An EEG coherence test of the frontal dorsal versus ventral hypothesis in N-back working memory.

We examined Goldman-Rakic's conceptualization of working memory (WM) involving modality-specific reverbatory circuits using electrophysiological measures. An n-back WM task, with either spatial information or object information to be remembered, was administered with EEG coherence used to provide a functional measure of corticocortical communication. Support was not found for modality-specific WM systems in this task. Instead, results suggest that there is a circuit that connects dorsal frontal with dorsal parietal areas which is activated during all levels of the WM vigilance task, regardless of the type of stimuli involved. Data also suggest that left frontal areas are sensitive to the level of difficulty of the WM task (0,1,2, and 3-back), as well as familiarity of task demands. Overall, our results support a model that conceptualizes a unitary WM system rather than a system composed of separate WM circuits for different modalities.