Cerebral hemodynamic and oxygenation changes induced by inner and heard speech: a study combining functional near-infrared spectroscopy and capnography

The aim of this study was to investigate the effects of inner and heard speech on cerebral hemodynamics and oxygenation in the anterior prefrontal cortex (PFC) using functional near-infrared spectroscopy and to test whether potential effects were caused by alterations in the arterial carbon dioxide pressure (PaCO2). Twenty-nine healthy adult volunteers performed six different tasks of inner and heard speech according to a randomized crossover design. During the tasks, we generally found a decrease in PaCO2 (only for inner speech), tissue oxygen saturation (StO2), oxyhemoglobin ([O2Hb]), total hemoglobin ([tHb]) concentration and an increase in deoxyhemoglobin concentration ([HHb]). Furthermore, we found significant relations between changes in [O2Hb], [HHb], [tHb], or StO2 and the participants’ age, the baseline PETCO2, or certain speech tasks. We conclude that changes in breathing during the tasks led to lower PaCO2 (hypocapnia) for inner speech. During heard speech, no significant changes in PaCO2 occurred, but the decreases in StO2, [O2Hb], and [tHb] suggest that changes in PaCO2 were also involved here. Different verse types (hexameter and alliteration) led to different changes in [tHb], implying different brain activations. In conclusion, StO2, [O2Hb], [HHb], and [tHb] are affected by interplay of both PaCO2 reactivity and functional brain activity.

Physiological effects of mechanical pain stimulation at the lower back measured by functional near-infrared spectroscopy and capnography

The aim was to investigate the effect of mechanical pain stimulation at the lower back on hemodynamic and oxygenation changes in the prefrontal cortex (PFC) assessed by functional near-infrared spectroscopy (fNIRS) and on the partial pressure of end-tidal carbon dioxide ( PetCO 2) measured by capnography. 13 healthy subjects underwent three measurements (M) during pain stimulation using pressure pain threshold (PPT) at three locations, i.e., the processus spinosus at the level of L4 (M1) and the lumbar paravertebral muscles at the level of L1 on the left (M2) and the right (M3) side. Results showed that only in the M2 condition the pain stimulation elicited characteristic patterns consisting of (1) a fNIRS-derived decrease in oxy- and total hemoglobin concentration and tissue oxygen saturation, an increase in deoxy-hemoglobin concentration, (2) a decrease in the PetCO 2 response and (3) a decrease in coherence between fNIRS parameters and PetCO 2 responses in the respiratory frequency band (0.2-0.5 Hz). We discuss the comparison between M2 vs. M1 and M3, suggesting that the non-significant findings in the two latter measurements were most likely subject to effects of the different stimulated tissues, the stimulated locations and the stimulation order. We highlight that PetCO 2 is a crucial parameter for proper interpretation of fNIRS data in experimental protocols involving pain stimulation. Together, our data suggest that the combined fNIRS-capnography approach has potential for further development as pain monitoring method, such as for evaluating clinical pain treatment.

A new methodical approach in neuroscience: assessing inter-personal brain coupling using functional near-infrared imaging (fNIRI) hyperscanning

Since the first demonstration of how to simultaneously measure brain activity using functional magnetic resonance imaging (fMRI) on two subjects about 10 years ago, a new paradigm in neuroscience is emerging: measuring brain activity from two or more people simultaneously, termed "hyperscanning". The hyperscanning approach has the potential to reveal inter-personal brain mechanisms underlying interaction-mediated brain-to-brain coupling. These mechanisms are engaged during real social interactions, and cannot be captured using single-subject recordings. In particular, functional near-infrared imaging (fNIRI) hyperscanning is a promising new method, offering a cost-effective, easy to apply and reliable technology to measure inter-personal interactions in a natural context. In this short review we report on fNIRI hyperscanning studies published so far and summarize opportunities and challenges for future studies.

