In studies of human episodic memory, the phenomenon of reactivation has traditionally been observed in regions of occipitotemporal cortex (OTC) involved in visual perception. However, reactivation also occurs in lateral parietal cortex (LPC), and recent evidence suggests that stimulus-specific reactivation may be stronger in LPC than in OTC. These observations raise important questions about the nature of memory representations in LPC and their relationship to representations in OTC. Here, we report two fMRI experiments that quantified stimulus feature information (color and object category) within LPC and OTC, separately during perception and memory retrieval, in male and female human subjects. Across both experiments, we observed a clear dissociation between OTC and LPC: while feature information in OTC was relatively stronger during perception than memory, feature information in LPC was relatively stronger during memory than perception. Thus, while OTC and LPC represented common stimulus features in our experiments, they preferentially represented this information during different stages. In LPC, this bias toward mnemonic information co-occurred with stimulus-level reinstatement during memory retrieval. In Experiment 2, we considered whether mnemonic feature information in LPC was flexibly and dynamically shaped by top-down retrieval goals. Indeed, we found that dorsal LPC preferentially represented retrieved feature information that addressed the current goal. In contrast, ventral LPC represented retrieved features independent of the current goal. Collectively, these findings provide insight into the nature and significance of mnemonic representations in LPC and constitute an important bridge between putative mnemonic and control functions of parietal cortex. When humans remember an event from the past, patterns of sensory activity that were present during the initial event are thought to be reactivated. Here, we investigated the role of lateral parietal cortex (LPC), a high-level region of association cortex, in representing prior visual experiences. We find that LPC contained stronger information about stimulus features during memory retrieval than during perception. We also found that current task goals influenced the strength of stimulus feature information in LPC during memory. These findings suggest that, in addition to early sensory areas, high-level areas of cortex, such as LPC, represent visual information during memory retrieval, and that these areas may play a special role in flexibly aligning memories with current goals.

Memory retrieval can strengthen, but also distort memories. Parietal cortex is a candidate region involved in retrieval-induced memory changes as it reflects retrieval success and represents retrieved content. Here, we conducted an fMRI experiment to test whether different forms of parietal reactivation predict distinct consequences of retrieval. Subjects studied associations between words and pictures of faces, scenes, or objects, and then repeatedly retrieved half of the pictures, reporting the vividness of the retrieved pictures ("retrieval practice"). On the following day, subjects completed a recognition memory test for individual pictures. Critically, the test included lures highly similar to studied pictures. Behaviorally, retrieval practice increased both hit and false alarm (FA) rates to similar lures, confirming a causal influence of retrieval on subsequent memory. Using pattern similarity analyses, we measured two different levels of reactivation during retrieval practice: generic "category-level" reactivation and idiosyncratic "item-level" reactivation. Vivid remembering during retrieval practice was associated with stronger category- and item-level reactivation in parietal cortex. However, these measures differentially predicted subsequent recognition memory performance: whereas higher category-level reactivation tended to predict FAs to lures, item-level reactivation predicted correct rejections. These findings indicate that parietal reactivation can be decomposed to tease apart distinct consequences of memory retrieval.

Memory retrieval can strengthen, but also distort memories. Parietal cortex is a candidate region involved in retrieval-induced memory changes as it reflects retrieval success and represents retrieved content. Here, we conducted an fMRI experiment to test whether different forms of parietal reactivation predict distinct consequences of retrieval. Subjects studied associations between words and pictures of faces, scenes, or objects, and then repeatedly retrieved half of the pictures, reporting the vividness of the retrieved pictures ('retrieval practice'). On the following day, subjects completed a recognition memory test for individual pictures. Critically, the test included lures highly similar to studied pictures. Behaviorally, retrieval practice increased both hit and false alarm rates to similar lures, confirming a causal influence of retrieval on subsequent memory. Using pattern similarity analyses, we measured two different levels of reactivation during retrieval practice: generic 'category-level' reactivation and idiosyncratic 'item-level' reactivation. Vivid remembering during retrieval practice was associated with stronger category-and itemlevel reactivation in parietal cortex. However, these measures differentially predicted subsequent recognition memory performance: whereas higher category-level reactivation tended to predict false alarms to lures, item-level reactivation predicted correct rejections. These findings indicate that parietal reactivation can be decomposed to tease apart distinct consequences of memory retrieval.

