To investigate the neural basis of age-related source memory (SM) deficits, young and older adults were scanned with fMRI while encoding faces, scenes, and face-scene pairs. Successful encoding activity was identified by comparing encoding activity for subsequently remembered versus forgotten items or pairs. Age deficits in successful encoding activity in hippocampal and prefrontal regions were more pronounced for SM (pairs) compared to item memory (faces and scenes). Age-related reductions were also found in regions specialized in processing faces (fusiform face area) and scenes (parahippocampal place area), but these reductions were similar for item and SM. Functional connectivity between the hippocampus and the rest of the brain was also affected by aging; whereas connections with posterior cortices were weaker in older adults, connections with anterior cortices including prefrontal regions were stronger in older adults. Taken together, the results provide a link between SM deficits in older adults and reduced recruitment of hippocampal and prefrontal regions during encoding. The functional connectivity findings are consistent with a posterior-anterior shift with aging (PASA), previously reported in several cognitive domains and linked to functional compensation. KeywordsfMRI; episodic memory; hippocampus; prefrontal cortex; fusiform face area; parahippocampal place area One of the most consistent findings in the cognitive aging literature is that memory deficits in healthy older adults are larger for source memory than for item memory (for a review, see Spencer & Raz, 1995). Item memory (IM) refers to remembering what happened in the past whereas source memory (SM) refers to remembering where, when, and how it happened. More broadly, SM is involved whenever a task requires memory for individual features or details associated with the encoding event -such as distinguishing between internally or externally generated events (i.e., reality monitoring, Johnson & Raye, 1981) or in which voice a sentence was heard (for a review see Johnson, Hashtroudi, & Lindsay, 1993 NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript context. One common, real-world example of SM involves the everyday need to remember when and where you meet people. In any given day you may experience many different events such as being at work or the grocery store or a cocktail party, during which time you may meet several new people in each context. Without the ability to form a link between the people and the location in which you meet them (i.e., bind item and source information) it would be impossible to later recall where you know someone from.Greater age-related impairments for SM than for IM have been demonstrated for a variety of stimuli and experimental paradigms (e.g., Chalfonte & Johnson, 1996;Kausler & Puckett, 1981a, , 1981b e.g., Naveh-Benjamin & Craik, 1995;Park & Puglisi, 1985;Park, Puglisi, & Lutz, 1982;Spaniol, Madden, & Voss, 2006). These findings are consistent with evidence that older adults ar...

Previous research has investigated intentional retrieval of contextual information and contextual influences on object identification and word recognition, yet few studies have investigated context effects in episodic memory for objects. To address this issue, unique objects embedded in a visually rich scene or on a white background were presented to participants. At test, objects were presented either in the original scene or on a white background. A series of behavioral studies with young adults demonstrated a context shift decrement (CSD)-decreased recognition performance when context is changed between encoding and retrieval. The CSD was not attenuated by encoding or retrieval manipulations, suggesting that binding of object and context may be automatic. A final experiment explored the neural correlates of the CSD, using functional Magnetic Resonance Imaging.Parahippocampal cortex (PHC) activation (right greater than left) during incidental encoding was associated with subsequent memory of objects in the context shift condition. Greater activity in right PHC was also observed during successful recognition of objects previously presented in a scene. Finally, a subset of regions activated during scene encoding, such as bilateral PHC, was reactivated when the object was presented on a white background at retrieval. Although participants were not required to intentionally retrieve contextual information, the results suggest that PHC may reinstate visual context to mediate successful episodic memory retrieval. The CSD is attributed to automatic and obligatory binding of object and context. The results suggest that PHC is important not only for processing of scene information, but also plays a role in successful episodic memory encoding and retrieval. These findings are consistent with the view that spatial information is stored in the hippocampal complex, one of the central tenets of Multiple Trace Theory.Keywords episodic memory; parahippocampal gyrus; hippocampus; context; multiple trace theory The term context is often used to refer to information that is present in the environment but is irrelevant or at least incidental to the cognitive task being performed. The influence of context on memory has been investigated almost exclusively in studies using verbal NIH Public Access Author ManuscriptHippocampus. Author manuscript; available in PMC 2013 April 03. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript materials, with changes in context between learning and retrieval having a detrimental effect on memory performance (Godden and Baddeley, 1975;Eich, 1985; Guthrie, 1921 cited in Dulsky, 1935; for a review, see Smith, 1988), although results were not always consistent (Smith et al., 1978;Godden and Baddeley, 1980;Fernandez and Glenberg, 1985). The detrimental effect of context change initially appeared to be stronger for recall than recognition; however, a meta-analysis by Smith and Vela (2001) indicated similar effect sizes (~0.27) for environmental context manipulations irre...

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.

The reliable neuroimaging finding that older adults often show greater activity (over-recruitment) than younger adults is typically attributed to compensation. Yet, the neural mechanisms of over-recruitment in older adults (OAs) are largely unknown. Rodent electrophysiology studies have shown that as number of afferent fibers within a circuit decreases with age, the fibers that remain show higher synaptic field potentials (less wiring, more firing). Extrapolating to system-level measures in humans, we proposed and tested the hypothesis that greater activity in OAs compensates for impaired white-matter connectivity. Using a neuropsychological test battery, we measured individual differences in executive functions associated with the prefrontal cortex (PFC) and memory functions associated with the medial temporal lobes (MTLs). Using event-related functional magnetic resonance imaging, we compared activity for successful versus unsuccessful trials during a source memory task. Finally, we measured white-matter integrity using diffusion tensor imaging. The study yielded 3 main findings. First, low-executive OAs showed greater success-related activity in the PFC, whereas low-memory OAs showed greater success-related activity in the MTLs. Second, low-executive OAs displayed white-matter deficits in the PFC, whereas low-memory OAs displayed white-matter deficits in the MTLs. Finally, in both prefrontal and MTL regions, white-matter decline and success-related activations occurred in close proximity and were negatively correlated. This finding supports the less-wiring-more-firing hypothesis, which provides a testable account of compensatory over-recruitment in OAs.