New research with rats shows that changes in sensory experiences can rewire the brain at any age.
The study also found that this rewiring involves fibers that supply input to the cerebral cortex, the part of the brain that is responsible for sensory perception, motor control, and cognition.
“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,” said Marcel Oberlaender, Ph.D., a neuroscientist at the Max Planck Florida Institute (MPFI) and first author on the paper. “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.”
The researchers examined the brains of older rats, focusing on an area of the brain known as the thalamus, which processes and delivers information obtained from sensory organs to the cerebral cortex. Connections between the thalamus and the cortex have been thought to stop changing by early adulthood, but this was not found to be the case in this study, according to Oberlaender.
As nocturnal animals, rats rely on their whiskers as sensory organs to explore and navigate their environment. This makes the whisker system an ideal model for studying whether the brain can be remodeled by changing sensory experiences, the researchers note. By trimming the whiskers, and preventing the rats from receiving sensory input, the scientists sought to determine whether extensive rewiring of the connections between the thalamus and cortex would occur.
They found that the animals with trimmed whiskers had altered axons, fibers along which information is conveyed from one nerve cell to many others, while those whose whiskers were not trimmed had no changes.
The researchers said their findings were particularly striking as the rats were considered relatively old. This implies that rewiring can still take place at an age not previously thought possible, according to the researchers. Also notable was that the rewiring happened rapidly — in as little as a few days, the researchers add.
“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,” said Oberlaender.
“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).”
The study was possible due to advances in high-resolution imaging and reconstruction techniques, developed in part by Oberlaender at MPFI. These techniques enable researchers to trace the fine and complex branching patterns of individual axons, with typical diameters less than a thousandth of a millimeter, throughout the entire brain.
The study was published in the May 24 issue of Neuron.
Source: Max Planck Florida Institute