Selective BOLD responses to individual finger movement measured with fMRI at 3T

Abstract

Although the gross somatotopic organization of the posterior bank of the precentral gyrus is well established, a fine scale organization of the representations of the digits of the hand has not been fully characterized. Previous neuroimaging studies have failed to find clear evidence for a specificity of digit representations in motor cortex, but rather report a distributed network of control. Reported here are the results of two experiments; in Experiment 1 a sequential finger tapping task produced strong blood oxygen level dependent (BOLD) responses in the contralateral precentral gyrus, but there was a lack of specificity for distinguishing individual representations. A randomly ordered task did accomplish this goal. In the second experiment, a randomly ordered finger-tapping task was used and the findings demonstrated BOLD responses in clusters of voxels specific to movement of a single digit. The region of interest defined for each digit comprised several noncontiguous clusters. A “selectivity index” was developed to quantify the magnitude of the BOLD response to the movement of a specific digit, relative to BOLD response associated with movement of other digits. Strong evidence of BOLD selectivity (albeit not exclusivity) was found in the hemisphere contralateral to the cued digit; however, there was no evidence for an orderly spatial topography. These findings demonstrate that a selectivity of activation is quantifiable, supports a theory of noncontiguous distribution of control, and provides a method for comparing between healthy and impaired populations and investigating changes following training or intervention.

Bundled-Optode Method in Functional Near-Infrared Spectroscopy

“…Additionally, the highly active locations of little finger movements are deeper than those of thumb movements (see Fig 5, Subjects 1 and 4). Our obtained results are quite consistent with the relevant previous studies [35,37,42,44]. Even though the obtained results are preliminary, they will certainly contribute to the development of future brain-computer interface applications using non-invasive technique [61–69].…”

“…Furthermore, our proposed method was applied to detect the HRs of little and thumb finger movements and identified their highly active territories as well. In some recent works, the active locations of individual finger movements were determined by using the center of mass, according to which voxel clusters greater than 4 mm 2 were extracted for each finger [37,42]. In our work, the ROIs were identified and plotted in the 3D space in order to present the highly active territories upon individual finger movements.…”

“…Fig 4 presents the brain regions related to fingers (blue dashed rectangle) established by electrocorticogram [41]. In our experiment, the movements of little and thumb fingers are randomly performed to enhance the activity strength in the corresponding brain regions [37]. For each experiment, 48 channels with 10 trials per channel (i.e., 48 × 10 = 480 total trials) are considered.…”

“…Penfield and Rasmussen [41] illustrated the corresponding positions of brain functions in the cerebral cortex (both in the somatosensory and motor areas) by means of an electrical stimulation method (i.e., electrodes placed directly on the patient’s cortices). Recently, the active regions of finger movements in the motor cortex have been located using the functional magnetic resonance imaging technique [36,37,42,43]. Some demonstrated thumb movement to be located in the lateral site and little finger movement in the medial site [35,42,44].…”

Event‐related fMRI at 7T reveals overlapping cortical representations for adjacent fingertips in S1 of individual subjects

“…Whereas we cannot exclude that somatotopic maps found in the anterior bank of the central sulcus (e.g., subject 4) are due to possible spatial spread of activation from S1 across the sulcus due to registration errors, somatotopic maps on the precentral gyrus (e.g., subject 1) could correspond to somatotopically organized somatotopic responses in the motor cortex (for a more detailed discusion, see Besle et al, in press). At this point, we cannot exclude the explanation that small movements of the fingers in reaction to the vibrotactile stimulation might be responsible for this anterior map [Olman et al, ].…”