A research collaboration between the labs of Vincent Bonin at NERF and Bruce McNaughton at the Canadian Centre for Behavioural Neuroscience at the University of Lethbridge, Canada, has provided new insight into how the brain learns about the environment and why the hippocampus, a key part of the brain, is so important in this process.
A 2017 study conducted by Dr. Dun Mao (PhD ’17), then a graduate student working in the labs of McNaughton and Bonin, was the first to show that cells in the cerebral neocortex, specifically the retrosplenial cortex, look very much like ‘place cells’ in the hippocampus. Place cells are involved in navigation and learning. However, the researchers didn’t know whether the retrosplenial cortex developed activity patterns on its own or relied on instructions from the hippocampus.
In the current study, Mao damaged very precise locations in the hippocampus in mice so that the hippocampus was no longer functional but the cortex remained intact. He then used 2-photon calcium imaging to track the activity of neurons in the cortex as the mice navigated and learned about the environment. This allowed him to witness how retrosplenial activity develops and to determine the role of the hippocampus in that learning.
“In those mice, we found that there was a loss of this place-cell like activity in the cortex, thereby strongly supporting the conclusion that the cortex gets its spatial code, or its index code, from the hippocampus itself,” says McNaughton.
“Most compelling are the strength and specificity of the effects,” says Bonin. “The effects are stunning. With an intact hippocampus, activity in the retrosplenial cortex is precise and orderly. In the absence of it, it’s a complete mess, as if the animal had never been exposed to the environment. Having such a strong phenomenon to rely on will be helpful in basic studies but also in studies of brain disorders and neurodegeneration.”
The study, Hippocampus-dependent emergence of spatial sequence coding in retrosplenial cortex, has been published in PNAS.