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Use Ask VA to send us your questions, updates, and documents online. Contact us online through Ask VA Media inquiries should be directed to the Office of Media Relations at vapublicaffairs@va.gov Sign up for our newsletter Last updated November 3, 2025 United States Department of Veterans Affairs U.S. Department of Veterans Affairs 810 Vermont Ave., NW Washington, DC 20420 1-800-698-2411 VA News An official website of the U.S. Department of Veterans Affairs Looking for U.S. government information and services? Visit USA.gov Go to Top -------- https://news.va.gov/144353/transcranial-magnetic-stimulation-offers-hope/ Home Health Transcranial Magnetic Stimulation offers hope Black and white image of a woman in military uniform next to the text "From Struggle to Strength: Shirley Benoit's Journey with TMS" on a blurred background. TMS is Transcranial Magnetic Stimulation. Transcranial Magnetic Stimulation offers hope January 9, 2026 Katie Butler Public Affairs Specialist, Malcom Randall VA Medical Center Share this story Facebook Twitter LinkedIn Reddit Telegram Tumblr WhatsApp Email Appears In Health For Veteran living with depression For Army Veteran Shirley Benoit, the battle with depression lasted more than a decade. Medications didn’t work and the side effects often made things worse. When she began Transcranial Magnetic Stimulation (TMS) therapy at VA, she finally found relief. “It was doing something for my depression,” Benoit said. “Now I’m doing the maintenance. It really has helped, even with my back pain.” Benoit served a combined 17 years with the Army National Guard and on active duty, holding roles in combat medicine, supply, engineering, recruiting and administrative support. She first began TMS treatment at the Chillicothe VA Medical Center in Ohio in 2010, when the therapy was just being introduced as an alternative option for Veterans who had not responded well to medication or counseling. After just four weeks, Benoit noticed a change. “I could tell something was working,” she recalled. Now a traveling Veteran who spends time in Ohio and Florida, Benoit also continues her maintenance treatments at the Malcom Randall VA Medical Center in Gainesville. She credits her care team, led by Dr. Milankumar Nathani, psychiatrist at the Malcom Randall VAMC, for making each visit a positive experience.“Dr. Nathani and his staff, their patience, their professionalism, the way they handle me, I know that I’m important,” she said. “They listen. They are compassionate about me and the way I feel.” How TMS treatment works TMS is a non-invasive treatment that uses magnetic pulses to stimulate areas of the brain linked to mood regulation. It’s typically recommended for Veterans diagnosed with major depressive disorder or obsessive-compulsive disorder, particularly when medications or traditional therapy haven’t provided sufficient relief. During treatment, Veterans sit comfortably in a chair while a magnetic coil is placed against the scalp. The device delivers gentle tapping sensations for about 20 to 30 minutes, five days a week, for four to six weeks. Many patients begin noticing improvement after just a few weeks. Unlike other medical procedures, TMS requires no surgery, anesthesia or needles, and it has few to no side effects. Patients remain awake throughout the session. For Veterans like Benoit, the benefits go beyond symptom relief, they represent a return to hope. Veterans interested in learning more about TMS can speak with their VA mental health provider to see if the therapy is right for them. This article was originally published on the VA North Florida/South Georgia Health care System site and has been edited for style and clarity. ------------ https://pmc.ncbi.nlm.nih.gov/articles/PMC7590944/#:~:text=The%20Targeted%20Dream%20Incubation%20(TDI)%20protocol%20is,role%20of%20dream%20content%20in%20post%2Dsleep%20performance. Future studies will look at the predictive power of system thresholds combining these presumptive values. 4. Discussion 4.1. Dormio: The Dream Incubation Device The Targeted Dream Incubation (TDI) protocol is designed for controlled generation of specific dream content at sleep onset, enabling experiments which probe the causal role of dream content in post-sleep performance. This protocol is available to anyone with an array of sensors that can track sleep onset, as well as deliver and record audio. Dormio is designed to enact this protocol automatically, making the TDI protocol mobile and cheap in comparison to techniques that require PSG. Though the choosing not to use PSG for TDI will likely lead to less specificity in staging sleep onset, given the extensive evidence that sleep onset imagery occurs from early drowsiness into the early minutes of stage 2 NREM sleep (Rowley, Stickgold, and Hobson 1998; Nielsen, 2017), Dormio has a large margin of error for which sleep onset detection can be tolerated without sacrificing the hypnagogic dream incubation goal. This paper presents results suggesting that the Dormio device can track sleep onset with enough specificity and collect dream reports with sufficient reliability to enact TDI, incubating and capturing experimenter-chosen themes in hypnagogic dreams. Results suggest Dormio is an effective dream incubation device, with 67% of Sleep+Tree awakenings yielding dream reports that incorporate the auditory prime, ‘Tree’, automatically captured by Dormio’s audio recording system. There are significant limitations to keep in mind when interpreting this experiment. The age range of participants is limited, and all are university-affiliated, yielding a somewhat homogenous population. This study, designed to investigate efficacy of TDI using only Dormio, did not have PSG measurements. This leaves us with little information as to where participants were awoken within the range of the sleep-onset process, and means experimenters must trust verbal reports with regards to sleep onset, which can be unreliable. Further, there is a methodological issue with trusting dream reports, as dreams can be forgotten or fabricated due to demand characteristics. We are aware of these issues in the TDI protocol, and