Proceedings of the Second International Workshop on Modeling and Retrieval of Context (MRC 2005) (original) (raw)
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Proceedings of the Second International Workshop on Advances in Electrocorticography
Epilepsy & Behavior, 2011
The Second International Workshop on Advances in Electrocorticography (ECoG) was convened in San Diego, CA, USA, on November 11-12, 2010. Between this meeting and the inaugural 2009 event, a much clearer picture has been emerging of cortical ECoG physiology and its relationship to local field potentials and single-cell recordings. Innovations in material engineering are advancing the goal of a stable long-term recording interface. Continued evolution of ECoG-driven brain-computer interface technology is determining innovation in neuroprosthetics. Improvements in instrumentation and statistical methodologies continue to elucidate ECoG correlates of normal human function as well as the ictal state. This proceedings document summarizes the current status of this rapidly evolving field.
Spatial spectra of scalp EEG and EMG from awake humans
Clinical Neurophysiology, 2003
Objectives: Evaluate spectral scaling properties of scalp electroencephalogram (EEG) and electromyogram (EMG), optimal spacing of electrodes, and strategies for mitigating EMG. Methods: EEG was recorded referentially from 9 subjects with a 64 channel linear array (electrodes 3 mm apart) placed parasagittally or transversely on forehead or occiput, at rest with eyes open or closed, or with deliberate EMG. Temporal (PSD t) and spatial (PSD x) power spectral densities were calculated with 1-dimensional fast Fourier transform (FFT) for comparison with earlier analyses of intracranial EEG. Results: Scaling of PSD t from scalp resembled that from pia: near-linear decrease in log power with increasing log frequency (1/f a). Scalp PSD x decreased nonlinearly and more rapidly than PSD x from pia. Peaks in PSD t (especially 4-12 Hz) and PSD x (especially 0.1-0.4 cycles/cm) revealed departures from 1/f a. EMG power in PSD t was more 'white' than 1/f a. Conclusions: Smearing by dura-skull-scalp distorts PSD x more than PSD t of scalp EEG from 1/f a scaling at the pia. Spatial spectral peaks suggest that optimal scalp electrode spacing might be ~1 cm to capture nonlocal EEG components having the texture of gyri. Mitigation of EMG by filtering is unsatisfactory. A criterion for measuring EMG may support biofeedback for training subjects to reduce their EMG. Significance: High-density recording and log-log spectral display of EEG provide a foundation for holist studies of global human brain function, as an alternative to network approaches that decompose EEG into localized, modular signals for correlation and coherence.
Spatiotemporal scales and links between electrical neuroimaging modalities
Medical & Biological Engineering & Computing, 2011
Recordings of brain electrophysiological activity provide the most direct reflect of neural function. Information contained in these signals varies as a function of the spatial scale at which recordings are done: from single cell recording to large scale macroscopic fields, e.g., scalp EEG. Microscopic and macroscopic measurements and models in Neuroscience are often in conflict. Solving this conflict might require the developments of a sort of bio-statistical physics, a framework for relating the microscopic properties of individual cells to the macroscopic or bulk properties of neural circuits. Such a framework can only emerge in Neuroscience from the systematic analysis and modeling of the diverse recording scales from simultaneous measurements. In this article we briefly review the different measurement scales and models in modern neuroscience to try to identify the sources of conflict that might ultimately help to create a unified theory of brain electromagnetic fields. We argue that seen the different recording scales, from the single cell to the large scale fields measured by the scalp electroencephalogram, as derived from a unique physical magnitude-the electric potential that is measured in all cases-might help to conciliate microscopic and macroscopic models of neural function as well as the animal and human neuroscience literature.
Neuronal firing in human epileptic cortex: the ins and outs of synchrony during seizures
Epilepsy currents / American Epilepsy Society, 2013
Epileptic seizures propagate extensively across the brain. The associated electrophysiological mass phenomena can be captured by scalp or intracranial electroencephalography. Recent evidence shows the initiating mechanisms of seizures operate at the smaller scale of neuronal ensembles, producing phenomena such as high-frequency oscillations (1, 2) and microseizures (3, 4) that are best detected at a tighter spatial resolution of local field potentials recorded by microelectrodes. More recently, researchers have started using microelectrodes to analyze the activity of large numbers of individual neurons during seizures in neocortex (5) and hippocampus (6) and to relate this activity to the corresponding macroscopic EEG recordings. The main focus of this commentary is the most recent of these studies by Schevon et al., which provides potential solutions to puzzles arising from previous neocortical work.
Proceedings of the First International Workshop on Advances in Electrocorticography
Epilepsy & Behavior, 2010
In October 2009, a group of neurologists, neurosurgeons, computational neuroscientists, and engineers congregated to present novel developments transforming human electrocorticography (ECoG) beyond its established relevance in clinical epileptology. The contents of the proceedings advanced the role of ECoG in seizure detection and prediction, neurobehavioral research, functional mapping, and brain–computer interface technology. The meeting established the foundation for future work on
The spatial resolution of scalp EEG
Neurocomputing, 2001
The scalp electroencephalogram (EEG) exhibits spatiotemporal dynamics re#ecting synchronous dendritic activity of cortical pyramidal neurons. Recent advances in EEG acquisition and electric head modeling are improving the spatial resolution of scalp EEG, but the skull remains an obstacle. We use lead "eld theory to quantify the spatial resolution of scalp EEG, contrasting two electrode spacings and two values of skull conductivity. We show that, without cortical constraints, 19-electrode EEG systems have optimal spatial resolution near 22}37 cm, while 129-electrode systems have 6}8 cm. These results emphasize the bene"ts of more electrodes, but also the need for methods of measuring local skull conductivity.
