Recent brain imaging studies suggest that semantic processing of words and images may share a common neural network, although modality-specific activation can also be observed. Other studies using event-related potentials (ERPs) report that brain responses to words and images may already differ at ∼150 ms following stimulus presentation. The question thus remains, which differences are due to perceptual categorization processes and which differences are due to the semantic ones? Using ERP recordings and spatio-temporal source localization analysis, we investigated the dynamics of brain activation during a recognition task. The stimuli consisted of a randomized set of verbal (words vs. non-words) and pictorial items (line drawings of objects vs. scrambled drawings). After each stimulus, subjects had to decide whether it corresponds to a recognizable word or objects. ERP map series were first analyzed in terms of segments of quasi-stable map topography using a cluster analysis. This showed that verbal and pictorial stimuli elicited different field patterns in two time segments between ∼190-400 ms. Before and after this period, map patterns were similar between verbal and pictorial conditions indicating that the same brain structures were engaged during the early and late steps of processing. Source localization analysis of map segments corresponding to the P100 and the N150 components first showed activation of posterior bilateral regions and then of left temporo-posterior areas. During the period differentiating conditions, other patterns of activation, involving mainly left anterior and posterior regions for words and bilateral posterior regions for images, were observed. These findings suggest that, while sharing an initial common network, recognition of verbal and pictorial stimuli subsequently engage different brain regions during time periods generally allocated to the semantic processing of stimuli.
|Number of pages||17|
|State||Published - 2002|
Bibliographical noteFunding Information:
* Neuropsychology Unit, Department of Neurology, University Hospital, Geneva. + Functional Brain Mapping Laboratory, Department of Neurology, University Hospital, Geneva. ^ Plurifaculty Program of Cognitive Neuroscience, University of Geneva, Geneva. ~ Department of Neurology, University Hospital, Geneva. Accepted for publication: September 27, 2001. This research was supported by the Swiss National Science Foundation grant No. 31-61680-00 to J.M. Annoni and the "Programme commun de recherche en génie biomédicale 1999-2002" to C.M. Michel. We thank Denis Brunet for providing us with the computer programs used in this study and Simon O’Dochartaigh for his help in the correction of the manuscript. Correspondence and reprint requests should be addressed to Dr. Asaid Khateb, PhD , Department of Neurology, University Hospital, 24 rue Micheli-du-Crest, CH-1211 Geneva 14, Switzerland. Fax: +41 22 3728333 E-mail: Asaid.Khateb@hcuge.ch Copyright 2002 Human Sciences Press, Inc.
- Distributed source
- Event-related potentials
- Human brain mapping
- Map series
- Source localization
- Temporal segmentation
ASJC Scopus subject areas
- Radiological and Ultrasound Technology
- Radiology Nuclear Medicine and imaging
- Clinical Neurology