Transcranial Stimulation Methods Research Articles

A head template for computational dose modelling for transcranial focused ultrasound stimulation

Transcranial focused Ultrasound Stimulation (TUS) at low intensities is emerging as a novel non-invasive brain stimulation method with higher spatial resolution than established transcranial stimulation methods and the ability to selectively stimulate also deep brain areas. Accurate control of the focus position and strength of the TUS acoustic waves is important to enable a beneficial use of the high spatial resolution and to ensure safety. As the human skull causes strong attenuation and distortion of the waves, simulations of the transmitted waves are needed to accurately determine the TUS dose distribution inside the cranial cavity. The simulations require information of the skull morphology and its acoustic properties. Ideally, they are informed by computed tomography (CT) images of the individual head. However, suited individual imaging data is often not readily available. For this reason, we here introduce and validate a head template that can be used to estimate the average effects of the skull on the TUS acoustic wave in the population.The template was created from CT images of the heads of 29 individuals of different ages (between 20–50 years), gender and ethnicity using an iterative non-linear co-registration procedure. For validation, we compared acoustic and thermal simulations based on the template to the average of the simulation results of all 29 individual datasets. Acoustic simulations were performed for a model of a focused transducer driven at 500 kHz, placed at 24 standardized positions by means of the EEG 10–10 system. Additional simulations at 250 kHz and 750 kHz at 16 of the positions were used for further confirmation. The amount of ultrasound-induced heating at 500 kHz was estimated for the same 16 transducer positions. Our results show that the template represents the median of the acoustic pressure and temperature maps from the individuals reasonably well in most cases. This underpins the usefulness of the template for the planning and optimization of TUS interventions in studies of healthy young adults. Our results further indicate that the amount of variability between the individual simulation results depends on the position. Specifically, the simulated ultrasound-induced heating inside the skull exhibited strong interindividual variability for three posterior positions close to the midline, caused by a high variability of the local skull shape and composition. This should be taken into account when interpreting simulation results based on the template.

Advances in applications of head mounted devices (HMDs): Physical techniques for drug delivery and neuromodulation.

Head-mounted medical devices (HMDs) are disruptive inventions representing laboratories and clinical institutions worldwide are climbing the apexes of brain science. These complex devices are inextricably linked with a wide range knowledge containing the Physics, Imaging, Biomedical engineering, Biology and Pharmacology, particularly could be specifically designed for individuals, and finally exerting integrated bio-effect. The salient characteristics of them are non-invasive intervening in human brain's physiological structures, and alterating the biological process, such as thermal ablating the tumor, opening the BBB to deliver drugs and neuromodulating to enhance cognitive performance or help to manipulate prosthetic. The increasing demand and universally accepted of them have set off a dramatic upsurge in HMDs' studies, seminal applications of them span from clinical use to psychiatric disorders and neurological modulation. With subsequent pre-clinical studies and human trials emerging, the mechanisms of transcranial stimulation methods of them were widely studied, and could be basically came down to three notable approach: magnetic, electrical and ultrasonic stimulation. This review provides a comprehensive overviews of their stimulating mechanisms, and recent advances in clinic and military. We describe the potential impact of HMDs on brain science, and current challenges to extensively adopt them as promising alternative treating tools.

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Introduction:The evolution of electrical stimulation of brain as a treatment modality began with discovery of electrical properties of Catfish by Egyptians. The birth of DC generator in 1st century and study of its effects on neuronal excitability by Priori in 1998 led to the development of modern tDCS, a non-invasive, cost-effective neuromodulation technique. tDCS which is one of the transcranial stimulation methods among others (tACS, tPCS, tRNS, sotDCS) have shown therapeutic utility in schizophrenia, mood and anxiety/child psychiatric/substance use disorders, cognitive enhancement and pain management. Mechanism of action: tDCS causes polarization of RMP through two electrodes placed on scalp; anode with excitability-enhancing; and cathode with inhibitory-enhancing effects. Recent studies show that it reduces level of biomarkers implicated in various neuropsychiatric disorders, causing symptomatic improvement. Electrode Placement: Electrode positioning is made through precise measurements using the International 10–20 System of Electrode Placement. The DLPFC (F3/F4) is the most common site targeted effectively in depression, schizophrenia and substance use disorders and rATL is targeted in Insight and problem-solving. Parameters of Stimulation: The usual electrode sizes are of 25–35 cm2 with currents of 1–2 mA applied for up to 20–40 minutes. The 2.0 mA current for 5-30 minutes is the optimal therapeutic dose preferred in most studies. Safety and Tolerability of Procedure: The usual side effects are mild pain/itching/tingling, redness, insomnia and headache, which are transient and largely tolerable, and has proven to be in overall a safe procedure.

