Taking the body off the mind: Decreased functional connectivity between somatomotor and default‐mode networks following Floatation‐REST

Abstract Floatation‐Reduced Environmental Stimulation Therapy (REST) is a procedure that reduces stimulation of the human nervous system by minimizing sensory signals from visual, auditory, olfactory, gustatory, thermal, tactile, vestibular, gravitational, and proprioceptive channels, in addition to minimizing musculoskeletal movement and speech. Initial research has found that Floatation‐REST can elicit short‐term reductions in anxiety, depression, and pain, yet little is known about the brain networks impacted by the intervention. This study represents the first functional neuroimaging investigation of Floatation‐REST, and we utilized a data‐driven exploratory analysis to determine whether the intervention leads to altered patterns of resting‐state functional connectivity (rsFC). Healthy participants underwent functional magnetic resonance imaging (fMRI) before and after 90 min of Floatation‐REST or a control condition that entailed resting supine in a zero‐gravity chair for an equivalent amount of time. Multivariate Distance Matrix Regression (MDMR), a statistically‐stringent whole‐brain searchlight approach, guided subsequent seed‐based connectivity analyses of the resting‐state fMRI data. MDMR identified peak clusters of rsFC change between the pre‐ and post‐float fMRI, revealing significant decreases in rsFC both within and between posterior hubs of the default‐mode network (DMN) and a large swath of cortical tissue encompassing the primary and secondary somatomotor cortices extending into the posterior insula. The control condition, an active form of REST, showed a similar pattern of reduced rsFC. Thus, reduced stimulation of the nervous system appears to be reflected by reduced rsFC within the brain networks most responsible for creating and mapping our sense of self.


| INTRODUCTION
Modern society and its evergrowing reliance on digital technology have exposed the human nervous system to an unprecedented level of sensory stimulation. While the capacity to respond and interact with external sensory stimuli constitutes a vital function of the brain, the ability to focus on one's self and disengage from external stimulation can be just as vital, but is far less studied (Suedfeld & Kristeller, 1982), and can be quite difficult for most to accomplish on their own, even over short periods (Wilson et al., 2014). Floatation-Reduced Environmental Stimulation Therapy (REST) aims to effectively disengage the nervous system from sensory stimulation by creating a controlled environment which reduces most forms of external sensory input (including auditory, visual, olfactory, gustatory, tactile, thermal, vestibular, gravitational, and proprioceptive) while also minimizing musculoskeletal movement and speech (see Supporting Information for more details). The acute effect of this intervention appears to be one of heightened interoceptive awareness for cardiorespiratory sensations in the context of physiological relaxation, including reductions in blood pressure and muscle tension (Feinstein, Khalsa, Yeh, Al Zoubi, et al., 2018;Turner, Gerard, Hyland, Nieland, & Fine, 1993;Turner & Fine, 1983;Van Dierendonck & Te Nijenhuis, 2005). Subjectively, Floatation-REST has been shown to elicit short-term decreases in states of negative affect (e.g., anxiety, depression, and pain) and increases in states of positive affect (e.g., feeling refreshed, serene, and relaxed) Forgays & Belinson, 1986;Jacobs, Heilbronner, & Stanley, 1984;Kjellgren, Sundequist, Norlander, & Archer, 2001). To date, no neuroimaging studies have explored the neural effects of Floatation-REST, and in general, little is known about how the nervous system responds following a prolonged period of reduced sensory and motor stimulation.
The default-mode network (DMN) is thought to reflect the brain's intrinsic mental activity during periods of wakeful rest (Raichle, 2015;Raichle et al., 2001), making it a prime candidate for being impacted by the prolonged period of REST conferred by floatation. The DMN is comprised of two core regions: an anterior hub in the medial prefrontal cortex (mPFC) and a posterior hub in the posterior cingulate cortex (PCC) and precuneus. Beyond these hubs, the DMN also includes lateral flanks located near the temporoparietal junction in addition to regions within the medial temporal lobe (Andrews-Hanna, Reidler, Sepulcre, Poulin, & Buckner, 2010). During nonactive tasks (e.g., while fixated on a baseline cross), there is a significant increase in restingstate functional connectivity (rsFC) within and between hubs of the DMN. In line with this notion, the DMN is maximally active during times when external sensory stimulation is minimized and the mind is free to wander and reflect on the self. The inverse is also true such that DMN activity is rapidly suppressed whenever one is actively engaged with the outside world and attending to stimuli from the external environment. Over the past two decades, the observed increases in DMN rsFC during states of passive rest while one is conscious and awake has proven to be one of the most reliable and robust findings to emerge from the functional neuroimaging literature (Raichle, 2015;Termenon, Jaillard, Delon-Martin, & Achard, 2016;Whitfield-Gabrieli & Ford, 2012).
