Individually optimized multi-channel tDCS for targeting somatosensory cortex

Objective - Transcranial direct current stimulation (tDCS) is a non-invasive neuro-modulation technique that delivers current through the scalp by a pair of patch electrodes (2-Patch). This study proposes a new multi-channel tDCS (mc-tDCS) optimization method, the distributed constrained maximum intensity (D-CMI) approach. For targeting the P20/N20 somatosensory source at Brodmann area 3b, an integrated combined magnetoencephalography (MEG) and electroencephalography (EEG) source analysis is used with individualized skull conductivity calibrated realistic head modeling. - Methods - Simulated electric fields (EF) for our new D-CMI method and the already known maximum intensity (MI), alternating direction method of multipliers (ADMM) and 2-Patch methods were produced and compared for the individualized P20/N20 somatosensory target for 10 subjects. - Results - D-CMI and MI showed highest intensities parallel to the P20/N20 target compared to ADMM and 2-Patch, with ADMM achieving highest focality. D-CMI showed a slight reduction in intensity compared to MI while reducing side effects and skin level sensations by current distribution over multiple stimulation electrodes. - Conclusion - Individualized D-CMI montages are preferred for our follow up somatosensory experiment to provide a good balance between high current intensities at the target and reduced side effects and skin sensations. - Significance - An integrated combined MEG and EEG source analysis with D-CMI montages for mc-tDCS stimulation potentially can improve control, reproducibility and reduce sensitivity differences between sham and real stimulations

Optimising the Application of Transcranial Direct Current Stimulation

The ability of transcranial direct current stimulation (tDCS) to modulate brain activity has vast scientific and therapeutic potential, however, its effects are often variable which limit its utility. Both current flow direction and variance in electric field intensities reaching a cortical target may be vital sources of the variable tDCS effects on neuroplastic change. Controlling for these and exploring the subsequent effects on corticospinal excitability is the aim of this thesis. I here attempted to optimise the delivery of tDCS application by investigating the controlled application of current flow direction and whether through the use of current flow models, we can deliver comparable electric fields with reduced variability across differential montages. To assess whether current flow models are useful, I further investigated if dose-control translates to more consistent physiological outcomes. I demonstrate, firstly, that different current flow directions did not differentially affect the two banks of the central sulcus. Secondly, with the use of dose-control, high-definition tDCS (HD-tDCS) remains focally more advantageous, even with the delivery of comparable electric field intensity and variability as posterior-anterior tDCS (PA-tDCS) to a cortical region. Thirdly, dose-controlled tDCS does not translate to reduced physiological variability. Together, the work presented here suggests that current flow models are useful for informing dose-controlled protocols and montage comparisons for improved tDCS delivery, however, controlling for anatomical differences in the delivery of electric fields to a target is not sufficient to reduce the variability of tDCS effects in physiology. Thus, the methodology for optimised tDCS delivery remains a subject for further improvement and investigation. Advancements in this field may lead to a trusted methodology assisting stroke survivors with a more effective and efficient motor recovery journey

Targeting the Brain in Brain-Computer Interfacing: The Effect of Transcranial Current Stimulation and Control of a Physical Effector on Performance and Electrophysiology Underlying Noninvasive Brain-Computer Interfaces

University of Minnesota Ph.D. dissertation. July 2017. Major: Biomedical Engineering. Advisor: Bin He. 1 computer file (PDF); vii, 123 pages.Brain-computer interfaces (BCIs) and neuromodulation technologies have recently begun to fulfill their promises of restoring function, improving rehabilitation, and enhancing abilities and learning. However, lengthy user training to achieve acceptable accuracy is a barrier to BCI acceptance and use by patients and the general population. Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation technology whereby a low level of electrical current is injected into the brain to alter neural activity and has been found to improve motor learning and task performance. A barrier to optimizing behavioral effects of tDCS is that we do not yet understand how neural networks are affected by stimulation and how stimulation interacts with ongoing endogenous activity. The purpose of this dissertation was to elucidate strategies to improve BCI control by targeting the user through two approaches: 1. Subject control of a robotic arm to enhance user motivation and 2. tDCS application to improve behavioral outcomes and alter networks underlying sensorimotor rhythm-based BCI performance. The primary results illustrate that targeted tDCS of the motor network interacts with task specific neural activity to improve BCI performance and alter neural electrophysiology. This effect on neural activity extended across the task network, beyond the area of direct stimulation, and altered connectivity unilaterally and bilaterally between frontal and parietal cortical regions. These findings suggest targeted neuromodulation interacts with endogenous neural activity and can be used to improve motor-cognitive task performance

An Examination of Brain Network Organization and the Analgesic Mechanisms of a Non-Pharmacological Treatment in Chronic Centralized Pain

