This research was supported by the following funding sources: A NARSAD Young Investigator Award Grant from the Brain and Behavior Research Foundation (Grant #29736) (SSA), a Global Grand Challenges Grant from the Bill and Melinda Gates Foundation (Grant #INV-005792) (RNA) and a Discovery Fund Grant from the Department of Psychology at Yale University (RNA). The authors also wish to acknowledge Richard Watts (Yale Brain Imaging Center) for his support during data collection and Adam Eggebrecht, Ari Segel and Emma Speh (Washington University in St Louis) for their assistance in data analysis.

Publication fees for this article are sponsored by NIRx. The authors have nothing else to disclose.

This protocol for simultaneous data collection of fMRI&#160;and fNIRS signals uses a whole-head fNIRS optode array and short-distance channels for measuring and regressing out the systemic non-cortical physiological signals. Critical steps in this protocol include modification and development of the fNIRS equipment for collecting fNIRS signals in the MRI environment. To the best of our knowledge, there is no turn-key commercial system that is fully optimized for capturing simultaneous fMRI&#160;and fNIRS measurements usi...

Cognitive function has been studied in the adult human brain via functional magnetic resonance imaging (fMRI) for nearly three decades. Although fMRI provides high spatial resolution and both functional and structural images, it is often not practical for studies conducted in naturalistic contexts or for use with infants and clinical populations. These constraints substantially limit our understanding of brain function. An alternative to fMRI is the use of portable methodologies that are more cost-effective and robust to motion, such as functional near-infrared spectroscopy (fNIRS)1,2,3. fNIRS has been used with infants and young children to assess brain function across a range of cognitive domains, such as language development, processing of socially relevant information and object processing 4,5,6. fNIRS is also a neuroimaging modality especially suitable for testing clinical populations due to its potential for repeated testing and monitoring across ages7,8,9. Despite its wide applicability, there are no studies quantitatively comparing fMRI and fNIRS signals collected simultaneously from the same subjects with whole-head coverage. This comparison is necessary to comprehensively validate area-level activations and functional connectivity between regions of interest (ROIs) against the fMRI gold standard. Furthermore, establishing this inter-modality correspondence has the potential to enhance the interpretation of fNIRS when it is the only collected signal across both typical and atypical development.
Both fMRI and fNIRS signals detect changes in cerebral blood oxygenation (CBO) during functional brain activation10,11. fMRI relies on changes in electromagnetic fields and provides a high spatial resolution of CBO changes12. fNIRS, in contrast, measures absorption levels of near-infrared light using a series of light-emitting and light-detecting optodes2. Since fNIRS measures changes in absorption at different wavelengths, it can assess concentration changes in both oxy- and deoxyhemoglobin. Prior studies using simultaneous recordings of fMRI and fNIRS signals with a small number of optodes have shown that the two signals have high spatial and temporal correspondence10. There are strong correlations between blood-oxygen-level-dependent (BOLD) fMRI and optical measures11,13, with deoxyhemoglobin showing the highest correlation with the BOLD response, as reported by prior work comparing the temporal dynamics of the fNIRS and fMRI hemodynamic response functions (HRFs)14. These early studies implemented motor response paradigms (i.e., finger tapping) and used a limited number of optodes covering primary motor and premotor cortex areas. In the last decade, studies have expanded the focus to include a larger battery of cognitive tasks and resting-state sessions, although still using a limited number of optodes covering specific ROIs. These studies have shown that variability in fNIRS/fMRI correlations is dependent on the optode&#39;s distance from the scalp and the brain15. Furthermore, fNIRS can provide resting-state functional connectivity measures comparable to fMRI16,17.