Floatation-REST has been found to have short-term anxiolytic, antidepressant, and analgesic effects (Bood et al., 2006;Kjellgren et al., 2001), yet little is known about how the intervention impacts brain networks such as the DMN. Subjectively, the intervention has been found to induce altered states of consciousness, often described as a liminal state, somewhere between being asleep and awake (Kjellgren, Lyden, & Norlander, 2008). Subjects will also frequently describe out-of-body experiences (Kjellgren et al., 2008) characterized by difficulty discerning where their outer body begins and where it ends. While Floatation-REST has sometimes been referred to as a form of sensory deprivation, this term is now considered outdated and a misnomer for the experience (Suedfeld & Coren, 1989). Rather than depriving the senses, we have found that Floatation-REST actually enhances awareness for internal sensations such as the breath and heartbeat, making the float environment naturally conducive to meditative states (Feinstein, Khalsa, Yeh, Al Zoubi, et al., 2018). Since this was the first fMRI study to examine changes in rsFC related to Floatation-REST, we utilized an exploratory analytical approach that provided a comprehensive voxel-wise survey of functional connectivity (FC) across the whole brain using multivariate distance matrix regression (MDMR) (Anderson, 2001;Elliott, Romer, Knodt, & Hariri, 2018;Koyama, O'Connor, Shehzad, & Milham, 2017;Misaki et al., 2018aMisaki et al., , 2018bSatterthwaite et al., 2016;Shehzad et al., 2014;Talukdar, Román, Operskalski, Zwilling, & Barbey, 2018). This data-driven approach identified clusters showing a significant change in rsFC from pre-to post-float, and these MDMR-identified clusters were used to guide subsequent seed-based connectivity analyses. Finally, an active control condition (Chair-REST) was employed to determine whether the changes in rsFC were specific to floating, or more generally related to any form of REST characterized by: (a) resting wakefulness, (b) lying in a supine position, (c) minimal behavioral output, movement, and speech, and (d) reduced exposure to stimuli from the external environment.

| Participants
Fifty-six healthy adults between 18 and 55 years of age were recruited from a community sample using a subject database maintained at the Laureate Institute for Brain Research. All study procedures were approved by the Western Institutional Review Board (WIRB), and all participants provided their written informed consent prior to participation. Inclusion criteria selected healthy adults who were free of any current or past neurological or psychiatric illness and had no prior experience with Floatation-REST. Subjects were excluded if they: (a) met criteria for a psychiatric disorder based on the Mini-International Neuropsychiatric Interview (MINI) version 6.0, (b) failed a urine screen and/or breathalyzer test administered prior to each brain scan to ensure no one was acutely under the influence of any alcohol, drugs, or psychotropic medications (benzodiazepines, opiates, selective serotonin reuptake inhibitors, dopamine agonists, barbiturates, marijuana, MDMA, LSD, psilocybin, and peyote), (c) were pregnant (as detected by a urine test), (d) had noncorrectable vision or hearing problems, (e) had a skin condition or open wound that could cause pain when exposed to saltwater, (f) had any MRI contraindications (e.g., BMI >40 or any metal in the body), or (g) had any prior exposure to Floatation-REST. Eight subjects in the Floatation-REST condition were excluded from the final analysis ( Figure S1), requiring recruitment of additional float subjects to ensure a matched sample size. The final sample contained 48 subjects with clean and complete datasets (24 Float-REST subjects and 24 Chair-REST subjects) and these data are available from the corresponding author upon reasonable request. Participant demographics and baseline functioning are shown in Table 1 for each group. In both the Float-REST and Chair-REST conditions, a blue LED light remained illuminated in the background and could be turned off by the participant using an air switch. The air switch was linked to a digital clock in the control room, allowing for the automated calculation of the total amount of time that a participant was floating with the lights off. In addition, a microphone in each room provided a realtime continuous audio feed to a nearby control room, where the experimenter remained throughout the REST session so that they could quickly address any issues that may arise and monitor that the participant remained floating throughout the session. Following 90 min of REST, the experimenter remotely turned on an overhead light in the room to signal that the session was over. In order to standardize instructions, an identical script was read to participants prior to each REST session regardless of whether they were randomized to the Float-REST or Chair-REST condition (Supporting Information).

