1,721,093 research outputs found
Resting electroencephalogram alpha-power over posterior sites indexes baseline visual cortex excitability
No full textVariations of oscillatory brain activity have been related to distinct functional states depending on the frequency of oscillations. In the α-band (about 8-14 Hz), decreased oscillatory activity is thought to reflect a state of enhanced cortical excitability, and increased activity to reflect a state of cortical idling or inhibition in which excitability is reduced, but the α/excitability link has not been probed directly. Here, we studied the relationship between resting oscillatory activity and visual cortex excitability across participants using electroencephalography and transcranial magnetic stimulation to the occipital pole. We found individual posterior α-band power to correlate with the individual threshold for eliciting illusory, transcranial magnetic stimulation-induced visual percepts. This provides direct support for an α/excitability link and for baseline states of the visual brain to vary across individuals. © 2008 Lippincott Williams & Wilkins, Inc
Sounds reset rhythms of visual cortex and corresponding human visual perception
Full text linkAn event in one sensory modality can phase reset brain oscillations concerning another modality [1-5]. In principle, this may result in stimulus-locked periodicity in behavioral performance [6]. Here we considered this possible cross-modal impact of a sound for one of the best-characterized rhythms arising from the visual system, namely occipital alpha-oscillations (8-14 Hz) [7-9]. We presented brief sounds and concurrently recorded electroencephalography (EEG) and/or probed visual cortex excitability (phosphene perception) through occipital transcranial magnetic stimulation (TMS). In a first, TMS-only experiment, phosphene perception rate against time postsound showed a periodic pattern cycling at ∼10 Hz phase-aligned to the sound. In a second, combined TMS-EEG experiment, TMS-trials reproduced the cyclical phosphene pattern and revealed a ∼10 Hz pattern also for EEG-derived measures of occipital cortex reactivity to the TMS pulses. Crucially, EEG-data from intermingled trials without TMS established cross-modal phase-locking of occipitoparietal alpha oscillations. These independently recorded variables, i.e., occipital cortex excitability and reactivity and EEG phase dynamics, were significantly correlated. This shows that cross-modal phase locking of oscillatory visual cortex activity can arise in the human brain to affect perceptual and EEG measures of visual processing in a cyclical manner, consistent with occipital alpha oscillations underlying a rapid cycling of neural excitability in visual areas
Transcranial magnetic stimulation effects support an oscillatory model of ERP genesis
Full text linkWhether prestimulus oscillatory brain activity contributes to the generation of post-stimulus-evoked neural responses has long been debated, but findings remain inconclusive. We first investigated the hypothesized relationship via EEG recordings during a perceptual task with this correlational evidence causally probed subsequently by means of online rhythmic transcranial magnetic stimulation. Both approaches revealed a close link between prestimulus individual alpha frequency (IAF) and P1 latency, with faster IAF being related to shorter latencies, best explained via phase-reset mechanisms. Moreover, prestimulus alpha amplitude predicted P3 size, best explained via additive (correlational and causal evidence) and baseline shift mechanisms (correlational evidence), each with distinct prestimulus alpha contributors. Finally, in terms of performance, faster prestimulus IAF and shorter P1 latencies were both associated with higher task accuracy, while lower prestimulus alpha amplitudes and higher P3 amplitudes were associated with higher confidence ratings. Our results are in favor of the oscillatory model of ERP genesis and modulation, shedding new light on the mechanistic relationship between prestimulus oscillations and functionally relevant evoked components
Hearing brighter: changing in-depth visual perception through looming sounds.