Chronic pain is a global public health challenge, affecting nearly one third of adults worldwide. Current treatments are inadequate, especially since some of the mainstay therapies (e.g. opioids, NSAIDs) are often ineffective and/or associated with significant toxicity. The solution to these problems requires an improved understanding of chronic pain pathology, particularly the role that the brain plays in causing or amplifying pain perception, and how analgesic intervention might target these brain-based mechanisms. This dissertation aims to identify brain network alterations in fibromyalgia (FM), a common and canonical chronic pain condition with presumed CNS pathology, and determine how non-invasive brain stimulation may target aberrant brain network connectivity to promote analgesia. Across a wide range of diverse neurological disorders, hubs (i.e. highly connected brain regions) appear to be disrupted and the character of this disruption can yield insights into the pathophysiology of these disorders. In Chapter 2, we describe the application of a brain network based approach to examine hub topology in FM patients compared to healthy volunteers. We identified significant disruptions in hub rank order in FM patients. In FM, but not controls, the anterior insula was a hub with significantly higher inter-modular connectivity and membership in the rich club (a functional backbone of connectivity formed by highly interconnected hubs). Among FM patients, rich club membership varied with the intensity of clinical pain: the posterior insula, primary somatosensory and motor cortices belonged to the rich club only in FM patients with the highest pain. Further, we found that the eigenvector centrality (a measure of how connected a brain region is to other highly connected regions) of the posterior insula positively correlated with clinical pain, and mediated the relationship between levels of glutamate + glutamine within this structure and the patient’s subjective clinical pain report. Together, these findings demonstrate an altered hub topology in FM and are the first to suggest that disruptions in the excitatory tone within the insula could alter the strength of the insula as a hub and subsequently lead to increased clinical pain. Transcranial direct current stimulation (tDCS) has emerged as an attractive noninvasive treatment for pain, given its ability to target specific cortical regions with relatively few side effects. Motor cortex (M1) tDCS relieves pain in FM, but the analgesic mechanism remains unknown. In Chapter 3, we measured changes in resting state functional connectivity after sham and real M1 tDCS in twelve FM patients and examined if these changes were related to subsequent analgesia. M1 tDCS (compared to sham) reduced pro-nociceptive functional connectivity, specifically between the motor and sensory nuclei of the thalamus and multiple cortical regions, including primary motor and somatosensory areas. Interestingly, decreased connectivity between the thalamus and posterior insula, M1 and somatosensory cortices correlated with reductions in clinical pain after both sham and active treatment. These results suggest that while there may be a placebo response common to both sham and real tDCS, repetitive M1 tDCS causes distinct changes in functional connectivity that last beyond the stimulation period and may produce analgesia by inhibiting pro-nociceptive thalamic connectivity. This research offers new insight into the neurobiology of chronic centralized pain conditions and contributes to the understanding of how non-invasive brain stimulation causes analgesia. This knowledge could lead to more informed stimulation sites and personalized treatment based on network connectivity in each individual patient.PHDNeuroscienceUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143930/1/chelsmar_1.pd

Investigation of Methodological and Physiological Factors Influencing Non-Invasive Transcranial Electrical Brain Stimulation

Non-invasive transcranial electrical brain stimulation (tES) techniques, including transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS) and transcranial random noise stimulation (tRNS), can alter neuronal activity and related brain functions. However, tES effects seem to be modulated by various influencing factors, leading to high inter-individual variability in tES effects and often only low effect sizes, or even no effects. The present thesis therefore aimed to investigate methodological and physiological influencing factors of tDCS, tACS and tRNS that have not been sufficiently examined so far. A first study investigated the influence of montage and individual functional performance level on the effects of anodal tDCS over the left dorsolateral prefrontal cortex (DLPFC) in healthy adults. Compared with sham stimulation, a multichannel montage led to stronger effects than a bipolar montage. For both montages the effects of stimulation were dependent on the functional performance level of participants. A second study investigated the effects of multichannel tDCS over the left DLPFC in healthy children and adolescents, considering the influence of concurrent target task performance during stimulation and individual head anatomy. tDCS did not influence the target outcome but led to transfer effects on non-target task performance and neurophysiological activity, that were only partly influenced by task performance during stimulation. The individual head anatomy had no influence on stimulation effects. A third study investigated tACS and tRNS effects on motor cortex excitability in healthy children and adolescents in comparison to adults. The individual response to sham stimulation was investigated as marker for the individual physiological brain state. Motor cortex excitability was not modulated by age but by individual response to sham stimulation. All studies provide important insights into the modulatory factors of stimulation effects. Based on these results, future studies should aim at individualising tES application

Neuroenhancement in Military Personnel::Conceptual and Methodological Promises and Challenges

Military personnel face harsh conditions that strain their physical and mental well-being, depleting resources necessary for sustained operational performance. Future operations will impose even greater demands on soldiers in austere environments with limited support, and new training and technological approaches are essential. This report highlights the progress in cognitive neuroenhancement research, exploring techniques such as neuromodulation and neurofeedback, and emphasizes the inherent challenges and future directions in the field of cognitive neuroenhancement for selection, training, operations, and recovery