Scientists have believed for decades that most of the wiring of the brain is established by the time a person has reached adolescence. Now, a new study published in Neuron reveals that even in adulthood, changes in sensory experiences can cause massive rewiring of the brain.
Researchers from the Max Planck Florida Institute (MPFI) and New York’s Columbia University have discovered that the rewiring involves fibers that provide primary input to the cerebral cortex, which is involved in cognition, sensory perception and motor control. The discovery could pave the way for future research on ageing and brain remodeling.
First author, MPFI neuroscientist Marcel Oberlaender, PhD, declared:
“This study overturns decades-old beliefs that most of the brain is hard-wired before a critical period that ends when one is a young adult. By changing the nature of sensory experience, we were able to demonstrate that the brain can rewire, even at an advanced age. This may suggest that if one stops learning and experiencing new things as one ages, a substantial amount of connections within the brain may be lost.”
In their study, the researchers examined the brains of older rats, focusing on the thalamus, an area within the brain that processes and transmits information from sensory organs to the cerebral cortex. Scientists believed for years that the connections between the thalamus and the cortex would be fixed by early adulthood. However, the researchers observed that this was not true in the animals they studied.
Given that rats are nocturnal and depend on their whiskers as sensory organs to explore and navigate makes them an ideal model for investigating whether the brain can be remodeled through changes in sensory experience. To find out whether extensive rewiring would occur between the thalamus and the cortex, the researchers simply trimmed the rats whiskers, hence preventing them receiving important and frequent sensory input.
They discovered that rats with trimmed whiskers had altered axons, i.e. neurons or nerve cells that act like a fiber-optic cables carrying outgoing impulses, whilst in those with untrimmed whiskers the axons remained unchanged. The finding was significant considering that the rats were older, which means that rewiring still occurs at a later age. Furthermore, the researchers observed that the rewiring occurred in as little as a few days.
Dr. Oberlaender stated:
“We’ve shown that the structure of the rodent brain is in constant flux, and that this rewiring is shaped by sensory experience and interaction with the environment. These changes seem to be life-long and may pertain to other sensory systems and species, including people. Our findings open the possibility of new avenues of research on development of the aging brain using quantitative anatomical studies combined with noninvasive imaging technologies suitable for humans, such as functional MRI (fMRI).”
Recent advances in high-resolution imaging and reconstruction techniques, which Dr. Oberlaender helped to develop in part, enabled the team to automatically and reliably trace the fine and complex branching patterns of individual axons throughout the entire brain. To put things into perspective, axons have a typical diameter of less than a thousandth of a millimeter.
Dr. Oberlaender and Nobel laureate Dr. Bert Sakmann are part of the Max Planck Florida Institute’s Digital Neuroanatomy group that focuses on the functional anatomy of circuits in the cerebral cortex that form the basis of simple behaviors (e.g. decision making). The group’s most significant development is to develop a three-dimensional map of the rodent brain. This will provide new insight into the functional architecture of entire cortical areas as well as offering a better mechanical understanding of sensory perception and behavior.
Written By Petra Rattue