| Procedure
Before and after each REST session, participants rated their current subjective state on the Spielberger State Anxiety Inventory (Spielberger, 1983), a 20-item questionnaire designed to assess an Note: Both groups were well-matched, with no significant between-group differences (p >.05 across all variables using Welch's t-test). Values in parentheses represent the standard deviation. Abbreviations: IDAS, Inventory of Depression and Anxiety Symptoms (Watson et al., 2007); KSS, Karolinska Sleepiness Scale (Kaida et al., 2006); STAI, State-Trait Anxiety Inventory-Trait Version (Spielberger, 1983).
individual's level of anxiety at the present moment. Participants also completed the Serenity scale on the expanded form of the Positive and Negative Affect Schedule (PANAS-X), which has participants rate how calm, relaxed, and at ease they feel at the present moment using a 5-point Likert-type response scale (Watson & Clark, 1999). State anxiety and serenity scores were converted into the percent of maximum possible (POMP units) for each scale (Cohen, Cohen, Aiken, & West, 1999) and change scores were computed between the pre-and post-REST ratings. In addition, after each REST session, participants rated the overall pleasantness of their REST experience on a 100-point bipolar valence scale going from 0 (Extremely Unpleasant) to 100 (Extremely Pleasant), with the slider starting in the middle of the scale at 50 (Neutral). After each MRI scan, participants rated their level of sleepiness during the scan using the Karolinska Sleepiness Scale (Kaida et al., 2006).

| MRI measurement
Magnetic resonance imaging was conducted using a whole-body

| MR image processing
Imaging analyses were carried out using the Analysis of Functional NeuroImages (AFNI) software (http://afni.nimh.nih.gov/afni/). The afni_proc.py command was used to preprocess the data using the default parameters unless otherwise noted. The first three volumes were omitted from the analysis. The despike option was applied to replace outlier time points with interpolation. RETROICOR (Glover, Li, & Ress, 2000) and respiration volume per time (RVT) correction F I G U R E 1 Experimental design. The entire protocol took approximately 1 month for each subject to complete. Participants first underwent a baseline MRI scan ("Pre-REST MRI") where they completed an eyes-open resting state run at the beginning of the scan. Afterward, participants were randomly assigned to complete three 90-min sessions of either Floatation-REST ("Float-REST"; top picture) or the Zero-Gravity Chair ("Chair-REST"; bottom picture). All REST sessions were completed over a 3-week time period, with approximately 1 week between each session. The first two sessions were designed to help acclimate participants to the environment and ensure that everyone could complete a 90-min session in the dark. Immediately following the third REST session, participants underwent another MRI scan ("Post-REST MRI") where they completed a second eyes-open resting state run at the beginning of the scan (Birn, Smith, Jones, & Bandettini, 2008) were applied to remove cardiac-and respiration-induced noise in the blood oxygenation leveldependent (BOLD) signal, and spatially smoothed with a Gaussian kernel (FWHM = 6 mm).
Slice-timing differences were adjusted by aligning to the first slice, and motion correction was applied by aligning all functional volumes to the first volume. EPI volumes were acquired using the 3dvolreg AFNI program with two-pass registration. The volume with the minimum outlier fraction of the short EPI dataset acquired immediately after the high-resolution anatomical (MPRAGE) brain image was used as the registration base. Linear warping was applied to the MNI space and resampled to 2 mm 3 voxels. To minimize noise related to movement, subjects were excluded who had a scan with an average FD >0.25 mm or a DVARS >0.5% change in BOLD (Power et al., 2014). In addition, we censored individual time points, and the prior TR whenever the average root mean square (RMS) motion was greater than 0.2 mm.

