Summary: Researchers find that plasticity in older brains is not absent but dysregulated; raising GABA levels can help produce longer-lasting changes in the auditory cortex.
Source: McGill University.
Contrary to the adage that you can’t teach an old dog new tricks, new research shows that older brains can be taught to respond to new sounds — although the changes are often unstable unless inhibitory signaling is restored.
Researchers at the Montreal Neurological Institute and Hospital (The Neuro) at McGill University investigated how aging affects neuroplasticity in the primary auditory cortex, the brain region that processes sound. Neuroplasticity is the brain’s capacity to change its connections and function in response to experience, and it underlies learning and sensory adaptation.
Plasticity is pronounced during early development, when sensory systems are tuned to map the environment. As we mature, many of those sensory maps become stabilized. This stabilization depends in part on inhibitory signaling mediated by the neurotransmitter gamma-Aminobutyric acid (GABA), which dampens neuronal excitability. The role of GABA in regulating cortical inhibition was first described at The Neuro in 1956 by K.A.C. Elliot and Ernst Florey.
Led by first author Dr. Mike Cisneros-Franco and lab director Dr. Étienne de Villers-Sidani, the team tested whether the mechanisms that normally stabilize plasticity become dysregulated with age. They exposed adult rats of different ages to repeated tones at a single frequency and measured how neurons in the primary auditory cortex adjusted their frequency tuning in response to that passive sensory experience.
The experiments revealed that passive tone exposure caused neurons in older adult rats to become more responsive, or sensitized, to the presented frequency. In contrast, the same exposure produced little change in younger adult animals. Crucially, the enhancement observed in older rats faded rapidly after the exposure ended, indicating an ongoing instability in the aged auditory cortex’s tuning. In a separate group of older rats, pharmacologically increasing GABA levels in the auditory cortex made the exposure-induced changes more persistent, demonstrating that restoring inhibitory tone can stabilize learning-related alterations.
These results indicate that aging does not abolish the brain’s capacity to change; rather, plasticity becomes elevated but improperly regulated when inhibitory GABAergic mechanisms decline. In other words, the aged brain may be more prone to change but less able to retain those changes without adequate inhibitory control. By boosting GABA levels, the investigators were able to restore more stable auditory cortical representations and improve the retention of learning in older animals.
“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 supported by 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.
doi: 10.1523/ENEURO.0051-18.2018
MLA: McGill University. “New Insight Into Aging.” NeuroscienceNews. NeuroscienceNews, 19 September 2018.
APA: McGill University (2018, September 19). New Insight Into Aging. NeuroscienceNews. Retrieved September 19, 2018.
Chicago: McGill University. “New Insight Into Aging.” (accessed September 19, 2018).
Abstract
A Brain without Brakes: Reduced Inhibition Is Associated with Enhanced but Dysregulated Plasticity in the Aged Rat Auditory Cortex
During early critical periods of development, passive changes in sensory input can reshaping cortical sensory maps, producing long-lasting distortions in how stimuli are represented. When those critical periods close, representations are stabilized through the maturation of inhibitory networks and by maintaining sufficient cortical GABAergic tone. In humans and rodents, cortical inhibition decreases with age, suggesting that the regulation of plasticity may be altered in older individuals. To test this, the researchers examined whether aging causes destabilization of sensory representations and maladaptive, dysregulated plasticity in the rat primary auditory cortex (A1). They found that passive tone exposure was sufficient to distort frequency tuning in older but not younger adult rats, and that these passive changes decayed rapidly in the aged cortex, reflecting an ongoing instability. These functional changes were accompanied by lower GABA concentration and reduced expression of parvalbumin and perineuronal nets. Importantly, artificially increasing GABA tone in aged A1 restored representational stability and improved retention of learning.