Mapping Out Memory

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Study combines experimental and computational research to link a type of brain cell to memory.
Posted On: March 31, 2020
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Spatial memory enables us to record information about our environment and our spatial orientation in it. Impaired spatial memory can be an early clinical sign of Alzheimer disease.
Imagine how difficult life would be if we had to use a map every time we went somewhere—even to places where we travel to every day, like to work or to the grocery store. 
Luckily, an area of the brain known as the hippocampus stores and remembers this type of information. The hippocampus plays a key role in learning and spatial memory and helps us navigate through our surroundings. 
During learning and memory formation, the hippocampus displays rhythmic patterns of electrical activity known as theta waves. Although theta waves were discovered in the 1950s, researchers still do not fully understand how different types of cells in the hippocampus contribute to and/or are controlled by theta waves.
Krembil Senior Scientist Dr. Frances Skinner and Laval University Professor Dr. Lisa Topolnik led a tour de force study leveraging experimental and computational methods to determine whether a particular type of cell in the hippocampus, known as an IS3 cell, is linked to theta waves. 
“It is very challenging—and sometimes impossible—to establish what a specific type of brain cell is doing during a behaviour or mental task by using laboratory experiments alone,” says Dr. Skinner. 
To overcome this, Dr. Alexandre Guet-McCreight, then a member of the Skinner lab, developed computational models, informed by experimental data from the Topolnik lab, simulating the activity of cells in the hippocampus. The models predicted that IS3 cells are active during theta waves. 
Using a powerful imaging technique known as two-photon microscopy, Dr. Topolnik’s team corroborated these predictions by probing the activity of IS3 cells in an experimental model of the hippocampus producing theta waves.
“Our findings indicate that IS3 cells are recruited by theta waves and may thus play a vital role in controlling the flow of information in the hippocampus during learning and spatial navigation,” comments Dr. Skinner. “Understanding how specific cell types contribute to these mental processes could provide new insight into conditions that compromise memory, such as Alzheimer disease and epilepsy.” 
This work was supported by the Canadian Institutes of Health Research, the Natural Sciences and Engineering Research Council of Canada, the Savoy Foundation and the Toronto General & Western Hospital Foundation. 
Luo X, Guet-McCreight A, Villette V, Francavilla R, Marino B, Chamberland S, Skinner FK, Topolnik L. Synaptic mechanisms underlying the network state-dependent recruitment of VIP-expressing interneurons in the CA1 hippocampus. Cereb Cortex. 2020 Feb 20. doi: 10.1093/cercor/bhz334.  

Dr. Frances Skinner, Senior Scientist, Krembil Research Institute. Photo courtesy of the Globe and Mail.