The neural substrate of orientation working memory

We have used positron emission tomography (PET) to identify, the neural sub strate of two major cognitive components of working memory (WM), maintenanc e and manipulation of a single elementary visual attribute, i.e., the orien tation of a grating presented in central vision. This approach allowed us t o equate difficulty across tasks and prevented subjects from using verbal s trategies or vestibular cues, Maintenance of orientations involved a distri buted fronto-parietal network, that is, left and right lateral superior fro ntal sulcus (SFSl), bilateral ventrolateral prefrontal cortex (VLPFC), bila teral precuneus, and right superior parietal lobe (SPL). A more medial supe rior frontal sulcus region (SFSm) was identified as being instrumental in t he manipulative operation of updating orientations retained in the WM. Func tional connectivity analysis revealed that orientation WM relies on a coord inated interaction between frontal and parietal regions. In general, the cu rrent findings confirm the distinction between maintenance and manipulative processes, highlight the functional heterogeneity in the prefrontal cortex (PFC), and suggest a more dynamic view of WM as a process requiring the co ordinated interaction of anatomically distinct brain areas.