High-resolution spatio-temporal neuronal activation in the visual oddball task: a simultaneous EEG/fMRI study
ABSTRACT The combined use of EEG and fMRI allows for the fusion of electrophysiological and hemodynamic information in the study of human cognitive functions. In order to investigate cerebral activity during a visual oddball task, simultaneous EEG/fMRI recording from 10 healthy subjects was performed. A devoted data-analysis method based on trial-by-trial coupling of concurrent EEG and fMRI for the high-resolution spatio-temporal analysis of P300 neuronal activation was developed. Our results obtained from fMRI data showed the involvement of inferior and medial frontal gyrus, cingulated motor area, middle temporal gyrus, and inferior parietal lobule in the oddball task; furthermore, activations were generally right lateralized, in accordance with previous findings. Using the high temporal resolution of EEG, we could separate neuronal activations specifically related to P300 activity, and therefore study the activation timing. We found that the detection of rare targets, that is able to elicit the P300 component, stimulates a limbic-parietofrontal circuit, with latencies ranging between 300 and 400 ms. Our findings suggest that the proposed approach might be extended to other event-related experimental paradigms, and might represent an valuable tool for a clearer understanding of the cerebral mechanisms underlying a wide range of cognitive functions.
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ABSTRACT: In this study, a linear decomposition technique, independent component analysis (ICA), is applied to single-trial multichannel EEG data from event-related potential (ERP) experiments. Spatial filters derived by ICA blindly separate the input data into a sum of temporally independent and spatially fixed components arising from distinct or overlapping brain or extra-brain sources. Both the data and their decomposition are displayed using a new visualization tool, the “ERP image,” that can clearly characterize single-trial variations in the amplitudes and latencies of evoked responses, particularly when sorted by a relevant behavioral or physiological variable. These tools were used to analyze data from a visual selective attention experiment on 28 control subjects plus 22 neurological patients whose EEG records were heavily contaminated with blink and other eye-movement artifacts. Results show that ICA can separate artifactual, stimulus-locked, response-locked, and non-event-related background EEG activities into separate components, a taxonomy not obtained from conventional signal averaging approaches. This method allows: (1) removal of pervasive artifacts of all types from single-trial EEG records, (2) identification and segregation of stimulus- and response-locked EEG components, (3) examination of differences in single-trial responses, and (4) separation of temporally distinct but spatially overlapping EEG oscillatory activities with distinct relationships to task events. The proposed methods also allow the interaction between ERPs and the ongoing EEG to be investigated directly. We studied the between-subject component stability of ICA decomposition of single-trial EEG epochs by clustering components with similar scalp maps and activation power spectra. Components accounting for blinks, eye movements, temporal muscle activity, event-related potentials, and event-modulated alpha activities were largely replicated across subjects. Applying ICA and ERP image visualization to the analysis of sets of single trials from event-related EEG (or MEG) experiments can increase the information available from ERP (or ERF) data. Hum. Brain Mapping 14:166–185, 2001. © 2001 Wiley-Liss, Inc.Human Brain Mapping 10/2001; 14(3):166 - 185. · 6.88 Impact Factor
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ABSTRACT: Event-related potentials were recorded from 537 sites in the superior temporal plane and parietal lobe of 41 patients. Depth electrodes were implanted to localize seizure origin prior to surgical treatment. Subjects received an auditory discrimination task with target and non-target rare stimuli ("standard oddball paradigm"). In some cases, the target, distracting and frequent tones were completely balanced across blocks for pitch and volume. Variants included an analogous visual discrimination task, or auditory tasks where the rare target event was the omission of a tone, or the repetition of a tone within a series of alternating tones. In some subjects, the same auditory stimuli were delivered but the patient ignored them while reading. Three general response patterns could be distinguished on the basis of their wave forms, latencies and task correlates. First, potentials apparently related to rarity per se, as opposed to differences in sensory characteristics, or in habituation, were observed in the posterior superior temporal plane, beginning with a large positivity superimposed on early components. This positivity peaked at 150 msec after stimulus onset and inverted in sites superior to the Sylvian fissure. Subsequent components could be large, focal and/or inverting in polarity, and usually included a positivity at 230 msec and a negativity at 330 msec. All components in this area were specific to the auditory modality. Second, in the posterior cingulate and supramarginal gyri, a sharp triphasic negative-positive-negative wave form with peaks at about 210-300-400 msec was observed. This wave form was of relatively small amplitude and diffuse, and seldom inverted in polarity. It was multimodal but most prominent to auditory stimuli, appeared to remain when the stimuli were ignored, and was not apparent to repeated words and faces. Third, a broad, often monophasic, wave form peaking at about 380 msec was observed in the superior parietal lobe, similar to that which has been recorded in the hippocampus. This wave form could be of large amplitude, often highly focal, and could invert over short distances. It was equal to visual and auditory stimuli and was also evoked by repeating words and faces. The early endogenous activity in auditory cortex may embody activity that is antecedent to the other patterns in multimodal association cortex. The "triphasic" pattern may embody a diffuse non-specific orienting response that is also reflected in the scalp P3a. The later broad pattern may embody the cognitive closure that is also reflected in the scalp P3b or late positive component.Electroencephalography and Clinical Neurophysiology 04/1995; 94(3):191-220.
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ABSTRACT: The brain acts as an integrated information processing system, which methods in cognitive neuroscience have so far depicted in a fragmented fashion. Here, we propose a simple and robust way to integrate functional MRI (fMRI) with single trial event-related potentials (ERP) to provide a more complete spatiotemporal characterization of evoked responses in the human brain. The idea behind the approach is to find brain regions whose fMRI responses can be predicted by paradigm-induced amplitude modulations of simultaneously acquired single trial ERPs. The method was used to study a variant of a two-stimulus auditory target detection (odd-ball) paradigm that manipulated predictability through alternations of stimulus sequences with random or regular target-to-target intervals. In addition to electrophysiologic and hemodynamic evoked responses to auditory targets per se, single-trial modulations were expressed during the latencies of the P2 (170-ms), N2 (200-ms), and P3 (320-ms) components and predicted spatially separated fMRI activation patterns. These spatiotemporal matches, i.e., the prediction of hemodynamic activation by time-variant information from single trial ERPs, permit inferences about regional responses using fMRI with the temporal resolution provided by electrophysiology.Proceedings of the National Academy of Sciences 01/2006; 102(49):17798-803. · 9.74 Impact Factor