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

Relationship between electroencephalographic data and comfort perception captured in a Virtual Reality design environment of an aircraft cabin

Successful aircraft cabin design depends on how the different stakeholders are involved since the first phases of product development. To predict passenger satisfaction prior to the manufacturing phase, human response was investigated in a Virtual Reality (VR) environment simulating a cabin aircraft. Subjective assessments of virtual designs have been collected via questionnaires, while the underlying neural mechanisms have been captured through electroencephalographic (EEG) data. In particular, we focused on the modulation of EEG alpha rhythm as a valuable marker of the brain's internal state and investigated which changes in alpha power and connectivity can be related to a different visual comfort perception by comparing groups with higher and lower comfort rates. Results show that alpha-band power decreased in occipital regions during subjects' immersion in the virtual cabin compared with the relaxation state, reflecting attention to the environment. Moreover, alpha-band power was modulated by comfort perception: lower comfort was associated with a lower alpha power compared to higher comfort. Further, alpha-band Granger connectivity shows top-down mechanisms in higher comfort participants, modulating attention and restoring partial relaxation. Present results contribute to understanding the role of alpha rhythm in visual comfort perception and demonstrate that VR and EEG represent promising tools to quantify human-environment interactions

Role of Anterior Cingulate Cortex in Saccade Control

Cognitive control is referred to the guidance of behavior based on internal goals rather than external stimuli. It has been postulated that prefrontal cortex is mainly involved in higher order cognitive functions. Specifically, anterior cingulate cortex (ACC), which is part of the prefrontal cortex, is suggested to be involved in performance monitoring and conflict monitoring that are considered to be cognitive control functions. Saccades are the fast eye movements that align the fovea on the objects of interest in the environment. In this thesis, I have explored the role of ACC in control of saccadic eye movements. First, I performed a resting-state fMRI study to identify areas within the ACC that are functionally connected to the frontal eye fields (FEF). It has been shown that FEF is involved in saccade generation. Therefore, the ACC areas that are functionally connected to FEF could be hypothesized to have a role in saccade control. Then, I performed simultaneous electrophysiological recordings in the ACC and FEF. Furthermore, I explored whether ACC exerts control over FEF. My results show that ACC is involved in cognitive control of saccades. Furthermore, the ACC and FEF neurons communicate through synchronized theta and beta band activity in these areas. The results of this thesis shine light on the mechanisms by which these brain areas communicate. Moreover, my findings support the notion that ACC and FEF have a unique oscillatory property, and more specifically ACC has a prominent theta band, and to a lesser extent beta band activity

Synchronous beta rhythms of frontoparietal networks support only behaviorally relevant representations

Categorization has been associated with distributed networks of the primate brain, including the prefrontal cortex (PFC) and posterior parietal cortex (PPC). Although category-selective spiking in PFC and PPC has been established, the frequency-dependent dynamic interactions of frontoparietal networks are largely unexplored. We trained monkeys to perform a delayed-match-to-spatial-category task while recording spikes and local field potentials from the PFC and PPC with multiple electrodes. We found category-selective beta- and delta-band synchrony between and within the areas. However, in addition to the categories, delta synchrony and spiking activity also reflected irrelevant stimulus dimensions. By contrast, beta synchrony only conveyed information about the task-relevant categories. Further, category-selective PFC neurons were synchronized with PPC beta oscillations, while neurons that carried irrelevant information were not. These results suggest that long-range beta-band synchrony could act as a filter that only supports neural representations of the variables relevant to the task at hand.National Institute of Mental Health (U.S.) (4R01MH065252)Prop. 63 the Mental Health Services ActUniversity of California, Davis. Behavioral Health Center of Excellenc

