Abstract
BackgroundIt is well established that the left inferior frontal gyrus plays a key role in the cerebral cortical network that supports reading and visual word recognition. Less clear is when in time this contribution begins. We used magnetoencephalography (MEG), which has both good spatial and excellent temporal resolution, to address this question.Methodology/Principal FindingsMEG data were recorded during a passive viewing paradigm, chosen to emphasize the stimulus-driven component of the cortical response, in which right-handed participants were presented words, consonant strings, and unfamiliar faces to central vision. Time-frequency analyses showed a left-lateralized inferior frontal gyrus (pars opercularis) response to words between 100–250 ms in the beta frequency band that was significantly stronger than the response to consonant strings or faces. The left inferior frontal gyrus response to words peaked at ∼130 ms. This response was significantly later in time than the left middle occipital gyrus, which peaked at ∼115 ms, but not significantly different from the peak response in the left mid fusiform gyrus, which peaked at ∼140 ms, at a location coincident with the fMRI–defined visual word form area (VWFA). Significant responses were also detected to words in other parts of the reading network, including the anterior middle temporal gyrus, the left posterior middle temporal gyrus, the angular and supramarginal gyri, and the left superior temporal gyrus.Conclusions/SignificanceThese findings suggest very early interactions between the vision and language domains during visual word recognition, with speech motor areas being activated at the same time as the orthographic word-form is being resolved within the fusiform gyrus. This challenges the conventional view of a temporally serial processing sequence for visual word recognition in which letter forms are initially decoded, interact with their phonological and semantic representations, and only then gain access to a speech code.
Highlights
Like most complex behaviours, visual word recognition is thought to result from the dynamic interplay between the elements of a distributed cortical and sub-cortical network
A right mid fusiform response is visible in the later time windows but remains weaker than the response in the left mid fusiform gyrus (FG)
The main focus of the present study was on the response to written words in the left dorsal inferior frontal gyrus (IFG)
Summary
Visual word recognition is thought to result from the dynamic interplay between the elements of a distributed cortical and sub-cortical network. In order to chart the spatiotemporal evolution of cortical events during the first half-second of visual word recognition, Pammer et al [1] recently employed magnetoencephalography (MEG) in combination with beamforming analyses [2,3,4]. Before describing the findings of Pammer et al [1], we will introduce the beamforming techniques that were originally developed to improve the sensitivity of fixed array radars to locate signals of interest [5]. These algorithms have been exploited successfully to reconstruct the neuronal sources generating MEG data [2,3,6,7,8].
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