐noise ratio (CNR) compared with conventional field strength (3 T), 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 normalisation 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 multivariate pattern analysis, allowing UHF to be fully exploited in cognitive neuroscience.

A probabilistic atlas of finger dominance in the primary somatosensory cortex

“…We also observe that individual digit overlap is generally greater in the surface atlas than in the volume atlas ( Table S1 in Supplementary Material). This may be due to at least two factors: 1) surface-based normalisation provides better data registration to a standard template (here fsaverage ), and therefore offers better overlapping group data ( Aquino et al., 2019 ; Fischl et al., 2008 , 1999b ; Lerch et al., 2017 ; Wang et al., 2015 ), which is also reflected in this study from lower blurring metrics for the surface-based digit maps compared to their volumetric counterparts ( Fig. 7 A); 2) the cortical surface offers a finer spatial resolution than the 2 ​mm volumetric brain – a subject averaged inter-vertex distance of 0.8 ​± ​0.1 ​mm over the digit hand area – allowing for finer sampling of the data for investigating overlapping representations.…”

Pragmatic spatial sampling for wearable MEG arrays

“…The clinical question does not require the spatial discrimination between sources at a millimetre scale. In the case of basic neuroscience applications that average results across subjects their spatial discrimination is limited by the functional and anatomical variability that exists between subjects 38 – 41 . Furthermore, in studies which investigate electrophysiological functional connectomes, the spatial discrimination required may be on the scale of 1–2 cm, as a single time course representing an entire atlas-defined parcel is often utilised 42 .…”

Pragmatic spatial sampling for wearable MEG arrays

“…The clinical question does not require the spatial discrimination between sources at a millimetre scale. In the case of basic neuroscience applications that average results across subjects have their spatial discrimination limited by the functional and anatomical variability that exists between subjects (Aquino et al, 2019;Devlin & Poldrack, 2007;Geyer & Turner, 2013;Sabuncu et al, 2010). Furthermore, in studies which investigate electrophysiological functional connectomes, the spatial discrimination required may be on the scale of 1-2 centimetres, as a single time course representing an entire atlas-defined parcel is often utilised (O'Neill et al, 2018).…”