The current protocol builds on prior work and addresses key limitations by i) providing whole-head fNIRS coverage, ii) including short-distance measurements for regression of non-cortical physiological signals, iii) implementing two different methods for optode-to-scalp co-registration of fNIRS measurements and iv) enabling assessment of the test-retest reliability of the signal across two independent sessions. This protocol for simultaneous data collection of fMRI&#160;and fNIRS signals was initially developed for testing young adults. However, one of the goals of the study was to create an experimental setup for collecting simultaneous fMRI/fNIRS signals that can be subsequently adapted for testing developmental populations. Therefore, the current protocol can also be used as a starting point for developing a protocol to test young children. In addition to using whole-head fNIRS coverage, the protocol also aims to incorporate recent advances in the field of fNIRS hardware, such as the inclusion of short-distance channels to measure the systemic physiological signal (i.e., vascular changes arising from noncortical sources, such as blood pressure, respiratory and cardiac signals)18,19 ;and the use of a 3D structure sensor for optode-to-scalp co-registration20. Although the focus of the present protocol is on the results of a visual flashing checkerboard task, the entire experiment includes two sessions with a mix of traditional block-task designs, resting-state sessions, and naturalistic movie-viewing paradigms.
The protocol describes the steps needed to adapt the fNIRS equipment for use in the MRI environment, including cap design, temporal alignment via trigger synchronization and phantom tests required before the start of data collection. As noted, the focus here is on the results of the flashing checkerboard task, but the overall procedure is not task-specific and can be appropriate for any number of experimental paradigms. The protocol further outlines the steps required during data collection, which include fNIRS cap placement and signal calibration, participant&#160;and experimental equipment setup, as well as post-experiment clean up and data storage. The protocol ends by providing an overview of the analytic pipelines specific for preprocessing fNIRS and fMRI data.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>280 low-profile MRI-compatible grommets for NIRs caps</td>
			<td>NIRx</td>
			<td>GRM-LOP</td>
			<td></td>
		</tr>
		<tr>
			<td>4 128-position NIRS caps with 128x unpopulated slits in 10-5 layout</td>
			<td>NIRx</td>
			<td>CP-128-128S</td>
			<td>Sizes: 52, 54, 56, 60</td>
		</tr>
		<tr>
			<td>8 bundles of 4x detector fibers with low-profile tip; MRI-, MEG-, and TMS-compatible.&#160;</td>
			<td>NIRx</td>
			<td>DET-FBO- LOW</td>
			<td>10 m long</td>
		</tr>
		<tr>
			<td>8 bundles of 4x laser source fibers with MRI-compatible low-profile tip</td>
			<td>NIRx</td>
			<td>SRC-FBO- LAS-LOW</td>
			<td>10 m long</td>
		</tr>
		<tr>
			<td>Bundle set of 8 short-channel detectors with specialized ring grommets that fit to low-profile grommets</td>
			<td>NIRx</td>
			<td>DET-SHRT-SET</td>
			<td>Splits a single detector into 8 short channels that may be placed anywhere on a single NIRS cap</td>
		</tr>
		<tr>
			<td>Magnetom 3T PRISMA</td>
			<td>Siemens</td>
			<td>N/A</td>
			<td>128 channel capacity, 64/32/20 channel head coils, 80 mT/m max gradient amplitude, 200 T/m/s slew rate, full neuro sequences</td>
		</tr>
		<tr>
			<td>NIRScout XP Core System Unit</td>
			<td>NIRx</td>
			<td>NSXP- CHS</td>
			<td>Up to 64x Laser-2 (or 32x laser-4) illuminators or 64 LED-2 illuminators; up to 32x detectors; capable of tandem (multi-system) and hyperscanning (multi-subject) measurements; compatible with EEG, tDCS, eye-tracking, and other modalities; modules available for fMRI, TMS, MEG compatibility</td>
		</tr>
		<tr>
			<td>NIRStar software</td>
			<td>NIRx</td>
			<td>N/A</td>
			<td>Version 15.3</td>
		</tr>
		<tr>
			<td>NIRx parallel port replicator</td>
			<td>NIRx</td>
			<td>ACC-LPT-REP</td>
			<td>The parallel prot replicator&#160; comes with three components: parallel port replicator box, USB power cable and BNC adapter</td>
		</tr>
		<tr>
			<td>Physiological pulse unit</td>
			<td>Siemens</td>
			<td>PPU098</td>
			<td>Optical plethysmography allowing the acquisiton of the cardiac rhythm.</td>
		</tr>
		<tr>
			<td>Respiratory unit</td>
			<td>Siemens</td>
			<td>PERU098&#160;</td>
			<td>Unit intended for the acquisition of the respiratory amplitude (by means of a pneumatic system and a restraint belt).</td>
		</tr>
		<tr>
			<td>Structure Sensor Mark II</td>
			<td>Occipital</td>
			<td>101866 (SN)</td>
			<td>3D structure sensor for optode digitization.</td>
		</tr>
	</tbody>
</table>

