Electrostimulation mapping of spatial neglect.

BACKGROUND: Cortical and subcortical electrostimulation mapping during awake brain surgery for tumor removal is usually used to minimize deficits. OBJECTIVE: To use electrostimulation to study neuronal substrates involved in spatial awareness in humans. METHODS: Spatial neglect was studied using a line bisection task in combination with electrostimulation mapping of the right hemisphere in 50 cases. Stimulation sites were identified with Talairach coordinates. The behavioral effects induced by stimulation, especially eye movements and deviations from the median, were quantified and compared with preoperative data and a control group. RESULTS: Composite and highly individualized spatial neglect maps were generated. Both rightward and leftward deviations were induced, sometimes in the same patient but for different stimulation sites. Group analysis showed that specific and reproducible line deviations were induced by stimulation of discrete cortical areas located in the posterior part of the right superior and middle temporal gyri, inferior parietal lobe, and inferior postcentral and inferior frontal gyri (P < .05). Fiber tracking identified stimulated subcortical areas important to spare as sections of fronto-occipital and superior longitudinal II fascicles. According to preoperative and postoperative neglect battery tests, the specificity and sensitivity of intraoperative line bisection tests were 94% and 83%, respectively. CONCLUSION: In humans, discrete cortical areas that are variable in location between individuals but mainly located within the right posterior Sylvian fissure sustain visuospatial attention specifically toward the contralateral or ipsilateral space direction. Line bisection mapping was found to be a reliable method for minimizing spatial neglect caused by brain tumor surgery.

Anatomical correlates for category-specific naming of living and non-living things.

INTRODUCTION: Selective naming categories impairments for living and non-living things are widely reported in brain damaged patients. Electrostimulation mapping was used to study the possible anatomical segregation of living/non-living categories in a prospective series of patients operated on for tumor removal. MATERIALS AND METHODS: Fifty brain mappings (patients with no language impairment; range: 14-80 years; mean: 48 years; 26 males; 5 left handed) were performed in 46 left and 4 right hemispheres using two linguistically controlled tasks (naming for living and non-living things) during an awake surgery procedure. Fifteen regions and four macro cortical areas were designed to analyze the distribution of the interference sites. RESULTS: Over 761 sites stimulated in the lateral hemispheres, 130 naming interferences sites were detected in small cortical areas (<1cm(2)). High individual variability was observed for living/non-living word retrieval localization and organization with a majority (62%) of shared living/non-living interferences. Specific living (12%) or non-living (26%) interferences were found too. In group analysis, no statistical significant anatomical localization was observed for living items in left lateral hemispheric cortex. A statistical significant representation of interference sites for non-living objects was found (Generalized Estimating Equation methodology, z-test=2.28, p=0.027) in the left posterolateral temporoparietal cortex. No influence of histopathology, gender and age on anatomical localization of naming categories was detected. CONCLUSION: The existence of dedicated neural structures for naming non-living things in the left posterolateral temporoparietal cortex is supported by this study although high individual differences exist in the organization of word categories retrieval.

Cortical calculation localization using electrostimulation.

OBJECT: A naming task has been used to spare cortical areas involved in language. In the present study, a calculation task was combined with electrostimulation mapping (awake surgery) to spare cortical areas involved in calculation in patients undergoing surgery for brain lesions. The organization of language and calculation areas was analyzed in relation to these surgical data. METHODS: Twenty patients with brain lesions close to areas possibly involved in calculation (dominant parietal lobe and F2) were prospectively studied over a 4-year period. Four patients had preoperative symptoms of acalculia and therefore were not included in the brain mapping procedure. RESULTS: In 16 patients, direct electrostimulation caused calculation interferences in localized small cortical areas (< 2 cm(2)). Of the 53 calculation interferences found, 23 were independent of language areas, especially those in the inferior left parietal lobule. Various patterns of interference were observed (11 complete acalculia, 5 acalculia with wrong answers, 2 hesitations, and 5 mixed responses), although error patterns were fairly similar across angular, parietal, and frontal stimulation sites. Calculation areas in 4 patients could not be spared for oncological reasons; postoperatively, 3 of these patients showed significant acalculia symptoms. In contrast, none of the patients whose calculation areas were spared had arithmetic difficulties 1 month after surgery. Improvements in acalculia symptoms after surgery were also found in 3 of the 4 patients with preoperative calculation difficulties. CONCLUSIONS: To limit the risk of personal and professional disturbances caused by acquired anarithmetia in patients undergoing surgery for brain tumors or epilepsy, the authors think it is necessary to use a calculation task during brain mapping, especially when operating in the dominant parietal lobe.