Variability of fMRI activation during a phonological and semantic language task in healthy subjects

Abstract

Assessing inter-individual variability of functional activations is of practical importance in the use of functional magnetic resonance imaging (fMRI) in a clinical context. In this fMRI study we addressed this issue in 30 right-handed, healthy subjects using rhyme detection (phonologic) and semantic categorization tasks. Significant activations, found mainly in the left hemisphere, concerned the inferior frontal gyrus, the superior/middle temporal gyri, the prefrontal cortex, the inferior parietal lobe, the superior parietal lobule/superior occipital gyrus, the pre-central gyrus, and the supplementary motor area. Intensity/spatial analysis comparing activations in both tasks revealed an increased involvement of frontal regions in the semantic task and of temporo-parietal regions in the phonologic task. The frequency of activation analyzed in nine regional subdivisions revealed a high inter-subject variability but showed that the most frequently activated regions were the inferior frontal gyrus and the prefrontal cortex. Laterality indices, strongly lateralizing in both tasks, were slightly higher in the semantic (0.76 +/- 0.19) than the phonologic task (0.66 +/- 0.27). Frontal dominance indices (a measure of frontal vs. posterior left hemisphere dominance) indicated more robust frontal activations in the semantic than the phonologic task. Our study allowed the characterization of the most frequently involved foci in two language tasks and showed that the combination of these tasks constitutes a suitable tool for determining language lateralization and for mapping major language areas.

Atypical functional lateralization of language in autism spectrum disorders

“…Right hemisphere activation was present in all controls during the category fluency task, compared to only 4 controls in the letter fluency task. This is consistent with previous studies that have reported right hemisphere involvement in tasks which require semantic processing (Bookheimer, 2002;Gold and Kertesz, 2000;Kang et al, 1999;Seger et al, 2000;Seghier et al, 2004).…”

A rapid fMRI task battery for mapping of visual, motor, cognitive, and emotional function

“…Large betweensubjects variability previously has been reported for a language task (Seghier, et al 2004) and a working memory task (Wei, et al 2004). The observed variability of activations across groups and cortical areas can be explained by a combination of anatomic variability in gyri formation (Ojemann et al, 1989;Woods et al, 1999) and individual cognitive strategy (Nadeau, Williamson et al 1998).…”

“…Individual subject clusters were determined to belong to an ROI if they fell within 15 mm from the group cluster center. The value of 15 mm was chosen based on the published inter-subject variability for similar tasks (Seghier et al, 2004), and on our own preliminary data where activated regions for a subset of subjects with different genders and ages were identified according to their relative Talairach coordinates and corresponding anatomical landmarks. Brodmann areas (BA) for these ROIs were determined on the basis of the closest BA reported by the Talairach Daemon (Lancaster, et al 2000), which accepts single point coordinates and reports BA labels and anatomical structures within a predefined spatial-query range.…”

Spatio‐temporal distribution of brain activity associated with audio‐visually congruent and incongruent speech and the McGurk Effect

“…The left superior parietal cortex (BA7) has been implicated in a phonologic and semantic language task (Seghier et al. 2004), visual attention to phonemes (McDermott et al. 2003) as well as observing gestures and pantomime (Ohgami et al.…”

“…2004), visual attention to phonemes (McDermott et al. 2003), observing gestures and pantomime (Ohgami et al.…”