A review on continuous wave functional near-infrared spectroscopy and imaging instrumentation and methodology

This year marks the 20th anniversary of functional near-infrared spectroscopy and imaging (fNIRS/fNIRI). As the vast majority of commercial instruments developed until now are based on continuous wave technology, the aim of this publication is to review the current state of instrumentation and methodology of continuous wave fNIRI. For this purpose we provide an overview of the commercially available instruments and address instrumental aspects such as light sources, detectors and sensor arrangements. Methodological aspects, algorithms to calculate the concentrations of oxy- and deoxyhemoglobin and approaches for data analysis are also reviewed. From the single-location measurements of the early years, instrumentation has progressed to imaging initially in two dimensions (topography) and then three (tomography). The methods of analysis have also changed tremendously, from the simple modified Beer-Lambert law to sophisticated image reconstruction and data analysis methods used today. Due to these advances, fNIRI has become a modality that is widely used in neuroscience research and several manufacturers provide commercial instrumentation. It seems likely that fNIRI will become a clinical tool in the foreseeable future, which will enable diagnosis in single subjects.

End-tidal CO2 pressure: an important parameter for a correct interpretation of changes in cerebral hemodynamics and oxygenation measured with functional near infrared spectrophotometry (fNIRS)

The aim of the present study was to investigate the effects of different speech tasks (recitation of prose (PR), alliteration (AR) and hexameter (HR) verses) and a control task (mental arithmetic (MA) with voicing of the result) on endtidal CO2 (ET-CO2), cerebral hemodynamics; i.e. total hemoglobin (tHb) and tissue oxygen saturation (StO2). tHb and StO2 were measured with a frequency domain near infrared spectrophotometer (ISS Inc., USA) and ET-CO2 with a gas analyzer (Nellcor N1000). Measurements were performed in 24 adult volunteers (11 female, 13 male; age range 22 to 64 years) during task performance in a randomized order on 4 different days to avoid potential carry over effects. Statistical analysis was applied to test differences between baseline, 2 recitation and 5 recovery periods. The two brain hemispheres and 4 tasks were tested separately. Data analysis revealed that during the recitation tasks (PR, AR and HR) StO2 decreased statistically significant (p < 0.05) during PR and AR in the right prefrontal cortex (PFC) and during AR and HR in the left PFC. tHb showed a significant decrease during HR in the right PFC and during PR, AR and HR in the left PFC. During the MA task, StO2 increased significantly. A significant decrease in ET-CO2 was found during all 4 tasks with the smallest decrease during the MA task. In conclusion, we hypothesize that the observed changes in tHb and StO2 are mainly caused by an altered breathing during the tasks that led a lowering of the CO2 content in the blood provoked a cerebral CO2 reaction, i.e. a vasoconstriction of blood vessels due to decreased CO2 pressure and thereby decrease in cerebral blood volume. Therefore, breathing changes should be monitored during brain studies involving speech when using functional near infrared spectroscopy (fNIRS) to ensure a correct interpretation of changes in hemodynamics and oxygenation.

Changes in cerebral hemodynamics and oxygenation induced by different speech tasks – an assessment by combining functional near‐infrared spectroscopy and capnography

Introduction In several studies, we found that during guided rhythmic speech exercises, a decrease in cerebral hemodynamics and oxygenation occurred as the result of a decrease in the partial pressure of carbon dioxide in the arterial blood (PaCO2) during speaking. To further explore the effect of PaCO2 variations on cerebral hemodynamics and oxygenation, the aim of the present study was to investigate the impact of spoken, inner and heard speech tasks on these parameters. Material and Methods Speech tasks included recitation or inner recitation or listening to hexameter, alliteration, prose, or performing mental arithmetic. The following physiological parameters were measured: tissue oxygen saturation (StO2) and absolute concentrations of oxyhemoglobin, deoxyhemoglobin, total hemoglobin (over the left and right anterior prefrontal cortex, using an ISS OxiplexTS frequency domain near-infrared spectrometer) and end-tidal CO2 (PETCO2; using Nellcor N1000 and Datex NORMOCAP capnographs). Statistical analysis was applied to the differences between baseline, 2 tasks, and 3 post-baseline periods. Data of 3 studies with 24, 7 and 29 healthy subjects, respectively, were combined, and linear regression analyses were calculated. Results Linear regression analyses revealed significant relations between changes in oxyhemoglobin, deoxyhemoglobin, total hemoglobin or StO2 and the participants’ age, the baseline PETCO2 or certain speech tasks. While hexameter verses affected changes during the tasks, alliteration verses only affected changes during the recovery phase. Discussion and Conclusion The observed effects in hemodynamics and oxygenation indicate a combination of neurovascular coupling (increased neuronal activity leading to an increase in the cerebral metabolic rate of oxygen resulting in an increase in cerebral flood flow/volume) and CO2 reactivity (increased breathing during speech tasks causing a decrease in PaCO2 leading to vasoconstriction and decrease in cerebral blood flow). The neurovascular coupling characteristics are task-dependent. References Scholkmann F, Gerber U, Wolf M, Wolf U. End-tidal CO2: An important parameter for a correct interpretation in functional brain studies using speech tasks. Neuroimage 2013;66:71-79. Scholkmann F, Wolf M, Wolf U. The effect of inner speech on arterial CO2, cerebral hemodynamics and oxygenation – A functional NIRS study. Adv Exp Med Biol 2013;789:81-87.

