Direct demonstration of transcallosal disinhibition in language networks.

Neuroimaging studies in right-handed patients with left hemisphere brain lesions have demonstrated a shift of language activity from left to right inferior frontal gyrus (IFG). This shift may be caused by greater right hemisphere dominance before the injury or by reduced inhibitory activity of the injured left hemisphere. We simulated a brain lesion applying transcranial -magnetic stimulation over left IFG in normal subjects, while simultaneously measuring language activity with positron -emission tomography. Interference with transcranial -magnetic stimulation decreased activity in left and increased it in right IFG in all subjects. We thus demonstrate for the first time that a rightward shift of language activity is caused by the brain lesion and not by greater right-hemisphere dominance, thus supporting the hypothesis of reduced transcallosal inhibition.

F-18-FDG uptake is a reliable predictory of functional recovery of akinetic but viable infarct regions as defined by magnetic resonance imaging before and after revascularization.

Identification of akinetic but viable myocardium is important for the selection of patients for coronary revascularization. In order to assess predictive values of end-diastolic wall thickness and dobutamine induced wall thickening obtained by magnetic resonance imaging (MRI) and [18F]Fluorodeoxyglucose uptake assessed by positron emission tomography (F-18-FDG-PET), these parameters were compared to recovery of left ventricular function after successful revascularization. Forty patients with chronic myocardial infarction and regional a- or dyskinesia by ventriculography underwent rest- and dobutamine-MRI studies (10 microg dobutamine/kg body weight/min) and F-18-FDG-PET. Viability of the infarct region was considered to be present if; 1) end-diastolic wall thickness was > or =5.5 mm; 2) dobutamine induced wall thickening > or =2 mm could be measured; and 3) normalized F-18-FDG-uptake was > or =50% in > or =50% of akinetic segments. Preserved end-diastolic wall thickness was found in 32/40 patients, functional improvement during dobutamine infusion in 26/40 patients and preserved F-18-FDG-uptake in 29/40 patients. After revascularization regional left ventricular function improved in 25/40 patients. Positive and negative predictive values and diagnostic accuracy were 78%, 100%, and 83% for preserved end-diastolic wall thickness, 92%, 93%, and 93% for dobutamine inducible contraction reserve and 86%, 100%, and 90% for preserved F-18-FDG-uptake. Quantitative assessment of dobutamine induced systolic wall thickening by MRI and F-18-FDG-uptake by PET are highly accurate techniques for the identification of viable myocardium and prediction of functional recovery after successful revascularization. Preserved end-diastolic wall thickness results in an overestimation of viable myocardium compared to functional improvement, but wall thickness <5.5 mm excludes recovery of regional function.