Brain Activation Associated with Word Fluency Tasks: A Functional Magnetic Resonance Image Study

ABSTRACT

BACKGROUND: Two types of word fluency tasks, namely, word generation by semantic or phonemic cues, are part of the neuropsychological evaluation of neurological patients. Cognitive mechanisms, such as strategies of memory retrieval, may differ for these two tasks. We therefore used functional magnetic resonance image (fMRI) to examine whether brain areas activated by the phonemic word fluency task may differ from those activated by the semantic word fluency task. METHODS: Semantic and phonemic word fluency tasks were administered to 112 normal subjects with two categories for each (animal and fruit names for semantic word fluency, and 'ah' and 'd' sounds for phonemic word fluency). The number and the degree of scattering of generated words were examined for the analysis of cortical activation. With another seven normal subjects, fMRI experiments were conducted while they generated words with the two types of cues (five categories for each). RESULTS: Performance in terms of number of words generated was better with semantic cues than with phonemic cues (14.15 words for semantic cues and 10.36 words for phonemic cues on the average). The same words were more commonly generated across subjects in semantic fluency tasks than in phonemic fluency. In a fMRI experiment, higher signals were observed during phonemic than in semantic word fluency tasks at the bilateral posterior-inferior temporal gyri, left premotor area, right cerebellum, and bilateral superior parietal lobules. The opposite was observed at the bilateral posterior cingulate gyri. CONCLUSIONS: The fluency tasks showed differential performance and several cortical areas showed differential activation, depending on the type of cues given for word generation. This result is consistent with the hypothesis that an automated visual imagery is adopted as word-finding strategy for semantic fluency, whereas controlled articulatory evaluation is used as a strategy for phonemic fluency.