High-frequency gamma oscillations and human brain mapping with electrocorticography
Progress in Brain Research, 2006
Invasive EEG recordings with depth and/or subdural electrodes are occasionally necessary for the surgical management of patients with epilepsy refractory to medications. In addition to their vital clinical utility, electrocorticographic (ECoG) recordings provide an unprecedented opportunity to study the electrophysiological correlates of functional brain activation in greater detail than non-invasive recordings. The proximity of ECoG electrodes to the cortical sources of EEG activity enhances their spatial resolution, as well as their sensitivity and signal-to-noise ratio, particularly for high-frequency EEG activity. ECoG recordings have, therefore, been used to study the event-related dynamics of brain oscillations in a variety of frequency ranges, and in a variety of functional-neuroanatomic systems, including somatosensory and somatomotor systems, visual and auditory perceptual systems, and cortical networks responsible for language. These ECoG studies have confirmed and extended the original non-invasive observations of ERD/ERS phenomena in lower frequencies, and have discovered novel event-related responses in gamma frequencies higher than those previously observed in non-invasive recordings. In particular, broadband event-related gamma responses greater than 60 Hz, extending up to $200 Hz, have been observed in a variety of functional brain systems. The observation of these ''high gamma'' responses requires a recording system with an adequate sampling rate and dynamic range (we use 1000 Hz at 16-bit A/D resolution) and is facilitated by event-related time-frequency analyses of the recorded signals. The functional response properties of high-gamma activity are distinct from those of ERD/ERS phenomena in lower frequencies. In particular, the timing and spatial localization of high-gamma ERS often appear to be more specific to the putative timing and localization of functional brain activation than alpha or beta ERD/ERS. These findings are consistent with the proposed role of synchronized gamma oscillations in models of neural computation, which have in turn been inspired by observations of gamma activity in animal preparations, albeit at somewhat lower frequencies. Although ECoG recordings cannot directly measure the synchronization of action potentials among assemblies of neurons, they may demonstrate event-related interactions between gamma oscillations in macroscopic local field potentials (LFP) generated by different large-scale populations of neurons engaged by the same functional task. Indeed, preliminary studies suggest that such interactions do occur in gamma frequencies, including high-gamma frequencies, at latencies consistent with the timing of task performance. The neuronal mechanisms underlying high-gamma activity and its unique response properties in humans are still largely unknown, but their investigation through invasive methods is expected to facilitate and expand their potential clinical and research applications, including functional brain mapping, brain-computer interfaces, and neurophysiological studies of human cognition.
Journal of Visualized Experiments, 2012
Neuroimaging studies of human cognitive, sensory, and motor processes are usually based on noninvasive techniques such as electroencephalography (EEG), magnetoencephalography or functional magnetic-resonance imaging. These techniques have either inherently low temporal or low spatial resolution, and suffer from low signal-to-noise ratio and/or poor high-frequency sensitivity. Thus, they are suboptimal for exploring the short-lived spatio-temporal dynamics of many of the underlying brain processes. In contrast, the invasive technique of electrocorticography (ECoG) provides brain signals that have an exceptionally high signal-to-noise ratio, less susceptibility to artifacts than EEG, and a high spatial and temporal resolution (i.e., <1 cm/<1 millisecond, respectively). ECoG involves measurement of electrical brain signals using electrodes that are implanted subdurally on the surface of the brain. Recent studies have shown that ECoG amplitudes in certain frequency bands carry substantial information about task-related activity, such as motor execution and planning 1 , auditory processing 2 and visual-spatial attention 3. Most of this information is captured in the high gamma range (around 70-110 Hz). Thus, gamma activity has been proposed as a robust and general indicator of local cortical function 1-5. ECoG can also reveal functional connectivity and resolve finer task-related spatial-temporal dynamics, thereby advancing our understanding of large-scale cortical processes. It has especially proven useful for advancing brain-computer interfacing (BCI) technology for decoding a user's intentions to enhance or improve communication 6 and control 7. Nevertheless, human ECoG data are often hard to obtain because of the risks and limitations of the invasive procedures involved, and the need to record within the constraints of clinical settings. Still, clinical monitoring to localize epileptic foci offers a unique and valuable opportunity to collect human ECoG data. We describe our methods for collecting recording ECoG, and demonstrate how to use these signals for important real-time applications such as clinical mapping and brain-computer interfacing. Our example uses the BCI2000 software platform 8,9 and the SIGFRIED 10 method, an application for real-time mapping of brain functions. This procedure yields information that clinicians can subsequently use to guide the complex and laborious process of functional mapping by electrical stimulation.
Proceedings of the Fourth International Workshop on Advances in Electrocorticography
Epilepsy & Behavior, 2013
workshop serves as an accurate record of the most contemporary clinical and experimental work on brain surface recording and represents the insights of a unique multidisciplinary ensemble of expert clinicians and scientists. Presentations covered a broad range of topics, including innovations in passive functional mapping, increased understanding of pathologic high-frequency oscillations, evolving sensor technologies, a human trial of ECoG-driven brain-machine interface, as well as fresh insights into brain electrical stimulation.