Frontal lobe activation during word generation studied by functional MRI.
To further delimit the specific verbal operations occurring in the dorsolateral frontal cortex during the generation of words. Different verbal fluency tasks guided by distinct specifications (phonological, semantic, or automatic production of words) were used in a functional magnetic resonance study. The study group comprised 10 right-handed normal subjects ranging in age from 23 to 27 years. Functional magnetic resonance images were obtained in a 1.5-Tesla magnet using a spoiled GRASS sequence. Noticeable activation was found during the word generation tasks in the dorsolateral frontal cortex. The region showing the most prominent activation was the posterior part of the left middle frontal gyrus. Nevertheless, the different tasks each had a different activation effect. The phonologically guided generation of words produced the most consistent activation of the middle frontal gyrus, which mainly involved the premotor cortex. The results suggest that operations concerned with the generation of sound sequences, rather than the amount of produced words or their semantics, are responsible for sustained focal activity observed in the frontal lobes during verbal fluency tasks.