The purpose of this study was to investigate the effect of focal frontal lesions, identified by magnetic resonance imaging (MRI), in a group of traumatic brain injured (TBI) patients, in order to clarify the sensitivity of phonemic and semantic fluency tasks as tests of frontal lobe functioning. Thirteen TBI patients were included and matched with a normal control group of 26 subjects. Frontal lobe patients produced significantly fewer words than the control group in the phonemic fluency condition. Semantic performance correlated with lesion size, but phonemic performance did not, corroborating the idea that the two have different brain-based substrates. Although, as a group effect, frontal lesions impaired fluency, not all patients were impaired, even in the presence of large bilateral frontal lesions.
Jurado et al. (2000) studied this question.