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Transcranial alternating current stimulation (tACS) is a form of noninvasive brain stimulation and is capable of influencing brain oscillations and cortical networks. In humans, the endogenous oscillation frequency in sensorimotor areas peaks at 20 Hz. This beta-band typically occurs during maintenance of tonic motor output and seems to play a role in interhemispheric coordination of movements. Previous studies showed that tACS applied in specific frequency bands over primary motor cortex (M1) or the visual cortex modulates cortical excitability within the stimulated hemisphere. However, the particular impact remains controversial because effects of tACS were shown to be frequency, duration and location specific. Furthermore, the potential of tACS to modulate cortical interhemispheric processing, like interhemispheric inhibition (IHI), remains elusive. Transcranial magnetic stimulation (TMS) is a noninvasive and well-tolerated method of directly activating neurons in superficial areas of the human brain and thereby a useful tool for evaluating the functional state of motor pathways. The aim of the present study was to elucidate the immediate effect of 10 min tACS in the β-frequency band (20 Hz) over left M1 on IHI between M1s in 19 young, healthy, right-handed participants. A series of TMS measurements (motor evoked potential (MEP) size, resting motor threshold (RMT), IHI from left to right M1 and vice versa) was performed before and immediately after tACS or sham using a double-blinded, cross-over design. We did not find any significant tACS-induced modulations of intracortical excitation (as assessed by MEP size and RMT) and/or IHI. These results indicate that 10 min of 20 Hz tACS over left M1 seems incapable of modulating immediate brain activity or inhibition. Further studies are needed to elucidate potential aftereffects of 20 Hz tACS as well as frequency- specific effects of tACS on intracortical excitation and IHI.
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mitochondrial oscillator
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The electronic and crystallographic structure of the graphene/Rh(111) moiré lattice is studied via combination of density-functional theory calculations and scanning tunneling and atomic force microscopy(STM and AFM). Whereas the principal contrast between hills and valleys observed in STM does not depend on the sign of applied bias voltage, the contrast in atomically resolved AFM images strongly depends on the frequency shift of the oscillating AFM tip. The obtained results demonstrate the perspectives of application atomic force microscopy/spectroscopy for the probing of the chemical contrast at the surface.
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We set out to investigate whether beta oscillations in the human basal ganglia are modulated during reinforcement learning. Based on previous research, we assumed that beta activity might either reflect the magnitudes of individuals' received reinforcements (reinforcement hypothesis), their reinforcement prediction errors (dopamine hypothesis) or their tendencies to repeat versus adapt responses based upon reinforcements (status-quo hypothesis). We tested these hypotheses by recording local field potentials (LFPs) from the subthalamic nuclei of 19 Parkinson's disease patients engaged in a reinforcement-learning paradigm. We then correlated patients' reinforcement magnitudes, reinforcement prediction errors and response repetition tendencies with task-related power changes in their LFP oscillations. During feedback presentation, activity in the frequency range of 14 to 27 Hz (beta spectrum) correlated positively with reinforcement magnitudes. During responding, alpha and low beta activity (6 to 18 Hz) was negatively correlated with previous reinforcement magnitudes. Reinforcement prediction errors and response repetition tendencies did not correlate significantly with LFP oscillations. These results suggest that alpha and beta oscillations during reinforcement learning reflect patients' observed reinforcement magnitudes, rather than their reinforcement prediction errors or their tendencies to repeat versus adapt their responses, arguing both against an involvement of phasic dopamine and against applicability of the status-quo theory.
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Alternating current stimulation (ACS) is an established means to manipulate intrinsic cortical oscillations. While working towards clinical impact, ACS mechanisms of action remain unclear. For ACS's well-documented influence on occipital alpha, hypotheses include neuronal entrainment as well as rebound phenomena. As a retinal origin is also discussed, we employed a novel form of ACS with the advantage that it specifically targets occipital alpha-oscillations via retinofugal pathways retinofugal ACS (rACS). We aimed to confirm alpha-enhancement outlasting the duration of stimulation with 10 Hz rACS. To distinguish entrainment from rebound effects, we investigated the correlation between alpha peak frequency change and alpha-enhancement strength. We quantified the alpha band power before and after 10 Hz rACS in 15 healthy subjects. Alpha power enhancement and alpha peak frequency change were assessed over the occipital electrodes and compared to sham stimulation. RACS significantly enhanced occipital alpha power in comparison to sham stimulation (p < 0.05). Alpha peak frequency changed by a mean 0.02 Hz (+/- 0.04). A greater change in alpha peak frequency did not correlate with greater effects on alpha power. Our findings show an alpha-enhancement consistent with studies conducted for transcranial ACS (tACS) and contribute evidence for a retinal involvement in tACS effects on occipital alpha. Furthermore, the lack of correlation between alpha peak frequency change and alpha-enhancement strength provides an argument against entrainment effects and in favor of a rebound phenomenon.