look forward to future techniques which allow for direct capture of dream reports via neurophysiology as opposed to subjective report. Future studies on TDI should use multiple incubation themes, as opposed to our single theme ‘Tree’, as semantic or syntactic characteristic of auditory primes may influence incubation rates. Regardless of these limitations we think the Dormio device and TDI protocol warrant future study, and enable researchers to ask new questions about dream-related cognitive enhancement. The potential utility for a device like Dormio to specifically enhance performance on a task pre-determined by the user is tantalizing. Significant correlations between dream content and sleep-dependent memory processing have been reported in several studies, which used a variety of learning tasks, including learning a story (Barrett 1993; Nielsen and Stenstrom 2005)), a foreign language (De Koninck et al. 1990), word-picture associations (Schoch et al. 2019), a visual maze (Wamsley & Tucker, 2010; Wamsley & Stickgold, 2019), and explicit visuospatial memories (Plailly et al. 2019), although others have failed to find significant correlations (see Plailly et al., 2019 for summary). Taken as a whole, these studies provide substantial support for the existence of such correlations, although not necessarily for all forms of memory encoding. While correlations have been found, no studies have attempted to show a causal relationship between dream incorporation, and memory consolidation. 4.2. Uses of Targeted Dream Incubation(TDI) Establishing a causal link between dream incorporation and sleep-dependent memory processing requires the experimental manipulation of dream content through targeted dream incubation. The design of one such experiment is shown in Fig 5. This design tests the hypothesis that inducing dreams about the cue in a word pair enhances recall of the associated target word. Comparisons between the dream incubation condition and control conditions could confirm the specific contribution of dreaming about the cue word to subsequent, post-sleep memory enhancement. 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In our lab, we have used the Dormio device to carry out a TDI protocol using auditory stimuli. Credit: Fluid Interfaces group Frequently Asked Questions What is targeted dream incubation (TDI)? How does TDI work? How is TDI different from Targeted Memory Reactivation (TMR)? Why incubate dreams? Which studies have used TDI? What practices or past work inspired the development of TDI? Where can I read more about dream science? What is targeted dream incubation (TDI)? Targeted dream incubation (TDI) is a method for guiding (or “incubating”) dreams towards specific themes. In our lab, we have mainly explored using auditory and olfactory stimuli to achieve TDI, but the TDI methodology encompasses a wide range of possible interventions to achieve guiding dreams. The TDI protocol also includes serial awakenings that enable collection of dream reports following the incubation of a dream. How does TDI work? So far, we have applied TDI to Stage 1 (also called NREM1 or N1) sleep, which is the first stage of sleep. During sleep onset, hypnagogia (a special state occurring in the transition from wakefulness to sleep) occurs. Sleep onset is characterized by a gradual, piece-by-piece descent into sleep, as opposed to a sudden, binary on/off switch from wakefulness to sleep which some people imagine occurs. In fact, there are nine separate substages of sleep onset. In the middle of this gradual transition from wakefulness to sleep, the brain maintains sensitivity to outside stimuli (for example, people can still hear sounds and smell scents in the space around them) even as the brain enters a more dream-like state, both in terms of physiology and mental experience. In our work, we use a TDI protocol with auditory stimulation to guide sleep onset (N1) dreams. We carry out our TDI protocol with the Dormio system (read more on Dormio here), but TDI can be carried out with any combination of tools that can track sleep stages, play stimuli, and record dream reports. A person wears Dormio and lies down to fall asleep. The Dormio system tracks sleep onset. Once sleep onset is detected, a timer of a few minutes is started. At the end of the timer, an audio recording is played to ask the user for a dream report, bringing the wearer back into wakefulness briefly. We record everything the user says during their dream report, to avoid them forgetting a potentially useful idea. Following their dream report, the system then plays an audio cue, reminding the wearer to think of certain words (like "fork" or "rabbit"), with the aim of integrating the cued topic into their next set of dreams. The user then drifts back to sleep, with the cue in mind. In our laboratory testing, we have found that the cued words reliably entered the hypnagogic dreams of our users. The system continues to track the state (awake or asleep) of the user, repeating the process described above of waking them up after a few minutes of sleep to collect a dream report. This protocol is carried out repeatedly to guide dreams and collect dream reports. To better understand how our auditory stimulus makes its way into people’s dreams, just consider “a lion playing volleyball underwater.” This phrase, even written, conjures a mental image. The creation of a mental image from words also happens at sleep onset. Words heard by the napper just as they fall asleep serve as a seed for mental images/thoughts, allowing the ideas to slip into their dream. We wake the subject up after a few minutes and request a dream report in order to avoid them slipping into a deeper sleep, at which point the likelihood they forget their dream would increase. We began this work using the Dormio device for tracking sleep so we could incubate dreams. Since then we have also used the Masca, the Hypnodyne, and even typical polysomnography to enact TDI and produce targeted dreams. We emphasize that our TDI protocol can be carried out using a variety of technologies to track sleep, play, and record audio. We are working on new ways to do low-tech dream incubation, such as through just