On the Role of Prestimulus Alpha Rhythms over Occipito-Parietal Areas in Visual Input Regulation: Correlation or Causation?

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Attention plays a fundamental role in selectively processing stimuli in our environment despite distraction. Spatial attention induces increasing and decreasing power of neural alpha oscillations (8-12 Hz) in brain regions ipsilateral and contralateral to the locus of attention, respectively. This study tested whether the hemispheric lateralization of alpha power codes not just the spatial location but also the temporal structure of the stimulus. Participants attended to spoken digits presented to one ear and ignored tightly synchronized distracting digits presented to the other ear. In the magnetoencephalogram, spatial attention induced lateralization of alpha power in parietal, but notably also in auditory cortical regions. This alpha power lateralization was not maintained steadily but fluctuated in synchrony with the speech rate and lagged the time course of low-frequency (1-5 Hz) sensory synchronization. Higher amplitude of alpha power modulation at the speech rate was predictive of a listener's enhanced performance of stream-specific speech comprehension. Our findings demonstrate that alpha power lateralization is modulated in tune with the sensory input and acts as a spatiotemporal filter controlling the read-out of sensory content.attention | neural oscillations | alpha lateralization | synchronization | speech N eural oscillations are tenable biological substrates to instantiate attentional selection of sensory information from our environment (1-3). The power of alpha oscillations (8-12 Hz) is modulated by the degree of selective attention to a behaviorally relevant stimulus (4-6). Attentive focusing to one side in auditory, visual, or tactile space leads to a relative decrease in alpha power in contralateral compared with ipsilateral sensory brain regions (7-10) and governs success of selective attention, that is, of isolating one stimulus at a specific spatial location (11-13) in the context of other distracting stimuli. In speech, however, spatial selective attention alone does not suffice for successful speech comprehension given the multiple timescales (e.g., syllable and word rate) over which speech varies. Any attentional neural mechanism that respects the temporal structure of auditory sensory inputs must therefore be dynamic over time. Here, we tested the hypothesis that spatial attention to one of two concurrent speech streams induces a lateralization of alpha power that synchronizes with the speech rate over time and enhances speech comprehension.In addition to neural alpha oscillations and their role in selective attention, low-frequency neural oscillations (delta/theta band; 1-5 Hz) in sensory cortices synchronize with the temporal structure of acoustic stimuli (14, 15) such as human speech (16,17), and this synchronization supports perception (18). Furthermore, synchronization of low-frequency neural oscillations with speech is enhanced for speech streams to which participants attend (19,20). Critically, low-frequency oscillations are commonly specified as phase-locked activity (synchroni...

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Spatiotemporal dynamics of auditory attention synchronize with speech

Wöstmann

Herrmann

Maess

et al. 2016

181

229

“…Likewise in human visual cortex, 1 Hz vs. 10 Hz TMS regimes showed opposing effects on excitability, as measured by changes of phosphene thresholds (38,39). In particular, effectiveness of 10 Hz rTMS over human V1 was demonstrated by improved contrast sensitivity of amblyopic patients (40), as well as by modulation of performance in visual detection and feature discrimination tasks (41).…”

Section: Effects On Visual Cortical Processing-long-term Potentiationmentioning

confidence: 99%

Voltage-sensitive dye imaging of transcranial magnetic stimulation-induced intracortical dynamics