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Recently, transcranial alternating current stimulation (tACS) has emerged as a tool to enhance human cognitive processes. Here, we provide a brief summary of the rationale behind tACS-induced effects on task-relevant brain oscillations and associated cognitive functions and review previous studies in young subjects that have applied tACS in cognitive paradigms. Additionally, we present pilot data where we administered theta-tACS (6 Hz) over the temporoparietal cortex and a supraorbital reference for 20 min during implicit language learning in healthy young (mean/SD age: 22/2) and older (mean/SD age: 66/4) adults, in a sham-controlled crossover design. Linear mixed models revealed significantly increased retrieval accuracy following tACS-accompanied associative learning, after controlling for session order and learning success. These data provide the first implementation of tACS during cognitive performance in older adults and support recent studies suggesting that tACS in the theta frequency range may serve as a tool to enhance cognition, possibly through direct modulation of task-relevant brain oscillations. So far, studies have been heterogeneous in their designs, leaving a number of issues to be addressed in future research, including the setup of electrodes and optimal stimulation frequencies to be employed, as well as the interaction with age and underlying brain pathologies in specific patient populations.
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As the hippocampal output structure, the subiculum’s purpose is to integrate and distribute mne-monic and spatial information to various cortical and subcortical brain regions. The subiculum is also involved in the pathophysiology of neurological conditions such as epilepsy and schizo- phrenia. Network oscillations in the gamma (30-100 Hz) frequency range as well as sharp wave ripple oscillations (100-250 Hz) are most prominent within the hippocampal formation. Both rhythms appear to be functionally connected and are involved in memory storage and retrieval. Within the subiculum, there are two types of principal cells (PC) that can be discriminated based on their firing properties following a depolarizing current injection: intrinsically bursting (IB) and regular spiking (RS) neurons. So far, it remains uninvestigated how these two distinct su-bicular PC classes participate in oscillatory network activity. Using an in vitro model that allows the investigation of sharp wave and gamma frequency oscillations in the subiculum, simultane-ous local field potential and sharp microelectrode recordings were made in 400 μm thick murine hippocampal slices. The intrinsic and synaptic properties of subicular PCs as well as their func-tional involvement in the two major oscillatory rhythms were investigated. Biocytin was used for the morphological identification of recorded neurons. Morphologically, the electrically identified neurons display the typical shape of pyramidal cells. Interestingly, one pair of IB, but not RS cells, shows dye coupling which has been suggested to be the morphological correlate of electric synapses. The results reveal furthermore, that in addition to the electrophysiological dichotomy and distinct firing properties of the subicular PC classes, there exists a strict functional segrega-tion of the active, participating IB cells and mostly silent RS cells during both network states. The silent RS PCs appear to require a higher network activation than IB PCs in order to partici- pate in the oscillatory activity. When depolarized above threshold, they show a cell-type specific and independent firing pattern in correlation to the local field. This suggests a bimodal working model within the subiculum dependent on the level of network excitation. Additionally, the su-bicular IB and RS cells reveal divergent synaptic properties in the active network which suggest distinct synaptic connectivity and possibly input structures. These results altogether indicate a functional cell-type-specific segregation of subicular PCs representing two independent and par-allel streams of information processing within the subiculum resulting in two distinct processing channels within the hippocampal formation.,Als efferentes Organ der hippocampalen Formation entsendet das Subiculum prozessierte mne-monische und räumliche Information zu verschiedenen kortikalen und subkortikalen Gehirnregi-onen. Außerdem ist das Subiculum an der Pathophysiologie neurologischer