Neural synchrony in cortical networks : history, concept and current status

Following the discovery of context-dependent synchronization of oscillatory neuronal responses in the visual system, the role of neural synchrony in cortical networks has been expanded to provide a general mechanism for the coordination of distributed neural activity patterns. In the current paper, we present an update of the status of this hypothesis through summarizing recent results from our laboratory that suggest important new insights regarding the mechanisms, function and relevance of this phenomenon. In the first part, we present recent results derived from animal experiments and mathematical simulations that provide novel explanations and mechanisms for zero and nero-zero phase lag synchronization. In the second part, we shall discuss the role of neural synchrony for expectancy during perceptual organization and its role in conscious experience. This will be followed by evidence that indicates that in addition to supporting conscious cognition, neural synchrony is abnormal in major brain disorders, such as schizophrenia and autism spectrum disorders. We conclude this paper with suggestions for further research as well as with critical issues that need to be addressed in future studies

Neural synchrony in cortical networks : history, concept and current status

Following the discovery of context-dependent synchronization of oscillatory neuronal responses in the visual system, the role of neural synchrony in cortical networks has been expanded to provide a general mechanism for the coordination of distributed neural activity patterns. In the current paper, we present an update of the status of this hypothesis through summarizing recent results from our laboratory that suggest important new insights regarding the mechanisms, function and relevance of this phenomenon. In the first part, we present recent results derived from animal experiments and mathematical simulations that provide novel explanations and mechanisms for zero and nero-zero phase lag synchronization. In the second part, we shall discuss the role of neural synchrony for expectancy during perceptual organization and its role in conscious experience. This will be followed by evidence that indicates that in addition to supporting conscious cognition, neural synchrony is abnormal in major brain disorders, such as schizophrenia and autism spectrum disorders. We conclude this paper with suggestions for further research as well as with critical issues that need to be addressed in future studies

Tensor Analysis and Fusion of Multimodal Brain Images

Current high-throughput data acquisition technologies probe dynamical systems with different imaging modalities, generating massive data sets at different spatial and temporal resolutions posing challenging problems in multimodal data fusion. A case in point is the attempt to parse out the brain structures and networks that underpin human cognitive processes by analysis of different neuroimaging modalities (functional MRI, EEG, NIRS etc.). We emphasize that the multimodal, multi-scale nature of neuroimaging data is well reflected by a multi-way (tensor) structure where the underlying processes can be summarized by a relatively small number of components or "atoms". We introduce Markov-Penrose diagrams - an integration of Bayesian DAG and tensor network notation in order to analyze these models. These diagrams not only clarify matrix and tensor EEG and fMRI time/frequency analysis and inverse problems, but also help understand multimodal fusion via Multiway Partial Least Squares and Coupled Matrix-Tensor Factorization. We show here, for the first time, that Granger causal analysis of brain networks is a tensor regression problem, thus allowing the atomic decomposition of brain networks. Analysis of EEG and fMRI recordings shows the potential of the methods and suggests their use in other scientific domains.Comment: 23 pages, 15 figures, submitted to Proceedings of the IEE

A speech envelope landmark for syllable encoding in human superior temporal gyrus.

The most salient acoustic features in speech are the modulations in its intensity, captured by the amplitude envelope. Perceptually, the envelope is necessary for speech comprehension. Yet, the neural computations that represent the envelope and their linguistic implications are heavily debated. We used high-density intracranial recordings, while participants listened to speech, to determine how the envelope is represented in human speech cortical areas on the superior temporal gyrus (STG). We found that a well-defined zone in middle STG detects acoustic onset edges (local maxima in the envelope rate of change). Acoustic analyses demonstrated that timing of acoustic onset edges cues syllabic nucleus onsets, while their slope cues syllabic stress. Synthesized amplitude-modulated tone stimuli showed that steeper slopes elicited greater responses, confirming cortical encoding of amplitude change, not absolute amplitude. Overall, STG encoding of the timing and magnitude of acoustic onset edges underlies the perception of speech temporal structure

Intrinsic multi-scale analysis: a multi-variate empirical mode decomposition framework.