| Multivariate distance matrix regression
As previously mentioned, Floatation-REST is an intervention that has not yet been explored using fMRI. Thus, we harnessed an exploratory data-driven approach using MDMR (Elliott et al., 2018;Shehzad et al., 2014) to guide subsequent seed-based connectivity analyses. MDMR performs a comprehensive voxel-wise survey of FC changes across the whole brain using a permutation test which minimizes falsepositives and identifies voxels whose whole-brain connectivity patterns vary significantly according to a prespecified variable. Since the aim of the study was focused on understanding the rsFC changes elicited by Floatation-REST, the prespecified variable in our MDMR analysis was the difference between the pre-and post-REST scans in the Float-REST group. Significant MDMR clusters were utilized in subsequent seed-based analyses examining for significant group × time interactions (using an ANOVA) as well as significant changes within each condition (using paired t-tests). The following steps were applied to the resting-state fMRI data. First, we downsampled images to 4 mm 3 voxels after applying an anatomical brain mask to avoid mixing noise from outside the brain. The downsampling stage was necessary to alleviate the computational overheads of the whole-brain voxelwise connectivity matrix. Regression of white matter and the ventricles was not applied during resampling since it was already completed at the preprocessing stage. The data was further reduced by applying a gray matter mask extracted from the MNI152 template brain, reducing the total number of voxels to 18,592 for each subject.
In each voxel, a connectivity map from that voxel to all other voxels was made with Pearson's correlations, and the dependent variable was a distance matrix of the connectivity maps between subjects. The MDMR procedure (Shehzad et al., 2014) In the above formula, n is the number of participants, I is the n × n identity matrix, and 1 is a vector of 1's. C serves as mean-centering of the columns and rows of A, and tr is the matrix trace operator. The design matrix X was formed to have one column that represents the group factor encoded as 0's and 1's (e.g., 1's indicates postscans and 0's indicates prescans). Finally, a column of 1's was added for the intercept. In our analysis, we found the design matrix to be rankdeficient due to collinearity between nuisance variables and subjectwise regressors. Thus, we solved this issue by applying the singular value decomposition (SVD) on the design matrix (Mandel, 1982). SVD decomposed the design matrix to X = USVT in which columns of repeats and thresholded at p <.005 voxel-wise, across the whole brain. Clusters with at least nine adjacent voxels in MDMR space (72 voxels in our original fMRI space) were used as seeds to avoid spurious correlations that can occur with smaller seeds (e.g., Fox, Liu, & Pascual-Leone, 2013).

| Seed-based FC analysis
Whole-brain FC analysis was conducted by calculating the Pearson's correlation between the mean time series of each MDMR seed's voxels and the time courses of all other voxels in the brain. Fisher's r-to-z transformation was applied to all correlation coefficients. A group-by-time interaction analysis was conducted using a 3-way analysis of variance implemented in the AFNI program 3dANOVA3.
The model option was set to type = 5 in which the group (Float-REST and Chair-REST; df = 1) and session (pre-and post-REST; df = 1) were set as fixed factors, while subjects were set as a random factor (df = 47). To reveal brain regions that showed significant within-subject changes in FC from the pre-to post-REST scans, a paired t-test was applied within each group (Float-REST and Chair-REST) using AFNI's 3dttest++ program for each of the 9 MDMR seeds. AFNI's 3dClustSim was applied along with the non-Gaussian spatial autocorrelation function (ACF) option (Cox, Chen, Glen, Reynolds, and Taylor (2017)

| RESULTS
The two groups (Float-REST and Chair-REST) were well matched on age, sex, and education (Table 1). Since subjects were screened to be free of any psychiatric illnesses, both groups had similarly low levels of depression and anxiety, with no significant between-group differences on any baseline measures (Table 1). All subjects remained awake and alert during the resting-state fMRI scans, and there were no significant between-group differences in self-reported sleepiness during the MRI scans (Table 1) Consistent with prior studies (Feinstein, Khalsa, Yeh, Al Zoubi, et al., 2018; Chair-REST session = 69.54 ± 18.08).
