Hand-grasping and finger tapping induced similar functional near-infrared spectroscopy cortical responses

Abstract

Despite promising advantages such as low cost and portability of functional near-infrared spectroscopy (fNIRS), it has yet to be widely implemented outside of basic research. Specifically, fNIRS has yet to be proven as a standalone tool within a clinical setting. The objective of this study was to assess hemodynamic concentration changes at the primary and premotor motor cortices as a result of simple whole-hand grasping and sequential finger-opposition (tapping) tasks. These tasks were repeated over 3 days in a randomized manner. Ten healthy young adults ([Formula: see text]) participated in the study. Quantitatively, no statistically significant differences were discovered between the levels of activation for the two motor tasks ([Formula: see text]). Overall, the signals were consistent across all 3 days. The findings show that both finger-opposition and hand grasping can be used interchangeably in fNIRS for assessment of motor function which would be useful in further advancing techniques for clinical implementation.

Keywords: finger tapping; functional near-infrared spectroscopy; hand grasping; motor cortex; motor stimulation; near-infrared spectroscopy.

Fig. 1

(a) Sources (gray) and detectors (white) layout for both hemispheres based on 10 to 20 system (denoted by color coded borders) to give a total of eight sources and 12 detectors. (b) Illustration of (i) finger-opposition and (ii) grasping tasks trials. A total of eight cycles were used for each trial. This included tasks for right-hand, left-hand, and both for a total of six trials each day.

Fig. 2

Typical hemodynamic responses for three trials of the finger-opposition task—one from each data collection session. All eight stimulus events from each trial are overlaid on a single graph for a representative channel. HbO curves range from red (first event) to yellow (eighth event) and HbD curves range from blue to green. The shaded region indicates the duration of the stimulus.

Fig. 3

Summary of qualitative statistics for motor cortex trials. A total of 48 motor cortex stimulation events were analyzed for each of 10 participants. Each event possessed a total of 36 possible data channels to give a total of 1726 channels for each participant that were analyzed for the presence of an observable hemodynamic response. The number of (a) events and (b) channels in which a response was observed are illustrated. Note that the largest number of events and channels were obtained for the first two participants.

Fig. 4

Summary of quantitative results obtained for task types using the most consistent motor cortex channel in each of the 10 participants. Associated error bars for the HbO (red) and HbD (blue) responses are given in black. Differences in response magnitudes did not reach significance ($p<0.05$) for any participant.

Fig. 5

Summary of quantitative results obtained across the three data collection sessions for the most consistent motor cortex channel in each of the 10 participants. Associated error bars for the HbO (red) and HbD (blue) responses are given in black. Differences in response magnitudes for both HbO and HbD only reached significance ($p<0.05$) for 2 out of 10 participants.

Fig. 6

Distributions of HbD and HbO concentration changes by task ($\mathrm{G}=\text{grasping}$ and $\mathrm{T}=\text{tapping}$) and hand ($\mathrm{L}=\text{left}$, $\mathrm{R}=\text{right}$, and $\mathrm{B}=\text{both}$). For each task $\times$ hand combination, there were 10 subjects $\times$ 8 cycles $\times$ 3 days (240 measurements per boxplot).

Fig. 7

Distributions of HbD (top) and HbO (bottom) concentration changes across days/sessions by task ($\mathrm{G}=\text{grasping}$ and $\mathrm{T}=\text{tapping}$) and hand ($\mathrm{L}=\text{left}$, $\mathrm{R}=\text{right}$, and $\mathrm{B}=\text{both}$). For each $\text{day}\times \text{task}\times \text{hand}$ combination, there were 10 subjects $\times$ 8 cycles (80 measurements per boxplot).