A novel multi-scale approach for quantifying both inter- and intra-component dependence of a complex system is introduced. This is achieved using empirical mode decomposition (EMD), which, unlike conventional scale-estimation methods, obtains a set of scales reflecting the underlying oscillations at the intrinsic scale level. This enables the data-driven operation of several standard data-association measures (intrinsic correlation, intrinsic sample entropy (SE), intrinsic phase synchrony) and, at the same time, preserves the physical meaning of the analysis. The utility of multi-variate extensions of EMD is highlighted, both in terms of robust scale alignment between system components, a pre-requisite for inter-component measures, and in the estimation of feature relevance. We also illuminate that the properties of EMD scales can be used to decouple amplitude and phase information, a necessary step in order to accurately quantify signal dynamics through correlation and SE analysis which are otherwise not possible. Finally, the proposed multi-scale framework is applied to detect directionality, and higher order features such as coupling and regularity, in both synthetic and biological systems

Movement Intermittency in Social Coordination

Coordination of movements in humans has been extensively studied at a macroscopic level, such as the pacing of movements, particularly in tasks of interpersonal and bimanual coordination. However, by examining the fine structure of movement, another form of rhythmicity becomes apparent at a microscopic level. Movement is never completely smooth, but rather is organized into smaller units known as submovements, which appear as recurrent speed breaks occurring at faster timescales (2-3 Hz). These submovements may reflect intermittent feedback-based motor adjustments. To better understand the relationship between submovements in different coordination contexts, we characterized the timing of submovements emission in a series of rhythmic motor coordination task by asking participants to coordinate their index fingers either in-phase or anti-phase with themselves or with a real/virtual partner. In Study 1, we analysed the temporal relationship between submovements emitted by both hands of a single participant during a bimanual coordination task. We also manipulated the availability of visual feedback to understand its impact on the emission of submovements, which are believed to reflect a vision based movement correction mechanism. In Study 2, we explored the dynamics of submovements during interpersonal coordination, and thus with the goal of moving beyond their temporal emission in single individuals. In Study 3, we combined interpersonal and bimanual coordination into a single task by asking participants to coordinate with each other using both their hands. In Study 4, we tested the validity of our results on mutual adaptation of submovements during interpersonal coordination by replacing one member of the pair with an unresponsive virtual partner. Finally, in Study 5, building on the ease of transferability of the previous task to clinical settings, we investigated the pattern of submovements emission in individuals with Parkinson's disease and cerebellar disorders to identify potentially new diagnostic markers and gain novel insights into the neural substrates underlying movement intermittency. Overall, our results suggest that the mechanism responsible for the organization of movement into submovements is at least partly shared across different effectors, such as the two hands, and might be modulated by the availability and usability of visual and proprioceptive feedback. Moreover, the identification of different temporal patterns of submovements emission leads us to conclude that the mechanisms controlling submovements production are highly flexible and tunable depending on the coordinative context. Submovements control can thus provide valuable insights into the low-level motor control mechanisms involved in achieving intra- and interpersonal motor coordination. Finally, submovement-level control may serve as a novel objective marker of individual and social motor coordination capabilities that may be selectively impaired in some neurological and psychiatric conditions.La coordinazione dei movimenti negli esseri umani è stata ampiamente studiata a livello macroscopico, ad es. il ritmo dei movimenti, in particolare in compiti di coordinazione interpersonale e bimanuale. Tuttavia, esaminando la struttura fine del movimento, un'altra forma di ritmicità appare evidente a livello microscopico. Il movimento non è mai completamente fluido, ma è organizzato in unità più piccole note come sottomovimenti, che si manifestano come interruzioni di velocità ricorrenti su una scala temporale più veloce (2-3 Hz). Questi sottomovimenti possono riflettere aggiustamenti motori intermittenti basati sul feedback. Per comprendere meglio la relazione tra i sottomovimenti in contesti di coordinazione diversi, abbiamo caratterizzato i pattern di emissione temporale dei sottomovimenti in una serie di compiti di coordinazione motoria ritmica, chiedendo ai partecipanti di coordinare i loro indici in-fase o in anti-fase con se stessi o con un partner reale/virtuale. Nello Studio 1, abbiamo analizzato la relazione temporale tra i sottomovimenti emessi da entrambe le mani di un singolo partecipante durante un compito di coordinazione bimanuale. Abbiamo anche manipolato la disponibilità del feedback visivo per comprendere il suo impatto sull'emissione dei sottomovimenti, che si ritiene riflettano un meccanismo di correzione dei movimenti basato sulla visione. Nello Studio 2, abbiamo esplorato la dinamica dei sottomovimenti durante la coordinazione interpersonale, con l’obiettivo di indagare i loro pattern di emissione temporale in coppie di individui. Nello Studio 3, abbiamo combinato la coordinazione interpersonale e bimanuale in un unico compito, chiedendo ai partecipanti di coordinarsi reciprocamente utilizzando entrambe le mani. Nello Studio 4, abbiamo testato la validità dei nostri risultati sull'adattamento reciproco dei sottomovimenti durante la coordinazione interpersonale sostituendo uno dei membri della coppia con un partner virtuale non reattivo. Infine, nello Studio 5, considerata la facile trasferibilità del compito precedente in contesti clinici, abbiamo indagato il modello di emissione dei sottomovimenti in individui con malattia di Parkinson e disturbi cerebellari per identificare potenziali nuovi marker diagnostici e acquisire nuove informazioni sui substrati neurali alla base dell'intermittenza del movimento. Complessivamente, i nostri risultati suggeriscono che il meccanismo responsabile dell'organizzazione del movimento in sottomovimenti è almeno in parte condiviso tra differenti effettori, come le due mani, e potrebbe essere modulato dalla disponibilità e utilizzabilità del feedback visivo e propriocettivo. Inoltre, l'identificazione di diversi modelli temporali di emissione dei sottomovimenti ci porta a concludere che i meccanismi che controllano la produzione dei sottomovimenti sono altamente flessibili e adattabili in base al contesto coordinativo. Il controllo dei sottomovimenti può quindi fornire preziose informazioni sui meccanismi di controllo motorio di basso livello coinvolti nel raggiungimento della coordinazione motoria intra- e interpersonale. Infine, il controllo motorio a livello dei sottomovimenti potrebbe fungere da nuovo marker oggettivo delle capacità individuali e sociali di coordinazione motoria che potrebbero essere selettivamente compromesse in alcune condizioni neurologiche e psichiatriche

