A team of researchers utilize molecular tools to study where and how Memories are stored
Orange County, CA - June 27th 2016 - In the early 20th century, psychologist Karl Lashley systematically subdivided and removed sections of rats’ brains in search of an engram—a term coined to represent the physical collection of cells that convey a memory.
He dedicated his life’s work to proving that memories were the product of particular cells firing in the cortex. When stimuli, such as olfactory or auditory, are triggered in the brain, cells from the initial formation of the memory fire and manifest in the same pattern. With the introduction of new details however, the cells can be subsequently changed due to brain elasticity.
In his experiments, Lashley trained rats to traverse a maze before removing areas of their cortex. Working under the presumption that engrams were localized in one distinct area of the brain, Lashley expected the rat to forget how to get through the maze, if the corresponding engram was removed. Critics speculate that Lashley’s method failed due to the amount of complex systems necessary to navigate a maze, including vision, spatial sense, kinesthesis, and olfaction. As such, eliminating a single factor is insufficient to completely obscuring the entirety of a rat’s memory.
With the failure of his 30 year endeavor, Lashley considered the possibility that memories could be evenly distributed across the brain. Neuroscientist Sheena Josselyn kept Lashley’s scientific journey in mind when she attempted to modify cells for mind manipulation for the first time in the 1990’s. During her tenure as a postdoc at Yale, Josselyn altered cells in the amygdala of a rodent, which improved its memory. In reimagining Lashley’s technique, Josselyn found his white whale. A century later, her work has proved both his hypotheses to be partially true; engrams are believed to be the result of synaptic connections among neurons that create a mini-network.
The advancement of sophisticated molecular tools has given researchers the ability to evoke, erase, and implant memories via manipulation of particular cells in the engram. Josselyn works with the belief that cells active during learning events develop into critical components of the memories, allowing the brain to quell and repress or queue and resurface a memory.
At the University of Toronto, Josselyn and her team of researchers utilize a custom set of molecular instruments to mess with the minds of Mice. In 2009, they realized that these tools could be used to mark brain cells that were fired when a learning event took place. The scientists took a Pavlovian approach to classically condition the mice with fear. Researchers took a neutral stimulus, a sound, and associated it with an electric shock so the mice would respond to the shock upon hearing the tone.
Eventually, just playing the sound itself would elicit fear. To prove their hypothesis, however, researchers used the tools to label molecular tags, allowing them to identify which cells ought to be eliminated when trying to eradicate certain memories. By the end of the experiment, they could activate the cells that held the shock/sound engram and the mice would react as if they heard the sound.
Josselyn has also found success in manipulation of a cocaine-based memory. After teaching the mice to associate a place with cocaine, the mice began to spend most of their time in the cocaine-laced area. After researchers erased the memory of the location by destroying cells in the cocaine engram, the animal no longer preferred that location.
While the rest of us contemplate what painful or embarrassing memories we’d like erased, Josselyn hopes her research will be used to expand treatment options for those with memory-related diseases and conditions, such as Alzheimer’s, addiction, and post-traumatic stress disorder.
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