Kozyrev

Eysel

Jancke

2014

Transcranial magnetic stimulation (TMS) is widely used in clinical interventions and basic neuroscience. Additionally, it has become a powerful tool to drive plastic changes in neuronal networks. However, highly resolved recordings of the immediate TMS effects have remained scarce, because existing recording techniques are limited in spatial or temporal resolution or are interfered with by the strong TMS-induced electric field. To circumvent these constraints, we performed optical imaging with voltage-sensitive dye (VSD) in an animal experimental setting using anaesthetized cats. The dye signals reflect gradual changes in the cells' membrane potential across several square millimeters of cortical tissue, thus enabling direct visualization of TMS-induced neuronal population dynamics. After application of a single TMS pulse across visual cortex, brief focal activation was immediately followed by synchronous suppression of a large pool of neurons. With consecutive magnetic pulses (10 Hz), widespread activity within this "basin of suppression" increased stepwise to suprathreshold levels and spontaneous activity was enhanced. Visual stimulation after repetitive TMS revealed long-term potentiation of evoked activity. Furthermore, loss of the "deceleration-acceleration" notch during the rising phase of the response, as a signature of fast intracortical inhibition detectable with VSD imaging, indicated weakened inhibition as an important driving force of increasing cortical excitability. In summary, our data show that high-frequency TMS changes the balance between excitation and inhibition in favor of an excitatory cortical state. VSD imaging may thus be a promising technique to trace TMS-induced changes in excitability and resulting plastic processes across cortical maps with high spatial and temporal resolutions. (1) (TMS) has become a frequently used method for noninvasive diagnostics, therapeutic treatment, and intervention for neurorehabilitation of neurological disorders (2-8). Additionally, TMS has proved a valuable tool in basic brain research as its perturbative effects allow area-selective manipulation of immediate cortical function (9-11), as well as its long-lasting alteration through plasticity and learning protocols (12, 13). However, direct measurements of the TMS-induced cortical dynamics at highly resolved spatiotemporal scales are missing because "online approaches" (14), using modern neuroimaging techniques such as functional MRI (fMRI) (15-18), magnetoencephalography (19), EEG (20), and near-infrared (21) or intrinsic optical imaging (22), are limited in either spatial or temporal resolutions or in both.Here we overcame these limitations, using optical imaging with voltage-sensitive dyes (VSD), which exploits the dye's property to transduce gradual changes in voltage across neuronal membranes into fluorescent light signals. In contrast to imaging methods applicable in humans, this method is invasive but allows avoiding the commonly experienced contamination of signals by artifacts due to the strong ...

“…For example, evidence suggests that the processing of visual information employs underlying α-band oscillations (38), whereas the processing of higher level cognitive information might be coordinated by other frequencies. The interactions between these high-and low-frequency bands are thought to play an important role in neuronal computation and communication (39).…”

Section: Spatiotemporal Interhemispheric Communicationmentioning

confidence: 99%

Dynamic network structure of interhemispheric coordination

Doron

Bassett

Gazzaniga

2012

136

146

Fifty years ago Gazzaniga and coworkers published a seminal article that discussed the separate roles of the cerebral hemispheres in humans. Today, the study of interhemispheric communication is facilitated by a battery of novel data analysis techniques drawn from across disciplinary boundaries, including dynamic systems theory and network theory. These techniques enable the characterization of dynamic changes in the brain's functional connectivity, thereby providing an unprecedented means of decoding interhemispheric communication. Here, we illustrate the use of these techniques to examine interhemispheric coordination in healthy human participants performing a split visual field experiment in which they process lexical stimuli. We find that interhemispheric coordination is greater when lexical information is introduced to the right hemisphere and must subsequently be transferred to the left hemisphere for language processing than when it is directly introduced to the language-dominant (left) hemisphere. Further, we find that putative functional modules defined by coherent interhemispheric coordination come online in a transient manner, highlighting the underlying dynamic nature of brain communication. Our work illustrates that recently developed dynamic, network-based analysis techniques can provide novel and previously unapproachable insights into the role of interhemispheric coordination in cognition.T he field of split-brain research began several decades ago with the use of a drastic surgical solution for intractable epilepsy (1-3): the severing of the corpus callosum. This procedure significantly decreased the connectivity between the hemispheres, thereby irrevocably altering interhemispheric communication. Although a few interhemispheric pathways remained through subcortical structures and the anterior commissure, examination of callosal function using split visual field experiments clearly demonstrated its role in interhemispheric communication (2). The callosal projection plays a particularly crucial role in a variety of sensory-motor integrative functions of the two hemispheres (4), shows changes with age, and demonstrates the potential for dynamic changes with training (5). In fact, experiments in patients with severance of the callosum revealed that it subserves a large range of behaviors and cognitive functions that underlie the varied workings of the mind.Interhemispheric communication has been studied using two basic approaches. The first uses behavioral experiments to examine cognitive phenotypes, and the second uses neuroscientific experiments to examine brain phenotypes. Split-brain research initially focused on the former: Patients demonstrated striking behavioral phenotypes that provided clues regarding the underlying mechanics of brain communication. For example, although most perceptual processing appears to be isolated in each hemisphere following surgery, some attentional and emotional mechanisms initiated in one hemisphere can still be communicated to the other, cortically disconnected,...