Imaging cognition II: An empirical review of 275 PET and fMRI studies

Positron emission tomography (PET) and functional magnetic resonance imagin g (fMRI) have been extensively used to explore the functional neuroanatomy of cognitive functions. Here we review 275 PET and fMRI studies of attentio n (sustained, selective, Stroop, orientation, divided), perception (object, face, space/motion, smell), imagery (object, space/motion), language (writ ten/spoken word recognition, spoken/no spoken response), working memory (ve rbal/numeric, object, spatial, problem solving), semantic memory retrieval (categorization, generation), episodic memory encoding (verbal, object, spa tial), episodic memory retrieval (verbal, nonverbal, success, effort, mode, context), priming (perceptual, conceptual), and procedural memory (conditi oning, motor, and nonmotor skill learning). To identify consistent activati on patterns associated with these cognitive operations, data from 412 contr asts were summarized at the level of cortical Brodmann's areas, insula, tha lamus, medial-temporal lobe (including hippocampus), basal ganglia, and cer ebellum. For perception and imagery, activation patterns included primary a nd secondary regions in the dorsal and ventral pathways. For attention and working memory, activations were usually found in prefrontal and parietal r egions. For language and semantic memory retrieval, typical regions include d left prefrontal and temporal regions. For episodic memory encoding, consi stently activated regions included left prefrontal and medial-temporal regi ons. For episodic memory retrieval, activation patterns included prefrontal , medial-temporal, and posterior midline regions. For priming, deactivation s in prefrontal (conceptual) or extrastriate (perceptual) regions were cons istently seen. For procedural memory, activations were found in motor as we ll as in non-motor brain areas. Analysis of regional activations across cog nitive domains suggested that several brain regions, including the cerebell um, are engaged by a variety of cognitive challenges. These observations ar e discussed in relation to functional specialization as well as functional integration.