No full textRapidly approaching (looming) sounds are ecologically salient stimuli that are perceived as nearer than they are due to overestimation of their loudness change and underestimation of their distance (Neuhoff, 1998; Seifritz et al., 2002). Despite evidence for crossmodal influence by looming sounds onto visual areas (Romei, Murray, Cappe, & Thut, 2009, 2013; Tyll et al., 2013), it is unknown whether such sounds bias visual percepts in similar ways. Nearer objects appear to be larger and brighter than distant objects. If looming sounds impact visual processing, then visual stimuli paired with looming sounds should be perceived as brighter and larger, even when the visual stimuli do not provide motion cues, i.e. are static. In Experiment 1 we found that static visual objects paired with looming tones (but not static or receding tones) were perceived as larger and brighter than their actual physical properties, as if they appear closer to the observer. In a second experiment, we replicate and extend the findings of Experiment 1. Crucially, we did not find evidence of such bias by looming sounds when visual processing was disrupted via masking or when catch trials were presented, ruling out simple response bias. Finally, in a third experiment we found that looming tones do not bias visual stimulus characteristics that do not carry visual depth information such as shape, providing further evidence that they specifically impact in-depth visual processing. We conclude that looming sounds impact visual perception through a mechanism transferring in-depth sound motion information onto the relevant in-depth visual dimensions (such as size and luminance but not shape) in a crossmodal remapping of information for a genuine, evolutionary advantage in stimulus detection
Information-Based Approaches of Noninvasive Transcranial Brain Stimulation
Full text linkProgress in cognitive neuroscience relies on methodological developments to increase the specificity of knowledge obtained regarding brain function. For example, in functional neuroimaging the current trend is to study the type of information carried by brain regions rather than simply compare activation levels induced by task manipulations. In this context noninvasive transcranial brain stimulation (NTBS) in the study of cognitive functions may appear coarse and old fashioned in its conventional uses. However, in their multitude of parameters, and by coupling them with behavioral manipulations, NTBS protocols can reach the specificity of imaging techniques. Here we review the different paradigms that have aimed to accomplish this in both basic science and clinical settings and follow the general philosophy of information-based approaches
On the role of prestimulus alpha rhythms over occipito-parietal areas in visual input regulation: correlation or causation?
Full text linkThe posterior alpha rhythm (8-14 Hz), originating in occipito-parietal areas through thalamocortical generation, displays characteristics of visual activity in anticipation of visual events. Posterior alpha power is influenced by visual spatial attention via top-down control from higher order attention areas such as the frontal eye field. It covaries with visual cortex excitability, as tested through transcranial magnetic stimulation (TMS), and predicts the perceptual fate of a forthcoming visual stimulus. Yet, it is still unknown whether the nature of the relationship between this prestimulus alpha oscillation and upcoming perception is causal or only correlative. Here, we tested in the human brain whether the oscillation in the alpha band is causally shaping perception through directly stimulating visual areas via short trains of rhythmic TMS. We compared stimulation at alpha frequency (10 Hz) with two control frequencies in the theta (5 Hz) and beta bands (20 Hz), and assessed immediate perceptual outcomes. Target visibility was significantly modulated by alpha stimulation, relative to both control conditions. Alpha stimulation selectively impaired visual detection in the visual field opposite to the stimulated hemisphere, while enhancing detection ipsilaterally. These frequency-specific effects were observed both for stimulation over occipital and parietal areas of the left and right hemispheres and were short lived: they were observed by the end of the TMS train but were absent 3 s later. This shows that the posterior alpha rhythm is actively involved in shaping forthcoming perception and, hence, constitutes a substrate rather than a mere correlate of visual input regulation
M1 contributes to the intrinsic but not the extrinsic components of motor skills
No full textProcedural skills consist of several components that can be simultaneously acquired. During a motor-learning task we can distinguish between how a movement is performed (intrinsic component) and the spatial-related (extrinsic) component of this movement. The intrinsic movement component is thought to be supported by motor loops, including primary motor cortex (M1) as assessed with neuroimaging studies. Here we want to test further whether M1 makes a critical contribution to the movement rather than spatial-related component of skill learning. To this purpose, we used repetitive Transcranial Magnetic Stimulation (rTMS) and the serial reaction time (SRT) task. Twenty right-handed participants performed the SRT-task starting with their left or right hand. After this learning session, participants switched to the untrained hand by performing original (spatial-related) and mirror-ordered (movement-based) sequences. rTMS was applied to M1 ipsi- or contralateral to the transfer hand and both sequences were retested. Results revealed rTMS-interference with motor-skill transfer of mirror-ordered but not original sequences, showing that M1 is critically involved in the retrieval/transformation of the intrinsic but not the extrinsic movement coordinates. rTMSinterference in the mirror-condition consisted of both (i) disruption and (ii) release of motor skill transfer depending on the stimulated hemisphere and on transfer-hand. The pattern of results suggests (i) contralateral (right) M1 involvement in retrieval/transformation of motor information during left hand reproduction of previously acquired right-hand motor-skills; and (ii) modulatory interactions of inhibitory nature from the dominant (left) to the non-dominant (right) M1 in the same transfer condition. These results provide further evidence that M1 is essential to intrinsic movement-based skill-learning and novel insight on models of motor learning and hemispheric specialization, suggesting the involvement of interhemispheric inhibition
