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fNIRS for future use in auditory diagnostics

  • Günther Bauernfeind EMAIL logo , Sabine Haumann and Thomas Lenarz
Published/Copyright: September 30, 2016
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Current Directions in Biomedical Engineering
From the journal Current Directions in Biomedical Engineering Volume 2 Issue 1

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 (AC) activity in cochlear implant (CI) users. In the present study we report on initial measurements of AC activation due to spatial sound presentation with a first target to generate data for comparison with CI user and the future use in auditory diagnostics.

Keywords: auditory cortex (AC); auditory diagnostics; functional near-infrared spectroscopy (fNIRS); neuroimaging

1 Introduction

In cases of severe hearing loss or deafness the hearing ability can be restored in parts, for example, by using a cochlear implant (CI; for a review see [1], [2]). Therefore, the CI mimics the function of the inner ear. The challenge is to objectively measure and verify whether the stimulation of the CI reaches the auditory cortex (AC) and induces the desired neural activity. This is primarily caused by the fact that the use of traditional neuroimaging modalities (i.e. EEG, MEG, fMRI) is limited due to electrical artifacts and ferromagnetic components of the CI. Therefore other, also repeatedly and frequently usable methods, have to be investigated. Functional near-infrared spectroscopy (fNIRS; for a review see [3]), which can be used stand alone or in combination with other modalities (multimodal recording), seems therefore a promising approach. fNIRS is an non-invasive optical technique for the assessment of cerebral oxygenation (changes of oxygenated (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) concentration) which strongly correlates with cortical (neuronal) activity [4], [5]. Recently fNIRS was proposed as a novel neuroimaging approach in CI recipients (for a first review see [6]). However, the existing literature is limited and mainly focusing on higher-level auditory processing (for an overview see [7]) or speech perception [6]. Therefore further, basic research on lower-level auditory perception [7] is necessary to investigate the future use of fNIRS on CI users and the application in the field of auditory diagnostics.

In the present work we report on first pilot measurements of cortical activation patterns in normal-hearing adults with the target to generate normative data of AC activation.

2 Methods

2.1 Participants and experimental paradigm

The initial investigations were carried out on a group of four normal hearing subjects (three male, one female; aged 25.0 ± 4.9 years). The subjects performed a passive listening task consisting of six different auditory stimuli (1 kHz sine wave, amplitude modulated by 4 and 10 Hz sine waves; modified from [7]). Stimuli were presented spatially (binaural “Bin” & loudness matched [8] monaural left “MonL” and right “MonR”) with two different intensities (“HIGH-”: 70dB and “LOW-”: 40 dB sound pressure level, SPL). For each subject 2 (Intensity: “HIGH-”, “LOW-”) × 3 (Spatial: “Bin”, “MonL”, “MonR”) × 10 trials plus 10 additional trials without stimulation (“Silence”) were recorded in a random order (total 70 trials). Each trial consisted of an auditory stimuli presented for 10 s (“Silence”: no stimulus within this time) followed by a fixed pause of 20 s taking into account the time needed for the hemodynamic response to return back to baseline [4]. In addition an inter-trial interval randomly varying in duration from 0 to 5 s was included to reduce temporal adjustment of the subjects to the paradigm. During the experiment the subjects lay comfortably in a semi-supine position (about 30 degrees elevation of head, Figure 1). No attempt was made to control the subjects thought content. Subjects were instructed to avoid head movements and were told to restrict movements like swallowing to the pause and inter-trial interval.

Figure 1 (A) Schematic illustration of the bilateral 38-channel array. (B) Array mounted on cap. (C) Projections of the source (red), detector (blue) and fNIRS channel positions (white) on the cortical surface. Positions are overlaid on an MNI-152 compatible canonical brain [9]. (D) Array mounted on a subject’s head.
Figure 1

(A) Schematic illustration of the bilateral 38-channel array. (B) Array mounted on cap. (C) Projections of the source (red), detector (blue) and fNIRS channel positions (white) on the cortical surface. Positions are overlaid on an MNI-152 compatible canonical brain [9]. (D) Array mounted on a subject’s head.

