Results 1 - 10
of
140
A neural mass model for MEG/EEG: coupling and neuronal dynamics
- NeuroImage
, 2003
"... Although MEG/EEG signals are highly variable, systematic changes in distinct frequency bands are commonly encountered. These frequency-specific changes represent robust neural correlates of cognitive or perceptual processes (for example, alpha rhythms emerge on closing the eyes). However, their func ..."
Abstract
-
Cited by 81 (21 self)
- Add to MetaCart
Although MEG/EEG signals are highly variable, systematic changes in distinct frequency bands are commonly encountered. These frequency-specific changes represent robust neural correlates of cognitive or perceptual processes (for example, alpha rhythms emerge on closing the eyes). However, their functional significance remains a matter of debate. Some of the mechanisms that generate these signals are known at the cellular level and rest on a balance of excitatory and inhibitory interactions within and between populations of neurons. The kinetics of the ensuing population dynamics determine the frequency of oscillations. In this work we extended the classical nonlinear lumped-parameter model of alpha rhythms, initially developed by Lopes da Silva and colleagues [Kybernetik 15 (1974) 27], to generate more complex dynamics. We show that the whole spectrum of MEG/EEG signals can be reproduced within the oscillatory regime of this model by simply changing the population kinetics. We used the model to examine the influence of coupling strength and propagation delay on the rhythms generated by coupled cortical areas. The main findings were that (1) coupling induces phase-locked activity, with a phase shift of 0 or π when the coupling is bidirectional, and (2) both coupling and propagation delay are critical determinants of the MEG/EEG spectrum. In forthcoming articles, we will use this model to (1) estimate how neuronal interactions are expressed in MEG/EEG oscillations and establish the construct validity of various indices of nonlinear coupling, and (2) generate event-related transients to derive physiologically informed basis functions for statistical modelling of average evoked responses.
Fractionating language: Different neural subsystems with different sensitive periods
- Cerebral Cortex
, 1992
"... Theoretical considerations and psycholinguistic studies have alternately provided criticism and support for the proposal that semantic and grammatical functions are distinct subprocesses within the language domain. Neu-robiological evidence concerning this hypothesis was sought by (1) comparing, in ..."
Abstract
-
Cited by 78 (5 self)
- Add to MetaCart
(Show Context)
Theoretical considerations and psycholinguistic studies have alternately provided criticism and support for the proposal that semantic and grammatical functions are distinct subprocesses within the language domain. Neu-robiological evidence concerning this hypothesis was sought by (1) comparing, in normal adults, event-related brain potentials (ERPs) elicited by words that provide primarily semantic information (open class) and gram-matical information (closed class) and (2) comparing the effects of the altered early language experience of congenitally deaf subjects on ERPs to open and closed class words. In normal-hearing adults, the different word types elicited qualitatively different ERPs that were compatible with the hypothesized different roles of the word classes in language processing. In addition, where-
Imaging brain dynamics using independent component analysis
- Proceedings of the IEEE
"... The analysis of electroencephalographic (EEG) and magnetoencephalographic (MEG) recordings is important both for basic brain research and for medical diagnosis and treatment. Independent component analysis (ICA) is an effective method for removing artifacts and separating sources of the brain signal ..."
Abstract
-
Cited by 77 (25 self)
- Add to MetaCart
(Show Context)
The analysis of electroencephalographic (EEG) and magnetoencephalographic (MEG) recordings is important both for basic brain research and for medical diagnosis and treatment. Independent component analysis (ICA) is an effective method for removing artifacts and separating sources of the brain signals from these recordings. A similar approach is proving useful for analyzing functional magnetic resonance brain imaging (fMRI) data. In this paper, we outline the assumptions underlying ICA and demonstrate its application to a variety of electrical and hemodynamic recordings from the human brain. Keywords—Blind source separation, EEG, fMRI, independent component analysis.
