Cortical activation patterns to spatially presented pure tone stimuli with different intensities measured by functional near-infrared spectroscopy

Abstract

Functional near-infrared spectroscopy (fNIRS) is an emerging technique for the assessment of functional activity of the cerebral cortex. Recently fNIRS was also envisaged as a novel neuroimaging approach for measuring the auditory cortex activity in the field of in auditory diagnostics. This study aimed to investigate differences in brain activity related to spatially presented sounds with different intensities in 10 subjects by means of functional near-infrared spectroscopy (fNIRS). We found pronounced cortical activation patterns in the temporal and frontal regions of both hemispheres. In contrast to these activation patterns, we found deactivation patterns in central and parietal regions of both hemispheres. Furthermore our results showed an influence of spatial presentation and intensity of the presented sounds on brain activity in related regions of interest. These findings are in line with previous fMRI studies which also reported systematic changes of activation in temporal and frontal areas with increasing sound intensity. Although clear evidence for contralaterality effects and hemispheric asymmetries were absent in the group data, these effects were partially visible on the single subject level. Concluding, fNIRS is sensitive enough to capture differences in brain responses during the spatial presentation of sounds with different intensities in several cortical regions. Our results may serve as a valuable contribution for further basic research and the future use of fNIRS in the area of central auditory diagnostics.

Keywords: auditory cortex; auditory diagnostics; functional near-infrared spectroscopy; laterality effects; neuroimaging; spatial sound presentation.

Figure 1

(a) Picture of the fNIRS recording system Imagent™ (ISS Inc., Champaign, USA). (b) Plastic (detector) and (c) metal ferrule (source) based fibers with corresponding probe holder (ISS Inc., EASYCAP GmbH). (d) Schematic illustration of the bilateral 38‐channel array. (e) Array mounted on a custom made cap (EASYCAP GmbH). (f) Projections of the sources (squares), detectors (circles), and fNIRS channel positions (white areas) on the cortical surface. Positions are overlaid on an MNI‐152‐compatible canonical brain (Singh et al., 2005)

Figure 2

Group‐specific (N = 10) multichannel ROI map illustrating the mean [oxy‐Hb] patterns of “MonR” (Red), “Bin” (Black), and “MonL” (Magenta) for “HIGH‐” (solid) and “LOW‐” (dashed) stimulus intensity during stimulus presentation (seconds 0–10) and half of the pause interval (seconds 10–20). Further significant differences in the average concentration changes are indicated by arrows

Figure 3

Topographic distributions (including ROI‐related color‐coded channel positions) of [oxy‐Hb] patterns for a subject (S2) with pronounced patterns for “Bin,” “MonL,” and “MonR” in the “HIGH‐” condition. [oxy‐Hb] patterns during the task at one point in time (between 10 and 12 s, corresponds to the end of the task) are visualized in different plots, but use the same scale. Increases are plotted in red and decreases in blue (no changes are plotted in white). Further calculated [oxy‐Hb] contrasts for “HIGH‐” versus “LOW‐” are shown. Channels with significant differences in the contrast are indicated by a dotted black line. For better comparability to fMRI studies, also the corresponding t maps are shown

Figure 4

ROI‐related hemodynamic responses for subject S2. ROI maps illustrate [oxy‐Hb] patterns of “MonR” (red), “Bin” (black), and “MonL” (magenta) for “HIGH‐” (solid) and “LOW‐” (dashed) stimulus intensity during stimulus presentation (seconds 0–10) and half of the pause interval (seconds 10–20). Calculated [oxy‐Hb] contrasts are shown in Green. Further significant differences and trends in the concentration changes are indicated by arrows and with asterisk (*) or via a superscript t (^t), respectively

Figure 5

Topographic distributions and corresponding t maps (between 10 and 12 s) including ROI‐related color‐coded channel positions. Also ROI‐related [oxy‐Hb] patterns (during stimulus presentation and half of the pause interval) for “HIGH‐MonL” (magenta) and “HIGH‐MonR” (red) for two subjects (S1 and S2). Furthermore, calculated [oxy‐Hb] contrasts (green) for “HIGH‐MonL” versus “HIGH‐MonR” are shown. Significant differences in the ROI‐related concentration changes are indicated by arrows and with asterisk (*). Significant laterality differences between ROIs are indicated via color‐coded arrows