simultaneous data collection of fmri and fnirs measurements using a whole-head optode array and short-distance channels

Functional near-infrared spectroscopy (fNIRS) is a portable neuroimaging methodology, more robust to motion and more cost-effective than functional magnetic resonance imaging (fMRI), which makes it highly suitable for conducting naturalistic studies of brain function and for use with developmental and clinical populations. Both fNIRS and fMRI methodologies detect changes in cerebral blood oxygenation during functional brain activation, and prior studies have shown high spatial and temporal correspondence between the two signals. There is, however, no quantitative comparison of the two signals collected simultaneously from the same subjects with whole-head fNIRS coverage. This comparison is necessary to comprehensively validate area-level activations and functional connectivity against the fMRI gold standard, which in turn has the potential to facilitate comparisons of the two signals across the lifespan. We address this gap by describing a protocol for simultaneous data collection of fMRI&#160;and fNIRS signals that: i) provides whole-head fNIRS coverage; ii) includes short-distance measurements for regression of the non-cortical, systemic physiological signal; and iii) implements two different methods for optode-to-scalp co-registration of fNIRS measurements. fMRI and fNIRS data from three subjects are presented, and recommendations for adapting the protocol to test developmental and clinical populations are discussed. The current setup with adults allows scanning sessions for an average of approximately 40 min, which includes both functional and structural scans. The protocol outlines the steps required to adapt the fNIRS equipment for use in the magnetic resonance (MR) environment, provides recommendations for both data recording and optode-to-scalp co-registration, and discusses potential modifications of the protocol to fit the specifics of the available MR-safe fNIRS system. Representative subject-specific responses from a flashing-checkerboard task illustrate the feasibility of the protocol to measure whole-head fNIRS signals in the MR environment. This protocol will be particularly relevant for researchers interested in validating fNIRS signals against fMRI across the lifespan.

This section presents representative subject-specific responses for the flashing checkerboard task for both fMRI and fNIRS signals. First, representative raw fNIRS data and quality assessments are shown in Figure 6 and Figure 7 to illustrate the feasibility of the experimental setup to measure fNIRS signals in the MRI environment. A diagram of the whole head optode array and sensitivity profile is shown in Figure 8....

Watch this Scientific Journal Video about Simultaneous Data Collection of fMRI and fNIRS Measurements Using a Whole-Head Optode Array and Short-Distance Channels at JoVE.com

Simultaneous Data Collection of fMRI and fNIRS Measurements Using a Whole-Head Optode Array and Short-Distance Channels

We present a method for simultaneously collecting fMRI and fNIRS signals from the same subjects with whole-head fNIRS coverage. The protocol has been tested with three young adults and can be adapted for data collection for developmental studies and clinical populations.

Functional near-infrared spectroscopy (fNIRS) is a portable neuroimaging methodology, more robust to motion and more cost-effective than functional ...

simultaneous-data-collection-fmri-fnirs-measurements-using-whole-head

Research

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Neuroscience

894 Views.  Yale University School of Medicine. We present a method for simultaneously collecting fMRI and fNIRS signals from the same subjects with whole-head fNIRS coverage. The protocol has been tested with three young adults and can be adapted for data collection for developmental studies and clinical populations. 