Who did what and when? Using word- and clause-level ERPs to monitor working memory usage in reading
- Journal of Cognitive Neuroscience
, 1995
"... ERPs were recorded from 24 undergraduates as they read sentences known to differ in syntactic complexity and working memory requirements, namely Object and Subject Relative sentences. Both the single-word and multiword analyses revealed significant differences due to sentence type, while multiword E ..."
Abstract
-
Cited by 75 (6 self)
- Add to MetaCart
(Show Context)
ERPs were recorded from 24 undergraduates as they read sentences known to differ in syntactic complexity and working memory requirements, namely Object and Subject Relative sentences. Both the single-word and multiword analyses revealed significant differences due to sentence type, while multiword ERPs also showed that sentence type effects differed for Good and Poor comprehenders. At the single-word level, ERPs to both verbs in Object Relative sentences showed a left anterior negativity between 300 and 500 msec postword-onset relative to those to Subject Relative verbs. At the multiword level, a slow frontal positivity characterized Subject Relative sentences, but was absent for Object Relatives. This slow positivity appears to index ease of processing or integration, and was more robust in Good than in Poor comprehenders.
Who said what? An event-related potential investigation of source and item memory
- Journal of Experimental Psychology: Learning, Memory, and Cognition
, 1998
"... Event-related potentials (ERPs) were recorded uring recognition tasks for spoken words alone (items) or for both words and the voice of the speaker (sources). Neither performance nor ERP measures suggested that voice information was retrieved automatically during the item-recognition task. In both t ..."
Abstract
-
Cited by 51 (4 self)
- Add to MetaCart
(Show Context)
Event-related potentials (ERPs) were recorded uring recognition tasks for spoken words alone (items) or for both words and the voice of the speaker (sources). Neither performance nor ERP measures suggested that voice information was retrieved automatically during the item-recognition task. In both tasks, correctly recognized old words elicited more positive ERPs than new words, beginning around 400 ms poststimulus onset. In the source task only, old words also elicited a focal prefrontal positivity beginning about 700 ms. The prefrontal task effect did not distinguish trials with accurate and inaccurate voice judgments and is interpreted as reflecting the search for voice information i memory. More posterior recording sites were sensitive to the successful recovery of voice or source information. The results indicate that word and voice information were retrieved hierarchically and distinguish retrieval attempt from retrieval success. Everyone has had the experience of remembering a fact without being able to recall how it was learned. Remember-ing the source of one's knowledge is not always important, but in some cases, it may be critical for one's subsequent
Serial deployment of attention during visual search
- Journal of Experimental Psychology: Human Perception and Performance
, 2003
"... This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 ..."
Abstract
-
Cited by 47 (7 self)
- Add to MetaCart
(Show Context)
This study examined whether objects are attended in serial or in parallel during a demanding visual search task. A component of the event-related potential waveform, the N2pc wave, was used as a continuous measure of the allocation of attention to possible targets in the search arrays. Experiment 1 demonstrated that the relative allocation of attention shifts rapidly, favoring one item and then another. In Experiment 2, a paradigm was used that made it possible to track the absolute allocation of attention to individual items. This experiment showed that attention was allocated to one object for 100–150 ms before attention began to be allocated to the next object. These findings support models of attention that posit serial processing in demanding visual search tasks. The primate visual system must solve complex computational problems to process scenes that contain more than one object
Independent component analysis for EEG source localization
- IEEE Eng. Med. Biol. Mag
, 2000
"... A pervasive problem in neuroscience is determining which regions of the brain are active, given voltage measurements at the scalp. If accurate solutions to such problems could be obtained, neurologists would gain non-invasive access to patient-specific cortical activity. Access to such data would ul ..."
