Multiple routes to memory: Distinct medial temporal lobe processes build item and source memories

Abstract

A central function of memory is to permit an organism to distinguish between stimuli that have been previously encountered and those that are novel. Although the medial temporal lobe (which includes the hippocampus and surrounding perirhinal, parahippocampal, and entorhinal cortices) is known to be crucial for recognition memory, controversy remains regarding how the specific subregions within the medial temporal lobe contribute to recognition. We used event-related functional MRI to examine the relation between activation in distinct medial temporal lobe subregions during memory formation and the ability (i) to later recognize an item as previously encountered (item recognition) and (ii) to later recollect specific contextual details about the prior encounter (source recollection). Encoding activation in hippocampus and in posterior parahippocampal cortex predicted later source recollection, but was uncorrelated with item recognition. In contrast, encoding activation in perirhinal cortex predicted later item recognition, but not subsequent source recollection. These outcomes suggest that the subregions within the medial temporal lobe subserve distinct, but complementary, learning mechanisms.

When memory does not fail: Familiarity-based recognition in mild cognitive impairment and Alzheimer's disease.

“…The key postulate is that perirhinal cortex can produce a familiarity signal sufficient for normal recognition on the forced-choice test with highly similar foils, which is consistent with other evidence suggesting that perirhinal cortex supports familiarity (Brown & Xiang, 1998;Davachi et al, 2003;Henson et al, 2003;Ranganath et al, 2004). However, the present data would cast doubt on a perirhinal proposal if this region were subject to severe dysfunction in MCI; further evidence on this point from AD and MCI patients is required given that even subtle pathology could have significant Figure 5.…”

Visual paired comparison performance is impaired in a patient with selective hippocampal lesions and relatively intact item recognition

“…First, there are no obvious candidates for the role of intentionally directed compensatory processes that will produce normal familiarity. Second, there is growing evidence that the hippocampus is not engaged in normal people either by encoding that produced subsequent familiarity memory (Davachi, Mitchell, & Wagner, 2003;Ranganath et al, 2004) or by familiarity memory per se (Eldridge, Knowlton, Furmanski, Bookheimer, & Engel, 2000).…”

Functional Heterogeneity in Posterior Parietal Cortex Across Attention and Episodic Memory Retrieval

“…Participants were presented with either a previously studied or a novel word and then made 1 of 8 possible memory responses (Table 1). Stimuli consisted of 620 visually presented adjectives, taken from a corpus used in 2 prior fMRI studies (Davachi et al 2003;Kahn et al 2004). The adjectives ranged in length from 3 to 10 letters (mean = 6.93).…”