Video: Simultaneous Data Collection of fMRI and fNIRS Measurements Using a Whole-Head Optode Array and Short-Distance Channels

Functional Mapping with Simultaneous MEG and EEG

We use magnetoencephalography (MEG) and electroencephalography (EEG) to locate and determine the temporal evolution in brain areas involved in the processing of simple sensory stimuli. We will use somatosensory stimuli to locate the hand somatosensory areas, auditory stimuli to locate the auditory cortices, visual stimuli in four quadrants of the visual field to locate the early visual areas. These type of experiments are used for functional mapping in epileptic and brain tumor patients to locate eloquent cortices. In basic neuroscience similar experimental protocols are used to study the orchestration of cortical activity. The acquisition protocol includes quality assurance procedures, subject preparation for the combined MEG/EEG study, and acquisition of evoked-response data with somatosensory, auditory, and visual stimuli. We also demonstrate analysis of the data using the equivalent current dipole model and cortically-constrained minimum-norm estimates. Anatomical MRI data are employed in the analysis for visualization and for deriving boundaries of tissue boundaries for forward modeling and cortical location and orientation constraints for the minimum-norm estimates.

We use magnetoencephalography (MEG) and electroencephalography (EEG) to map brain areas involved in the processing of simple sensory stimuli.

We use magnetoencephalography (MEG) and electroencephalography (EEG) to locate and determine the temporal evolution in brain areas involved in the ...

Multielectrode Array Recordings of the Vomeronasal Epithelium

Understanding neural circuits requires methods to record from many neurons simultaneously. For in vitro studies, one currently available technology is planar multielectrode array (MEA) recording. Here we document the use of MEAs to study the mouse vomeronasal organ (VNO), which plays an essential role in the detection of pheromones and social cues via a diverse population of sensory neurons expressing hundreds of types of receptors. Combining MEA recording with a robotic liquid handler to deliver chemical stimuli, the sensory responses of a large and diverse population of neurons can be recorded. The preparation allows us to remove the intact neuroepithelium of the VNO from the mouse and stimulate with a battery of chemicals or potential ligands while monitoring the electrical activity of the neurons for several hours. Therefore, this technique serves as a useful method for assessing ligand activity as well as exploring the properties of receptor neurons. We present the techniques needed to prepare the vomeronasal epithelium, MEA recording, and chemical stimulation.

Multielectrode array (MEA) recordings provide a method for studying the electrical activity of large populations of neurons. Here, we present the details of a MEA preparation to record from the mouse vomeronasal epithelium while simultaneously stimulating the tissue.

Understanding neural circuits requires methods to record from many neurons simultaneously. For in vitro studies, one currently available technology is ...

Simultaneous fMRI and Electrophysiology in the Rodent Brain

To examine the neural basis of the blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) signal, we have developed a rodent model in which functional MRI data and in vivo intracortical recording can be performed simultaneously. The combination of MRI and electrical recording is technically challenging because the electrodes used for recording distort the MRI images and the MRI acquisition induces noise in the electrical recording. To minimize the mutual interference of the two modalities, glass microelectrodes were used rather than metal and a noise removal algorithm was implemented for the electrophysiology data. In our studies, two microelectrodes were separately implanted in bilateral primary somatosensory cortices (SI) of the rat and fixed in place. One coronal slice covering the electrode tips was selected for functional MRI. Electrode shafts and fixation positions were not included in the image slice to avoid imaging artifacts. The removed scalp was replaced with toothpaste to reduce susceptibility mismatch and prevent Gibbs ringing artifacts in the images. The artifact structure induced in the electrical recordings by the rapidly-switching magnetic fields during image acquisition was characterized by averaging all cycles of scans for each run. The noise structure during imaging was then subtracted from original recordings. The denoised time courses were then used for further analysis in combination with the fMRI data. As an example, the simultaneous acquisition was used to determine the relationship between spontaneous fMRI BOLD signals and band-limited intracortical electrical activity. Simultaneous fMRI and electrophysiological recording in the rodent will provide a platform for many exciting applications in neuroscience in addition to elucidating the relationship between the fMRI BOLD signal and neuronal activity.

We have developed a method for simultaneous functional magnetic resonance imaging and electrophysiological recording in the rodent brain, providing a platform for the investigation of the relationship between neural activity and the blood oxygenation level dependent (BOLD) MRI signal.