Erkrankungen wie der Epilepsie und Schizophrenie beteiligt. Netzwerkoszillationen im Gamma-Frequenzbereich (30-100 Hz) und Sharp Wave Ripple Oszillationen (100-250 Hz) spielen eine besondere Rolle in der hippocampalen Formation. Beide Rhythmen sind funktionell vergesellschaftet und an der Speicherung und dem Abruf von Gedächtnisinhalten beteiligt. Im Subiculum gibt es zwei Arten von Prinzipalzellen, die anhand ihrer Reaktion auf die Applikation depolarisierender Strominjek-tionen unterschieden werden: intrinsically bursting (IB) und regular spiking (RS) Zellen. Bisher ist es allerdings unklar, wie die beiden Zelltypen an der subicularen Netzwerkaktivität beteiligt sind. Anhand eines in vitro Modells, das sowohl die Untersuchung von Sharp Waves als auch von Gamma Oszillationen erlaubt, wurden in 400 μm dicken murinen hippocampalen Schnitten simultan Aufnahmen lokaler Feldpotentiale und mithilfe der sharp microelectrode Technik intra-zelluläre Aufnahmen durchgeführt. Die intrinsischen und synaptischen Eigenschaften subicularer Prinzipalzellen und ihre funktionelle Bedeutung während beider Netzwerkrhythmen wurden un-tersucht. Biocytin diente der morphologischen Identifizierung. Die elektrophysiologisch identifi-zierten Zellen zeigen die typische Form von Pyramidalzellen. Dye Coupling, das dem morpholo-gischen Korrelat elektrischer Synapsen entsprechen soll, kann in einem IB Zellpaar aber nicht in RS Zellen nachgewiesen werden. In Ergänzung zu der elektrophysiologischen Dichotomie und dem individuellen Feuerverhalten, wird zudem eine funktionelle und zelltyp-spezifische Tren-nung der Netzwerkbeteiligung im Subiculum deutlich. Die Mehrheit der IB Zellen zeigen aktives und am Netzwerk beteiligtes Verhalten, während die RS Zellen im Großteil unbeteiligt und „still“ sind. RS Zellen scheinen eine stärkere Netzwerkerregung zu benötigen, um an den Net-zoszillationen teilzunehmen. Werden die RS Zellen jedoch über das Schwellenpotential hinaus depolarisiert, zeigen sie ein zelltyp-spezifisches und unabhängiges Aktivitätsmuster in strikter Korrelation zum Netzwerk. Folglich kann ein bimodales Arbeitsmodell im Subiculum ange-nommen werden, das abhängig von dem Level subiculärer Netzwerkerregung ist. Des Weiteren unterscheiden sich die synaptischen Potentiale subicularer IB und RS Zellen deutlich voneinan-der. Das deutet darauf hin, dass sowohl die zelluläre Verschaltung als auch die afferenten Struk-turen subicularer Prinzipalzellen unterschiedlich sein müssen. Zusammenfassend erlauben die Ergebnisse den Rückschluss, dass eine funktionelle und zelltyp-spezifische Separation subicularer IB und RS Zellen existiert, die zwei voneinander unabhängige und parallele Kanäle der In- formationsverarbeitung repräsentieren.,
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oscillations
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Schizophrenia is associatedwith a number of cognitive impairments such as deficient sensory encoding or working memory processing. However, it is largely unclear how dysfunctions on these various levels of cortical processing contribute to alterations of stimulus-specific information representation. To test this, we used a wellestablished sequential frequency comparison paradigm, in which sensory encoding of vibrotactile stimuli can be assessed via frequency-specific steady-state evoked potentials (SSEPs) over primary somatosensory cortex (S1). Further, we investigated the maintenance of frequency information in working memory (WM) in terms of parametric power modulations of induced beta-band EEG oscillations. In the present study schizophrenic patients showed significantly less pronounced SSEPs during vibrotactile stimulation than healthy controls. In particular, inter-trial phase coherence was reduced. While maintaining vibrotactile frequencies in WM, patients showed a significantly weaker prefrontal beta-power modulation compared to healthy controls. Crucially, patients exhibited no general disturbances in attention, as inferred from a behavioral test and from alpha- band event-related synchronization. Together, our results provide novel evidence that patients with schizophrenia show altered neural correlates of stimulus-specific sensory encoding and WM maintenance, suggesting an early somatosensory impairment as well as alterations in the formation of abstract representations of taskrelevant stimulus information.
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SEP high frequency oscillation
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