Rhythmic Transcranial Magnetic Stimulation Research Articles

IS 41. Attention, brain oscillations and frequency-tuned TMS

Brain oscillations reflect interactions between neuronal elements which functionally assemble through synchronization in specific frequency bands, depending on the state of the brain and on the task that is currently being executed. This gives rise to brain rhythms that can be measured on the scalp by electroencephalography (EEG). Transcranial magnetic stimulation (TMS) can be used to stimulate cortical areas in rhythmic pulse-trains, at frequencies that characterize EEG-signals. This raises two intriguing questions: Could frequency-tuned TMS be used to transiently entrain brain oscillations, and would this result in behavioural consequences? My talk covers (1) EEG-signatures that carry information on the excitability of visual cortex (amenable to attention control) and predict perception of an upcoming visual event. It then addresses the questions whether (2) these signatures can be transiently entrained by frequency-tuned rhythmic TMS, and whether (3) this alters perception in expected directions, i.e. in line with the proposed functional roles of these oscillations in perception and attention.

P 49. Modulation of spontaneous and TMS-evoked alpha oscillations by top-down visual attention

Simultaneous transcranial magnetic stimulation (TMS) and electroencephalography (EEG) allows the direct assessment of cortico-thalamic responsiveness by TMS-evoked EEG potentials (TEPs). Notably, the frequency composition of TEPs corresponds to the dominant spontaneous oscillation at the respective stimulation site, e.g. ′alpha′ in the visual cortex (Rosanova et al., J Neurosci 2009). Furthermore, TEPs change dramatically with shifts in neuromodulatory levels during sleep (Massimini et al., Science 2005; Bergmann et al., J Neurosci 2012), suggesting that both are generated by the same neuronal mechanisms. Indeed, rhythmic TMS of the parieto-occipital cortex can mimic alpha band (8–12 Hz) oscillations in the EEG (Thut et al., Curr Biol 2011) as well as their known impact on perceptual performance (Romei et al., J Neurosci 2010) due to gating by inhibition (Jensen et al., TICS 2012). However, does the alpha-like TEP as response to visual cortex stimulation actually resemble spontaneous alpha oscillations or rather visual evoked potentials (VEPs)? Importantly, VEPs are amplified by visual attention (Rajagovindan and Ding, J Cog Neurosci, 2011), whereas spontaneous alpha oscillations are suppressed (Foxe et al., Neurorep 1998; Fu et al., Cog Brain Res 2001). To test the similarity between transcranially evoked and spontaneous alpha oscillations, we currently investigate whether they show comparable responses to covert shifts in attention, i.e., decrease and increase in amplitude when attending the visual and auditory modality, respectively (Foxe and Snyder, Front Psychol 2011). Here, we measure TEPs my means of simultaneously applied 61-channel EEG and neuronavigated single-pulse TMS to the visual cortex while subjects attend to either visual or auditory noise patterns in order to detect slight contrast modulations. Since auditory stimuli have been shown to evoke an alpha-like response in the visual cortex (Romei, Gross and Thut, Curr Biol 2012), we use a constant stream of auditory masking noise as well as sham TMS to control for these effects. Preliminary results suggest that the TMS-evoked alpha oscillation is in fact modulated by top-down visual attention in analogy to spontaneous alpha oscillations, suggesting that both are generated by the same underlying neural mechanisms.

Navigated transcranial magnetic stimulation as a method of early locomotor rehabilitation after stroke

The objective of the present study was to compare the safety and effectiveness of navigated and non-navigated rhythmic transcranial magnetic stimulation rTMS in the patients presenting with post-stroke hemiparesis. Methods: Group 1 consisted of 31 patients with post-stroke hemiparesis treated by navigated rTMS. Thirty comparable patients treated without navigation were included in Group 2. The patients were examined 3.2±1.1 month after stroke. Their mean age was 42±10.1 years. The average NIHSS score declined from 15.9±3.5 to 10.2±3.9 in Group 1 and from 15.8±3.0 to 13.1±3.4 in Group 2 (p=0.05). The Barthel index characterizing the degree of functional independence increased from 14.5±4.4 to 25.7±6.8 in Group 1 and from 14.3±4.2 to 18.1±5.9 in Group 2 (p=0.07). Navigated rTMS should be preferred as a method for locomotor rehabilitation after stroke.

Causal implication by rhythmic transcranial magnetic stimulation of alpha frequency in feature‐based local vs. global attention

Although oscillatory activity in the alpha band was traditionally associated with lack of alertness, more recent work has linked it to specific cognitive functions, including visual attention. The emerging method of rhythmic transcranial magnetic stimulation (TMS) allows causal interventional tests for the online impact on performance of TMS administered in short bursts at a particular frequency. TMS bursts at 10 Hz have recently been shown to have an impact on spatial visual attention, but any role in featural attention remains unclear. Here we used rhythmic TMS at 10 Hz to assess the impact on attending to global or local components of a hierarchical Navon-like stimulus (D. Navon (1977) Forest before trees: The precedence of global features in visual perception. Cognit. Psychol., 9, 353), in a paradigm recently used with TMS at other frequencies (V. Romei, J. Driver, P.G. Schyns & G. Thut. (2011) Rhythmic TMS over parietal cortex links distinct brain frequencies to global versus local visual processing. Curr. Biol., 2, 334-337). In separate groups, left or right posterior parietal sites were stimulated at 10 Hz just before presentation of the hierarchical stimulus. Participants had to identify either the local or global component in separate blocks. Right parietal 10 Hz stimulation (vs. sham) significantly impaired global processing without affecting local processing, while left parietal 10 Hz stimulation vs. sham impaired local processing with a minor trend to enhance global processing. These 10 Hz outcomes differed significantly from stimulation at other frequencies (i.e. 5 or 20 Hz) over the same site in other recent work with the same paradigm. These dissociations confirm differential roles of the two hemispheres in local vs. global processing, and reveal a frequency-specific role for stimulation in the alpha band for regulating feature-based visual attention.