an online timer interface: https://christinatchen.github.io/dormio/timer. How is TDI different from Targeted Memory Reactivation (TMR)? TDI is similar to a technique called Targeted Memory Reactivation (TMR). In this TMR, sensory cues are paired with a task while subjects are awake. Then, during a subsequent sleep (which typically includes later phases of sleep such as N2, N3, and REM), these sensory cues are presented again, with the goal of reactivating the memory of the learned material from the task associated with the cue. When the task is tested after sleep, memory performance for items that were cued during sleep is typically better as compared to memory for items not cued during sleep (suggesting important sleep-dependent processing for learning and showing that TMR can affect such processing). TMR is a powerful technique, but it is not focused on changing dreams, and does not involve collecting dream reports. Instead, it is focused on affecting the topics the sleeping brain is working on consolidating, using cues to direct the brain to augment specific memories over others, without regard for how this is experienced by the sleeper. Why incubate dreams? The first reason is to facilitate personal introspection. We find the idea that there is a state of mind (sleep) which composes and constructs the conscious self, but remains inaccessible to it during the day, both frustrating and alluring. Hypnagogia is a version of oneself that the waking self is unfamiliar with, a self that slips past memory as we drift into unconsciousness. Good neuroscience can aspire to be effective self-examination. Good technology in service of making neuroscience relevant outside the laboratory, then, should facilitate self-examination. The ends of this project are both practical and philosophical. We have no doubt that hypnagogia holds applications for augmenting memory, learning, and creativity. Yet also, after having explored the state ourselves, it seems a deeply valuable and inspiring sort of self-seeing which was inaccessible to us previously. As Nobel Prize winner Eric Kandel said, "human creativity...stems from access to underlying, unconscious forces." To know ourselves, and to be our most creative selves, we are interested in building tools for self-exploration in this sleep state. TDI aims to be a tool for people to use on their own terms to explore and augment themselves. Beyond personal introspection, the second reason this method is so exciting to us is that it opens up new avenues for exploring the mind. Scientifically, having a method to guide dreams means that we can now do controlled experiments on how dreams and dream content influence cognition, including questions about emotion, creativity, memory, and more. We know from correlational studies and anecdotal reports that different dreams are linked to different post-sleep outcomes – such as creative performance and emotion – but without controlled studies, we still lack solid scientific evidence for a causal effect of guiding dreams to improve these outcomes. So long as we cannot guide dreams, we cannot do controlled experiments on dream content. TDI represents a breakthrough in this long standing methodological hurdle. A third reason is to open possibilities in the therapeutic domain. TDI may give patients and clinicians a lever of control to gain insight via dreams and to combat nightmares, which take a huge toll on people who struggle with anxiety and trauma. We have already begun a study in collaboration with Westley Youngren and the Veterans Affairs Office to test this application of TDI. Creatively, the rich history of luminaries using their dreams, and specifically the hypnagogic state (Sylvia Plath, Salvador Dalí, Edgar Allen Poe to name a few), to release creative potential points to the possibility of using TDI for targeted creative brainstorming. We've already run one experiment showing TDI can enhance creativity, but the real test is putting it in the hands of creatives all over. Which studies have used TDI? TDI was published in a 2020 paper in the journal Consciousness and Cognition, which was a collaboration between MIT, Harvard, and Boston College. This paper forms part of the journal’s larger Special Issue on Dream Engineering, collecting papers from sleep scientists around the world on their methods for researching and guiding dreams. This Special Issue came out of the Dream Engineering workshop which we hosted at the MIT Media Lab in 2019, gathering a community of researchers from around the world to empower the dream engineering field and link technologists with scientists for new collaboration. The community of dream engineers is growing; a recent paper from the Gori lab outlines a vision for engineering dreams to understand blindness. Together we’re hoping to generate and answer questions about the parts of our minds which can be hard to see, and make the tools that make answering them possible, and build dream-based therapies and interventions. You can read about our vision for the dream engineering movement here. In addition, TDI was central to Adam Haar Horowitz’s Master's thesis and PhD thesis. The experiments in Adam’s thesis focused on augmenting creativity with TDI (now published in Scientific Reports), using TDI to incubate REM dreams (not yet published), and using TDI to decrease feelings of helplessness/loss of agency related to nightmares (not yet published). If you want to see what the press is saying about those experiments, here is an article in The Scientist and here is one in MIT News. In other labs, TDI is being used in an experiment on PTSD related nightmares at University of Kansas and in an experiment on mind-wandering and dreams at Duke. ------------ What practices or past work inspired the development of TDI? The goal of TDI is both magnetic and unlikely: Can we really “engineer” dreams, our internal worlds that feel so fundamentally out of our control? We are far from the first to be excited about dreams and the possibility of guiding them. The incubation of specific dream content has fascinated people for millennia, from Ancient Egyptian spiritual practices and Canadian Indigenous dream sharing rituals to contemporary