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Closed-Loop Feedback Control for Transcranial Direct Current Stimulation


TECHNOLOGY AREA(S): Human Systems 

OBJECTIVE: Develop a physiological recording and feedback control system to monitor operator cognitive state and control a small, head mounted transcranial direct current stimulation system. 

DESCRIPTION: Due to the increasing need for intelligence, surveillance, and reconnaissance missions in modern warfare, human analysts are in great demand. However, human analyst resources are limited and costly to produce. Multiple trends and technical innovations in ISR continue to increase demands upon analysts, such as: (i) a growing need for persistent operation of ISR platforms; (ii) the use of heterogeneous sensor suites to address more challenging obscured and cluttered environments; (iii) generation of increasingly large volumes of imagery by ISR sensors and platforms; and (iv) the need for efficient fusion of information extracted by different analysts from different segments of data. These trends, together with the perishable nature of information contained in the raw data, create a critical and growing need for novel approaches and techniques that enhance analysts' ability to perform at high levels of proficiency for extended periods of operation. The limits of performance of image analysts are dominantly determined by their neuro- and psycho- physiological characteristics (e.g. learning capacity, fatigue resistance, attention span, motivation, engagement) that are jointly referred to as dynamic brain information processing capacity (dBIPC). Their dBIPC fluctuates under the influence of numerous intrinsic and extrinsic factors, including chronic and acute stressors, pharmacological agents, mood state, and environmental distracters [1]. In theory, operational performance could be improved by continuously monitoring dBIPC to determine an analysts' cognitive state and then modify (boost) dBIPC during operations. Practical implementation of the concept has, however, been hampered by lack of tools for unobtrusive monitoring of relevant aspects of dBICP and lack of validated methods for their augmentation. Recent developments in brain and physiological monitoring hardware may have bridged this gap so that a deployable system can be developed that is effective in boosting dBIPC, easy to use, inexpensive, safe and deployable in operational environments. For example, inexpensive multichannel, portable, battery-powered EEG recording platforms are now available that could be utilized for safe and unobtrusive monitoring of the electrical activity of the brain during relevant tasks. Likewise, modern eye tracking systems are small and can be easily incorporated on or off-body. Numerous studies have correlated changes in EEG and eye tracking features with various aspects of cognition or underlying task performance [2]. Similar findings have been reported for functional near-infrared spectroscopy (fNIRS), another brain monitoring technology that is potentially field-deployable [3]. Transcranial direct current stimulation (tDCS) is one method that can be used to modulate cognitive state [4] without potentially addictive pharmaceuticals or the addition of additional obligations, such as stress management programs, on the already thinly stretched human analyst resources. The tDCS technique is an attractive option for increasing or sustaining dBIPC during the task because of its comparative technical simplicity and ease of integration with a physiological monitoring platform into a system capable of delivering the stimulation when and where needed to enhance or sustain performance. For example, such system could operate in a closed-loop and (1) detect performance degradation through physiology, (2) deliver targeted stimulation to relevant brain regions to counter the degradation, (3) evaluate the effects of tDCS on performance, and (4) adjust the tDCS parameters accordingly. 

PHASE I: Design/develop an innovative concept for monitoring human operator cognitive state and modulating dBIPC with transcranial direct current stimulation. The system/concept designed should be capable of measuring changes in operator fatigue and attention. Develop design requirements and engineering specifications for a fully deployable system. 

PHASE II: Develop, test, and evaluate a deployable closed loop tDCS system with physiologic feedback and demonstrate accurate operator state assessment and performance sustainment/improvement compared to a sham control. Sensors and electrodes must be easily applied and suitable for operational settings with real-time data analysis to provide a means for closed-loop integration with the tDCS. The hardware should be small and lightweight. 

PHASE III: Ultimately, this effort will result in a neuromodulation device capable of assessing the operator's attentional and fatigue state and apply stimulation when needed to enhance performance or reduce effects of stressors. Military: Image analysis, special operations, cyber defense, etc. 


1. Lieberman HR, Tharion WJ, Shukitt-Hale B, Speckman, KL, Tulley, R. Effects of caffeine, sleep loss, and stress on cognitive performance and mood during U.S. Navy SEAL training. Psychopharmacology 164:250-261, 2002.

2. Jerbi K, Ossandon T, Hamame CM, Senova S, Dalal SS, Jung J, Minotti L, Bertrand O, Berthoz A, Kahane P, Lachaux JP. Task-related gamma-band dynamics from an intracerebral perspective: review and implications for surface EEG and MEG. Human Brain Mapping, 2009.

3. James DR, Orihuela-Espina F, Leff DR, Mylonas GP, Kwok KW, Darzi AW, Yang GZ. Cognitive burden estimation for visuomotor learning with fNIRS. MICCAI 2010.

4. Silvanto J, Muggleton N, Walsh V. State-dependency in brain stimulation studies of perception and cognition. Trends Cogn Sci. Dec;12(12):447-54, 2008.


KEYWORDS: Transcranial Direct Current Stimulation (tDCS), Non-invasive Brain Stimulation (NIBS), Attention, Vigilance, Cognition, Fatigue, Neuroscience 

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