Doctor of Philosophy, Boston University (2012)
Bachelor of Arts, Boston University (2007)
Anthony Wagner, Postdoctoral Faculty Sponsor
Noninvasive functional and anatomical imaging of the human medial temporal lobe.
Cold Spring Harbor perspectives in biology
2015; 7 (4)
The ability to remember life's events, and to leverage memory to guide behavior, defines who we are and is critical for everyday functioning. The neural mechanisms supporting such mnemonic experiences are multiprocess and multinetwork in nature, which creates challenges for studying them in humans and animals. Advances in noninvasive neuroimaging techniques have enabled the investigation of how specific neural structures and networks contribute to human memory at its many cognitive and mechanistic levels. In this review, we discuss how functional and anatomical imaging has provided novel insights into the types of information represented in, and the computations performed by, specific medial temporal lobe (MTL) regions, and we consider how interactions between the MTL and other cortical and subcortical structures influence what we learn and remember. By leveraging imaging, researchers have markedly advanced understanding of how the MTL subserves declarative memory and enables navigation of our physical and mental worlds.
View details for DOI 10.1101/cshperspect.a021840
View details for PubMedID 25780085
- Noninvasive Functional and Anatomical Imaging of the Human Medial Temporal Lobe COLD SPRING HARBOR PERSPECTIVES IN BIOLOGY 2015; 7 (4)
- The medial prefrontal cortex and the deceptiveness of memory. journal of neuroscience 2014; 34 (41): 13569-13570
Hippocampus and Retrosplenial Cortex Combine Path Integration Signals for Successful Navigation
JOURNAL OF NEUROSCIENCE
2013; 33 (49): 19304-19313
The current study used fMRI in humans to examine goal-directed navigation in an open field environment. We designed a task that required participants to encode survey-level spatial information and subsequently navigate to a goal location in either first person, third person, or survey perspectives. Critically, no distinguishing landmarks or goal location markers were present in the environment, thereby requiring participants to rely on path integration mechanisms for successful navigation. We focused our analysis on mechanisms related to navigation and mechanisms tracking linear distance to the goal location. Successful navigation required translation of encoded survey-level map information for orientation and implementation of a planned route to the goal. Our results demonstrate that successful first and third person navigation trials recruited the anterior hippocampus more than trials when the goal location was not successfully reached. When examining only successful trials, the retrosplenial and posterior parietal cortices were recruited for goal-directed navigation in both first person and third person perspectives. Unique to first person perspective navigation, the hippocampus was recruited to path integrate self-motion cues with location computations toward the goal location. Last, our results demonstrate that the hippocampus supports goal-directed navigation by actively tracking proximity to the goal throughout navigation. When using path integration mechanisms in first person and third person perspective navigation, the posterior hippocampus was more strongly recruited as participants approach the goal. These findings provide critical insight into the neural mechanisms by which we are able to use map-level representations of our environment to reach our navigational goals.
View details for DOI 10.1523/JNEUROSCI.1825-13.2013
View details for Web of Science ID 000328110100026
View details for PubMedID 24305826
Contributions of Medial Temporal Lobe and Striatal Memory Systems to Learning and Retrieving Overlapping Spatial Memories.
Cerebral cortex (New York, N.Y. : 1991)
Many life experiences share information with other memories. In order to make decisions based on overlapping memories, we need to distinguish between experiences to determine the appropriate behavior for the current situation. Previous work suggests that the medial temporal lobe (MTL) and medial caudate interact to support the retrieval of overlapping navigational memories in different contexts. The present study used functional magnetic resonance imaging (fMRI) in humans to test the prediction that the MTL and medial caudate play complementary roles in learning novel mazes that cross paths with, and must be distinguished from, previously learned routes. During fMRI scanning, participants navigated virtual routes that were well learned from prior training while also learning new mazes. Critically, some routes learned during scanning shared hallways with those learned during pre-scan training. Overlap between mazes required participants to use contextual cues to select between alternative behaviors. Results demonstrated parahippocampal cortex activity specific for novel spatial cues that distinguish between overlapping routes. The hippocampus and medial caudate were active for learning overlapping spatial memories, and increased their activity for previously learned routes when they became context dependent. Our findings provide novel evidence that the MTL and medial caudate play complementary roles in the learning, updating, and execution of context-dependent navigational behaviors.
