Lyn Balsamo

Language dominance in partial epilepsy patients identified with an fMRI reading task

Background fMRI language tasks readily identify frontal language areas; temporal activation has been less consistent. No studies have compared clinical visual judgment to quantitative region of interest (ROI) analysis. Objective To identify temporal language areas in patients with partial epilepsy using a reading paradigm with clinical and ROI interpretation. Methods Thirty patients with temporal lobe epilepsy, aged 8 to 56 years, had 1.5-T fMRI. Patients silently named an object described by a sentence compared to a visual control. Data were analyzed with ROI analysis from t-maps. Regional asymmetry indices (AI) were calculated ([L−R]/[L+R]) and language dominance defined as >0.20. t-Maps were visually rated by three readers at three t thresholds. Twenty-one patients had intracarotid amobarbital test (IAT). Results The fMRI reading task provided evidence of language lateralization in 27 of 30 patients with ROI analysis. Twenty-five were left dominant, two right, one bilateral, and two were nondiagnostic; IAT and fMRI agreed in most patients, three had partial agreement, none overtly disagreed. Interrater agreement ranged between 0.77 to 0.82 (Cramer V;p < 0.0001); agreement between visual and ROI reading with IAT was 0.71 to 0.77 (Cramer V;p < 0.0001). Viewing data at lower thresholds added interpretation to 12 patients on visual analysis and 8 with ROI analysis. Conclusions An fMRI reading paradigm can identify language dominance in frontal and temporal areas. Clinical visual interpretation is comparable to quantitative ROI analysis.

fMRI language task panel improves determination of language dominance.

Background: fMRI language tasks reliably identify language areas in presurgical epilepsy patients, but activation using single paradigms may disagree with the intracarotid amobarbital test (IAT). Objective: To determine whether a panel of fMRI tasks targeting different aspects of language processing increases accuracy in determining hemisphere language dominance. Methods: Twenty-six patients age 12 to 56 years, predominantly with temporal lobe epilepsy, were studied using whole-brain 1.5 T fMRI (echo planar imaging, blood oxygenation level–dependent) with three task categories using a block design: verbal fluency, reading comprehension, and auditory comprehension. fMRI t maps were visually rated at three thresholds. All patients had assessment of language lateralization by IAT. Results: fMRI showed left dominance in 21 patients, right dominance in 2, and bilateral activation in 2; raters disagreed over a left vs right bilateral rating in 1 patient. There was full agreement between IAT and fMRI in 21 of 25 patients (IAT failed in 1). In three instances of partial disparity with IAT, the fMRI panel showed consistent findings across raters. Agreement between raters was excellent (partial disagreement in only one patient); the panel of tasks was superior to any single task for interrater agreement (Cramer V 0.93 [range 0.91 to 1.0] vs 0.72 [range 0.60 to 0.86]). Conclusions: A panel of fMRI language paradigms may be more accurate for evaluating partial epilepsy patients than a single task. A panel of tasks reduces the likelihood of nondiagnostic findings, improves interrater reliability, and helps confirm language laterality.

Developmental aspects of language processing: fMRI of verbal fluency in children and adults†

We examined developmental differences, in location and extent of fMRI language activation maps, between adults and children while performing a semantic fluency task. We studied 29 adults and 16 children with echo planar imaging BOLD fMRI at 1.5 T using covert semantic verbal fluency (generation of words to categories compared to rest) using a block design. Post task testing was administered to assess performance. Individual data were analyzed with an a priori region of interest approach from t maps (t = 4) and asymmetry indices (AI). Group studies were analyzed using SPM 99 (Wellcome, UK; fixed effect, corrected P < 0.0001). We found no significant differences in location or laterality of activation between adults and children for a semantic verbal fluency task. Adults activated more pixels than children in left inferior frontal gyrus and left middle frontal gyrus, but AIs were the similar across ages (r2 < 0.09). Extent or laterality of activation was not affected by performance (r2 < 0.15). The brain areas that process semantic verbal fluency are similar in children and adults. The laterality of activation does not change appreciably with age and appears to be strongly lateralized by age 7 years. Hum. Brain Mapping 18:176–185, 2003.