Transcranial Alternating Current Stimulation Affects Decision Making

GENERAL COMMENTARY article Front. Syst. Neurosci., 25 May 2012 | https://doi.org/10.3389/fnsys.2012.00039

Rhythmic TMS Causes Local Entrainment of Natural Oscillatory Signatures

SummaryBackgroundNeuronal elements underlying perception, cognition, and action exhibit distinct oscillatory phenomena, measured in humans by electro- or magnetoencephalography (EEG/MEG). So far, the correlative or causal nature of the link between brain oscillations and functions has remained elusive. A compelling demonstration of causality would primarily generate oscillatory signatures that are known to correlate with particular cognitive functions and then assess the behavioral consequences. Here, we provide the first direct evidence for causal entrainment of brain oscillations by transcranial magnetic stimulation (TMS) using concurrent EEG.ResultsWe used rhythmic TMS bursts to directly interact with an MEG-identified parietal α-oscillator, activated by attention and linked to perception. With TMS bursts tuned to its preferred α-frequency (α-TMS), we confirmed the three main predictions of entrainment of a natural oscillator: (1) that α-oscillations are induced during α-TMS (reproducing an oscillatory signature of the stimulated parietal cortex), (2) that there is progressive enhancement of this α-activity (synchronizing the targeted, α-generator to the α-TMS train), and (3) that this depends on the pre-TMS phase of the background α-rhythm (entrainment of natural, ongoing α-oscillations). Control conditions testing different TMS burst profiles and TMS-EEG in a phantom head confirmed specificity of α-boosting to the case of synchronization between TMS train and neural oscillator.ConclusionsThe periodic electromagnetic force that is generated during rhythmic TMS can cause local entrainment of natural brain oscillations, emulating oscillatory signatures activated by cognitive tasks. This reveals a new mechanism of online TMS action on brain activity and can account for frequency-specific behavioral TMS effects at the level of biologically relevant rhythms.

Rhythmic TMS over Parietal Cortex Links Distinct Brain Frequencies to Global versus Local Visual Processing

SummaryNeural networks underlying visual perception exhibit oscillations at different frequencies (e.g., [1–6]). But how these map onto distinct aspects of visual perception remains elusive. Recent electroencephalography data indicate that theta or beta frequencies at parietal sensors increase in amplitude when conscious perception is dominated by global or local features, respectively, of a reversible visual stimulus [6]. But this provides only correlative, noninterventional evidence. Here we show via transcranial magnetic stimulation (TMS) interventions that short rhythmic bursts of right-parietal TMS at theta or beta frequency can causally benefit processing of global or local levels, respectively, for hierarchical visual stimuli, especially in the context of salient incongruent distractors. This double dissociation between theta and beta TMS reveals distinct causal roles for particular frequencies in processing global versus local visual features.

On entrainment of occipito-parietal brain rhythms, and modulation of perception by rhythmic transcranial magnetic stimulation (rTMS)

On entrainment of occipito-parietal brain rhythms, and modulation of perception by rhythmic transcranial magnetic stimulation (rTMS)

Cerebral responses of healthy humans to rhythmic transcranial magnetic stimulation of different intensities

The effect of rhythmic transcranial magnetic stimulation (rTMS) of different intensities (single superthreshold rTMS more intense than 1.2 T and subthreshold one with an intensity of 70–80% of the motor threshold) of sagittal premotor cortical areas on the human functional activity was estimated in eight volunteers on the basis of combined EEG, neuropsychological, and hemodynamic examinations. The objectives of the study included the selection of the frequency of activating stimulation and revision of the objective EEG criteria of rTMS efficiency. It has been demonstrated that analysis of the EEG response to photostimulation at different frequencies is efficient in selecting the rTMS frequency. The EEG coherence is one of the most informative characteristics of the rTMS effect on central neurodynamics. The functional effects of stimulation (activating or inhibitory) have been shown to depend on the initial level of intercentral coherent relationships It has been found that rTMS of the sagittal premotor cortex causes definite changes in the functional activity of a healthy brain different from those caused by placebo. These changes are greater in the left hemisphere (in the form of intrahemispheric changes in coherence and depend on the stimulation intensity (superor subthreshold) and the initial state. The vascular factor has been shown to play an important role in the formation of cerebral responses to rTMS.

Frequency-dependent increase of regional cerebral blood flow in the human sensorimotor cortex during rhythmic transcranial magnetic stimulation—a parametric PET study

Frequency-dependent increase of regional cerebral blood flow in the human sensorimotor cortex during rhythmic transcranial magnetic stimulation—a parametric PET study