Redefining the functional organization of working memory processes within human lateral prefrontal cortex

Abstract

It is widely held that the frontal cortex plays a critical part in certain aspects of spatial and non-spatial working memory. One unresolved issue is whether there are functionally distinct subdivisions of the lateral frontal cortex that subserve different aspects of working memory. The present study used positron emission tomography (PET) to demonstrate that working memory processes within the human mid-dorsolateral and mid-ventrolateral frontal regions are organized according to the type of processing required rather than according to the nature (i.e. spatial or non-spatial), of the information being processed, as has been widely assumed. Two spatial working memory tasks were used which varied in the extent to which they required different executive processes. During a 'spatial span' task that required the subject to hold a sequence of five previously remembered locations in working memory a significant change in blood-flow was observed in the right mid-ventrolateral frontal cortex, but not in the anatomically and cytoarchitectonically distinct mid-dorsolateral frontal-lobe region. By contrast, during a '2-back' task that required the subject to continually update and manipulate an ongoing sequence of locations within working memory, significant blood flow increases were observed in both mid-ventrolateral and mid-dorsolateral frontal regions. When the two working memory tasks were compared directly, the one that emphasized manipulation of information within working memory yielded significantly greater activity in the right mid-dorsolateral frontal cortex only. This dissociation provides unambiguous evidence that the mid-dorsolateral and mid-ventrolateral frontal cortical areas make distinct functional contributions to spatial working memory and corresponds with a fractionation of working memory processes in psychological terms.

Internally generated and directly cued task sets: an investigation with fMRI

“…Activations along the inferior frontal sulcus, especially the mid-MFG have been shown by a variety of tasks where a high degree of cognitive control was required in order to "monitor", "maintain", and "integrate" information over a period of time (D'Esposito et al, 1999;Fletcher & Henson, 2001;Frith & Dolan, 1996;Owen et al, 1999). With the transition cue, differential sources of contextual information (N-1 task set) and the present cue information have to be integrated.…”

Selection for Cognitive Control: A Functional Magnetic Resonance Imaging Study on the Selection of Task-Relevant Information

“…In line with this assumption, Monchi and colleagues (2001) assumed that the lateral prefrontal cortex is involved when current information has to be related to previous events stored in working memory. In the terminology of research on working memory, this would mean the manipulation of information in working memory (Owen et al, 1999;Fletcher and Henson, 2001). …”

Motor function under lower and higher controlled processing demands in early and continuously treated phenylketonuria.

“…Within the two-level model of executive control, DLPFC is activated when conscious active control of planned behavior and cognition is required (Owen et al, 1999;Petrides, 1994Petrides, , 2000. The two-level model further incorporates a maintenance component, which is involved in holding information in short-term memory and mnemonic operations such as active selection, comparison, and judgment of stimuli held in short-term and long-term memory (Petrides, 2000).…”