2.2 Data acquisition and processing

For fNIRS recordings a multichannel system (Imagent™, ISS Inc., Champaign, USA) was used. The system consists of 12 detectors and 16 emitters (38 channels, details see Figure 1) and enables to measure the changes of (de)oxy-Hb in the unit of mm*mm. To allow a probabilistic reference to cortical areas underlying the measurement channels, a procedure was used which projects topographical data based on skull landmarks into a 3D reference frame (MNI-space, Montreal Neurological Institute) optimized for fNIRS analysis [9]. For each fNIRS channel position (Figure 1C), a set of MNI coordinates (x, y and z) was calculated.

For data analysis the following steps were performed: After a visual inspection of the raw data, trials containing artifacts were excluded. After high- (0.01 Hz) and low- (0.09 Hz) pass filtering global influences [10] were reduced by a spatial filtering approach (details see [11]). Mean task-related changes referred to a 5 s baseline interval prior to the task were calculated. To generate topographic distributions (de)oxy-Hb values (mean over 10–12 s; end of task) were interpolated and plotted corresponding to their spatial positions.

3 Results

Subsequent first results of the measured cortical patterns (only oxy-Hb) for binaural stimulation with two different intensities (“HIGH-Bin” & “LOW-Bin”) are presented. In general, all subjects exhibited pronounced and spatially localized pattern, either for one or for both (40 dB in 3, 70 dB in four subjects) stimulus intensities. Oxy-Hb increases could be found in both hemispheres and were mainly related to channels overlaying Brodmann areas (BA) 21 & 22, 44 & 45 (Broca’s area) and 47. Comparing both intensities, significant differences (in at least three channels) in oxy-Hb responses were found in three subjects. As an example Figure 2 depicts the recorded patterns of a subject with highly pronounced contrast.

Figure 2 (A) Topographical oxy-Hb maps for “High-Bin” and “Low-Bin” stimulation. (B) Comparison of the time courses of the oxy-Hb signals at channel positions 6 (BA 45, LH) and 24 (BA 45, RH).
Figure 2

(A) Topographical oxy-Hb maps for “High-Bin” and “Low-Bin” stimulation. (B) Comparison of the time courses of the oxy-Hb signals at channel positions 6 (BA 45, LH) and 24 (BA 45, RH).

Comparing both stimulus intensities (“HIGH-Bin”–“LOW-Bin” contrast, Figure 3) this subject displays significant (p < 0.05) bilateral, but slightly more left lateralized (6 vs. 4 channels), oxy-Hb contrast increases in channels overlaying BA 21 & 22, 44 & 45 and 47. In parallel significant decreases in the oxy-Hb contrast are localized to channels overlaying BA 1 & 2 and 40.

Figure 3 (A) Calculated oxy-Hb contrast for “HIGH-Bin”-“LOW-Bin”. (B) Projections of subject specific channel positions including significant (p < 0.05, color-coded) oxy-Hb contrasts.
Figure 3

(A) Calculated oxy-Hb contrast for “HIGH-Bin”-“LOW-Bin”. (B) Projections of subject specific channel positions including significant (p < 0.05, color-coded) oxy-Hb contrasts.

4 Discussion and conclusion

Already with the pilot investigations it was possible to achieve promising initial results. We found pronounced activation patterns in cortical areas which are related with auditory processing. Based on these results, detailed measurements on intensity related AC activation patterns are in work. Also investigations on the comparison of binaural and monaural stimulus presentation are in progress. Future investigations also include the measurement of brain activity patterns in hearing impaired subjects and patients with cochlear implants and the comparison with normal hearing subjects.