Auditory comprehension of language in young children Neural networks identified with fMRI

Objective: The organization of neuronal systems that process language in young children is poorly understood. The authors used fMRI to identify brain regions underlying auditory comprehension in healthy young children. Methods: Fifteen right-handed children (mean age 6.8 years) underwent fMRI at 1.5-T using blood oxygen level dependent echoplanar imaging. They listened to stories with a reverse speech control condition. Group data were analyzed with statistical parametric mapping. Individual subject data were analyzed with a region of interest approach based on t-maps. An asymmetry index (AI = [(L−R)/(L+R)]) was calculated for each region. Results: Group analysis showed significant activation in the left middle temporal gyrus (Brodmann area [BA] 21) and left superior temporal gyrus (BA 22) along the superior temporal sulcus extending back to the angular gyrus (BA 39). Individual maps showed lateralized activation in temporal regions (AI > 0.49 ± 0.39). There was minimal activation in the frontal lobe. There were no significant correlations between age and regional AI. Conclusion: Networks for auditory language processing are regionally localized and lateralized by age 5. These data may provide a means to interpret language fMRI studies performed in preparation for brain surgery, and may be employed to investigate the effect of chronic disease states, such as epilepsy, on language organization during critical periods for plasticity.

fMRI identifies regional specialization of neural networks for reading in young children

Background: fMRI allows mapping of neural networks underlying cognitive networks during development, but few studies have systematically examined children 7 and younger, in whom language networks may be more diffusely organized than in adults. Objective: To identify neural networks during early reading consolidation in young children. Methods: The authors studied 16 normal, right-handed, native English-speaking children with a mean age of 7.2 years (range 5.8 to 7.9) with fMRI reading paradigms adjusted for reading level. Data were acquired with the echoplanar imaging BOLD technique at 1.5 T. Group data were analyzed with statistical parametric mapping (SPM-99); individual data sets were analyzed with a region of interest approach from individual study t maps (t = 4). The number of activated pixels in brain regions was determined and an asymmetry index (AI) ([L-R]/[L+R]) calculated for each region. Results: In group analysis the authors found prominent activation in left inferior temporal occipital junction and left fusiform gyrus (Brodmann area [BA] 37), middle temporal gyrus (BA 21, 22), middle frontal gyrus (BA 44, 45), and the supplementary motor area. Activation was strongly lateralized in middle frontal gyrus and Wernicke areas (AI 0.54, 0.62). Fourteen subjects had left-sided language lateralization, one was bilateral, and one had poor activation. Conclusions: The neural networks that process reading are strongly lateralized and regionally specific by age 6 to 7 years. Neural networks in early readers are similar to those in adults.

Cortical localization of reading in normal children An fMRI language study

Background: fMRI provides a noninvasive means of identifying the location and organization of neural networks that underlie cognitive functions. Objective: To identify, using fMRI, brain regions involved in processing written text in children. Methods: The authors studied nine normal right-handed native English-speaking children, aged 10.2 years (range 7.9 to 13.3 years), with two paradigms: reading Aesop’s Fables and “Read Response Naming” (reading a description of an object that was then silently named). Data were acquired using blood oxygen level-dependent fMRI. Group data were analyzed with statistical parametric mapping; individual data sets were analyzed with a region-of-interest approach from individual study t maps. The number of activated pixels was determined in brain regions and an asymmetry index (AI = [L − R]/[L + R]) calculated for each region. Results: The authors found strong activation in the left middle temporal gyrus and left midfrontal gyrus and variable activation in left inferior frontal gyrus for both reading tasks in the group analysis (z > 5.5 to 9.1). All subjects had strong left-sided lateralization for both tasks in middle/superior temporal gyrus, inferior frontal gyrus, and middle frontal gyrus (AI = 0.76 to 1.0 for t = 4). Reading Fables activated twice as many pixels in temporal cortex as the Read Response Naming task; activation in dorsolateral prefrontal cortex was similar for both tasks. Small homologous right middle temporal region activation was seen with reading a fable. Conclusions: The neural networks that process reading appear to be lateralized and localized by middle to late childhood. Reading text paradigms may prove useful for identifying frontal and temporal language-processing areas and for determining language dominance in children experiencing epilepsy or undergoing tumor surgery.

Seizure focus affects regional language networks assessed by fMRI.

Objective: To investigate the degree of language dominance in patients with left and right hemisphere seizure foci compared to normal volunteers using a fMRI reading comprehension task. Methods: Fifty patients with complex partial epilepsy, aged 8 to 56 years and 33 normal volunteers, aged 7 to 34 had fMRI (1.5 T) and neuropsychological testing. Participants silently named an object described by a sentence compared to a visual control. Data were analyzed with region of interest (ROI) analysis based on t maps for inferior frontal gyrus (IFG), midfrontal gyrus (MFG), and Wernicke area (WA). Regional asymmetry indices (AIs) were calculated [(L − R)/(L + R)]; AI >0.20 was deemed left dominant and AI <0.20 as atypical language. Results: Left hemisphere focus patients had a higher likelihood of atypical language than right hemisphere focus patients (21% vs 0%, χ2 < 0.002). Left hemisphere focus patients, excluding those with atypical language, had lower regional AI in IFG, MFG, and WA than controls. Right hemisphere focus patients were all left language dominant and had a lower AI than controls in WA and MFG, but not for IFG. AI in MFG and WA were similar between left hemisphere focus/left language patients and right hemisphere focus patients. Patients activated more voxels than healthy volunteers. Lower AIs were attributable to greater activation in right homologous regions. Less activation in the right-side WA correlated with better verbal memory performance in right focus/left hemisphere-dominant patients, whereas less strongly lateralized activation in IFG correlated better with Verbal IQ in left focus/left hemisphere-dominant patients. Conclusions: Patients had lower asymmetry indices than healthy controls, reflecting increased recruitment of homologous right hemisphere areas for language processing. Greater right hemisphere activation may reflect greater cognitive effort in patient populations, the effect of epilepsy, or its treatment. Regional activation patterns reflect adaptive efforts at recruiting more widespread language processing networks that are differentially affected based on hemisphere of seizure focus.

