Brain disorders produce distinct behavioral patterns, depending on the side and locus of injury. Two models account for these changes in emotionality: one posits that the right brain is dominant for all emotions while an alternate view argues that positive and negative emotions are generated by the left and right brain, respectively. In a series of studies, hemispheric inactivation by intracarotid amytal (Wada) produced dysphoria and anxiety reactions to the induced dysphasia, this did not represent a mood state. The euphoria seen with a right intracarotid injection was intense and not situational or related to the performance of the patient. Overall, patients with right temporal epileptogenic lesions were more likely than left temporal patients to display an emotional reaction. These data suggest that the right hemisphere is dominant for the perception and expression of emotions, primarily of a biological or primary character. In contrast, the emotions generated by the left brain are driven by cognition and social overtones such as that seen with depression, anxiety and catastrophic reactions by patients who manifest dysplasia after left brain stroke. This interpretation is supported by the anatomic view that there is greater limbic-cortical connectivity ont he right and more cortical-cortical exchange in the left hemisphere which accounts for the different organic psychosyndromes that follow unilateral brain damage. One salient cognitive finding with the Wada established that phonological processing is an excellent indicator of dominant language hemisphere activity. We showed a marked inability of patients to read pseudowords with the left and not the right injection. Related pilot studies of phonological processing with functional MRI revealed selective activation of the left frontal region in producing rhymes, and temporoparietal activation with semantic categorization tasks. Intraoperative stimulation in two patients produced similar functional maps and also showed that working memory for verbal material was distributed along the same anterior-posterior axis.
