David S. Sabsevitz

Modulation of the semantic system by word imageability

A prevailing neurobiological theory of semantic memory proposes that part of our knowledge about concrete, highly imageable concepts is stored in the form of sensory-motor representations. While this theory predicts differential activation of the semantic system by concrete and abstract words, previous functional imaging studies employing this contrast have provided relatively little supporting evidence. We acquired event-related functional magnetic resonance imaging (fMRI) data while participants performed a semantic similarity judgment task on a large number of concrete and abstract noun triads. Task difficulty was manipulated by varying the degree to which the words in the triad were similar in meaning. Concrete nouns, relative to abstract nouns, produced greater activation in a bilateral network of multimodal and heteromodal association areas, including ventral and medial temporal, posterior-inferior parietal, dorsal prefrontal, and posterior cingulate cortex. In contrast, abstract nouns produced greater activation almost exclusively in the left hemisphere in superior temporal and inferior frontal cortex. Increasing task difficulty modulated activation mainly in attention, working memory, and response monitoring systems, with almost no effect on areas that were modulated by imageability. These data provide critical support for the hypothesis that concrete, imageable concepts activate perceptually based representations not available to abstract concepts. In contrast, processing abstract concepts makes greater demands on left perisylvian phonological and lexical retrieval systems. The findings are compatible with dual coding theory and less consistent with single-code models of conceptual representation. The lack of overlap between imageability and task difficulty effects suggests that once the neural representation of a concept is activated, further maintenance and manipulation of that information in working memory does not further increase neural activation in the conceptual store.

Use of preoperative functional neuroimaging to predict language deficits from epilepsy surgery

Background: Left anterior temporal lobectomy (L-ATL) may be complicated by confrontation naming deficits. Objective: To determine whether preoperative fMRI predicts such deficits in patients with epilepsy undergoing L-ATL. Methods: Twenty-four patients with L-ATL underwent preoperative language mapping with fMRI, preoperative intracarotid amobarbital (Wada) testing for language dominance, and pre- and postoperative neuropsychological testing. fMRI laterality indexes (LIs), reflecting the interhemispheric difference between activated volumes in left and right homologous regions of interest, were calculated for each patient. Relationships between the fMRI LI, Wada language dominance, and naming outcome were examined. Results: Both the fMRI LI (p < 0.001) and the Wada test (p < 0.05) were predictive of naming outcome. fMRI showed 100% sensitivity and 73% specificity in predicting significant naming decline. Both fMRI and the Wada test were more predictive than age at seizure onset or preoperative naming performance. Conclusions: Preoperative fMRI predicted naming decline in patients undergoing left anterior temporal lobectomy surgery.

Use of preoperative functional MRI to predict verbal memory decline after temporal lobe epilepsy surgery.

Purpose: Verbal memory decline is a frequent complication of left anterior temporal lobectomy (L‐ATL). The goal of this study was to determine whether preoperative language mapping using functional magnetic resonance imaging (fMRI) is useful for predicting which patients are likely to experience verbal memory decline after L‐ATL.

A comparison of five fMRI protocols for mapping speech comprehension systems.

Aims:  Many fMRI protocols for localizing speech comprehension have been described, but there has been little quantitative comparison of these methods. We compared five such protocols in terms of areas activated, extent of activation, and lateralization.

Recognition and identification of famous faces in patients with unilateral temporal lobe epilepsy

We examined the performance of 21 patients with unilateral temporal lobe epilepsy (TLE) and hippocampal damage (10 lefts, and 11 rights) and 10 age-matched controls on the recognition and identification (name and occupation) of well-known faces. Famous face stimuli were selected from four time periods; 1970s, 1980s, 1990-1994, and 1995-1996. Differential patterns of performance were observed for the left and right TLE group across distinct face processing components. The left TLE group showed a selective impairment in naming famous faces while they performed similar to the controls in face recognition and semantic identification (i.e. occupation). In contrast, the right TLE group was impaired across all components of face memory; face recognition, semantic identification, and face naming. Face naming impairment in the left TLE group was characterized by a temporal gradient with better naming performance for famous faces from more distant time periods. Findings are discussed in terms of the role of the temporal lobe system for the acquisition, retention, and retrieval of face semantic networks, and the differential effects of lateralized temporal lobe lesions in this process.

Memory outcome after left anterior temporal lobectomy in patients with expected and reversed Wada memory asymmetry scores.

Summary:  Purpose: The ideal candidate for anterior temporal lobectomy surgery shows a Wada memory asymmetry (WMA) score characterized by better memory performance in the hemisphere contralateral to the seizure focus relative to the ipsilateral (surgical) hemisphere. However, some surgical candidates show a reversed WMA or better Wada memory performance in the hemisphere of surgical interest relative to the hemisphere contralateral to the seizure focus. To date, no data are available contrasting memory and seizure outcome for these two Wada groups. The present study compared memory and seizure outcome after left anterior temporal lobectomy (L‐ATL) in patients showing expected and reversed WMA scores, and also examined the relationship of the individual hemisphere Wada memory scores for predicting verbal memory outcome after L‐ATL.

A comparison of two fMRI methods for predicting verbal memory decline after left temporal lobectomy: language lateralization versus hippocampal activation asymmetry.

Purpose:  Language lateralization measured by preoperative functional magnetic resonance imaging (fMRI) was shown recently to be predictive of verbal memory outcome in patients undergoing left anterior temporal lobe (L‐ATL) resection. The aim of this study was to determine whether language lateralization or functional lateralization in the hippocampus is a better predictor of outcome in this setting.

Language lateralization by fMRI and Wada testing in 229 patients with epilepsy: rates and predictors of discordance.

To more definitively characterize Wada/functional magnetic resonance imaging (fMRI) language dominance discordance rates with the largest sample of patients with epilepsy to date, and to examine demographic, clinical, and methodologic predictors of discordance.

Functional Magnetic Resonance Imaging of Language in Epilepsy

Functional magnetic resonance imaging (fMRI) has revolutionized our understanding of functional networks and cerebral organization in both normal and pathological brains. In the present review, we describe the use of fMRI for mapping language in epilepsy patients prior to surgical intervention including a discussion of methodological issues and task design, comparisons between fMRI and the intracarotid sodium amobarbital test, fMRI studies of language reorganization, and the use of fMRI laterality indexes to predict outcome after anterior temporal lobectomy.

Functional MRI and Wada studies in patients with interhemispheric dissociation of language functions

Rare patients with chronic epilepsy show interhemispheric dissociation of language functions on intracarotid amobarbital (Wada) testing. We encountered four patients with interhemispheric dissociation in 490 consecutive Wada language tests. In all cases, performance on overt speech production tasks was supported by the hemisphere contralateral to the seizure focus, whereas performance on comprehension tasks was served by the hemisphere with the seizure focus. These data suggest that speech production capacity is more likely to shift hemispheres than is language comprehension. Wada and fMRI language lateralization scores were discordant in three of the four patients. However, the two methods aligned more closely when Wada measures loading on comprehension were used to calculate lateralization scores. Thus, interhemispheric dissociation of language functions could explain some cases of discordance on Wada/fMRI language comparisons, particularly when the fMRI measure used is not sensitive to speech production processes.