Discrepancies in hemispheric dominance of language and memory: A case report using the super-selective Wada test

<p>The Wada test is a standard examination protocol for determining hemispheric dominance of language and memory functions. In the Wada test, a short-acting anesthetic is injected into the internal carotid artery, temporarily suppressing brain function on one side. In this study, we performed more precise estimations of memory lateralization using the super-selective Wada test (ssWada), which relies on region-selective short-acting anesthetic administration via a microcatheter. The patient is a 16-year-old right-handed woman who has experienced focal impaired awareness seizures since the age of 6. Imaging studies and electroencephalography indicated right medial temporal lobe epilepsy with right hippocampal sclerosis. As the functional magnetic resonance imaging suggested an atypical hemispheric dominance of language function, we tried directly evaluating her memory lateralization via deactivation study. During the ssWada test of the middle cerebral artery, administering the anesthetic to the right side caused global aphasia, whereas the left infusion produced no language symptoms. During ssWada testing of the posterior cerebral artery, left anesthetic injection significantly impaired encoding of verbal and nonverbal items, whereas right anesthetic injection minimally decreased encoding for both types of items. Following a right anterior temporal lobectomy, the seizures ceased, with no significant postoperative memory loss or decline in daily living activities. In this case, anesthetic injected into the right side of the middle cerebral artery caused language impairment, whereas anesthetic administration into the left posterior cerebral artery caused more severe impairment in verbal and nonverbal memory compared to the contralateral trial. The super-selective Wada test may reveal atypical lateralization of verbal and nonverbal memory and language distribution.</p>