Motor Cortex Hyperexcitability, Neuroplasticity, and Degeneration in Amyotrophic Lateral Sclerosis

Neuronal hyperexcitability is a well-known phenomenon in amyotrophic lateral sclerosis and other neurodegenerative diseases. The use of transcranial magnetic stimulation in clinical and research practice has recently made it possible to detect motor cortex hyperexcitability under clinical conditions. Despite numerous studies, the mechanisms and sequelae of the development of hyperexcitability still have not been completely elucidated. In this chapter, we discuss the possibilities for detecting motor cortex hyperexcitability in patients with amyotrophic lateral sclerosis using transcranial magnetic stimulation. The potential relationship between hyperexcitability and neuronal degeneration or neuroplasticity processes is discussed using the data obtained by navigated transcranial magnetic stimulation and neuroimaging data, as well as the data of experimental studies

Theta-gamma phase-amplitude coupling: physiological basics, analysis methods, and perspectives of translation into clinical practice

Studying rhythmic neural synchronization (cross-frequency coupling in various ranges) is an emerging topic in present-day neurophysiology. One of the best-studied cross-frequency couplings is theta-gamma phase-amplitude coupling that contributes to the cognitive function and may vary in patients with several conditions associated with cognitive impairment. Changes in theta-gamma coupling can be registered in a wide range of diseases associated with cognitive decline. The review covers the physiological basics of theta-gamma coupling, its registration and calculation, correlation with cognitive test results in healthy volunteers, and changes in patients. We have discussed the results of the preliminary studies of frequency-dependent non-invasive brain stimulation based on theta-gamma coupling

Navigated repetitive transcranial magnetic stimulation to correct eating behavior in obesity (clinical cases)

Obesity is a pathological condition caused by overweight and requiring medical intervention. The clinical and scientific experience gained over the past decades has allowed researchers to consider this problem as an independent disease with its own pathophysiological features, prevalence, incidence, approaches to therapy and prevention. One of the most important factors in the pathogenesis of obesity is disordered eating behavior, the central regulation of which is carried out with the active participation of the prefrontal cortex. Impact on this area (for example, using non-invasive brain stimulation) may be one of the promising ways to modulate eating behavior. The article describes clinical cases of treatment of morbid obesity using navigated rhythmic transcranial magnetic stimulation (rTMS). Different patterns of dorsolateral prefrontal cortex (DLPFC) activation before and after rTMS are demonstrated. Possible mechanisms of the influence of DLPFC on the formation of eating behavior are also considered. These data underline the important role of DLPFC dysregulation in obesity, as well as show potentially effective neuromodulation techniques

Conjugated polymer charge-transfer complexes: A new route to low-bandgap photostable materials

Polymer solar cells have high potential to convert solar energy into electricity in a cost-effective way. To date, the best polymer solar cells show the efficiency about 5%, and significant efforts are underway to increase their efficiency to the level of practical applications. One of the key strategies towards improving the performance of polymer solar cells is the development of low-bandgap polymers allowing more efficient harvesting of the solar light in the red and near-IR spectral regions. In this chapter, we consider an alternative (or complimentary) route to low-bandgap organic materials based on utilization of Mulliken type donor-acceptor charge-transfer complexes (CTCs) of conjugated polymers. We present the results of our recent studies on the ground- and excited state properties of CTCs based on a model conjugated polymer, MEH-PPV. By using a number of photophysical methods, including ultrafast photoinduced absorption and surface photovoltage spectroscopies, we show that usage of conjugated polymer CTCs has a number of attractive virtues. First, the donor-acceptor interactions result in a CTC absorption band extending deeply into the optical gap of the polymer, thereby enhancing the absorption in the low-energy part of the solar spectrum. Second, the efficiency of charge separation in the polymer CTCs can be close to unity, similarly to polymer:fullerene blends. Third, the CTC formation can dramatically improve the photooxidation stability of the polymer involved in the CTC that is of high importance for increasing the life span of polymer solar cells. Fourth, ground-state charge-transfer interaction can be an important factor controlling the morphology of donor:acceptor blends that is critical for bulk heterojunction solar cells. Although the photosensitivity of the CTCs studied extends down to 1 eV, the crucial drawback in the studied CTCs is efficient geminate recombination of photogenerated charges. To overcome this limitation, we realize in a model ternary blend with a consecutive photoinduced electron transfer from the polymer to the CTC-acceptor in the first step and then, in the second step, to the fullerene. This illustrates a proof-of-principle approach to the usage of the CTCs in organic solar cells where CTCs act as a narrow-bandgap photostable absorber and fullerenes work as a charge collector via a consecutive CTC-fullerene electron transfer