Author’s Statement

Research funding: This work is supported by the Cluster of Excellence “Hearing4all” (EXC 1077/1). Conflict of interest: Authors state no conflict of interest. Material and Methods: Informed consent: Informed consent has been obtained from all individuals included in this study. Ethical approval: The research related to human use complies with all the relevant national regulations, institutional policies and was performed in accordance the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board or equivalent committee.

References

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Published Online: 2016-9-30
Published in Print: 2016-9-1

©2016 Günther Bauernfeind et al., licensee De Gruyter.

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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https://doi.org/10.1515/cdbme-2016-0051
Keywords for this article
auditory cortex (AC); auditory diagnostics; functional near-infrared spectroscopy (fNIRS); neuroimaging
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BY-NC-ND 4.0

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  116. Development of a desiccant based dielectric for monitoring humidity conditions in miniaturized hermetic implantable packages
  117. Development of an artifact-free aneurysm clip
  118. Enhancing the regeneration of bone defects by alkalizing the peri-implant zone – an in vitro approach
  119. Rapid prototyping of replica knee implants for in vitro testing
  120. Protecting ultra- and hyperhydrophilic implant surfaces in dry state from loss of wettability
  121. Advanced wettability analysis of implant surfaces
  122. Patient-specific hip prostheses designed by surgeons
  123. Plasma treatment on novel carbon fiber reinforced PEEK cages to enhance bioactivity
  124. Wear of a total intervertebral disc prosthesis
  125. Digital health and digital biomarkers – enabling value chains on health data
  126. Usability in the lifecycle of medical software development
  127. Influence of different test gases in a non-destructive 100% quality control system for medical devices
  128. Device development guided by user satisfaction survey on auricular vagus nerve stimulation
  129. Empirical assessment of the time course of innovation in biomedical engineering: first results of a comparative approach
  130. Effect of left atrial hypertrophy on P-wave morphology in a computational model
  131. Simulation of intracardiac electrograms around acute ablation lesions
  132. Parametrization of activation based cardiac electrophysiology models using bidomain model simulations
  133. Assessment of nasal resistance using computational fluid dynamics
  134. Resistance in a non-linear autoregressive model of pulmonary mechanics
  135. Inspiratory and expiratory elastance in a non-linear autoregressive model of pulmonary mechanics
  136. Determination of regional lung function in cystic fibrosis using electrical impedance tomography
  137. Development of parietal bone surrogates for parietal graft lift training
  138. Numerical simulation of mechanically stimulated bone remodelling
  139. Conversion of engineering stresses to Cauchy stresses in tensile and compression tests of thermoplastic polymers
  140. Numerical examinations of simplified spondylodesis models concerning energy absorption in magnetic resonance imaging
  141. Principle study on the signal connection at transabdominal fetal pulse oximetry
  142. Influence of Siluron® insertion on model drug distribution in the simulated vitreous body
  143. Evaluating different approaches to identify a three parameter gas exchange model
  144. Effects of fibrosis on the extracellular potential based on 3D reconstructions from histological sections of heart tissue
  145. From imaging to hemodynamics – how reconstruction kernels influence the blood flow predictions in intracranial aneurysms
  146. Flow optimised design of a novel point-of-care diagnostic device for the detection of disease specific biomarkers
  147. Improved FPGA controlled artificial vascular system for plethysmographic measurements
  148. Minimally spaced electrode positions for multi-functional chest sensors: ECG and respiratory signal estimation
  149. Automated detection of alveolar arches for nasoalveolar molding in cleft lip and palate treatment
  150. Control scheme selection in human-machine- interfaces by analysis of activity signals
  151. Event-based sampling for reducing communication load in realtime human motion analysis by wireless inertial sensor networks
  152. Automatic pairing of inertial sensors to lower limb segments – a plug-and-play approach
  153. Contactless respiratory monitoring system for magnetic resonance imaging applications using a laser range sensor
  154. Interactive monitoring system for visual respiratory biofeedback
  155. Development of a low-cost senor based aid for visually impaired people
  156. Patient assistive system for the shoulder joint
  157. A passive beating heart setup for interventional cardiology training
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