Optical properties of rabbit brain in the red and near-infrared: changes observed under in vivo, postmortem, frozen, and formalin-fixated conditions.

The outcome of light-based therapeutic approaches depends on light propagation in biological tissues, which is governed by their optical properties. The objective of this study was to quantify optical properties of brain tissue in vivo and postmortem and assess changes due to tissue handling postmortem. The study was carried out on eight female New Zealand white rabbits. The local fluence rate was measured in the VIS/NIR range in the brain in vivo, just postmortem, and after six weeks’ storage of the head at −20∘C or in 10% formaldehyde solution. Only minimal changes in the effective attenuation coefficient μeff were observed for two methods of sacrifice, exsanguination or injection of KCl. Under all tissue conditions, μeff decreased with increasing wavelengths. After long-term storage for six weeks at −20∘C, μeff decreased, on average, by 15 to 25% at all wavelengths, while it increased by 5 to 15% at all wavelengths after storage in formaldehyde. We demonstrated that μeff was not very sensitive to the method of animal sacrifice, that tissue freezing significantly altered tissue optical properties, and that formalin fixation might affect the tissue’s optical properties.

A New Approach for Automatic Removal of Movement Artifacts in Near-Infrared Spectroscopy Time Series by Means of Acceleration Data

Abstract: Near-infrared spectroscopy (NIRS) enables the non-invasive measurement of changes in hemodynamics and oxygenation in tissue. Changes in light-coupling due to movement of the subject can cause movement artifacts (MAs) in the recorded signals. Several methods have been developed so far that facilitate the detection and reduction of MAs in the data. However, due to fixed parameter values (e.g., global threshold) none of these methods are perfectly suitable for long-term (i.e., hours) recordings or were not time-effective when applied to large datasets. We aimed to overcome these limitations by automation, i.e., data adaptive thresholding specifically designed for long-term measurements, and by introducing a stable long-term signal reconstruction. Our new technique (“acceleration-based movement artifact reduction algorithm”, AMARA) is based on combining two methods: the “movement artifact reduction algorithm” (MARA, Scholkmann et al. Phys. Meas. 2010, 31, 649–662), and the “accelerometer-based motion artifact removal” (ABAMAR, Virtanen et al. J. Biomed. Opt. 2011, 16, 087005). We describe AMARA in detail and report about successful validation of the algorithm using empirical NIRS data, measured over the prefrontal cortex in adolescents during sleep. In addition, we compared the performance of AMARA to that of MARA and ABAMAR based on validation data.

Sentinel node mapping using hysteroscopic injection of indocyanine green and laparoscopic near-infrared fluorescence imaging in endometrial cancer staging.

Herein is presented a technique for minimally invasive sentinel node mapping. The patient had apparently early stage endometrial cancer. Sentinel node mapping was performed using a hysteroscopic injection of indocyanine green followed by laparoscopic sentinel node detection via near-infrared fluorescence. This technique ensures delineation of lymphatic drainage from the tumor area, thus achieving accurate detection of sentinel nodes.