Somatotopic Mapping of the Fingers in the Somatosensory Cortex Using Functional Magnetic Resonance Imaging: A Review of Literature

Abstract

Multiple studies have demonstrated finger somatotopy in humans and other primates using a variety of brain mapping techniques including functional magnetic resonance imaging (fMRI). Here, we review the literature to better understand the reliability of fMRI for mapping the somatosensory cortex. We have chosen to focus on the hand and fingers as these areas have the largest representation and have been the subject of the largest number of somatotopic mapping experiments. Regardless of the methods used, individual finger somatosensory maps were found to be organized across Brodmann areas (BAs) 3b, 1, and 2 in lateral-to-medial and inferior-to-superior fashion moving from the thumb to the pinky. However, some consistent discrepancies are found that depend principally on the method used to stimulate the hand and fingers. Therefore, we suggest that a comparative analysis of different types of stimulation be performed to address the differences described in this review.

Keywords: cortical magnification; digit distance; digit overlap; fMRI; finger somatotopy; neuroimaging; somatosensory cortex.

FIGURE 1

Original work showing lateral view of the primary motor cortex, central sulcus (CS), primary somatosensory cortex, and corresponding Brodmann areas (BAs) (4, 3a, 3b, 1, and 2). Red–Primary motor cortex, Blues–Primary somatosensory cortex. The figure was created using Biorender.com.

FIGURE 2

Original work showing 3 designs used for investigating the finger somatotopy. The timings in the figure are tentative and may vary based on the investigators’ preferences and other factors. This figure was created using Biorender.com.