16.03.17 Dementia Study Sheds Light on Selective Memories

Why do we remember some things and not others? In a unique imaging study, two Northwestern University researchers have discovered how neurons in the brain might allow some experiences to be remembered while others are forgotten. It turns out, if you want to remember something about your environment, you better involve your dendrites. Dendrites are the tree-like branches on each neuron in your brain.

Using a high-resolution, one-of-a-kind microscope, Daniel A. Dombeck and Mark E. J. Sheffield peered into the brain of a living animal and saw exactly what was happening in individual neurons called ‘place cells’ whilst the animal navigated a virtual reality maze.

The scientists found that, contrary to previous studies, the activity of a neuron’s cell body and its dendrites can be different. They observed that, during the animal’s experience, when cell bodies were activated but the dendrites were not activated, a lasting memory of that experience was not formed by the neurons. This suggests that the cell body seems to represent ongoing experience, while dendrites help to store that experience as a memory.

In the brain’s hippocampus, there are hundreds of thousands of place cells — neurons essential to the brain’s GPS system. Dombeck and Sheffield are the first to image the activity of individual dendrites in place cells. Their findings contribute to our understanding of how the brain represents the world around it and also point to dendrites as a new potential target for therapeutics to combat memory deficits and debilitating diseases, such as Alzheimer’s disease (AD). Disruption to the brain’s GPS system is one of the first symptoms of AD, with many patients unable to find their way home. Understanding how place cells and their dendrites store these types of memories could help us find new ways to treat the disease.

Scientists have long believed that the neuronal tasks of computing and storing information are connected — when neurons compute information, they are also storing it, and vice versa. The Northwestern study provides evidence against this classic view of neuronal function.

“We experience events all the time, which must be represented in the brain by the activity of neurons, but not all these events can be recalled later,” said Mark E. J. Sheffield, a postdoctoral fellow in Dombeck’s lab and first author of the study.

“A daily commute to work, for example, requires the activity of millions of neurons, but you would be hard pressed to remember what was happening halfway through your commute last Tuesday,” Sheffield said. “How is it then that the neurons could be activated during the commute without storing that information in the brain? Now we may have an explanation for how this occurs.”

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