Joint analysis of eye blinks and brain activity to investigate attentional demand during a visual search task

In several fields, the need for a joint analysis of brain activity and eye activity to investigate the association between brain mechanisms and manifest behavior has been felt. In this work, two levels of attentional demand, elicited through a conjunction search task, have been modelled in terms of eye blinks, brain activity, and brain network features. Moreover, the association between endogenous neural mechanisms underlying attentional demand and eye blinks, without imposing a time-locked structure to the analysis, has been investigated. The analysis revealed statistically significant spatial and spectral modulations of the recorded brain activity according to the different levels of attentional demand, and a significant reduction in the number of eye blinks when a higher amount of attentional investment was required. Besides, the integration of information coming from high-density electroencephalography (EEG), brain source localization, and connectivity estimation allowed us to merge spectral and causal information between brain areas, characterizing a comprehensive model of neurophysiological processes behind attentional demand. The analysis of the association between eye and brain-related parameters revealed a statistically significant high correlation (R > 0.7) of eye blink rate with anterofrontal brain activity at 8 Hz, centroparietal brain activity at 12 Hz, and a significant moderate correlation with the participation of right Intra Parietal Sulcus in alpha band (R = -0.62). Due to these findings, this work suggests the possibility of using eye blinks measured from one sensor placed on the forehead as an unobtrusive measure correlating with neural mechanisms underpinning attentional demand