Summary: Researchers report plasticity is dysregulated in older brains, but increasing levels of GABA can induce longer lasting changes in the auditory cortex.
Source: McGill University.
They say you can’t teach old dogs new tricks, but new research shows you can teach an old rat new sounds, even if the lesson doesn’t stick very long.
Researchers at the Montreal Neurological Institute and Hospital (The Neuro) of McGill University examined the effects of aging on neuroplasticity in the primary auditory cortex, the part of the brain that processes auditory information. Neuroplasticity refers to the brain’s ability to modify its connections and function in response to environmental demands, an important process in learning.
Plasticity in the young brain is very strong as we learn to map our surroundings using the senses. As we grow older, plasticity decreases to stabilize what we have already learned. This stabilization is partly controlled by a neurotransmitter called gamma-Aminobutyric acid (GABA), which inhibits neuronal activity. This role of GABA was discovered by K.A.C. Elliot and Ernst Florey at The Neuro in 1956.
First author Dr. Mike Cisneros-Franco and lab director Dr. Étienne de Villers-Sidani wanted to test the hypothesis that plasticity stabilization processes become dysregulated as we age. They ran an experiment where rats were exposed to audio tones of a specific frequency to measure how neurons in the primary auditory cortex adapt their responses to the tones.
They found that tone exposure caused neurons in older adult rats to become increasingly sensitized to the frequency, but this did not happen in younger adult rats. The effect in the older adult rats quickly disappeared after exposure, showing that plasticity was indeed dysregulated. However, by increasing the levels of the GABA neurotransmitter in another group of older rats, the exposure-induced plastic changes in the auditory cortex lasted longer.
These findings suggest the brain’s ability to adapt its functional properties does not disappear as we age. Rather, they provide evidence that plasticity is, in fact, increased but dysregulated in the aged brain because of reduced GABA levels. Overall, the findings suggest that increasing GABA levels may improve the retention of learning in the aging brain.
“Our work showed that the aging brain is, contrary to a widely-held notion, more plastic than the young adult brain,” says Cisneros-Franco. “On the flip side, this increased plasticity meant that any changes achieved through stimulation or training were unstable: both easy to achieve and easy to reverse.”
“However, we also showed that it is possible to reduce this instability using clinically available drugs. Researchers and clinicians may build upon this knowledge to develop rehabilitation strategies to harness the full plastic potential of the aging brain.”
Funding: The study was made possible with funding from the Canadian Institutes of Health Research (CIHR) and the Mexican Council of Science and Technology (CONACYT).
Source: Shawn Hayward – McGill University
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “A Brain without Brakes: Reduced Inhibition Is Associated with Enhanced but Dysregulated Plasticity in the Aged Rat Auditory Cortex” by J. Miguel Cisneros-Franco, Lydia Ouellet, Brishna Kamal and Etienne de Villers-Sidani in eNeuro. Published August 21 2018.
A Brain without Brakes: Reduced Inhibition Is Associated with Enhanced but Dysregulated Plasticity in the Aged Rat Auditory Cortex
During early developmental windows known as critical periods (CPs) of plasticity, passive alterations in the quality and quantity of sensory inputs are sufficient to induce profound and long-lasting distortions in cortical sensory representations. With CP closure, those representations are stabilized, a process requiring the maturation of inhibitory networks and the maintenance of sufficient GABAergic tone in the cortex. In humans and rodents, however, cortical inhibition progressively decreases with advancing age, raising the possibility that the regulation of plasticity could be altered in older individuals. Here we tested the hypothesis that aging results in a destabilization of sensory representations and maladaptive dysregulated plasticity in the rat primary auditory cortex (A1). Consistent with this idea, we found that passive tone exposure is sufficient to distort frequency tuning in the A1 of older but not younger adult rats. However, we also found that these passive distortions decayed rapidly, indicating an ongoing instability of A1 tuning in the aging cortex. These changes were associated with a decrease in GABA neurotransmitter concentration and a reduction in parvalbumin and perineuronal net expression in the cortex. Finally, we show that artificially increasing GABA tone in the aging A1 is sufficient to restore representational stability and improve the retention of learning.