Prefrontal control over motor cortex cycles at beta-frequency during movement inhibition
Full text linkA fully adapted behavior requires maximum efficiency to inhibit processes in the motor domain [ 1 ]. Although a number of cortical and subcortical brain regions have been implicated, converging evidence suggests that activation of right inferior frontal gyrus (r-IFG) and right presupplementary motor area (r-preSMA) is crucial for successful response inhibition [ 2, 3 ]. However, it is still unknown how these prefrontal areas convey the necessary signal to the primary motor cortex (M1), the cortical site where the final motor plan eventually has to be inhibited or executed. On the basis of the widely accepted view that brain oscillations are fundamental for communication between neuronal network elements [ 4–6 ], one would predict that the transmission of these inhibitory signals within the prefrontal-central networks (i.e., r-IFG/M1 and/or r-preSMA/M1) is realized in rapid, periodic bursts coinciding with oscillatory brain activity at a distinct frequency. However, the dynamics of corticocortical effective connectivity has never been directly tested on such timescales. By using double-coil transcranial magnetic stimulation (TMS) and electroencephalography (EEG) [ 7, 8 ], we assessed instantaneous prefrontal-to-motor cortex connectivity in a Go/NoGo paradigm as a function of delay from (Go/NoGo) cue onset. In NoGo trials only, the effects of a conditioning prefrontal TMS pulse on motor cortex excitability cycled at beta frequency, coinciding with a frontocentral beta signature in EEG. This establishes, for the first time, a tight link between effective cortical connectivity and related cortical oscillatory activity, leading to the conclusion that endogenous (top-down) inhibitory motor signals are transmitted in beta bursts in large-scale cortical networks for inhibitory motor control
A TMS/EEG protocol for the causal assessment of the functions of the oscillatory brain rhythms in perceptual and cognitive processes
Full text linkThe combined use of transcranial magnetic stimulation (TMS), electroencephalogram (EEG), and behavioral performance allows investigation of causal relationships between neural markers and their functional relevance across a number of perceptual and cognitive processes. Here, we present a protocol for combining and applying these techniques on human subjects. We describe correlation approach and causal approach to disentangle the role of different oscillatory parameters, namely alpha frequency and amplitude that control for accuracy and metacognitive abilities, respectively, in a visual detection task. For complete details on the use and execution of this protocol, please refer to Di Gregorio et al. (2022)
Effects of Rhythmic Transcranial Magnetic Stimulation in the Alpha-Band on Visual Perception Depend on Deviation From Alpha-Peak Frequency: Faster Relative Transcranial Magnetic Stimulation Alpha-Pace Improves Performance
Full text linkAlpha-band oscillatory activity over occipito-parietal areas is involved in shaping perceptual and cognitive processes, with a growing body of electroencephalographic (EEG) evidence indicating that pre-stimulus alpha-band amplitude relates to the subjective perceptual experience, but not to objective measures of visual task performance (discrimination accuracy). The primary aim of the present transcranial magnetic stimulation (TMS) study was to investigate whether causality can be established for this relationship, using rhythmic (alpha-band) TMS entrainment protocols. It was anticipated that pre-stimulus 10 Hz-TMS would induce changes in subjective awareness ratings but not accuracy, in the visual hemifield contralateral to TMS. To test this, we administered 10 Hz-TMS over the right intraparietal sulcus prior to visual stimulus presentation in 17 participants, while measuring their objective performance and subjective awareness in a visual discrimination task. Arrhythmic and 10 Hz sham-TMS served as control conditions (within-participant design). Resting EEG was used to record individual alpha frequency (IAF). A study conducted in parallel to ours with a similar design but reported after we completed data collection informed further, secondary analyses for a causal relationship between pre-stimulus alpha-frequency and discrimination accuracy. This was explored through a regression analysis between rhythmic-TMS alpha-pace relative to IAF and performance measures. Our results revealed that contrary to our primary expectation, pre-stimulus 10 Hz-TMS did not affect subjective measures of performance, nor accuracy, relative to control-TMS. This null result is in accord with a recent finding showing that for influencing subjective measures of performance, alpha-TMS needs to be applied post-stimulus. In addition, our secondary analysis showed that IAF was positively correlated with task accuracy across participants, and that 10 Hz-TMS effects on accuracy—but not awareness ratings—depended on IAF: The slower (or faster) the IAF, relative to the fixed 10 Hz TMS frequency, the stronger the TMS-induced performance improvement (or worsening), indicating that 10 Hz-TMS produced a gain (or a loss) in individual performance, directly depending on TMS-pace relative to IAF. In support of recent reports, this is evidence for alpha-frequency playing a causal role in perceptual sensitivity likely through regulating the speed of sensory sampling
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