View details for DOI 10.1093/cercor/bht041
View details for PubMedID 23448868
Cooperative interactions between hippocampal and striatal systems support flexible navigation
2012; 60 (2): 1316-1330
Research in animals and humans has demonstrated that the hippocampus is critical for retrieving distinct representations of overlapping sequences of information. There is recent evidence that the caudate nucleus and orbitofrontal cortex are also involved in disambiguation of overlapping spatial representations. The hippocampus and caudate are functionally distinct regions, but both have anatomical links with the orbitofrontal cortex. The present study used an fMRI-based functional connectivity analysis in humans to examine the functional relationship between the hippocampus, caudate, and orbitofrontal cortex when participants use contextual information to navigate well-learned spatial routes which share common elements. Participants were trained outside the scanner to navigate virtual mazes from a first-person perspective. Overlapping condition mazes began and ended at distinct locations, but converged in the middle to share some hallways with another maze. Non-overlapping condition mazes did not share any hallways with any other maze. Successful navigation through the overlapping hallways required contextual information identifying the current navigational route to guide the appropriate response for a given trial. Results revealed greater functional connectivity between the hippocampus, caudate, and orbitofrontal cortex for overlapping mazes compared to non-overlapping mazes. The current findings suggest that the hippocampus and caudate interact with prefrontal structures cooperatively for successful contextually dependent navigation.
View details for DOI 10.1016/j.neuroimage.2012.01.046
View details for Web of Science ID 000303272300047
View details for PubMedID 22266411
Which Way Was I Going? Contextual Retrieval Supports the Disambiguation of Well Learned Overlapping Navigational Routes
JOURNAL OF NEUROSCIENCE
2010; 30 (21): 7414-7422
Groundbreaking research in animals has demonstrated that the hippocampus contains neurons that distinguish between overlapping navigational trajectories. These hippocampal neurons respond selectively to the context of specific episodes despite interference from overlapping memory representations. The present study used functional magnetic resonance imaging in humans to examine the role of the hippocampus and related structures when participants need to retrieve contextual information to navigate well learned spatial sequences that share common elements. Participants were trained outside the scanner to navigate through 12 virtual mazes from a ground-level first-person perspective. Six of the 12 mazes shared overlapping components. Overlapping mazes began and ended at distinct locations, but converged in the middle to share some hallways with another maze. Non-overlapping mazes did not share any hallways with any other maze. Successful navigation through the overlapping hallways required the retrieval of contextual information relevant to the current navigational episode. Results revealed greater activation during the successful navigation of the overlapping mazes compared with the non-overlapping mazes in regions typically associated with spatial and episodic memory, including the hippocampus, parahippocampal cortex, and orbitofrontal cortex. When combined with previous research, the current findings suggest that an anatomically integrated system including the hippocampus, parahippocampal cortex, and orbitofrontal cortex is critical for the contextually dependent retrieval of well learned overlapping navigational routes.
View details for DOI 10.1523/JNEUROSCI.6021-09.2010
View details for Web of Science ID 000278102600030
View details for PubMedID 20505108
The Retrieval of Learned Sequences Engages the Hippocampus: Evidence From fMRI
2009; 19 (9): 790-799
Computational models suggest that the hippocampus plays an important role in the retrieval of sequences. However, empirical evidence supporting hippocampal involvement during sequence retrieval is lacking. The current study used functional magnetic resonance imaging (fMRI) to examine the role of the human hippocampus during the learning and retrieval of sequences. Participants were asked to learn four sequences comprised of six faces each. An overlapping condition, where sequences shared common elements, was comprised of two sequences in which two identical faces were shown as the middle images of both sequences. A nonoverlapping condition contained two sequences that did not share any faces between them. A third random condition contained two sets of six faces that were always presented in a random order. The fMRI data were split into a learning phase and an experienced phase based upon each individual's behavioral performance. Patterns of hippocampal activity during presentation, delay, and choice periods were assessed both during learning (learning phase) and after subjects learned the sequences to criteria (experienced phase). The results revealed hippocampal activation during sequence learning, consistent with previous findings in rats and humans. Critically, the current results revealed hippocampal activation during the retrieval of learned sequences. No difference in hippocampal activation was seen between the overlapping and nonoverlapping sequences during either sequence learning or retrieval of sequences. The results extend our current knowledge by providing evidence that the hippocampus is active during the retrieval of learned sequences, consistent with current computational models of sequence learning and retrieval.
View details for DOI 10.1002/hipo.20558
View details for Web of Science ID 000269787100003
View details for PubMedID 19219919