Final Activity and Management Report Summary - PARIETAL MEMORY (Role of the parietal lobe in episodic memory retrieval) The overarching aim of Dr Ciaramelli's project was to understand the role of the posterior parietal cortex in episodic memory retrieval, as stated in her original project. The role of posterior parietal cortex (PPC) in episodic memory retrieval, i.e. conscious memory for personally-experienced events, is a scientific puzzle. On the one hand, PPC is one of the most frequently activated regions in functional neuroimaging (fMRI) studies of episodic retrieval, and activations involve both the ventral PPC and the dorsal PPC, mainly in the left hemisphere. On the other hand, damage to PPC does not yield severe memory deficits, such as the ones that follow medial temporal lobe damage. Thus, whether PPC has a crucial role during memory retrieval, and what this role is, is a matter of fervent debate. Ciaramelli and colleagues have proposed that dorsal and ventral PPC mediate different, complementary attention processes in the service of memory retrieval, analogous to those they play in the perceptual domain, i.e. the Attention-to-Memory (AtoM) hypothesis (Ciaramelli et al., 2008 ; cabeza et al., 2008). According to the AtoM hypothesis, dorsal PPC mediates top-down attention processes guided by retrieval goals, whereas ventral PPC mediates bottom-up attention processes captured by the retrieval output (Ciaramelli et al., 2008). Consistent with the AtoM hypothesis, recent reviews of episodic memory studies have shown that processing in dorsal PPC is prominent when retrieval relies on controlled operations that require top-down attention, i.e. when the recognition decision is difficult, accompanied by low confidence and a vague sense of familiarity, and when source (context) information is probed in addition to item recognition (Ciaramelli et al., 2008). Processing in ventral PPC, on the other hand, is prominent when relevant memory contents are retrieved that capture attention bottom-up, as in the case of strong memories retrieved with high confidence, and accompanied by the subjective feeling of recollection (Ciaramelli et al., 2008). In a recent study (Ciaramelli et al., 2010), we have tested the AtoM hypothesis empirically, looking for dissociations in the role of dorsal and ventral PPC during memory retrieval within the same paradigm. Using a "Posner-like" recognition memory paradigm, we found that dorsal PPC was preferentially engaged when participants searched for/anticipated memory targets upon presentation of relevant memory cues and predicted the ensuing behavioural advantage, consistent with a role in top-down attention. In contrast, ventral PPC predicted efficacy and speed of target detection on non-cued trials, and was largest for memory targets that were invalidly cued, consistent with a role in bottom-up attention (Ciaramelli et al., 2010). Consistently, patients with lesions in the dorsal VPC had problems at anticipating memory targets based on memory cues, whereas patients with ventral parietal lesions had problems at detecting invalidly cued memory targets (Ciaramelli et al., 2010). The AtoM hypothesis is to date one of the main hypotheses regarding the role of the PPC in memory retrieval. This hypothesis has been published in well-recognised international journals, and has received much consensus in the field. The scientific relevance of the topic is reflected in the fact that papers describing the AtoM hypothesis were published in high impact journals, found wide acceptance in the field, and have been cited extensively (Ciaramelli et al., 2008: 66 times since 2008; Cabeza et al., 2008: 113 times). This research substantially advances our understanding of the role of PPC in cognition, showing that this brain region is necessary to mediate attention to internal (memory) contents, in addition to external information, thus revealing a crucial system for directing attention inward, and for interrupting ongoing processing so that memories gain access to awareness.