To examine the neural basis of the blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI) signal, we have developed a rodent model in ...

Combining Transcranial Magnetic Stimulation and fMRI to Examine the Default Mode Network

The default mode network is a group of brain regions that are active when an individual is not focused on the outside world and the brain is at "wakeful rest."1,2,3 It is thought the default mode network corresponds to self-referential or "internal mentation".2,3
It has been hypothesized that, in humans, activity within the default mode network is correlated with certain pathologies (for instance, hyper-activation has been linked to schizophrenia 4,5,6 and autism spectrum disorders 7 whilst hypo-activation of the network has been linked to Alzheimer's and other neurodegenerative diseases 8). As such, noninvasive modulation of this network may represent a potential therapeutic intervention for a number of neurological and psychiatric pathologies linked to abnormal network activation. One possible tool to effect this modulation is Transcranial Magnetic Stimulation: a non-invasive neurostimulatory and neuromodulatory technique that can transiently or lastingly modulate cortical excitability (either increasing or decreasing it) via the application of localized magnetic field pulses.9
In order to explore the default mode network's propensity towards and tolerance of modulation, we will be combining TMS (to the left inferior parietal lobe) with functional magnetic resonance imaging (fMRI). Through this article, we will examine the protocol and considerations necessary to successfully combine these two neuroscientific tools.

In this article, we examine the methodology and considerations relevant to the combination of TMS and fMRI to examine the effects of brain stimulation on the default network.

The default mode network is a group of brain regions that are active when an individual is not focused on the outside world and the brain is at "wakeful ...

Co-analysis of Brain Structure and Function using fMRI and Diffusion-weighted Imaging

The study of complex computational systems is facilitated by network maps, such as circuit diagrams. Such mapping is particularly informative when studying the brain, as the functional role that a brain area fulfills may be largely defined by its connections to other brain areas. In this report, we describe a novel, non-invasive approach for relating brain structure and function using magnetic resonance imaging (MRI). This approach, a combination of structural imaging of long-range fiber connections and functional imaging data, is illustrated in two distinct cognitive domains, visual attention and face perception. Structural imaging is performed with diffusion-weighted imaging (DWI) and fiber tractography, which track the diffusion of water molecules along white-matter fiber tracts in the brain (Figure 1). By visualizing these fiber tracts, we are able to investigate the long-range connective architecture of the brain. The results compare favorably with one of the most widely-used techniques in DWI, diffusion tensor imaging (DTI). DTI is unable to resolve complex configurations of fiber tracts, limiting its utility for constructing detailed, anatomically-informed models of brain function. In contrast, our analyses reproduce known neuroanatomy with precision and accuracy. This advantage is partly due to data acquisition procedures: while many DTI protocols measure diffusion in a small number of directions (e.g., 6 or 12), we employ a diffusion spectrum imaging (DSI)1, 2 protocol which assesses diffusion in 257 directions and at a range of magnetic gradient strengths. Moreover, DSI data allow us to use more sophisticated methods for reconstructing acquired data. In two experiments (visual attention and face perception), tractography reveals that co-active areas of the human brain are anatomically connected, supporting extant hypotheses that they form functional networks. DWI allows us to create a "circuit diagram" and reproduce it on an individual-subject basis, for the purpose of monitoring task-relevant brain activity in networks of interest.

We describe a novel approach for simultaneous analysis of brain function and structure using magnetic resonance imaging (MRI). We assess brain structure with high-resolution diffusion-weighted imaging and white-matter fiber tractography. Unlike standard structural MRI, these techniques allow us to directly relate anatomical connectivity to functional properties of brain networks.

The study of complex computational systems is facilitated by network maps, such as circuit diagrams. Such mapping is particularly informative when ...

