🧠 What happens to "misplaced" neurons in the brain?

Can the brain function when its architecture is altered? A team from the University of Geneva (UNIGE) demonstrates that neurons located in the wrong place can nevertheless ensure normal function, challenging our conceptions of brain organization. This work, published in Nature Neuroscience, reveals an unsuspected ability of the brain to adapt.

Neurons are specialized cells whose role is to transmit and process information in the form of electrical and chemical signals. They constitute the basic unit of brain and nervous system function. Until now, it was thought that each neuron had to be in the right place for the brain to function correctly. In a recent study, scientists from UNIGE reveal that misplaced neurons can not only survive, but also completely replace the function of the normal cerebral cortex.


To reach this conclusion, the scientists studied mice with "heterotopias." These malformations are characterized by "misplaced" neurons that can then form a mass, in the wrong location, beneath the cortex. This phenomenon is also observed in humans and, in severe cases, causes epileptic seizures and intellectual deficits. By observing these rodents, the UNIGE team made a surprising discovery: these neurons form circuits almost identical to those of the normal cortex, with similar connections to the rest of the brain and the spinal cord.

Neurons capable of taking over

Even more remarkably, when the researchers deactivated the normal cortex of these mice during a delicate sensory task - distinguishing the touch of two different whiskers - they continued to perform normally, with the misplaced neurons having taken over. Conversely, inhibiting these abnormally placed neurons led to complete failure of the task, demonstrating they had become essential for sensory processing.

"It's as if you moved an entire neighborhood of a city to another location, and the residents maintained the same relationships, the same connections with the rest of the city," explains Sergi Roig-Puiggros, a postdoctoral researcher in the Department of Basic Neurosciences at the UNIGE Faculty of Medicine and first author of the study.

Implications for medicine and evolution

The study sheds light on the evolutionary mechanisms by which new brain structures can emerge. It also opens perspectives for regenerative medicine: "If neurons can function normally in an abnormal architectural context, neuronal grafts or brain organoids might potentially not need to perfectly replicate the natural brain structure to be functional," notes Denis Jabaudon, full professor and director of the Department of Basic Neurosciences at the UNIGE Faculty of Medicine, who led the study.

For the research team, the next step will be to evaluate whether this preserved function of misplaced neurons is observed only in heterotopias, or if it also appears in other neurodevelopmental disorders.