Plasticity of language networks in patients with brain tumors: A positron emission tomography activation study

We investigated plasticity of language networks exposed to slowly evolving brain damage. Single subject O-15-water language activation positron emissi on tomography studies were analyzed in 61 right-handed patients with brain tumors of the left hemisphere, and 12 normal controls. In controls, activat ions were found in left Brodmann's Area (BA)44 and BA45, superior posterior temporal gyrus bilaterally, and right cerebellum. Patients additionally ac tivated left BA46, BA47, anterior insula, and left cerebellum. Superior tem poral activation was less frequent, and activations in areas other than pos terior temporal gyrus were found bilaterally. Frontolateral activations wit hin the nondominant hemisphere were only seen in patients (63%) with fronta l or posterior temporal lesions. Laterality indices of frontolateral cortex showed reversed language dominance in 18% of patients. Laterality indices of the cerebellum were negatively correlated with language performance. Two compensatory mechanisms in patients with slowly evolving brain lesions are described: An intrahemispheric mechanism with recruitment of left frontola teral regions other than classic language areas; and an interhemispheric co mpensatory mechanism with frontolateral activation in the nondominant hemis phere. The latter one was only found in patients with frontal or posterior temporal lesions, thus supporting the hypothesis that right frontolateral a ctivations are a disinhibition phenomenon.