The University of Michigan has published new research indicating that certain brain cells associated with spatial orientation have remained largely unchanged through millions of years of evolution. These findings may help explain why humans and other mammals can instinctively determine their location in an environment.
The study, funded by the National Institutes of Health and the Alzheimer’s Association, focused on neurons in the retrosplenial cortex—a brain region linked to navigation and early impairment in Alzheimer’s disease. According to Omar Ahmed, associate professor of psychology at the University of Michigan and senior author of the study, “The retrosplenial cortex functions as a subconscious GPS system for our brains. It has specialized neurons that calculate what direction we need to go in to head towards our desired destination.”
Ahmed added, “The retrosplenial cortex is also activated when we imagine ourselves in a future time or place. So, it’s a remarkable brain region, one that helps us subconsciously understand where we are in our real or imagined world. Unfortunately, the retrosplenial cortex is also one of the first regions to show impairments in Alzheimer’s disease.”
The research team previously identified a unique type of neuron within this brain region in mice. In this new work, Isla Brooks—first author and member of Ahmed’s lab—and Ahmed developed artificial intelligence-based tools to compare genetic signatures between mouse and rat retrosplenial cortex neurons. Despite millions of years separating these species on the evolutionary tree, this specific neuron type was found to be well preserved across both.
Additionally, researchers discovered another ancient neuron type exclusive to the retrosplenial cortex that plays a key role in spatial awareness. This second neuron type was not only conserved but slightly increased through evolutionary history.
“By comparing thousands of genes across thousands of neurons from distinct species, we can ask how specific types of neurons change across evolution,” said Ahmed.
The study highlights that at least two specialized neuron types exist solely within the retrosplenial cortex. “It’s easy to imagine why these neurons are of critical importance for the survival of a species and preserved over millions of years of evolution: they help to successfully find one’s way home,” Ahmed stated.
Spatial disorientation is common among people with Alzheimer’s disease; many cannot navigate familiar environments such as finding their way home. The research group is now investigating whether similar specialized neurons exist in human brains and how they might be affected by Alzheimer’s disease progression.
“We see neurons in the human brain that physically look like the specialized retrosplenial neurons seen in other species. By understanding how these neurons change in people with Alzheimer’s disease we can work towards targeted therapies to repair the neurons,” said Ahmed.
Other contributors include Izabela Jedrasiak-Cape, Chloe Rybicki-Kler, and Tyler Ekins. The study appears as the cover article in this month’s Journal of Neuroscience.