treatments for PTSD-related nightmares. While reliable techniques for dream incubation have proven elusive in the laboratory, yet it's crucial to know that targeted dream incubation (TDI) is a modern instantiation of an ancient technique. Here is a great summary of the myriad ways people have historically interfaced with dreams. Understanding that dream incubation is a practice that ranges from sacred to scientific space across cultures, and that it is a potentially powerful way to influence the mind, we are committed to (and continually updating) our ethics on the use of dream influencing technologies. Where can I read more about dream science? Dreams are a vast topic, touching everything from consciousness studies to sensor technologies to indigenous healing practices. Here we list a completely non-exhaustive set of potential ways to learn more about dreams, including many scholars who informed and inspired our own studies. Scientists like Stephen LaBerge and Benjamin Baird do wonderful work on later-stage lucid dreaming, focusing on the REM state. Scientists like Jonathan Smallwood, Paul Seli and Jonathan Schooler have done work on mind-wandering and creativity, inspiring our idea that fluid thinking outside of executive control in hypnagogia (like mind-wandering) could augment creativity. Work by Deirdre Barrett compiling moments of inspiration found in sleep, and work by Robert Stickgold and Tore Nielsen on microdream phenomenology, all encouraged and informed us. Andreas Mavromatis wrote a whole thesis on hypnagogia, and his writing gave us a sense of the poetry and practical applications of this state (as did Nabokov, Oliver Sacks, Yoga Nidra practitioners, and Edgar Allen Poe writing on hypnagogia). We also were inspired by Matthew Spellberg’s writing on dream sharing rituals, Kelly Bulkeley’s work on dreaming in world religions, and Robert Stickgold and Antonio Zadra’s book When Brains Dream. Research Topics #human-computer interaction #art #cognition #health #learning + teaching #neurobiology #wearable computing #behavioral science #ethics #creativity #technology #cognitive science #sleep #industry #wellbeing ------------- https://www.frontiersin.org/journals/human-neuroscience/articles/10.3389/fnhum.2025.1501209/full SYSTEMATIC REVIEW article Front. Hum. Neurosci., 03 March 2025 Sec. Brain Imaging and Stimulation Volume 19 - 2025 | https://doi.org/10.3389/fnhum.2025.1501209 This article is part of the Research TopicMethods in Brain StimulationView all 9 articles Transcutaneous and transcranial electrical stimulation for enhancing military performance: an update and systematic review Onno van der GroenOnno van der Groen1Sara A. RafiqueSara A. Rafique2Nick WillmotNick Willmot1Margaret G. Murphy,Margaret G. Murphy3,4Eulalia TisnovskyEulalia Tisnovsky4Tad T. Bruny, Tad T. Brunyé3,4* 1Defence Science and Technology Group, Human and Decision Sciences, Department of Defence, Edinburgh, SA, Australia 2Defence Science and Technology Laboratory, Salisbury, United Kingdom 3U.S. Army DEVCOM Soldier Center, Natick, MA, United States 4Center for Applied Brain and Cognitive Sciences, Tufts University, Medford, MA, United States Introduction: Electrical stimulation (ES), including transcranial electrical stimulation (tES) and transcutaneous vagus nerve stimulation (tVNS), has shown potential for cognitive enhancement in military contexts. Various types of ES, such as transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), modulate neuronal membrane potentials and cortical excitability, potentially improving cognitive functions relevant to military training and operations. Methods: This systematic review updates previous findings by examining studies published between 2019 and 2024 that investigated electrical stimulation effects on cognitive performance in military personnel and tasks. We focused on whether the studies addressed key questions about the generalizability of lab findings to military tasks, the frequency and intensity of adverse effects, the impact of repeated ES administration, and the ethical and regulatory considerations for its use in potentially vulnerable military populations. Results: Eleven studies met the inclusion criteria; most demonstrated overall low to some concerns, however, two of these had overall high risk of bias. While tES and tVNS showed some promise for enhancing multitasking and visual search performance, the results were mixed, with no reliable effects on vigilance tasks. Discussion: The reviewed studies highlight the need for a better understanding of ES mechanisms, optimal stimulation parameters, and individual differences in response to ES. They also highlight the importance of conducting high-powered research in military settings to evaluate the efficacy, safety, and ethical implications of ES. Future research should address the generalizability of lab-based results to real-world military tasks, monitor the frequency and intensity of adverse effects, and explore the long-term impacts of repeated administration. Furthermore, ethical and regulatory considerations are crucial for the responsible application of ES in military contexts, and a series of outstanding questions is posed to guide continuing research in this domain. 1 Introduction Electrical stimulation (ES) involves administering low intensity (0.5 m–3.0 mA) electrical current (direct or alternating) to the surface of the scalp or skin via two or more electrodes. Mechanistic models of transcranial ES (tES) suggest that the applied electrical current propagates through the skull, dura mater, arachnoid and subarachnoid space to modulate cortical neuronal membrane potentials (Galan-Gadea et al., 2023; Lefaucheur and Wendling, 2019; Molaee-Ardekani et al., 2013; Nitsche et al., 2008; Nitsche and Paulus, 2000; Reato et al., 2019). There are several different types of ES, including transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), transcranial random noise stimulation (tRNS), and transcutaneous vagus nerve stimulation (tVNS). tDCS applies a current, which can be excitatory (hypopolarization) or inhibitory (hyperpolarization), influencing local and distal networks of cortical and subcortical neurons (Kunze et al., 