Dynamic changes in parietal activation during encoding: implications for human learning and memory.

The ventral posterior parietal cortex (vPPC) monitors successful memory retrieval, yet its role during learning remains unclear. Indeed, increased vPPC activation during stimulus encoding is often negatively correlated with subsequent memory performance, suggesting that this region is suppressed during learning. Alternatively, the vPPC may engage in learning-related processes immediately after stimulus encoding thus facilitating retrieval at a later time. To investigate this possibility, we assessed vPPC activity during item presentation and immediately following its offset when a cue to remember was presented. We observed a dynamic change in vPPC response such that activity was negatively correlated with subsequent memory during stimulus presentation but positively correlated immediately following the stimulus during the cue phase. Furthermore, regional differences in this effect suggest a degree of functional heterogeneity within the vPPC. These findings demonstrate that the vPPC is engaged during learning and acts to facilitate post-encoding memory processes that establish long-term cortical representations.

The generation effect: activating broad neural circuits during memory encoding.

The generation effect is a robust memory phenomenon in which actively producing material during encoding acts to improve later memory performance. In a functional magnetic resonance imaging (fMRI) analysis, we explored the neural basis of this effect. During encoding, participants generated synonyms from word-fragment cues (e.g., GARBAGE-W_ST_) or read other synonym pairs (e.g., GARBAGE-WASTE). Compared to simply reading target words, generating target words significantly improved later recognition memory performance. During encoding, this benefit was associated with a broad neural network that involved both prefrontal (inferior frontal gyrus, middle frontal gyrus) and posterior cortex (inferior temporal gyrus, lateral occipital cortex, parahippocampal gyrus, ventral posterior parietal cortex). These findings define the prefrontal-posterior cortical dynamics associated with the mnemonic benefits underlying the generation effect.

Generation and context memory.

Generation enhances memory for occurrence but may not enhance other aspects of memory. The present study further delineates the negative generation effect in context memory reported in N. W. Mulligan (2004). First, the negative generation effect occurred for perceptual attributes of the target item (its color and font) but not for extratarget aspects of context (location and background color). Second, nonvisual generation tasks with either semantic or nonsemantic generation rules (antonym and rhyme generation, respectively) produced the same pattern of results. In contrast, a visual (or data-driven) generation task (letter transposition) did not disrupt context memory for color. Third, generating nonwords produced no effect on item memory but persisted in producing a negative effect on context memory for target attributes, implying that (a) the negative generation effect in context memory is not mediated by semantic encoding, and (b) the negative effect on context memory can be dissociated from the positive effect on item memory. The results are interpreted in terms of the processing account of generation. The original, perceptual-conceptual version of this account is too narrow, but a modified processing account, based on a more generic visual versus nonvisual processing distinction, accommodates the results.