Biology subjects

Libby, L. A.

Publications and source records attributed to Libby, L. A..

3 recordsLinked to original sources

bioRxiv2019

Representation of Task Structure in Human Hippocampus

The hippocampus is thought to support episodic memory, or memory for specific events, but recent work also suggests that it may be involved in extracting structure from the world to guide future decisions and predictions. Recent evidence in rodents suggests that the hippocampus supports decision-making in cooperation with orbitofrontal cortex (OFC), possibly based on representation of task structure. Here, we used functional magnetic resonance imaging (fMRI) to test how the human hippocampus and OFC represents decision-relevant information extracted from previous experiences. Participants performed a task in which they learned values of different foods in grocery store contexts. The task was structured such that we could examine the degree to which neural representations could reflect generalized information about different task structures. Specifically, we manipulated whether a foods desirability varied with store context or not. Some foods were desirable in some store contexts and not in others; some foods were always desirable or undesirable. Participants needed to extract these two task sub-structures (i.e., context-determined vs. context-invariant) from the task structure. We examined hippocampal and OFC activity patterns during a decision-making task after participants were trained with the task structure. Our results showed that both hippocampus and OFC carried task structure information that was relevant to the decision outcomes. Hippocampal and lateral OFC representations differentiated between context-determined (deterministic) and context-invariant (probabilistic) task structures. The degree of this differentiation, an index of task structure representation, was highly correlated between hippocampus and lateral OFC. These results add to a mounting evidence suggesting that the hippocampus and OFC support decision-making by representing task relevant information to the decision outcomes after the task structure is learned.

neuroscience↗

bioRxiv2019

Hippocampal subfields integrate information about past temporal and cognitive contexts

The hippocampus plays a critical role in supporting episodic memory, in large part by binding together experiences and items with surrounding contextual information. At present, however, little is known about the roles of different hippocampal subfields in supporting this item-context binding. To address this question, we constructed a task in which items were affiliated with differing types of context - cognitive associations that vary at the local, item level and membership in temporally organized lists that linked items together at a global level. Participants made item recognition judgments while undergoing high-resolution fMRI imaging. We performed voxel pattern similarity analyses to answer the question of how human hippocampal subfields represent retrieved information about cognitive states and the time at which a past event took place. As participants recollected previously presented items, activity patterns in the CA23DG subregion carried information about prior cognitive states associated with these items. We found no evidence to suggest reinstatement of information about temporal context at the level of list membership, but exploratory analyses revealed representations of temporal context at a coarse level in conjunction with representations of cognitive contexts. Results are consistent with characterizations of CA23DG as a critical site for binding together items and contexts in the service of memory retrieval.

neuroscience↗

bioRxiv2018

Dynamic integration of conceptual information during learning

The development and application of concepts is a critical component of cognition. Although concepts can be formed on the basis of simple perceptual or semantic features, conceptual representations can also capitalize on similarities across feature relationships. By representing these types of higher-order relationships, concepts can simplify the learning problem and facilitate decisions. Despite this, little is known about the neural mechanisms that support the construction and deployment of these kinds of higher-order concepts during learning. To address this question, we combined a carefully designed associative learning task with computational model-based functional magnetic resonance imaging (fMRI). Participants were scanned as they learned and made decisions about sixteen pairs of cues and associated outcomes. Associations were structured such that individual cues shared feature relationships, operationalized as shared patterns of cue pair-outcome associations. In order to capture the large number of possible conceptual representational structures that participants might employ and to evaluate how conceptual representations are used during learning, we leveraged a well-specified Bayesian computational model of category learning [1]. Behavioral and model-based results revealed that participants who displayed a tendency to link experiences in memory benefitted from faster learning rates, suggesting that the use of the conceptual structure in the task facilitated decisions about cue pair-outcome associations. Model-based fMRI analyses revealed that trial-by-trial integration of cue information into higher-order conceptual representations was supported by an anterior temporal (AT) network of regions previously implicated in representing complex conjunctions of features and meaning-based information.

neuroscience↗