2016; Lefaucheur and Wendling, 2019). tACS is thought to influence neuronal oscillations, thereby affecting neuronal communication within the brain (Fries, 2005; Herrmann et al., 2013), and tRNS is a type of tACS that applies a frequency spectrum of alternating current likely acting on sodium channels (Chaieb et al., 2015; Schoen and Fromherz, 2008). Electrical current applied transcutaneously, for example, with auricular or cervical tVNS can affect cortical processing likely via modulation of brainstem activity, autonomic nervous system activity, and perhaps changes in cortical excitability (Capone et al., 2015). These distributed effects on neuronal activity can produce a broad range of behavioral effects in both clinical and non-clinical participants (Bestmann et al., 2015; Brunoni et al., 2012; Sun et al., 2021), including faster reaction times and/or improved accuracy on cognitive and motor tasks, and improved spatial working memory performance. Thus, ES holds potential for improving performance in military domains including aviation, training, and operations. In a series of comprehensive reviews on enhancement research for military applications, tES is identified as a promising method for altering cognitive function in military personnel in addition to other interventions, for example, augmented reality, mindfulness training, and sleep modification (Brunyé et al., 2020; Davis and Smith, 2019; Feltman et al., 2019; Lu et al., 2022; Peltier et al., 2019). Research using tES to target the dorsolateral prefrontal cortex (DLPFC), medial temporal lobes, fusiform gyrus, and frontopolar regions have shown beneficial effects on cognitive functions ranging from vigilance and threat detection to executive function, face memory, and creative problem solving (Brunyé et al., 2017; Koizumi et al., 2020; McKinley et al., 2012). Despite these initial promising results, overarching conclusions from these reviews and others (including meta-analyses) consistently point to equivocal results across published research and a need to better understand a multitude of outstanding questions (see Table 1) (de Berker et al., 2013; Brunoni et al., 2012; Horvath et al., 2014, 2015, 2016; Imburgio and Orr, 2018; Paulus, 2014; Prehn and Flöel, 2015). These outstanding questions generally cover topics related to underlying mechanisms, experimental methodology, task-related outcomes, short-and long-term effects, adverse effects, individual differences, ethics and regulation, and generalizability of laboratory findings to military contexts and tasks. Table 1 www.frontiersin.org Table 1. Outstanding research questions to guide continuing research and development with ES, with an emphasis on eventual military applications. A recent systematic review of transcranial direct current stimulation (tDCS) effects on performance enhancement in military contexts examined 34 articles published between 2008 and 2018 (Feltman et al., 2019). This review was restricted to randomized controlled experimental designs with military-age (18–50 years) healthy non-clinical samples. Most examined articles (26 of 34) reported some positive effects of tDCS on cognitive performance, including executive function (2), learning (6), creativity and cognitive flexibility (2), perception and attention (8), memory (3), and working memory (7). Based on the results of the review, the authors suggest promise for tES, and tDCS in particular, imparting positive effects on cognitive functions with applicability to military contexts. The present systematic review was conducted to update the most recent review (Feltman et al., 2019). We identified articles using military personnel and/or military outcome tasks published in 2019–2024. We assessed whether the identified studies adequately addressed any of the questions posed in Table 1. We first briefly summarize the prospective application of ES in military training and operations, and some of the challenges in realizing this goal. We then discuss the questions posed in Table 1 and detail the methodology and results of our systematic review. 2 Cognitive performance in military contexts Cognitive performance is a critical factor responsible for successes and failures during military training and operations with cognitive decrements estimated to account for the majority (80–85%) of accidents during military training and operations (Thomas and Russo, 2007). Many core cognitive functions are therefore foundational to the successful performance of a broad range of military tasks. The cognitive tasks demanded of military personnel vary widely as a function of military occupational specialization and level of responsibility introduced by ascending rank (echelon). According to an international expert consensus panel, critical among those cognitive functions are attention and vigilance, processing speed, cognitive control (performance monitoring, response selection, inhibition, goal selection/updating/maintenance), shifting, self-knowledge, visual perception, and understanding others’ mental states (Albertella et al., 2023). Examples of tactical-level military tasks critically involving each of these cognitive functions are detailed in Table 2. ----------- One unique aspect of military training and operations is that they are conducted under high levels of cognitive and physical stress, energy imbalance, sleep loss, dehydration, and thermal burden (Adler et al., 2004; Brunyé et al., 2021; Campbell and Nobel, 2009). Many of these states independently and interactively produce acute impairments of cognitive function (Brunyé et al., 2021; Flood and Keegan, 2022; Lieberman et al., 2002, 2005, 2006, 2009; Orasanu and Backer, 1996; Vartanian et al., 2018). For example, the psychological stress imposed during combat-like training of elite military units is associated with impairments of attention and vigilance, memory, and reasoning (Lieberman et al., 2005). Sleep loss slows processing speed and lengthens reaction times, lowers task accuracy, and negatively influences moral decision making (Good et al., 2020; Petrofsky et al., 2022). Calorie deprivation causes decrements in executive function (Giles et al., 2019) (but also (see Lieberman et al., 2008)); dehydration impairs executive function, attention, and motor skills (Wittbrodt and Millard-Stafford, 2018); and both cold and heat stress negatively influence higher-level cognitive functions (Martin et al., 2019). Given that ES may hold potential for improving performance in each of these cognitive functions, it is explored as a tool to remediate cognitive decrements induced by the physical and cognitive demands of military training and operations. As such, some studies using ES interventions examine effects under conditions of relative stress and adversity, complementing basic research done in relatively comfortable settings. 