Dominant-side intracarotid amobarbital spares comprehension of word meaning

Abolition of speech production after intracarotid amobarbital injection is generally considered evidence for language laterality. However, complex auditory comprehension may be preserved after injection of the dominant (left) side. The possibility that this sparing may be due to the intracarotid amobarbital injection not adequately deactivating some of the areas responsible for speech comprehension in the posterior part of the hemisphere was tested with a task known to be critically dependent on the left posterotemporal-inferoparietal region, one assessing visuo-verbal semantic relatedness. Even when the intracarotid injection of the left side produced marked deficits of speech production, comprehension of semantic relations was still intact in eight of 15 patients. Ten of these 15 patients also received right carotid injections, none of which affected comprehension of semantic relatedness. These data indicate that the intracarotid amobarbital injection cannot always specify the laterality of all language functions, an important concern when considering surgical procedures in the dominant posterotemporal-inferoparietal region.