A probabilistic atlas of finger dominance in the primary somatosensory cortex

Abstract

With the advent of ultra-high field (7T), high spatial resolution functional MRI (fMRI) has allowed the differentiation of the cortical representations of each of the digits at an individual-subject level in human primary somatosensory cortex (S1). Here we generate a probabilistic atlas of the contralateral SI representations of the digits of both the left and right hand in a group of 22 right-handed individuals. The atlas is generated in both volume and surface standardised spaces from somatotopic maps obtained by delivering vibrotactile stimulation to each distal phalangeal digit using a travelling wave paradigm. Metrics quantify the likelihood of a given position being assigned to a digit (full probability map) and the most probable digit for a given spatial location (maximum probability map). The atlas is validated using a leave-one-out cross validation procedure. Anatomical variance across the somatotopic map is also assessed to investigate whether the functional variability across subjects is coupled to structural differences. This probabilistic atlas quantifies the variability in digit representations in healthy subjects, finding some quantifiable separability between digits 2, 3 and 4, a complex overlapping relationship between digits 1 and 2, and little agreement of digit 5 across subjects. The atlas and constituent subject maps are available online for use as a reference in future neuroimaging studies.

Somatotopic Arrangement of the Human Primary Somatosensory Cortex Derived From Functional Magnetic Resonance Imaging

“…Specifically, transposed representations or evidence of multiple representation of a single body part on the cortex were sought. Several fMRI studies have been published that have mapped somatosensory cortex of humans and that tend to agree with the prevailing homunculus model (Servos et al, 1999 ; Backes et al, 2000 ; Sanchez-Panchuelo et al, 2010 ; Besle et al, 2013 ; Wardman et al, 2014 ; Schweisfurth et al, 2018 ; Da Rocha Amaral et al, 2019 ; Luijten et al, 2020 ; O'Neill et al, 2020 ). Few fMRI studies seem to have addressed whole body sensory somatotopy, so this work helps to fill that knowledge gap (Sanchez-Panchuelo et al, 2018 ; Saadon-Grosman et al, 2020 ).…”

Evoking highly focal percepts in the fingertips through targeted stimulation of sulcal regions of the brain for sensory restoration

“…Sulcal stimulation in human S1 evoking fingertip percepts more often than gyral stimulation is in agreement with the imaging studies that have predominantly localized fingertip representation to the posterior wall of the central sulcus (area 3b) and occasionally at the crown of the postcentral gyrus (18–21, 28). The representation of fingertips might still extend into the posterior regions of the postcentral gyrus as shown by some imaging studies (25, 26, 30) and recent stimulation studies (13, 27). However, in our study, we had only two SEEG electrodes located deep in the postcentral sulcus in one participant that evoked percepts in the hand.…”

“…However, other studies show representation of distal phalanges along the posterior wall of the central sulcus but closer to the 3b/1 border (28, 29). Thus, it is still unclear how the representation of fingertips is distributed across the central sulcus and postcentral gyrus (30).…”

Multi-Scale Understanding of NMDA Receptor Function in Schizophrenia

“…The most important limitation of studies of psychiatric disorders are the ethical challenges associated with studying the human brain in vivo. Even when the most advanced ultra-high-field magnetic resonance imaging methods are used [35], it is extremely difficult to visualize circuit pathophysiology at synaptic resolution. Postmortem brain research is a useful strategy, but samples from the postmortem brain are subject to various artifacts related to medication, the cause of death, agonal state, and the length of the interval from death to post-mortem examination [36].…”