The MDMR whole-brain searchlight approach discovered nine clusters whose connectivity pattern varied significantly from the preto post-float scan ( Table 2). The clusters spanned different networks of the brain but were largely concentrated within the posterior DMN and somatomotor networks. When these clusters were subsequently applied as seed regions in a group-by-time interaction analysis using AFNI's 3dANOVA3, there were no connected clusters that survived ACF-correction, highlighting a lack of any significant between-group differences. Overall, both groups showed a consistent pattern of

| DISCUSSION
This study represents the first resting-state functional neuroimaging investigation of Floatation-REST, a unique method for systematically reducing stimulation of the human nervous system. The resting-state fMRI data was analyzed using MDMR, a statistically-stringent wholebrain searchlight approach aimed at finding peak clusters of connectivity change between the pre-and post-float brain scans. The results  (Boly et al., 2007). Indeed, there are multiple maps of the body contained within parietal cortices (Berlucchi & Aglioti, 2010;Longo, Azañón, & Haggard, 2010) that contribute to self-awareness. For example, recent work has discovered a causal role for posteromedial cortices in dissociation (Vesuna et al., 2020). The temporoparietal junction has been shown to be critical for the multisensory integration of visual, tactile, and vestibular signals that create our sense of the body in space, and when disturbed, can lead to out-of-body experiences (Ionta et al., 2011). The FC between temporoparietal junction and posterior insula (Ionta, Martuzzi, Salomon, & Blanke, 2014) is rapidly altered by shifts in self-location (i.e., the experience of where I am in the world) and first-person perspective (i.e., the experience of where I perceive the world from), and the posterior parieto-insular cortex is particularly involved in processing vestibular sensations (Eickhoff, Weiss, Amunts, Fink, & Zilles, 2006). The posterior insula is closely connected with both the somatosensory cortices and the posterior cingulate (Cauda et al., 2011;Deen, Pitskel, & Pelphrey, 2011), creating a strong interconnected system between hubs of the posterior DMN and the somatosensory cortices. Since Floatation-REST has been shown to significantly reduce muscle tension (Feinstein, Khalsa, Yeh, Al Zoubi, et al., 2018;Kjellgren et al., 2001), it may be possible that the intervention directly alters the F I G U R E 3 DMN seeds. Regions of significant rsFC change from pre-REST to post-REST for each group (blue = Float-REST; red = Chair-REST; yellow = overlap) across the 3 DMN MDMR seeds shown on the left side of the panel. All clusters shown survived ACF-correction (p <.05) and signify overall decreases in rsFC during the post-REST scan. Clusters are displayed using neurological convention (i.e., right side of image corresponds to the right hemisphere) F I G U R E 4 Somatomotor seeds. Regions of significant rsFC change from pre-REST to post-REST for each group (blue = Float-REST; red = Chair-REST; yellow = overlap) across the 3 somatomotor MDMR seeds shown on the left side of the panel. All clusters shown survived ACF-correction (p <.05) and signify overall decreases in rsFC during the post-REST scan. Clusters are displayed using neurological convention (i.e., right side of image corresponds to the right hemisphere) representation of this tension within the brain's body maps. This is consistent with a prior fMRI study that found reduced activity in the posterior cingulate, somatomotor, and insular cortices following progressive muscle relaxation (Kobayashi & Koitabashi, 2016). In an exploratory correlation analysis, we found that the greater the decrease in connectivity between posterior insula and somatosensory cortices, the greater the serenity induced by the float experience ( Figure S2), highlighting a potentially important role for these somatosensory rsFC changes in eliciting subjective relaxation.
With the exception of somatosensory cortices, the observed post-REST decreases in rsFC largely did not coincide with the other senses reduced by REST (e.g., primary and secondary visual and auditory cortices did not show significant changes in rsFC). Instead, the changes found in our study were largely concentrated within higherlevel association cortices such as the posterior hubs of the DMN.
Notably, a preserved DMN has been found in individuals who are congenitally blind suggesting that "the absence of a particular sensory modality does not qualitatively affect default functionality" (Burton, Snyder, & Raichle, 2014 (Raichle, 2015;Raichle et al., 2001), appears to be significantly reduced after a prolonged period of REST.
In contrast to the posterior DMN, there was comparatively little change found in the anterior DMN following Floatation-REST. This was somewhat surprising given the well-known role of the mPFC in self-related processing (Gusnard, Akbudak, Shulman, & Raichle, 2001), especially self-referential thought (Qin & Northoff, 2011) and rumination (Hamilton et al., 2015). Prior work from our lab has shown that the mPFC was not necessary for self-awareness in a rare lesion patient who had bilateral mPFC damage but preserved rsFC throughout his posterior DMN (Philippi et al., 2012). The only evidence of significant mPFC involvement in the present study was found in relation to the lMFG seed near the left dorsolateral prefrontal cortex ( Figure 5). This region of central executive network is often the target of transcranial magnetic stimulation (TMS) for the treatment of depression, an intervention that also appears to impact the mPFC (Liston et al., 2014). Since our study only employed healthy subjects, future studies will have to assess whether similar rsFC reductions in mPFC emerge in depressed patients following Floatation-REST.