No abstract

Emotional experiences are known to be both perceived and remembered differently from nonemotional experiences, often leading to heightened encoding of salient visual details and subjectively vivid recollection. The vast majority of previous studies have used static images to investigate how emotional event content modulates cognition, yet natural events unfold over time. Therefore, little is known about how emotion dynamically modulates continuous experience. Here we report a norming study wherein we developed a new stimulus set of 126 emotionally negative, positive, and neutral videos depicting real-life news events. Participants continuously rated the valence of each video during its presentation and judged the overall emotional intensity and valence at the end of each video. In a subsequent memory test, participants reported how vividly they could recall the video details and estimated each video's duration. We report data on the affective qualities and subjective memorability of each video. The results replicate the well-established effect that emotional experiences are remembered more vividly than nonemotional experiences. Importantly, this novel stimulus set will facilitate research into the temporal dynamics of emotional processing and memory.

In studies of human episodic memory, the phenomenon of reactivation has traditionally been observed in regions of occipitotemporal cortex (OTC) involved in sensory experience. However, reactivation also occurs in lateral parietal cortex (LPC), and recent evidence indicates that reactivation of stimulus-specific information may be stronger in LPC than in OTC. These observations raise a number of questions about the nature of memory representations in LPC and their relation to representations in OTC. Here, we report two fMRI experiments that quantify stimulus feature information (color and object category) within LPC and OTC, separately during perception and memory retrieval, in male and female human subjects. Across both experiments, we show a clear dissociation between OTC and LPC: while feature information in OTC is relatively stronger during perception than memory, feature information in LPC is relatively stronger during memory than perception. Thus, while OTC and LPC represent common stimulus features, they preferentially represent this information during different stages. We show that this transformation of feature information across regions co-occurs with stimulus-level reinstatement within LPC and high-level OTC. In Experiment 2, we consider whether feature information in LPC during memory retrieval is flexibly and dynamically shaped by top-down goals. Indeed, we find that dorsal LPC preferentially represents retrieved feature information that addresses current goals. In contrast, ventral LPC represents retrieved features independent of current goals.Collectively, these findings provide insight into the nature and significance of mnemonic representations in LPC and constitute an important bridge between putative mnemonic and control functions of parietal cortex.Traditional models of episodic memory posit that sensory activity evoked during perception is reactivated during recollection (Kosslyn, 1980;Damasio, 1989). There is considerable evidence for such reactivation in visual regions of occipitotemporal cortex (OTC) (Wheeler et al., 2000;Polyn et al., 2005). However, recent human neuroimaging work indicates that stimulus information is also reactivated in lateral parietal cortex (LPC) (Kuhl and Chun, 2014;Chen et al., 2016;Lee and Kuhl, 2016;Xiao et al., 2017). While these findings accord with evidence for univariate increases in LPC BOLD activity during successful remembering (Wagner et al., 2005;Kuhl and Chun, 2014), they also raise important questions about whether and how representations of retrieved memories differ between LPC and OTC.Univariate fMRI studies have consistently found that, in contrast to sensory regions, ventral LPC exhibits low activation when perceptual events are experienced but high activation when these events are successfully retrieved (Daselaar, 2009;Kim et al., 2010). The idea that LPC is relatively more involved in memory retrieval than perception has also received support from recent pattern-based fMRI studies. Long, Lee, and Kuhl (2016) found that reactivation of previously l...

Emotional experiences are known to be both perceived and remembered differently from non-emotional experiences, often leading to heightened encoding of salient visual details and subjectively vivid recollection. The vast majority of previous studies have used static images to investigate how emotional event content modulates cognition, yet natural events unfold over time. Therefore, little is known about how emotion dynamically modulates continuous experience. Here, we report a norming study wherein we develop a new stimulus set of 126 emotionally negative, positive, and neutral videos depicting real-life news events. Participants continuously rated the valence of each video during its presentation and judged the overall emotional intensity and valence at the end of each video. In a subsequent memory test, participants reported how vividly they could recall the video details and estimated each video’s duration. We report data on the affective qualities and subjective memorability of each video. The results replicate the well established effect that emotional experiences are more vividly remembered than non-emotional experiences. Importantly, this novel stimulus set will facilitate research into the temporal dynamics of emotional processing and memory.