Mack Lab News

In a new JNeuro paper by Yongzhen (Dory) Xie (which was selected a featured article!), we characterize how hippocampal subfields flexibly update category knowledge representations in the face of novel exceptions. By examining participants’ hippocampal representations before and after exception learning, we captured pattern differentiation and integration in DG, CA2/3, and CA1. In line with existing theories, we show that different subfields exhibit distinct representational shifts in exception learning. Interestingly, these shifts depend on exception type - the learning of a confusable exception (like dolphins that resembles fish but are mammals) involves greater differentiation in DG and integration in CA1, relative to an oddball exception (like the strange-looking platypus)!

Xie, Y., Mack, M.L. (2026). Distinct Hippocampal Subfield Representational Shifts Underlie Category Exception Learning. Journal of Neuroscience, 46(27), e1950252026. https://doi.org/10.1523/JNEUROSCI.1950-25.2026

A huge congratulations to Dr. Yongzhen (Dory) Xie! Dory’s victory lap of a final thesis defence was a perfect end to her very successful time in the Mack Lab. Her thesis focused on representational changes that occur during category learning, specifically when learning exceptions to category rules. She incorporated clever empirical tasks, sophisticated computational modelling, and human neuroimaging to comprehensively characterize learning-mediated shifts in how information is organized in conceptual knowledge. Her thesis is an amazing accomplishment and reflects Dory’s hard earned work as a graduate student. We are super proud of Dr. Xie!

Dory’s next stop is as a postdoctoral researcher working with Rob Mok at the Center for Information and Neural Networks (CiNet) and Osaka University in Japan. We already miss you! Best of luck, Dr. Xie!

We are very excited to share Melisa Gumus’ paper, “Distinct contributions of hippocampal pathways in learning regularities and exceptions revealed by functional footprints”, recently published in PNAS. In this work, Melisa proposes a new method that localizes hippocampal pathways with diffusion weighted imaging to interrogate their distinct functional signatures during category learning. She finds that whereas category regularities engage the monosynaptic pathway (i.e., the direct pathway between entorhinal cortex and hippocampal subfield CA1) early in learning, category exceptions engage the trisynaptic pathway (i.e., the pathway that loops in dentate gyrus and CA3) later in learning. These findings provide unique supporting evidence for the functional distinction for these pathways and offer a multimodal approach to further characterizing information flow in the brain. Fun fact: Melisa collected this dataset as an undergrad in 2018!

Read the paper and check out the press release!

A huge congratulations to Dr. Melisa Gumus for successfully defending her PhD thesis! Melisa’s impressive dissertation hit all the corners of the lab’s research: characterizing white matter pathways in the hippocampus and their relationship to cognition, linking computational mechanisms of learning to hippocampal processes and representations, and exploring how attention learning is encoded into flexible concept knowledge. Well done, Dr. Gumus!

Melisa was one of the first trainees in the Mack Lab, starting way back in 2016 as an undergraduate research assistant. In the following 9 years, she wore many hats in the lab including RA, lab manager, graduate RA while she completed a master’s degree with Carmela Tartaglia, and finally PhD student in Psychology. The Mack Lab is what it is today because of Melisa’s persistent motivation for innovative research, her infectious positive spirit, and her gracious support of everyone around her. We will miss her dearly!

Melisa’s next step is a postdoctoral position with Mariam Aly at UC Berkeley. Best of luck, Dr. Gumus!!

Congratulations to Dr. Mateja Perovic on a very successful defence of her PhD dissertation! Mateja’s dissertation details her impressive and ambitious research on how sex hormones and menstrual cycle impact the core mechanisms of category learning. Spanning behavioural experiments, fMRI, hormone analysis, and genotype testing, Mateja’s PhD work is comprehensive and provides key theoretical insights in fields of cognitive psychology, neuroscience, and women’s health. So very proud of Dr. Perovic!

Melisa, Mateja, Dory, Sanjivan, and Sagana presented posters on their new findings at Poster Session C and F, on Sunday April 30th and Monday the 31st, respectively.

Poster C21 - Children’s but not adults’ CA2,3/DG differentiates same category information in memory Sagana Vijayarajah, Margaret Schlichting

Poster C49 - Emergence of Attentional Templates in Concept Learning and the Underlying Neural Mechanisms Melisa Gumus, Wen Jia Zhao , Zoey Zhi Yi Lee, Michael L. Mack

Poster C144 - Menstrual cycle effects on rule-plus-exception category learning vary by BDNF genotype Mateja Perovic, Janice Hou, Shreeansha Bhattarai, Cathlin Han, Michael L. Mack

Poster C151 - Hippocampal Representational Shifts Underlie the Learning of Exceptions to Category Knowledge Yongzhen Xie, Michael L. Mack

Poster F47 - Familiarity to everyday scene categories in adults and children. Sanjivan Loganathan, Sagana Vijayarajah, Margaret Schlichting

We are excited to be presenting new studies and cool findings! Check out Mateja’s poster on Tuesday and Melisa’s talk on Wednesday! Melisa will also be presenting a poster as part of her SfN trainee professional development award! Congratulations!

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/sfn2024_poster_melisagumus.pdf

https://macklab.utoronto.ca/uploads/8/1/8/3/8183/sfn_2024_bdnf.pdf

Talk Category learning builds behaviourally relevant attentional templates Melisa Gumus, Zoey Lee, Michael Mack Wednesday, 8:00-11:15am on October 9th Nanosymposium Human LTM: Encoding and Retrieval III, Room S103

Poster Category learning builds behaviourally relevant attentional templates Melisa Gumus, Zoey Lee, Michael Mack Saturday, 6:30-8:30pm on October 5th Early Career Poster Session, poster board J20 in Hall A

Poster BDNF genetic polymorphism interacts with menstrual cycle phase to predict rule-plus-exception category learning Mateja Perovic, Janice Hou, Shreeansha Bhattarai, Cathlin J Han, Yao Chen, & Michael Mack Tuesday, 8:00am-12:00pm on October 8th Poster board LBA008.073

Congrats to Dr. Emily Heffernan for successfully defending her PhD thesis! Emily’s PhD studies have provided valuable insights into the attentional and neural mechanisms underlying the learning of surprising categorical information. Emily is now a postdoctoral fellow in the APPLY lab at the University of Toronto Mississauga, where she is investigating digital readability. We are all very proud of you, Dr. Heffernan!

Dr. Gaeun Son successfully defended her PhD thesis! Gaeun’s thesis included all her amazing work linking latent spaces of generative AI models to human perception. It is a true accomplishment! Gaeun’s next move is a postdoctoral position in Soojin Park’s lab at Yonsei University. Gaeun will be dearly missed, but we are so excited for her! Congratulations, Dr. Son!

Melisa gave an excellent data blitz (and was an outstanding Mack Lab representative) at this year’s CEMS. She presented her work on the functional footprints of hippocampal pathways in category learning. Well done, Melisa!