Archives for June 2014

Press release on our Stimulus Repetition Paper in Learning & Memory!

Our recent paper in Learning & Memory, which tests a key prediction of our Competitive Trace Theory, was covered in a UC Irvine press release today!

Here’s the write-up:

UC Irvine neurobiologists Zachariah Reagh and Michael Yassa have found that while repetition enhances the factual content of memories, it can reduce the amount of detail stored with those memories. This means that with repeated recall, nuanced aspects may fade away.

In the study, which appears this month in Learning & Memory, student participants were asked to look at pictures either once or three times. They were then tested on their memories of those images. The researchers found that multiple views increased factual recall but actually hindered subjects’ ability to reject similar “imposter” pictures. This suggests that the details of those memories may have been shaken loose by repetition.

This discovery supports Reagh’s and Yassa’s Competitive Trace Theory – published last year in Frontiers in Behavioral Neuroscience – which posits that the details of a memory become more subjective the more they’re recalled and can compete with bits of other similar memories. The scientists hypothesize that this may even lead to false memories, akin to a brain version of the telephone game.

Yassa, an assistant professor of neurobiology & behavior, said that these findings do not discredit the practice of repetitive learning. However, he noted, pure repetition alone has limitations. For a more enriching and lasting learning experience through which nuance and detail are readily recalled, other memory techniques should be used to complement repetition.

We’ve also gotten some buzz in other venues. See our media page for complete updates.

Buzz About the Temporal Discrimination Paper!

Our recent paper in Hippocampus on temporal discrimination in young and older adults recently got a great write up on Dr. Ryan Hunsaker’s blog, Why Haven’t They Done That Yet?

From the post:

Roberts and colleagues developed a task to test temporal pattern separation (as well as primacy and recency) in a cohort of young and aged adults. They were not only able to identify a clear pattern separation deficit in the temporal domain (which makes me very happy as I have been harping on their group to do so for quite a long time), but they also were able to identify successful and unsuccessful cognitive aging as well.

To me, the more important part of their work was that they developed a behavioral task that appears to be a rather sensitive marker for episodic memory deficits that emerge with age (at least the “when” component of episodic memory), and appears also to have a potential diagnostic value for early detection of age-related pathology. The authors obviously need to run a much larger cohort to see what individual differences exist in this task similar to their work with the behavioral pattern separation tasks (mnemonic discrimination tasks as now renamed), but it appears they are off to a great start.

Thanks for the buzz, Ryan! And a hearty congrats to Jared Roberts for the solid paper!

New paper: Stimulus repetition and memory interference.

zach_paper_ponyNew paper by Zach Reagh in Learning and Memory. Here he is with the paper pony!

Reagh, Z.M. & Yassa, M.A. (2014). Repetition strengthens target recognition but impairs similar lure discrimination: evidence for trace competition. Learning & Memory DOI doi/10.1101/lm.034546.114.


Most theories of memory assume that representations are strengthened with repetition. We recently proposed Competitive Trace Theory, building on the hippocampus’ powerful capacity to orthogonalize inputs into distinct outputs. We hypothesized that repetition elicits a similar but nonidentical memory trace, and that contextual details of traces may compete for representation over time. We designed a task in which objects were incidentally encoded either one or three times. Supporting our theory, repetition improved target recognition, but impaired rejection of similar lures. This suggests that, in contrast to past beliefs, repetition may reduce the fidelity of memory representations.

Zach Reagh awarded Holcomb Scholarship


Congratulations to Zach Reagh for being awarded the coveted Dr. William F. Holcomb Scholarship by the School of Biological Sciences! This award supports a graduate student in biomedical sciences and is in the amount of $2000. Zach is pictured here at the award ceremony with Dr. Mike Mulligan, Associate Dean for Graduate Studies, on the left and Dr. Frank LaFerla, Dean of the School of Biological Sciences, on the right.

New paper: Temporal discrimination in older adults


New paper by graduate student Jared Roberts. Here he is with the paper pony!