3 Outstanding questions for research and application In Table 1, we posed a series of questions valuable for guiding continuing research examining the prospective application of ES to military contexts and tasks. We briefly summarize each question below, and then detail the methods and results of our systematic review. A more exhaustive list of outstanding questions is included in the Discussion section, broadly motivating continuing research and application. 3.1 Question 1: can ES effects on performance in laboratory contexts generalize to realistic and complex military tasks? The generalizability of human sciences, particularly in the domain of human performance, offers both opportunities and challenges when transitioning from basic research to applied military settings (Blacker et al., 2019; Goodwin et al., 2018; Hedrick et al., 1993; Shenberger-Trujillo and Kurinec, 2016). Basic research provides a foundational and mechanistic understanding of human behavior, cognition, and performance, which can inform application to military contexts such as training and operations. The perceptual, cognitive, and affective processes responsible for executing laboratory tasks are foundational, theoretically underlying the performance of any cognitive task, in any context. Basic research therefore enables the development of broadly applicable strategies for adopting new tools and technologies. However, challenges arise in transferring discoveries made in basic research to diverse real-world scenarios. With respect to military applications, there are inherent contextual differences between controlled laboratory environments and complex military operations, inter-and intra-individual variability in human performance, operational constraints such as high-stress environments, and security concerns regarding the application of susceptible technologies to potentially vulnerable populations of military personnel (Blacker et al., 2019; Hedrick et al., 1993; Niemeyer, 2009). It is important to conduct high-powered research in military settings, with military personnel, using military tasks and relevant performance outcomes. Addressing these challenges necessitates interdisciplinary collaboration among researchers, military professionals, and policymakers to ensure that insights from basic research are effectively translated into practical applications while considering the unique complexities of military training and operations. For example, while tDCS targeting the DLPFC shows promise for improving outcomes on abstract working memory tasks performed in laboratory settings, does it improve outcomes in relatively demanding and dynamic contexts with challenging and highly applied tasks (e.g., processing and manipulating verbal and spatial information in the context of tactical communications)? The relatively small effect sizes seen on the aggregate when examining links between tES and cognitive performance (Brunoni and Vanderhasselt, 2014; Hill et al., 2016; Horvath et al., 2015) could suggest it is unlikely to affect performance on relatively variable tasks performed in noisy contexts. Similarly, the promising effects of combining tES with working memory training may or may not transfer to similar tasks performed outside of a laboratory context. It has indeed been challenging to find evidence for such transfer within the laboratory itself (Brunoni and Vanderhasselt, 2014; Melby-Lervåg et al., 2016; Pergher et al., 2022). 3.2 Question 2: what are the frequency and intensity of acute and/or long-term adverse effects? Acute adverse effects of ES administration include those occurring during or immediately after stimulation (Antal et al., 2017). An early systematic review of tDCS-associated adverse effects (Brunoni et al., 2011) found the most frequently reported effects compared to sham to be itching (39.3% vs. 32.9%), tingling (22.2% vs. 18.3%), a burning sensation at the electrode site(s) (8.7% vs. 10%), headache (14.8% vs. 16.2%), and discomfort (10.4% vs. 13.4%). However, the reporting of adverse events was generally inadequate and likely biased, limiting the ability to effectively assess their frequency, intensity, and presence across experimental conditions. A more recent review found that most adverse effects of tDCS are mild, not considered serious, and short-lived, but that relatively prolonged adverse effects can also occur—namely skin lesions; and mania or hypomania primarily in patients with depression. Similarly, these adverse events were inconsistently reported and the authors suggest that further investigations are needed to characterize their type, frequency, intensity, and duration (Matsumoto and Ugawa, 2017). A systematic review of tVNS found the most common adverse effects to be local skin irritation from electrode placement (18.2%), headache (3.6%), and nasopharyngitis (1.7%), with a minority (2.6%) dropping out of the studies due to tolerability. Stimulation was not accounted for in the heterogeneity of effects from these studies as many of the studies did not report all parameters (Redgrave et al., 2018). A more recent systematic review and meta-analysis of auricular tVNS reported that half of the studies did not disclose whether adverse effects were recorded. The most frequently reported adverse effects were ear pain, headache, and tingling. Overall, there were no differences in the risk of adverse effects following auricular tVNS when compared to controls. There appears to be no causal relationship between taVNS and severe adverse events (Kim et al., 2022). ------------- 3.3 Question 3: what