Frontal lobes and human memory - Insights from functional neuroimaging

The new functional neuroimaging techniques, PET and functional MRI (fMRI), offer sufficient experimental flexibility and spatial resolution to explore the functional neuroanatomical bases of different memory stages and proces ses. They have had a particular impact on our understanding of the role of the frontal cortex in memory processing. We review the insights that have b een gained, and attempt a synthesis of the findings from functional imaging studies of working memory, encoding in episodic memory and retrieval from episodic memory. Though these different aspects of memory have usually been studied in isolation, we suggest that there is sufficient convergence with respect to frontal activations to make such a synthesis worthwhile. We con centrate in particular on three regions of the lateral frontal cortex-ventr o-lateral, dorsolateral and anterior-that are consistently activated in the se studies, and attribute these activations to the updating/maintenance of information, the selection/manipulation/monitoring of that information, and the selection of processes/subgoals, respectively. We also acknowledge a n umber of empirical inconsistencies associated with this synthesis, and sugg est possible reasons for these. More generally, we predict that the resolut ion of questions concerning the functional neuroanatomical subdivisions of the frontal cortex will ultimately depend on a fuller cognitive psychologic al fractionation of memory control processes, an enterprise that will be gu ided and tested by experimentation. We expect that the neuroimaging techniq ues will provide an important part of this enterprise.