Neuroimaging Reveals Automatic Speech Coding during Perception of Written Word Meaning

The extent to which visual word perception engages speech codes (i.e., phonological recoding) remains a crucial question in understanding mechanisms of reading. In this study, we used functional magnetic resonance imaging techniques combined with behavioral response measures to examine neural responses to focused versus incidental phonological and semantic processing of written words. Three groups of subjects made simple button-pressing responses in either phonologically (rhyming-judgment) or semantically (category-judgment) focused tasks or both tasks with identical sets of visual stimuli. In the phonological tasks, subjects were given both words and pseudowords separated in different scan runs. The baseline task required feature search of scrambled letter strings created from the stimuli for the experimental conditions. The results showed that cortical regions associated with both semantic and phonological processes were strongly activated when the task required active processing of word meaning. However, when subjects were actively processing the speech sounds of the same set of written words, brain areas typically engaged in semantic processing became silent. In addition, subjects who performed both the rhyming and the semantic tasks showed diverse and significant bilateral activation in the prefrontal, temporal, and other brain regions. Taken together, the pattern of brain activity provides evidence of a neural basis supporting the theory that in normal word reading, phonological recoding is automatic and facilitates semantic processing of written words, while rapid comprehension of word meaning requires devoted attention. These results also raise questions about including multiple cognitive tasks in the same neuroimaging sessions.

Asymmetrical coupling of neural activities in the frontal and temporal regions during phonological and semantic processing of written words

Behavioral studies have shown that speech codes (i.e., phonology) and word meaning are activated automatically during visual word perception. However, the extent to which the perception of word meaning automatically engages phonological recoding remains a crucial question in understanding visual word perception. Behavioral studies (I, 2) have yielded data supporting at least two contrasting hypotheses: 1) Phonological processing is a necessary part of the perception of word meaning (the mediation hypothesis), and 2) Perception of word meaning can bypass phonological processes (the direct perception hypothesis). We used functional magnetic resonance imaging (fMRI) technique to examine the extent to which neural activity reflects a functionally dependent relationship between phonological recoding and active semantic processing with visually presented words. Eighteen right-handed healthy adults were randomly assigned to three groups. One group (Rhyming Only) performed rhymingjudgment tasks. A second group (Categorization Only) performed a category-judgment task. The third group (Mixed) of subjects did both the rhymingand the category-judgment tasks. The Mixed group was included to further examine whether the results of the first two groups could be reliably replicated in a separate group of subjects and whether patterns of neural activity change when semantic and rhyming tasks were carried out in the same experimental session. The same sets of stimuli were used for rhyming and categorization tasks. Each scan run (40 s) included a baseline control alternating with an experimental task in a box-car design. Our results revealed an asymmetrical coupling of neuronal activities in the let? posterior-prefrontal cortex and the mid posterior-temporal regions during phonological and semantic processing of visual words. When subjects were engaged in active semantic processing of visually presented words in a semantic-judgment task, both the mid posterior-temporal regions and the left posterior-prefrontal cortex were strongly activated. However, when subjects’ attention was directed to the speech codes of the same set of words in a rhyming-judgment task, little activation was observed in the temporal regions associated with semantic processing (3, 4). The same pattern of activation was observed with both very conservative and relaxed statistical criteria. Both the activation and behavioral results together suggest that active processing of word meaning engages neural systems associated with both semantic and phonological processes. This observation is concordant with the hypothesis that in normal word reading, the perception of visual word meaning necessarily couples with the activation of speech codes. 1. Van Orden, G. C. (1987). A ROWS is a ROSE: Spelling, sound, and reading. Memory and Cognition, 15(3), 181-198. 2. Brysbeart, M., & Praet, C. (1992). Reading isolated words: No evidence for automatic incorporation of the phonetic code. Psychological Research, 54, 91-102. 3. Geschwind, N. (1970). Science, 170: 940-944. 4. Binder, J. R., Frost, J. A., Hammeke, T. A., Cox, R. W., Rao, S. M., L Prieto, T. (1997). Human brain language areas identified by functional magnetic resonance imaging. The Journal of Neuroscience, 17: 353-362.