are the effects of repeated ES administration on tolerability, brain structure and function, and behavior? A large systematic review and meta-analysis on tolerability found that higher levels of tDCS exposure through repeated administration (typically separated by 1 day) do not increase the incidence or intensity of adverse events, and did not vary across clinical and non-clinical groups (Nikolin et al., 2018, 2019). An additional study examining five tDCS sessions within a 25-h period found no serious adverse events, but did report mild adverse effects including scalp erythema, tingling and burning sensation at the electrode site, and a transient metallic taste (Zappasodi et al., 2018). The effect of repeated tDCS assessed with neuroimaging has yielded variable results. No metabolite changes are observed during magnetic resonance spectroscopy following five tDCS sessions within 25-h periods (Zappasodi et al., 2018). Similarly, no change in blood-based metabolic biomarkers indicative of neuronal atrophy are observed following five tDCS sessions (Kortteenniemi et al., 2020). In contrast, three sessions of prefrontal tDCS were found to increase resting cerebral profusion in the locus coeruleus that persisted across sessions of active stimulation (Sherwood et al., 2021). Another study examining three sessions of prefrontal tDCS showed highly variable effects on resting-state functional connectivity that resulted in extremely low intra-participant reliability. Interestingly, intra-participant reliability was relatively high in a sham condition, suggesting that tDCS exerts markedly different functional effects across sessions, i.e., dose dependent effects (Wörsching et al., 2017). Moreover, low intra-individual variability is observed in tDCS-induced motor evoked potentials over the course of three sessions, suggesting a general lack of habituation (Ammann et al., 2017). These studies suggest that effects of repeated tDCS administration are very difficult to predict within and across individuals. While preliminary evidence suggests that repeated tDCS administration is safe and tolerable, this is far from exhaustive, and more research is needed to understand how higher exposures (intensity, duration, frequency) and other types of ES affect tolerability, brain, and behavior. Much remains unknown about the chronic risk profile of ES. With the proliferation of ES devices onto the open consumer market, this is a particularly important question to consider. While laboratory studies with humans might typically consider the effects of 3–5 sessions, home users of do-it-yourself consumer devices can administer ES multiple times a day for months or years, resulting in over 100 sessions of self-administered ES (Jwa, 2015; Wexler, 2016, 2018; Wexler and Reiner, 2017, 2019). In addition to skin lesions and burns reported by home users, there are potential long-term effects of repeated exposures to direct ES of the scalp, skull, meninges, and cortex. Additional insights can be gathered from clinical trials involving multi-session tDCS administration over the course of days and weeks. For example, when examining patients with bipolar depression, Sampai-Junior and colleagues demonstrated no difference in rates of adverse events between sham and active groups after 12 daily sessions over 6 weeks (at 2 mA for 30 min), but noted some evidence for increased reports of localized skin redness in the active group (Sampaio-Junior et al., 2018). Similar findings were noted in a clinical trial examining the effect of repeated tDCS (21 sessions, 2 mA for 30 min) in patients with major depressive disorder (MDD), demonstrating no differences between groups in the frequency or severity of adverse events, while noting increased rates of local skin redness and heat or burning sensations in the active group (Borrione et al., 2024). While these results are compelling, it will be important to understand not only subject experiences but also potential effects on biomarkers of neuronal integrity over the course of dozens or hundreds of sessions. 4 Systematic review method Herein we describe our search strategy, inclusion and exclusion criteria, study selection, data extraction, and risk of bias assessments. The full PRISMA diagram can be found in Figure 1. Figure 1 --------------- The authors conclude that there is an urgent need for research to parametrically manipulate and probe independent and interactive effects across relatively complex parameter spaces. 6.1.3 Understanding effects of individual differences How do individual differences influence ES effects? The effects of individual differences on ES-related outcomes have been examined in three primary ways. First, studies have examined how individual differences in brain structural and functional characteristics affect physiological and behavioral responses to ES. For example, individual differences in prefrontal cortical thickness influence tDCS effects on decision-making (Filmer et al., 2019). Additionally, tDCS-induced changes in resting-state functional connectivity are associated with differences in visual object-matching task performance (Pupíková et al., 2022). Secondly, studies have examined how individual differences in personality traits affect physiological and behavioral responses to tES (Brunyé et al., 2014, 2015; Krause and Cohen Kadosh, 2014). For example, tDCS affects reading speed of social sentences in readers with low scores on the behavioral approach and inhibition scales, but not those with high scores (Reyes et al., 2021); and trait anxiety modulates the effects of tDCS on creative task performance (Xiang et al., 2021). Third, studies have examined how individual differences in baseline knowledge or task proficiency affect physiological and behavioral responses to ES (Splittgerber et al., 2020). For example, tDCS increases the creativity of improvised instrument play for novices but harms expert performance (Rosen et al., 2016); and those with lower baseline reading proficiency show greater positive effects of tDCS on cross-language speech production (Bhattacharjee et al., 2020). Given the inherent heterogeneity of military personnel, the effects of relatively invariant individual characteristics is an important research topic. Individually tailored paradigms are likely needed, factoring in complex interacting variables (e.g., stimulating parameters, physiological, anatomical, and genetic differences). Personalized protocols do however raise challenges in a military setting, such as time constraints and practicalities. Recent research has further demonstrated large intra-individual variability in responses to repeat sessions of tDCS in that individuals did not respond consistently to tDCS when applied repeatedly over time (Willmot et al., 2024). 