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Biomedical subjects

Lila Davachi

Publications and source records attributed to Lila Davachi.

6 recordsLinked to original sources
PubMed2006

Item, context and relational episodic encoding in humans.

Recent functional imaging work supports the view that item and relational memory depend upon distinct encoding operations within the medial temporal lobe. Specifically, emerging findings demonstrate that the level of engagement of perirhinal cortex predicts later memory for individual items, whereas the level of hippocampal processing correlates with later relational memory, or recovery of additional episodic details. Furthermore, recent functional magnetic resonance imaging evidence in humans suggests that medial temporal lobe cortical input structures, the perirhinal and posterior parahippocampal cortices, differentially participate in the encoding of objects and their context, providing domain-specific input to the hippocampus. Taken together, these data help to construct a working model of how distinct medial temporal lobe structures participate in episodic memory formation with domain-general relational binding mechanisms supported by the hippocampus and provide emerging evidence for domain-specificity within the perirhinal and parahippocampal cortices.

Brain Mapping↗
PubMed2006

Differential encoding mechanisms for subsequent associative recognition and free recall.

Recent neuroimaging studies have successfully identified encoding mechanisms that support different forms of subsequent episodic recognition memory. In our everyday lives, however, much of our episodic memory retrieval is accomplished by means of free recall, i.e., retrieval without an external recognition cue. In this study, we used functional magnetic resonance imaging to investigate the encoding mechanisms that support later free recall and their relationship to those that support different forms of later recognition memory. First, in agreement with previous work, we found that activation in the left inferior frontal gyrus and hippocampus correlated with later associative/relational recognition. In these regions, activation was further enhanced for items later freely recalled, pointing to shared underlying relational encoding mechanisms whose magnitude of activation differentiates later successful free recall from successful associative recognition. Critically, we also found evidence for free recall-specific encoding mechanisms that did not, in our paradigm, support later associative recognition compared with item recognition. These free recall-specific effects were observed in left mid/dorsolateral prefrontal (DLPFC) and bilateral posterior parietal cortices (PPC). We speculate that the higher-level working memory operations associated with DLPFC and attention to internal mnemonic representations perhaps mediated via PPC may serve to embed an item into a rich associative network during encoding that facilitates later access to the item. Finally, activation in the perirhinal cortex correlated with successful associative binding regardless of the form of later memory, i.e., recognition or free recall, providing novel evidence for the role of the perirhinal cortex in episodic intra-item encoding.

Adult↗
PubMed2004

Functional-neuroanatomic correlates of recollection: implications for models of recognition memory.

Recognition decisions can be based on familiarity, the sense that an item was encountered previously (item memory), and on recollection, the conscious recovery of contextual information surrounding a previous encounter with the item (e.g., source memory). Recognition with recollection is thought to depend on multiple mechanisms, including prefrontal "control" processes that guide retrieval and recapitulation mechanisms that reactivate posterior neocortical representations that were present at encoding. However, uncertainty remains regarding the precise nature of prefrontal contributions to recollection and the selectivity of recapitulation to veridical recollection. The present event-related functional magnetic resonance imaging study sought to examine whether regions showing "old-new" effects support processes sensitive to recollection success or recollection attempt and whether recapitulation of neocortical representations emerge during veridical recollection as well as during false recognition (i.e., false alarms) or whether false recognition resembles familiarity-based responding. Results revealed that multiple left prefrontal cortical regions were engaged during attempts to recollect previous contextual (source) details, regardless of the nature of the to-be-recollected details and of source recollection outcome (successful vs unsuccessful). Recapitulation effects were observed in regions sensitive to the encoding task, suggesting that veridical recollection entails the reactivation of processes or representations present during encoding. Importantly, in contrast to leading models of recognition memory, false alarms also appeared to be based partially on recollection, as revealed through false recapitulation effects. Implications for neural and cognitive models of recognition are considered.

Adolescent↗
PubMed2003

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

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.

Adolescent↗
PubMed2002

Hippocampal contributions to episodic encoding: insights from relational and item-based learning.

The integrity of the hippocampus and surrounding medial-temporal cortices is critical for episodic memory, with the hippocampus being posited to support relational or configural associative learning. The present event-related functional magnetic resonance imaging (fMRI) study investigated the role of specific medial-temporal lobe structures in learning during relational and item-based processing, as well as the extent to which these structures are engaged during item-based maintenance of stimuli in working memory. fMRI indexed involvement of the hippocampus and underlying cortical regions during performance of two verbal encoding conditions, one that required item-based maintenance of word triplets in working memory and the other that entailed the formation of inter-item associations across the words in each triplet. Sixteen subjects were scanned using a rapid event-related fMRI design while they encountered the item-based and relational processing trials. To examine the correlation between fMRI signal in medial-temporal structures during learning and the subject's subsequent ability to remember the stimuli (a measure of effective memory formation), subjects were administered a yes-no recognition memory test following completion of the encoding scans. Results revealed that the hippocampus proper was engaged during both relational and item-based processing, with relational processing resulting in a greater hippocampal response. By contrast, entorhinal and parahippocampal gyri were differentially engaged during item-based processing, providing strong evidence for a functional neuroanatomic distinction between hippocampal and parahippocampal structures. Analysis of the neural correlates of subsequent memory revealed that activation in the bilateral hippocampus was reliably correlated with behavioral measures of effective memory formation only for those stimuli that were encoded in a relational manner. Taken together, these data provide evidence that the hippocampus, while engaged during item-based working memory maintenance, differentially subserves the relational binding of items into an integrated memory trace so that the experience can be later remembered.

Adult↗