Highlights d Object addition/manipulation alters the spatial firing of dentate gyrus cells d Diverse object-related responses were observed, including landmark vector cells d Object-related activity was evaluated separately in granule and mossy cells d Object-related responses are not fixed within single cells or a dedicated population

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There has been considerable focus on investigating age-related memory changes in cognitively healthy older adults, in the absence of neurodegenerative disorders. Previous studies have reported age-related domain-specific changes in older adults, showing increased difficulty encoding and processing object information but minimal to no impairment in processing spatial information compared with younger adults. However, few of these studies have examined age-related changes in the encoding of concurrently presented object and spatial stimuli, specifically the integration of both spatial and nonspatial (object) information. To more closely resemble real-life memory encoding and the integration of both spatial and nonspatial information, the current study developed a new experimental paradigm with novel environments that allowed for the placement of different objects in different positions within the environment. The results show that older adults have decreased performance in recognizing changes of the object position within the spatial context but no significant differences in recognizing changes in the identity of the object within the spatial context compared with younger adults. These findings suggest there may be potential age-related differences in the mechanisms underlying the representations of complex environments and furthermore, the integration of spatial and nonspatial information may be differentially processed relative to independent and isolated representations of object and spatial information.

Episodic memory enables novel inferences that bridge across experiences. A goal of memory science is to understand the factors that give rise to individual and group differences in memory-dependent cognition. In two experiments, we examined associative inference performance in young and older adults and how differences in sustained attention relate to differences in memory and inference. We report lower associative memory and inference performance in older compared to young adults; strikingly, age-related reductions in associative inference occur even when controlling for associative memory and in the absence of group-differences in attention. At the same time, we report that individual differences in sustained attention explain between-person variability in memory and inference performance. While age-related reductions in associative memory and inference performance can occur independent of attention, individual differences in the propensity to suffer attention lapses partially explain why some young and older adults remember and bridge across experiences better than others.

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