Theta rhythm, attention and transcranial stimulation method

Noninvasive methods of transcranial stimulation in clinical and research activity have become widely applied for the last few years. Due to the high spatial and temporal resolution, these methods allow to explore oscillatory processes that underlie important cognitive functions on a new level. In particular, researchers got an opportunity to influence rhythmic processes, which provide function of attention by these methods. By the way, stimulation of different brain zones with theta-rhythm frequency appears to be interesting, as far as oscillations of attention on this frequency reveal itself both in external activity of subject and in oscillatory activity of neurons and neural ensembles. Aim – analysis and summarize of domestic and foreign researches with usage of transcranial stimulation method to identify role of theta-rhythm in attention processes. Analysis of modern data concerning significance of theta-rhythm in organization of attention processes was performed analyzed. Different modes of transcranial stimulation methods, that allow to discover fundamental role of theta-rhythm in oscillatory activity of neural assembles, which are the base for attention mechanisms were considered. The review noted that the method of transcranial magnetic stimulation (TMS), which is based on the principle of electromagnetic induction with potential excellent temporal and sufficiently decent spatial resolution, is extensively widely used. Usually, TMS is performed with usage single-pulse, paired-pulse, or repetitive rhythmic stimulation. In current review special attention is salaried to the theta burst stimulation protocol. It was suggested that current protocol hypothesizes to influence brain plasticity and simulates the effect of theta-gamma coupling, which is to change the amplitude of the potentials at the frequency of the gamma rhythm depending on the theta wave phase. During the applying of the TMS different variants, several research methodological approaches were applied. Thus, usage of TMS may disrupt functioning in certain cortex areas , also it is possible to increase the oscillatory activity of a particular region at a particular frequency and to enhance or decrease the synchronization of remote cortical areas in a certain frequency range. These approaches may be used directly during the execution of the test task by the subjects or in the period prior the test performing. Many researches show that transcranial stimulation of some zones of cortex contributes to the achievement of better results of examinee in tests on memory and attention. This effect is most often observed while usage of stimulation with theta-rhythm frequency. Improvement of memory and attention functions has high practical meaning for wide range of activity. Understanding of regularities and mechanisms of stimulation with theta-rhythm frequency would allow to create systems and protocols of stimulation, which would effectively improve these functions for the long period.

Addiction history moderates the effect of prefrontal 10-Hz transcranial alternating current stimulation on habitual action selection.

Individuals with substance use disorders (SUDs) transition more quickly from goal-directed to habitual action-selection, but the neural mechanisms underlying this phenomenon remain unclear. Data from animal models suggest that drugs of abuse can modify the neurocircuits that regulate action-selection, enhancing circuits that drive inflexible, habit-based stimulus-response (S-R) action-selection and weakening circuits that drive flexible, goal-directed actions. Here, we tested the effect of bilateral 10-Hz transcranial alternating current stimulation (10Ηz-tACs) of the dorsolateral prefrontal cortex on action-selection in men and women with a SUD history and an age- and sex-matched control group. We tested the hypothesis that true 10Ηz-tACS versus active sham stimulation would reduce perseverative errors after changed response contingencies for well-learned S-R associations, reflecting reduced habit-based action-selection, specifically in the SUD group. We found that 10 Hz-tACS increased perseverative errors in the control group, but in the SUD group, 10 Hz-tACS effects on perseverative errors depended on substance abuse duration: a longer addiction history was associated with a greater reduction of perseverative errors. These results suggest that 10Ηz-tACs altered circuit level dynamics regulating behavioral flexibility, and provide a foundation for future studies to test stimulation site, frequency, and timing specificity. Moreover, these data suggest that chronic substance abuse is associated with altered circuit dynamics that are ameliorated by 10Ηz-tACs. Determining the generalizability of these effects and their duration merits investigation as a direction for novel therapeutic interventions. These findings are timely based on growing interest in transcranial stimulation methods for treating SUDs.NEW & NOTEWORTHY Treating the executive dysfunction associated with addiction is hampered by redundancies in pharmacological regulation of different behavioral control circuits. Thus, nonpharmacological interventions hold promise for addiction treatment. Here, we show that, among people with an addiction history, 10-Hz transcranial alternating current stimulation (10Hz-tACS) of the dorsolateral prefrontal cortex can reduce habitual actions. The fact that 10Hz-tACS can regulate behavioral flexibility suggests its possible utility in reducing harmful habitual actions.