Roberts J.M., Ly, M., Murray, E., Yassa, M.A. (2014) Temporal discrimination deficits as a function of lag interference in older adultsHippocampus DOI:10.1002/hipo.22303


A vital component of episodic memory is the ability to determine the temporal order of remembered events. Although it has been demonstrated that the hippocampus plays a crucial role in this ability, the details of its contributions are not yet fully understood. One proposed contribution of the hippocampus is the reduction of mnemonic interference through pattern separation. Prior studies have used behavioral paradigms designed to assess this function in the temporal domain by evaluating the ability to determine the order of remembered events as a function of proximity in time. Results from these paradigms in older adults (OA) have been mixed, possibly due to limitations in controlling elapsed time and narrow range of temporal lags. Here, we introduce a novel behavioral paradigm designed to overcome these limitations. We report that OAs are impaired relative to younger adults at moderate and high temporal lags but not at low lags (where performance approached floor). We evaluated OAs’ ability to benefit from primacy (enhanced order judgment on the first few items of any given sequence) and found two distinct subgroups: one group was on par with young adults [aged-unimpaired (AU)] and the other group was two standard deviations below the mean of young adults [aged-impaired (AI)]. Temporal discrimination performance in AU adults was consistent with a pattern separation deficit, while performance in AI adults was consistent with a generalized temporal processing deficit. We propose that the task introduced is a sensitive marker for episodic memory deficits with age, and may have diagnostic value for early detection of age-related pathology.

New paper: Pattern separation and emotional information


New paper by graduate student Stephanie Leal. Here she is holding the paper pony!

Leal, S.L., Tighe, S.K., Jones, C.K., Yassa, M.A. (2014) Pattern separation of emotional information in  hippocampal dentate and CA3.Hippocampus DOI:10.1002/hipo.22298.


Emotional arousal, mediated by the amygdala, is known to modulate episodic memories stored by the hippocampus, a region involved in pattern separation (the process by which similar representations are independently stored). While emotional modulation and pattern separation have been examined independently, this study attempts to link the two areas of research to propose an alternative account for how emotion modulates episodic memory. We used an emotional discrimination task designed to tax pattern separation of emotional information by concurrently varying emotional valence and similarity of stimuli. To examine emotional modulation of memory at the level of hippocampal subfields, we used high-resolution fMRI (1.5 mm isotropic) of the medial temporal lobe. Consistent with prior reports, we observed engagement of the hippocampal dentate gyrus (DG) and CA3 during accurate discrimination of highly similar items (behavioral correlate of pattern separation). Furthermore, we observed an emotional modulation of this signal (negative > neutral) specific to trials on which participants accurately discriminated similar emotional items. The amygdala was also modulated by emotion, regardless of the accuracy of discrimination. Additionally, we found aberrant amygdala-hippocampal network activity in a sample of adults with depressive symptoms. In this sample, amygdala activation was enhanced and DG/CA3 activation was diminished during emotional discrimination compared to those without depressive symptoms. Depressive symptom severity was also negatively correlated with DG/CA3 activity. This study suggests a novel mechanistic account for how emotional information is processed by hippocampal subfields as well as how this network may be altered in mood disorders.

Jared Roberts awarded Haycock Memorial Travel Award


Congratulations to Jared Roberts who was just awarded the John Haycock Memorial Travel Award. The award was established to honor John W. Haycock; friend and mentor to many, and an influential scientist.

John’s family has established a memorial graduate student award named for John in the Center for the Neurobiology of Learning and Memory at UC Irvine. John was a graduate student and received his Ph.D. from UC Irvine before going on to do research and teach at several universities, including The Rockefeller University. The purpose of the John W. Haycock Memorial Graduate Student Travel Award is to provide funding to outstanding graduate students in neuroscience to travel to the annual Society for Neuroscience meeting. This is the most important and informative annual meeting for neuroscientists world-wide, and one that John, himself, greatly enjoyed attending.

Jared will be able to use the award to cover expenses for travel to Washington DC to present his research at the Society for Neuroscience meeting this year. Congrats Jared!