Modality-Specific and Modality-General Encoding of Auditory and Visual Rhythms

The perception of timing information plays a large role in our everyday activities, yet we still do not accurately understand the mechanisms underlying these perceptions. Both modality-general and modality specific mechanisms have been suggested to account for perceptual timing. The use of a new auditory tempo perception paradigm can be used to examine various brain responses - measured via electroencephalography (EEG) - thought to index timing perception. This study applied this paradigm to both auditory and visual rhythms, and compared event-related potentials (ERPs) to task performance. Auditory and visual contingent negative variation (CNV) components showed two distinct voltage patterns across the scalp: The auditory CNV appears to show contributions from temporal areas, while the visual CNV appears to show contributions from occipital areas. There were larger CNV amplitudes in the auditory modality than in the visual, suggesting the CNV indexes modality-specific processing. A late, memory-dependent positive-voltage component did not show these modality-related topographical or amplitude differences, and instead reflects modality-general processing. This suggests timing information is encoded intrinsically at a sensory level, and this information is then routed to a cognitive, decision-making area for further processing

The effect of mental stress on brain dynamics and performance related to attention control during a vigilance task: An electroencephalographic investigation

Anxiety can increase distractibility and undermine the quality of psychomotor performance. Models of attention processing postulate that anxiety consumes limited executive resources necessary for maintaining goal-oriented, "top-down" attention control and suppressing stimulus-driven "bottom-up" distraction. Attention Control Theory (ACT) predicts that anxiety adversely affects the efficiency, and particularly inhibitory components of executive, frontally mediated top-down attention control. We used two approaches for examining this model. First, though attention affects synchrony among neural structures, information regarding how human oscillatory patterns (measured with electroencephalography, EEG) change as state anxiety increases is limited. Second, while anxiety affects the balance between top-down and bottom-up mechanisms, to our knowledge no one has yet measured anxiety's effect on attention using a neural measure of top-down control in conjunction with more traditional bottom-up measures of attention capture (e.g., the P3 event related potential, or ERP). Purpose: Study 1 examines the oscillatory patterns (spectral dynamics) of the cortex in order to investigate whether frontal regions exhibit patterns of reduced efficiency and altered networking with posterior regions during threat of shock. In order to assess the relationship between top-down and bottom-up attention dynamics, Study 2 uses the same threat protocol to measure attention-directed top-down modulation of sensory signaling (steady-state visual evoked potential, or ssVEP modulation) and of bottom-up attention capture by discrete targets and distractors (Event Related Potentials, ERPs). Results: The spectral analyses in Study 1 suggest decreased processing efficiency and decreased frontal networking (coherence) with more posterior regions as anxiety increased. Reduced coherence, however, could indicate either increased or decreased top-down focus; Study 2 provides more insight. Neural responses to task-relevant targets (ERPs) diminished as threat increased, while responses to task-irrelevant distractors remained unchanged. Contrary to what ACT would predict, we observed an increase in attention modulation of an ssVEP frequency associated with amplifying the task-relevant signal and no change in an ssVEP associated with inhibiting task-irrelevant stimuli. These findings suggest top-down attention control increased under threat, but was not enough to prevent degraded processing of task-relevant targets coincident with reduced efficiency on task performance. Implications and suggestions for refining ACT are discussed

THE LEFT HEMISPHERE’S STRUCTURAL CONNECTIVITY FOR THE INFERIOR FRONTAL GYRUS, STRIATUM, AND THALAMUS, AND INTRA-THALAMIC TOPOGRAPHY

The neuroanatomy of language cognition has an extensive history of scientific interest and inquiry. Over a century of behavioral lesion studies and decades of functional neuroimaging research have established the left hemisphere’s inferior frontal gyrus (IFG) as a critical region for speech and language processing. This region’s subcortical projections are thought to be instrumental for supporting and integrating the cognitive functions of the language network. However, only a subset of these projections have been shown to exist in humans, and structural evidence of pars orbitalis’ subcortical circuitry has been limited to non-human primates. This thesis demonstrates direct, intra-structural connectivity of each of the left IFG’s gyral regions with the thalamus and the putamen in humans, using high-angular, deterministic tractography. Novel processing and analysis methods elucidated evidence of predominantly segregated cortical circuits within the thalamus, and suggested the presence of parallel circuits for motor/language integration along the length of the putamen