Dissociable roles of the posterior parietal and the prefrontal cortex in manipulation and monitoring processes

Abstract

Numerous functional neuroimaging studies reported increased activity in the middorsolateral prefrontal cortex (MDLFC) and the posterior parietal cortex (PPC) during the performance of working memory tasks. However, the role of the PPC in working memory is not understood and, although there is strong evidence that the MDLFC is involved in the monitoring of information in working memory, it is also often stated that it is involved in the manipulation of such information. This event-related functional magnetic resonance imaging study compared brain activity during the performance of working memory trials in which either monitoring or manipulation of information was required. The results show that the PPC is centrally involved in manipulation processes, whereas activation of the MDLFC is related to the monitoring of the information that is being manipulated. This study provides dissociation of activation in these two regions and, thus, succeeds in further specifying their relative contribution to working memory.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Behavioral tasks. Schematic diagram of the manipulation (a), monitoring (b), and recognition control (c) trials. To perform the manipulation task, the subjects had memorized, before scanning, a fixed sequence of the four designs used during the experiment. The fixed sequence of the four abstract designs that the subjects had learned before scanning is shown in d. The number under each abstract design represents its position in the learned sequence that was essential for the performance of the different trials during scanning (see SI Fig. 5 and SI Text for details on the prescanning training session). These numbers are indicated here simply for the benefit of the reader and did not appear anywhere during the performance of the tasks. L, left response; R, right response.

Fig. 2.

Mean BOLD signal change within the IPS and the MDLFC in the comparison of the manipulation and monitoring conditions minus the control condition. The mean BOLD signal change in the left IPS was significantly greater in the manipulation condition in comparison with the monitoring condition. In contrast, the mean BOLD signal change within the MDLFC was significantly greater in the monitoring condition in comparison with the manipulation condition. The error bars illustrate the standard errors.

Fig. 3.

Activity in the manipulation minus monitoring and in the monitoring minus manipulation comparisons. Cortical surface renderings in standard stereotaxic space of a subject's brain are shown on the left. (a) Increased activity in the left IPS obtained from the manipulation minus monitoring comparison. The vertical blue line on the left hemisphere cortical surface rendering indicates the anteroposterior level of the coronal section illustrated on the right. (b) Increased activity in the right MDLFC obtained from the monitoring minus manipulation comparison. The vertical green line on the right hemisphere cortical surface rendering indicates the anteroposterior level of the coronal section illustrated on the right side. CS, central sulcus; PoCS, postcentral sulcus; PCS, precentral sulcus; SFS, superior frontal sulcus; IFS, inferior frontal sulcus; MFS, middle frontal sulcus.

Fig. 4.

Trial-averaged time courses of the BOLD signal in the manipulation, monitoring, and control trials in IPS (a) and MDLFC (b). The BOLD signal is time-locked to the beginning of the trials. Pr., presentation phase.