Abstract
The majority of fMRI studies investigating somatotopic body representations in the human cortex have used either block or phase-encoding stimulation designs. Event-related (ER) designs allow for more natural and flexible stimulation sequences, while enabling the independent estimation of responses to different body parts in the same cortical location. Here we compared an efficiency-optimized fast ER design (2s inter stimulus interval, ISI) to a slow ER design (8s ISI) for mapping fingertip voxelwise tuning properties in the sensorimotor cortex of 6 participants at 7 Tesla. The fast ER design resulted in similar, but more robust, estimates compared to the slow ER design. Concatenating the fast and slow ER data, we demonstrate in each individual brain the existence of two separate somatotopically-organized representations of the fingertips, one in S1 on the post-central gyrus and the other at the border of the motor and pre-motor cortices on the pre-central gyrus. In both post-central and pre-central representations, fingertip tuning width increases progressively, from narrowly-tuned Brodmann areas 3b and 4a respectively, towards parietal and frontal regions responding equally to all fingertips.
Key Points
Fingertip population receptive fields (pRFs) in sensorimotor cortex can be efficiently mapped using a fast event-related design (ISI = 2 s) at 7T.
Somatotopically-organized tactile maps were found not only in primary somatosensory cortex but also at the border between motor and premotor cortex.
pRF size, reflecting the degree of integration between fingertips, increases from primary Brodmann areas 3b and 4a towards higher-order parietal and frontal regions.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Data Availability Statement: The data that support the findings of this study are openly available in OpenNeuro at https://doi.org/10.18112/openneuro.ds003990.v1.0.2, reference number ds003990.
Funding Statement: This work was supported by a BBSRC grant (BB/G008906/1) and by the University Research Board of the American University of Beirut. The funding sources had no involvement in the study design, collection, analysis and interpretation of data, writing of the manuscript or decision to submit the article for publication.
Conflict of Interest Disclosure: The authors declare that they have no conflicts of interest.
Ethics Approval Statement: Approval for the study was obtained from the University of Nottingham Ethics Committee.
Patient Consent Statement: Informed consent was obtained from all subjects involved in the study.
Added supplementary figures; added link to dataset on openneuro.org