Functional Imaging of Auditory Cortex in Adult Cats using High-field fMRI

Current knowledge of sensory processing in the mammalian auditory system is mainly derived from electrophysiological studies in a variety of animal models, including monkeys, ferrets, bats, rodents, and cats. In order to draw suitable parallels between human and animal models of auditory function, it is important to establish a bridge between human functional imaging studies and animal electrophysiological studies. Functional magnetic resonance imaging (fMRI) is an established, minimally invasive method of measuring broad patterns of hemodynamic activity across different regions of the cerebral cortex. This technique is widely used to probe sensory function in the human brain, is a useful tool in linking studies of auditory processing in both humans and animals and has been successfully used to investigate auditory function in monkeys and rodents. The following protocol describes an experimental procedure for investigating auditory function in anesthetized adult cats by measuring stimulus-evoked hemodynamic changes in auditory cortex using fMRI. This method facilitates comparison of the hemodynamic responses across different models of auditory function thus leading to a better understanding of species-independent features of the mammalian auditory cortex.

Functional studies of the auditory system in mammals have traditionally been conducted using spatially-focused techniques such as electrophysiological recordings. The following protocol describes a method of visualizing large-scale patterns of evoked hemodynamic activity in the cat auditory cortex using functional magnetic resonance imaging.

Current knowledge of sensory processing in the mammalian auditory system is mainly derived from electrophysiological studies in a variety of animal ...

Deep Brain Stimulation with Simultaneous fMRI in Rodents

In order to visualize the global and downstream neuronal responses to deep brain stimulation (DBS) at various targets, we have developed a protocol for using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) to image rodents with simultaneous DBS. DBS fMRI presents a number of technical challenges, including accuracy of electrode implantation, MR artifacts created by the electrode, choice of anesthesia and paralytic to minimize any neuronal effects while simultaneously eliminating animal motion, and maintenance of physiological parameters, deviation from which can confound the BOLD signal.&#160;Our laboratory has developed a set of procedures that are capable of overcoming most of these possible issues. For electrical stimulation, a homemade tungsten bipolar microelectrode is used, inserted stereotactically at the stimulation site in the anesthetized subject. In preparation for imaging, rodents are fixed on a plastic headpiece and transferred to the magnet bore. For sedation and paralysis during scanning, a cocktail of dexmedetomidine and pancuronium is continuously infused, along with a minimal dose of isoflurane; this preparation minimizes the BOLD ceiling effect of volatile anesthetics. In this example experiment, stimulation of the subthalamic nucleus (STN) produces BOLD responses which are observed primarily in ipsilateral cortical regions, centered in motor cortex. Simultaneous DBS and fMRI allows the unambiguous modulation of neural circuits dependent on stimulation location and stimulation parameters, and permits observation of neuronal modulations free of regional bias. This technique may be used to explore the downstream effects of modulating neural circuitry at nearly any brain region, with implications for both experimental and clinical DBS.

This protocol describes a standard method for simultaneous functional magnetic resonance imaging and deep brain stimulation in the rodent. The combined use of these experimental tools allows for the exploration of global downstream activity in response to electrical stimulation at virtually any brain target.

In order to visualize the global and downstream neuronal responses to deep brain stimulation (DBS) at various targets, we have developed a protocol for ...

Reliable Acquisition of Electroencephalography Data during Simultaneous Electroencephalography and Functional MRI

Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), EEG-fMRI, combines the complementary properties of scalp EEG (good temporal resolution) and fMRI (good spatial resolution) to measure neuronal activity during an electrographic event, through hemodynamic responses known as blood-oxygen-level-dependent (BOLD) changes. It is a non-invasive research tool that is utilized in neuroscience research and is highly beneficial to the clinical community, especially for the management of neurological diseases, provided that proper equipment and protocols are administered during data acquisition. Although recording EEG-fMRI is apparently straightforward, the correct preparation, especially in placing and securing the electrodes, is not only important for safety but is also critical in ensuring the reliability and analyzability of the EEG data obtained. This is also the most experience-demanding part of the preparation. To address these issues, a straightforward protocol that ensures data quality was developed. This article provides a step-by-step guide for acquiring reliable EEG data during EEG-fMRI using this protocol that utilizes readily available medical products. The presented protocol can be adapted to different applications of EEG-fMRI in research and clinical settings, and may be beneficial to both inexperienced and expert operators.

