Recurring utterances induced by local anesthetic administration to the left frontal lobe

Abstract

Recurring utterances (RUs) are a distinct language symptom observed in severe aphasia, known to be associated with global or Broca’s aphasia, though their neural basis remains unclear. We present a case of RU induced by selective left frontal suppression using a novel technique named the super-selective Wada test (ssWada), which involves temporary anesthetization of specific brain regions through super-selective catheterization of cerebral arteries. This method allows for precise simulation of localized brain dysfunction. We applied this technique on a 49-year-old right-handed man with drug-resistant epilepsy as a preoperative examination. Propofol administration to the superior branch of the left middle cerebral artery (MCA), supplying the pars triangularis, pars opercularis, middle frontal gyrus, and part of the precentral gyrus, induced Broca’s aphasia with RUs. The RU content was the phrase uttered at anesthesia administration. Notably, the anesthetic did not affect the temporal language area or basal ganglia. The patient showed minimal awareness of his abnormal speech despite preserved receptive language function and memory, aligning with previous observations of anosognosia in patients with RU. Contrastingly, anesthetic infusion into the inferior branch of the left MCA resulted in mixed aphasia, while right MCA infusion induced no language impairments. This case demonstrates that RUs can arise without deficits in the posterior language area or basal ganglia. It illustrates the potential of ssWada in investigating neural substrates of neuropsychological symptoms through temporary, localized brain disruption. This approach offers novel insights into brain-behavior relationships in language processing and cognition.