Neuroscience | 23
You can do anYthing: The reality of engrams and imagination BY MICHAEL ISKOLS, BEHAVIORAL NEUROSCIENCE, 2022
I
magine a horse wearing a red bowtie with a pineapple on its head.
While you (unfortunately) have never seen such a horse, you’re able to picture it effortlessly. Dr. Andrey Vyshedskiy of Boston University argues that prior observances of a horse, the color red, a bowtie, and a pineapple enable their aggregation into the imaginary. This transition from memory to imagery differentiates our virtual reality from actuality, in which external stimuli, like sound and light waves, are received and interpreted using memory processes. Each recalled component of the picture, whether the horse or the red bowtie, is encoded by a unique group of coordinated neurons in the brain’s frontal lobe—the area responsible for higher-level processing. Concurrent activation of the separate neuronal groups combines these images and initiates the creation of a novel object, a process that Vyshedskiy refers to as mental synthesis. Individual neuronal ensembles, often called engrams, exist to represent not only these seemingly menial memories of characteristics but also complex emotional content.
DESIGN BY KATIE GREEN, BIOENGINEERING, 2021
of two rooftops, you were asked to leap across? You will likely consider your outcome, simulating the jump in your mind before deciding if you would like to succumb to peer pressure. According to Dr. Michael Brecht of Humboldt University, this avatar resides in your sensory cortex. As new sensory information arrives, the cortex is constantly updating this mental simulation, storing stereotyped movements as memories, and initiating planned actions. In this situation, the engrams encoding the perceived gap distance, your possible jump length, and your body position would coactivate, enabling you to see your avatar’s leap across the gap. What if you were asked to imagine yourself riding that horse? Mental synthesis between your frontal, memory, and sensory centers will help you picture it, but only you can put a bowtie on a horse.
Eternal Sunshine of the Spotless Mind, the 2004 Sci-Fi/ Romance movie, depicts a seemingly outlandish procedure that targets and removes a man’s (played by Jim Carrey) recollection of his ex-girlfriend following a painful breakup. In reality, Dr. Susumu Tonegawa works at MIT to manipulate engram activity during fear conditioning to alter memories—bringing Jim Carrey’s bittersweet ignorance closer to reality. When mice are trained to fear environment A, a box with a shocking floor, Tonegawa captures the group of neurons active in the hippocampus, the brain’s memory center, with a light-sensitive protein. In environment B, of which the mice are not afraid, Tonegawa turns on a light-fiber and ultimately the emotional memory of environment A, eliciting a fear response. In this optogenetic technique, he demonstrates how engram activation is sufficient in activating fear memory, just as it might have enabled you to picture the horse in a bowtie with a pineapple. Tonegawa’s colleagues were also able to selectively remove a fear association using similar engramtargeting methods, so why can’t the same be done with Carrey’s former love? With neuronal groups in the frontal lobe building mental images from memory and others in the hippocampus storing those memories, the sensory cortex is responsible for representing the body in context. What if, at the meeting Neuron (2017). DOI: 10.1016/j.neuron.2017.05.018. Nature (2014). DOI: 10.1038/nature11028
Eternal Sunshine of the spotless mind