This article provides a straightforward protocol for acquiring good quality electroencephalography (EEG) data during simultaneous EEG and functional magnetic resonance imaging by utilizing readily available medical products.

Simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), EEG-fMRI, combines the complementary properties of scalp EEG ...

Measurement of the Directional Information Flow in fNIRS-Hyperscanning Data using the Partial Wavelet Transform Coherence Method

Social interaction is of vital importance for human beings. While the hyperscanning approach has been extensively used to study interpersonal neural synchronization (INS) during social interactions, functional near-infrared spectroscopy (fNIRS) is one of the most popular techniques for hyperscanning naturalistic social interactions because of its relatively high spatial resolution, sound anatomical localization, and exceptionally high tolerance of motion artifacts. Previous fNIRS-based hyperscanning studies usually calculate a time-lagged INS using wavelet transform coherence (WTC) to describe the direction and temporal pattern of information flow between individuals. However, the results of this method might be confounded by the autocorrelation effect of the fNIRS signal of each individual. For addressing this issue, a method termed partial wavelet transform coherence (pWTC) was introduced, which aimed to remove the autocorrelation effect and maintain the high temporal-spectrum resolution of the fNIRS signal. In this study, a simulation experiment was performed first to show the effectiveness of the pWTC in removing the impact of autocorrelation on INS. Then, step-by-step guidance was offered on the operation of the pWTC based on the fNIRS dataset from a social interaction experiment. Additionally, a comparison between the pWTC method and the traditional WTC method and that between the pWTC method and the Granger causality (GC) method was drawn. The results showed that pWTC could be used to determine the INS difference between different experimental conditions and INS's directional and temporal pattern between individuals during naturalistic social interactions. Moreover, it provides better temporal and frequency resolution than the traditional WTC and better flexibility than the GC method. Thus, pWTC is a strong candidate for inferring the direction and temporal pattern of information flow between individuals during naturalistic social interactions.

This protocol describes partial wavelet transform coherence (pWTC) for calculating the time-lagged pattern of interpersonal neural synchronization (INS) to infer the direction and temporal pattern of information flow during social interaction. The effectiveness of pWTC in removing the confounds of signal autocorrelation on INS was proved by two experiments.

Social interaction is of vital importance for human beings. While the hyperscanning approach has been extensively used to study interpersonal neural ...

Optrode Array for Simultaneous Optogenetic Modulation and Electrical Neural Recording

During the last decade, optogenetics has become an essential tool for the investigation of neural signaling due to its unique capability of selective neural modulation or monitoring. As specific types of neuronal cells can be genetically modified to express opsin proteins, optogenetics enables optical stimulation or inhibition of the selected neurons. There have been several technological advances in the optical system for optogenetics. Recently, it was proposed to combine the optical waveguide for light delivery with electrophysiological recording to simultaneously monitor the neural responses to optogenetic stimulation or inhibition. In this study, an implantable optrode array (2x2 optical fibers) was developed with embedded multichannel electrodes. 
A light-emitting diode (LED) was employed as a light source, and a microfabricated microlens array was integrated to provide sufficient light power at the tip of the optical fibers. The optrode array system comprises the disposable part and the reusable part. The disposable part has optical fibers and electrodes, while the reusable part has the LED and electronic circuitry for light control and neural signal processing. The novel design of the implantable optrode array system is introduced in the accompanying video in addition to the procedure of the optrode implantation surgery, optogenetic light stimulation, and the electrophysiological neural recording. The results of in vivo experiments successfully showed time-locked neural spikes evoked by the light stimuli from hippocampal excitatory neurons of mice.

Here, we present the fabrication method of an optrode system with optical fibers for light delivery and an electrode array for neural recording. In vivo experiments with transgenic mice expressing channelrhodopsin-2 show the feasibility of the system for simultaneous optogenetic stimulation and electrophysiological recording.

During the last decade, optogenetics has become an essential tool for the investigation of neural signaling due to its unique capability of selective ...