Hemispheric specialization of the lateral prefrontal cortex for strategic processing during spatial and shape working memory.

OBJECTIVE: We investigated whether spatial working memory (WM) is associated with functional specialization of the right prefrontal cortex (PFC) relative to WM for shapes. We designed spatial and shape WM tasks that are relatively easy to perform and that minimize both task-switching and manipulation demands. The tasks use identical stimuli and require the same motor response.

METHODS: We presented 12 subjects with target shapes that appeared in particular locations. Subjects maintained either the location or the shape of the targets in WM and responded to each probe by indicating whether it was a target. During a non-WM control task, subjects indicated whether the probe appeared on the right or left side of the screen. Subjects were scanned with a 3.0 T Siemens scanner and data were analyzed using SPM99. The WM tasks were compared to identify PFC activation that was different for spatial versus shape WM. Each WM task was also compared to the control task.

RESULTS: compared with shape WM, spatial WM performance was faster and more accurate and was associated with increased right ventrolateral and frontopolar PFC activation. In contrast, compared to spatial WM, shape WM was associated with increased left ventrolateral PFC activity.

CONCLUSIONS: These findings demonstrate hemispheric specialization for spatial versus shape WM in the ventrolateral PFC. The increased activity in the right PFC for spatial WM cannot be attributed to increased task difficulty, the stimuli used, or the response requirements. Rather, we propose that differences in performance and activation reflect the use of configural processing strategies for spatial WM.