Optimization of the Navigated TMS Mapping Algorithm for Accurate Estimation of Cortical Muscle Representation Characteristics

Navigated transcranial magnetic stimulation (nTMS) mapping of cortical muscle representations allows noninvasive assessment of the state of a healthy or diseased motor system, and monitoring changes over time. These applications are hampered by the heterogeneity of existing mapping algorithms and the lack of detailed information about their accuracy. We aimed to find an optimal motor evoked potential (MEP) sampling scheme in the grid-based mapping algorithm in terms of the accuracy of muscle representation parameters. The abductor pollicis brevis (APB) muscles of eight healthy subjects were mapped three times on consecutive days using a seven-by-seven grid with ten stimuli per cell. The effect of the MEP variability on the parameter accuracy was assessed using bootstrapping. The accuracy of representation parameters increased with the number of stimuli without saturation up to at least ten stimuli per cell. The detailed sampling showed that the between-session representation area changes in the absence of interventions were significantly larger than the within-session fluctuations and thus could not be explained solely by the trial-to-trial variability of MEPs. The results demonstrate that the number of stimuli has no universally optimal value and must be chosen by balancing the accuracy requirements with the mapping time constraints in a given problem

Brain Activations and Functional Connectivity Patterns Associated with Insight-Based and Analytical Anagram Solving

Insight is one of the most mysterious problem-solving phenomena involving the sudden emergence of a solution, often preceded by long unproductive attempts to find it. This seemingly unexplainable generation of the answer, together with the role attributed to insight in the advancement of science, technology and culture, stimulate active research interest in discovering its neuronal underpinnings. The present study employs functional Magnetic resonance imaging (fMRI) to probe and compare the brain activations occurring in the course of solving anagrams by insight or analytically, as judged by the subjects. A number of regions were activated in both strategies, including the left premotor cortex, left claustrum, and bilateral clusters in the precuneus and middle temporal gyrus. The activated areas span the majority of the clusters reported in a recent meta-analysis of insight-related fMRI studies. At the same time, the activation patterns were very similar between the insight and analytical solutions, with the only difference in the right sensorimotor region probably explainable by subject motion related to the study design. Additionally, we applied resting-state fMRI to study functional connectivity patterns correlated with the individual frequency of insight anagram solutions. Significant correlations were found for the seed-based connectivity of areas in the left premotor cortex, left claustrum, and left frontal eye field. The results stress the need for optimizing insight paradigms with respect to the accuracy and reliability of the subjective insight/analytical solution classification. Furthermore, the short-lived nature of the insight phenomenon makes it difficult to capture the associated neural events with the current experimental techniques and motivates complementing such studies by the investigation of the structural and functional brain features related to the individual differences in the frequency of insight-based decisions

Modern concepts of the pathogenesis of obesity and new approaches to its correction

The present review considers modern concepts of the physiological mechanisms of the formation of food behavior in a norm at several levels, beginning with the cellular level and ending with the level of functional systems. Neuroimaging methods used for both the study of the pathophysiological foundations of eating disorders and for determining the target for neurostimulation techniques are described. Methods of non-invasive brain stimulation such as transcranial magnetic stimulation and transcranial electrical stimulation, the mechanisms of their influence and aspects of safety of application are reviewed, the latest data on the results of studies on the use of the above methods in the therapy of obesity are summarized