Abstract
-
Cited by 38 (8 self)
- Add to MetaCart
(Show Context)
A pervasive problem in neuroscience is determining which regions of the brain are active, given voltage measurements at the scalp. If accurate solutions to such problems could be obtained, neurologists would gain non-invasive access to patient-specific cortical activity. Access to such data would ultimately increase the number of patients who could be effectively treated for neural pathologies such as multi-focal epilepsy. However, estimating the location and distribution of electric current source within the brain from electroencephalographic (EEG) recordings is an ill-posed problem. Specifically, there is no unique solution and solutions do not depend continuously on the data. The ill-posedness of the problem makes finding the correct solution a challenging analytic and computational problem. In this paper we consider a spatio-temporal method for sources localization, taking advantage of the entire EEG time series to reduce the configuration space we must evaluate. The EEG data is first decomposed into signal and noise subspaces using a Principal Component Analysis (PCA) decomposition. This partitioning allows us to easily discard the noise subspace, which has two primary benefits: the remaining signal is less noisy, and it has lower dimensionality. After PCA, we apply Independent Component Analysis (ICA) on the signal subspace. The ICA algorithm separates multichannel data into activation maps due to temporally independent stationary sources. For each activation map we perform an EEG source localization procedure, looking only for a single dipole per map. By localizing multiple dipoles independently, we substantially reduce our search complexity and increase the likelihood of efficiently converging on the correct solution.
Masking disrupts reentrant processing in human visual cortex
- Journal of Cognitive Neuroscience
, 2007
"... & In masking, a stimulus is rendered invisible through the presentation of a second stimulus shortly after the first. Over the years, authors have typically explained masking by postu-lating some early disruption process. In these feedforward-type explanations, the mask somehow ‘‘catches up’ ’ w ..."
Abstract
-
Cited by 29 (3 self)
- Add to MetaCart
(Show Context)
& In masking, a stimulus is rendered invisible through the presentation of a second stimulus shortly after the first. Over the years, authors have typically explained masking by postu-lating some early disruption process. In these feedforward-type explanations, the mask somehow ‘‘catches up’ ’ with the target stimulus, disrupting its processing either through lat-eral or interchannel inhibition. However, studies from recent years indicate that visual perception—and most notably vi-sual awareness itself—may depend strongly on cortico-cortical feedback connections from higher to lower visual areas. This has led some researchers to propose that masking derives its effectiveness from selectively interrupting these reentrant pro-cesses. In this experiment, we used electroencephalogram mea-surements to determine what happens in the human visual cortex during detection of a texture-defined square under nonmasked (seen) and masked (unseen) conditions. Electro-encephalogram derivatives that are typically associated with reentrant processing turn out to be absent in the masked condition. Moreover, extrastriate visual areas are still acti-vated early on by both seen and unseen stimuli, as shown by scalp surface Laplacian current source-density maps. This conclusively shows that feedforward processing is preserved, even when subject performance is at chance as determined by objective measures. From these results, we conclude that masking derives its effectiveness, at least partly, from disrupt-ing reentrant processing, thereby interfering with the neural mechanisms of figure–ground segmentation and visual aware-ness itself. &
The Potentials for Basic Sentence Processing: Differentiating Integrative Processes
"... We show that analyzing voltage fluctuations known as "event-related brain potentials," or ERPs, recorded from the human scalp can be an effective way of tracking integrative processes in language on-line. This is essential if we are to choose among alternative psychological accounts of lan ..."
Abstract
-
Cited by 25 (9 self)
- Add to MetaCart
We show that analyzing voltage fluctuations known as "event-related brain potentials," or ERPs, recorded from the human scalp can be an effective way of tracking integrative processes in language on-line. This is essential if we are to choose among alternative psychological accounts of language comprehension. We briefly review the data implicating the N400 as an index of semantic integration and describe its use in psycholinguistic research. We then introduce a cognitive neuroscience approach to normal sentence processing, which capitalizes on the ERP's fine temporal resolution as well as its potential linkage to both psychological constructs and activated brain areas. We conclude by describing several reliable ERP effects with different temporal courses, spatial extents, and hypothesized relations to comprehension skill during the reading of simple transitive sentences; these include (1) occipital potentials related to fairly low-level, early visual processing, (2) very slow frontal positive shifts related to high-level integration during construction of a mental model, and (3) various frontotemporal potentials associated with thematic role assignment, clause endings, and manipulating items that are in working memories.