Propagation of Endogenous Electric Fields as a Possible Mechanism of Synchronization of Interictal Spikes in the Rat Neocortex

The effects of weak electric fields with parameters close to those of the electrical activity of brain structures on neural networks in the brain have been studied for several decades. Interest in these studies has increased recently in connection with the fact that the treatment of a number of diseases uses transcranial stimulation methods. The present study used linear regression and correlation analysis to establish a relationship between the magnitude of the interictal spike potential and the magnitude of the potential at the cortical point located a few millimeters from the point at which the spike is generated. A link was also found between the occurrence of interictal spikes at one point of the cortex and the synchronous appearance of electric potentials in neighboring areas. Blockade of sodium channels at the recording points was followed by increases in the linear regression coefficient and the correlation coefficient. This indicated that the actions of electric field potentials were more significant. To identify whether this relationship was random, the time sequence of a single channel was shifted in relation to another using the random numbers principle. The magnitudes of the linear regression and correlation coefficients decreased by an order of magnitude. Our results showed that the electric potential of a small interictal spike arising at one point on the cortex propagates to other areas with a short time delay.

EFFECT OF A SINGLE TRANSCRANIAL STIMULATION ON THE RECOVERY OF SKI-RACERS

Aim. The article deals with assessing the effect of a single transcranial stimulation with impulse current on the recovery of ski-racers. Materials and methods. 18 skiers aged 20 ± 2 (skiers of the first rank or that of Candidate of Master of Sport) participated in the study. Skiing for 3 was used as a special load. To achieve the purpose of the study, we used the method of transcranial stimulation with impulse current after load. Results. During a single transcranial stimulation after a special load by the 20th minute, there is a statistically significant reduction of the urgent recovery of heart rate (HR), minute blood volume (MBV), the Robinson index (RI), the chronotropic index (CI). The time for the recovery of vegetative homeostasis also reduces. Conclusion. A single transcranial stimulation accelerates the recovery of the cardiovascular system in ski-racers by reducing the adrenergic effects of the autonomic nervous system. The efficiency of using transcranial stimulation is associated with individual-typological features of the vegetative regulation in athletes.

Noninvasive neurostimulation methods for migraine therapy: The available evidence.

Background Migraine is one of the most disabling neurological disorders. The current pharmacological armamentarium is not satisfying for a large proportion of patients because the responder rate does not exceed 50% on average and the most effective drugs often induce intolerable side effects. During recent years, noninvasive central and peripheral neuromodulation methods have been explored for migraine treatment. Overview A review of the available evidence suggests that noninvasive neuromodulation techniques could be beneficial for migraine patients. The transcranial stimulation methods allow modulating selectively cortical activity and can thus be curtailed to the patient's pathophysiological profile, while transcutaneous stimulation of pericranial nerves likely modulates central pain control centers. Occipital single-pulse transcranial magnetic stimulation and transcutaneous supraorbital stimulation have the strongest evidence respectively for acute and preventive treatment. Transcranial direct current stimulation and repetitive magnetic stimulation are promising in pilot studies, but large sham-controlled trials are not yet available. Conclusions The noninvasive neurostimulation methods are promising for migraine treatment and devoid of serious adverse effects allowing their combination with drug therapies. Their application in clinical practice will depend on the industry's capacity to develop portable and user-friendly devices, and on the scientists' capacity to prove their efficacy in randomized sham-controlled trials.

Transcranial stimulation in depression

Transcranial direct current stimulation is coming of age with the large treatment study published in this issue. We review transcranial stimulation methods, their efficacy and the likely impact on National Health Service (NHS) practice. Their use in individuals who do not respond to or cannot tolerate medication should now be explored in large controlled naturalistic studies in the NHS.

Task-specific hand dystonia: can too much plasticity be bad for you?

Patients with occupational hand dystonias have task-specific involuntary co-contraction and overflow of activity to inappropriate muscles. This interferes with highly skilled movements such as handwriting (writer's cramp) or playing a musical instrument (musician's cramp). Transcranial stimulation methods that probe mechanisms of synaptic plasticity in the motor cortex show an abnormal modifiability of sensorimotor circuits in patients with writer's cramp, probably because homeostatic control of the range of modification is deficient. We argue that during skilled motor practice, this leads to an excessive tendency to form associations between sensory inputs and motor outputs (abnormal potentiation) and to a failure to weaken already existing associations (deficient depotentiation). Deficient homeostatic control might be an important mechanism that triggers maladaptive reorganization and produces symptoms of occupational hand dystonias.