Selection for position: the role of left ventrolateral prefrontal cortex in sequencing language.

Patients with damage involving left ventrolateral prefrontal cortex (left VLPFC) often show syntactic deficits. They also show exaggerated interference effects during a variety of non-syntactic tasks, including picture naming and working memory. Conceivably, both deficits could arise from inadequate biasing of competitive interactions during language production. To test this hypothesis, we manipulated "positional" interference during multi-word naming by priming one of the nouns in the same or different position. Experimental case studies of four left VLPFC patients revealed that two of the patients showed exaggerated positional interference, greater number of errors, including omissions during multi-word production, increased production difficulty when the order of nouns did not match the predominant English pattern, as well as impaired comprehension of non-canonical reversible sentences. These results suggest that these two patients had an impairment in "selection for position". Different from the other two, their lesions included a subregion of frontal cortex (BA 44/6) that has been shown in neuroimaging studies to play a role in sequencing.