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.

The neural correlates of texture perception: A systematic review and activation likelihood estimation meta‐analysis of functional magnetic resonance imaging studies

“…Concordant activation peaked in BA 2 of the left SI, which is associated with the processing of tactile and proprioceptive input (Hyvärinen & Poranen, 1978;Padberg et al, 2019;Pons et al, 1985). Furthermore, the tactile stimulation of the fingers is consistently associated with activation of BA 2 (Hlushchuk & Hari, 2006;Holmes et al, 2019;Janko et al, 2022;Puckett et al, 2020), suggesting concordant activation in the SI corresponds to the finger area.…”

“…Concordant activation peaked in BA 2 of the left SI, which is associated with the processing of tactile and proprioceptive input (Hyvärinen & Poranen, 1978 ; Padberg et al., 2019 ; Pons et al., 1985 ). Furthermore, the tactile stimulation of the fingers is consistently associated with activation of BA 2 (Hlushchuk & Hari, 2006 ; Holmes et al., 2019 ; Janko et al., 2022 ; Puckett et al., 2020 ), suggesting concordant activation in the SI corresponds to the finger area. Active touch engages sensorimotor circuits in the PPC, including the SMG located in the IPL, and activation in these regions has been associated with sensorimotor integration (Arikan et al., 2021 ; Batista et al., 1999 ; Battaglia‐Mayer et al., 2000 ; Buneo et al., 2002 ; Buneo & Andersen, 2006 ; Ferraina et al., 1997 ; Hyvärinen, 1982 ; Lamp et al., 2019 ; Mountcastle et al., 1975 ; Naito et al., 2005 ; Snyder et al., 1997 ).…”

Effects of sensorimotor training on memory and brain plasticity in persons with amnestic mild cognitive impairment

“…78 Fingertip activations were analysed within the anatomically defined and joined Brodmann areas 1 and 2 (BA1&2) in the left primary somatosensory cortex (S1) cortex, separately for each participant (using FreeSurfer 6.0), 72,84,85 as target regions for the somatotopic representation of the hand. [86][87][88] Results were controlled for family-wise Type 1 error, 89 and represented in standard Montreal Neurological Institute (MNI) 305 space. 77 For paired associates learning, delayed matching to sample, pattern recognition memory and spatial recognition memory three repeated measures were considered (pre-, post-straining and follow-up), thus delta is Δ is the value at FU minus value at T1; for all other measures Δ is the value at T2 minus value at T1 c Group differences between ET and CT group pre-training were tested using t-test 95 ; CI, confidence interval; bold significant p-value above alpha inflation threshold (computed using the false discovery rate); bold* significant p-value below alpha inflation threshold b For paired associates learning, delayed matching to sample, pattern recognition memory and spatial recognition memory (i.e.…”

“…71,72,84,85 These regions are relevant for the somatotopic representation of the hand using pressure stimuli. [86][87][88] General linear modelling applied to individual data provided the estimate of the cortical location of each digit in BA1&2 (after the correction for multiple comparisons using a Monte-Carlo simulation), 89 represented by the centre of mass of the respective activation cluster (see Figure 3). 87 The relative distance between each pair of digits was determined along the cortical surface, 90,91 and the sum of relative distances of the thumb to all other digits, here called finger distance, was taken as outcome to represent somatotopic effects of the two trainings (see Supplement S11).…”

Hypo-connectivity of the primary somatosensory cortex in Parkinson’s disease: a resting-state functional MRI study

“…Seed-based correlation (SBC) analysis was employed to calculate the functional connectivity. Six paired somatosensory regions of interest (ROIs) ( Figure 1A ) were chosen based on block-design fMRI studies ( 27–30 ) and a review article ( 31 ). The MNI coordinates of the seeds were as follows: leg (representation, , ±8,−38,68 in MNI coordinates), back ( : ±18, −44, 64), chest ( : ±18, −36, 64), hand ( : ±28, −30, 50), finger ( : ±50, −16, 50), and face ( : ±60, −14, 40).…”