Abstract
The ventral part of lateral posterior parietal cortex (VPC) and the posterior midline region (PMR), including the posterior cingulate cortex and precuneus, tend to show deactivation during demanding cognitive tasks, and have been associated with the default mode of the brain. Interestingly, PMR and VPC activity has been associated with successful episodic retrieval but also with unsuccessful episodic encoding. However, the differential contributions of PMR and VPC to retrieval vs. encoding has never been demonstrated within-subjects and within the same experiment. Here, we directly tested the prediction that PMR and VPC activity should be associated with retrieval success but with encoding failure. Consistent with this prediction, we found across five different fMRI experiments that, during retrieval, activity in these regions is greater for hits than misses, whereas during encoding, it is greater for subsequent misses than hits. We also found that these regions overlap with the ones that show deactivations during conscious rest. Our findings further aid in clarifying the role of the default mode regions in learning and memory.
Highlights
Human brain imaging studies have revealed a network of brain regions including parietal, posterior midline and frontal regions that consistently show deactivation during active task conditions compared to passive rest conditions in a wide variety of experiments (Mazoyer et al, 2001; McKiernan et al, 2003; Shulman et al, 1997)
FMRI RESULTS Encoding-retrieval flip We predicted that, during encoding, activity in posterior midline region (PMR) and ventral parietal cortex (VPC) would be greater for encoding misses than for hits, whereas during retrieval, activity would be greater for retrieval hits than misses
The goal of the present study was to investigate the differential role of PMR and VPC in successful episodic encoding vs. retrieval
Summary
Human brain imaging studies have revealed a network of brain regions including parietal, posterior midline and frontal regions that consistently show deactivation during active task conditions compared to passive rest conditions in a wide variety of experiments (Mazoyer et al, 2001; McKiernan et al, 2003; Shulman et al, 1997). The interest in the functional significance of the default network has recently been intensified by indications of deviations from normal default activity in various clinical populations, including patients with Alzheimer’s dementia (Greicius et al, 2004; Lustig et al, 2003; Petrella et al, 2007; Rombouts et al, 2005), schizophrenia (Liang et al, 2006; Liu et al, 2006), and autism (Kennedy et al, 2006) Despite all this interest, the specific cognitive processes that are mediated by the “default” network remain unclear. VPC refers to lateral posterior parietal cortex ventral to the intraparietal sulcus, including the supramarginal gyrus (roughly Brodmann Area – BA 40) and the angular gyrus (roughly BA 39)
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