When examining the same MDMR seeds in subjects randomized to the Chair-REST condition, reduced rsFC was also observed, but there were no significant group by time interactions with Float-REST.
However, when comparing the degree of rsFC change, it became evident that the Chair-REST condition did not elicit as robust of a reduction in rsFC as the Float-REST condition ( Figure 2). Moreover, the vast majority of DMN and somatomotor clusters that survived ACFcorrection in the Float-REST group failed to surpass significance in the Chair-REST group (Figures 3-5). Thus, it remains possible that the added degree of weightlessness and loss of proprioception conferred by Floatation-REST may have preferentially impacted the brain's body maps. Nevertheless, the lack of significant between-group differences suggests that reduced stimulation of the nervous system via any form F I G U R E 5 Other seed regions. Regions of significant rsFC change from pre-REST to post-REST for each group (blue = Float-REST; red = Chair-REST; yellow = overlap) across the 3 final MDMR seeds shown on the left side of the panel. All clusters shown survived ACFcorrection (p <.05) and signify overall decreases in rsFC during the post-REST scan. The top seed (rIFG) is a hub of the salience network, and the bottom seed (lMFG) is a hub of the central executive network. Clusters are displayed using neurological convention (i.e., right side of image corresponds to the right hemisphere) of REST may be reflected by reduced rsFC within the brain networks most responsible for creating and mapping our sense of self.
While both the Float-REST and Chair-REST conditions shared many overlapping features (90-min sessions, supine position, reduced pressure on the spinal cord, being alone in a quiet and dark room, and the same instruction set emphasizing the need for stillness and staying awake), there were some notable differences. Firstly, the sensory reduction (e.g., light, sound, and proprioception) during the Chair-REST condition was not as complete as during Floatation-REST; the room housing the zero-gravity chair was not constructed to eliminate all outside light and sound, and the chair itself, even when reclined, still exerted some degree of pressure on the body and spinal cord.
Secondly, the Chair-REST condition did not entail any exposure to water or salt. Thirdly, participants remained clothed throughout Chair-REST (whereas individuals were naked during Float-REST). And finally, the temperature during the Chair-REST condition was not matched to skin temperature (95.0 F), but instead was maintained at a normal room temperature (73.0 F). Thus, while the zero-gravity chair condition contains many active ingredients of REST, the experience was not as immersive as floating in the pool, and the reduction in sensory stimulation was not nearly as complete and all-encompassing as Floatation-REST. In addition, the subjective changes elicited by the Chair-REST condition were not as robust as those elicited by Float-REST (which participants found to be significantly more pleasurable), and consequently, the Float-REST condition induced significantly greater increases in serenity and decreases in state anxiety. If future studies could find a REST intervention capable of eliciting similar subjective changes as those induced by Float-REST, then it may be possible to devise an intervention that would be easier to implement and disseminate.
There are several limitations that should be mentioned. Since this was the first functional neuroimaging study to examine the effects of Floatation-REST, it will be necessary for future work to confirm these findings. It should be acknowledged that there were several REST sessions and several weeks between brain scans, and these intervening variables could have also contributed to the findings. Even though the groups were well-matched, the lack of significant between-group differences in rsFC changes could be due to a number of factors. Since the control condition was an active form of REST, it appears to have elicited a similar pattern of reduced rsFC, making it difficult to discern significant differences. Moreover, with our moderate sample size of 24 subjects in each group (each scanned twice), we were likely underpowered to find a significant group by time interaction. Recent evidence has suggested that the duration of the resting state scan employed in the current study may be insufficient to provide high levels of test-retest reliability (Noble, Scheinost, & Constable, 2019), and therefore, it is possible that measurement variability contributed to the lack of significant differences found between conditions.
Finally, it is worth noting that the post-REST brain scans always occurred after the completion of REST, so no inferences can be made about neural activity changes that occurred during the actual time period of reduced sensory and motor stimulation. ClinicalTrials.gov identifier for the protocol associated with data published in the current paper is NCT02452203, "Examining the Effects of Reduced Environmental Stimulation on the Brain."