6.1.4 Quantifying enhancement beyond baseline functioning Can ES support and optimize performance, or does it truly enhance performance beyond baseline functioning? While the notion of cognitive enhancement is intriguing (Bostrom and Sandberg, 2009; Farah, 2015; Farah et al., 2014), it is challenging to truly demonstrate enhancement as opposed to performance sustainment or optimization, per se (Brunyé et al., 2020). Several philosophical positions conceptualize that enhancement must improve functioning of an individual beyond their normal range (Agar, 2013; Menuz et al., 2013). True enhancement would transcend the biological limits shaped by millennia of evolution—defining such biological limits will be critical, both within and across individuals. Demonstrating true enhancement requires quantitatively establishing baselines of an individual’s optimal biological performance potential under optimal conditions. For example, under an idealized set of hypothetical conditions, what could an individual achieve for reaction times, accuracy levels, or any other outcome of interest? Only when biotechnology-induced performance exceeds what has been established as innate optimal performance can it truly be deemed enhancement. In most cases, including when ES mitigates the performance deleterious effects of a contextual factor (e.g., sleep deprivation, stress, fatigue) (Hart-Pomerantz et al., 2024), performance is being sustained or optimized relative to a control condition that attempts to mimic some aspects of active experimental conditions (e.g., sham procedures with ES). These are important empirical comparisons, but they may not allow us to quantify the biological limits of performance or make inferences about enhancement. Moreover, military personnel might already be at their performance upper limit due to their training, limiting the effectiveness of ES. For example some tDCS studies in military samples did not observe any additional performance benefits (Blacker et al., 2020; Willmot et al., 2023). Visual search is required in many professions where an undetected threat, such as a weapon, can put the well-being of others at risk. Given the importance of detecting these threats, researchers have used various experimental techniques to improve performance in visual search tasks, albeit with varying degrees of success. Here, we explore two promising techniques to improve visual search using ecologically valid synthetic aperture radar stimuli: object recognition training and search strategy training. Search strategy training is intended to make observers search more systematically through a display, whereas object recognition training is intended to improve observers’ ability to recognize critical targets. Search strategy training was implemented by instructing participants to scan through the display in a pre-specified pattern. Object recognition training was implemented by having participants discriminate between targets and non-targets. We also manipulated whether observers received anodal or sham transcranial direct current stimulation (tDCS) during training, which has been shown to improve visual search performance and target learning. To measure the effectiveness of the training and stimulation conditions, we tested object recognition accuracy and overall visual search performance before and after three sessions of increasingly difficult training. Results indicated that object recognition training significantly improved object recognition accuracy relative to the search strategy group, whereas search strategy training was effective in improving visual search accuracy in those who adhered to the training. However, tDCS did not interact with training type, and although both training types yielded significant improvements, training-related improvements were not significantly different between the different approaches. This evidence suggests that strategy-based training could be as effective as the more prototypical object recognition training. Moreover, interactions between baseline performance and tDCS effectiveness have been demonstrated (Splittgerber et al., 2020). Whether ES can further improve performance in high performing individuals remains an open question. ----------- Author contributions OG: Conceptualization, Methodology, Writing – original draft, Writing – review & editing. SR: Conceptualization, Methodology, Writing – original draft, Writing – review & editing. NW: Conceptualization, Methodology, Writing – original draft, Writing – review & editing, Investigation. MM: Data curation, Investigation, Methodology, Writing – review & editing. ET: Conceptualization, Data curation, Investigation, Methodology, Writing – review & editing. TB: Conceptualization, Methodology, Writing – original draft, Writing – review & editing, Funding acquisition, Supervision. Funding The author(s) declare financial support was received for the research, authorship, and/or publication of this article. Personnel time to support OG, SR, NW, and TB was funded by the authors’ respective institutions. MM and ET were funded by the U. S. Army DEVCOM Soldier Center via grant W911QY-19–2–0003 awarded to Tufts University. Conflict of interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision. Publisher’s note All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher. Author disclaimer The views expressed in this article are solely those of the authors and do not reflect the official policies or positions of the Department of Army, the Department of Defense, or any other department or agency of the U.S. government. 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