Older adults can experience difficulties understanding speech in challenging environments, even in the absence of significant hearing loss. This indicates deteriorated processing in the aging central auditory system, and this may lead to reduced communication and social activities. Epidemiological studies have demonstrated a link between the degradation of communication, social activities, and declining cognitive abilities.
To improve central auditory processing in older adults, it may be necessary to use a combination of hearing aids and behavioral and pharmacological treatment approaches. But currently, no pharmacological approach exists to improve central auditory processing. It is also unclear if neural circuits in older individuals can be reactivated to a “young” level.
Neural oscillations—electrical activity in the central nervous system that occur spontaneously and in response to stimuli—at specific frequency bands are associated with cognitive functions and can identify abnormalities in cortical dynamics. In this study published in Neurobiology of Aging in December 2022, 2018 Emerging Research Grants scientist Khaleel Razak, Ph.D., and team analyzed electroencephalogram (EEG) signals recorded from the auditory and frontal cortex of freely moving mice across young, middle, and old ages, and found multiple robust and novel age-related changes in these oscillations.
The paper notes that prior research has shown that manipulating specific neuron signaling pathways by nicotine administration can enhance sensory acuity, reaction time, and attentional and cognitive performance. Other research showed that these pathways are impaired in the aging auditory system. Therefore, the team hypothesized that nicotine administration would reduce age-related impaired cortical processing in old mice.
Razak and colleagues found that an acute injection of nicotine (0.5 mg/kg) in old mice partially or fully reversed the age-related changes in EEG responses. Nicotine had no effect on auditory brainstem responses, suggesting the effects occur more centrally.
Importantly, their data suggest that the auditory circuits that generate “young” responses to sounds are present in old mice, and can be activated by nicotine.
The researchers write that a number of nicotine-like, non-addictive drugs that target cognitive deficits in Alzheimer’s disease and other age-related disorders have been developed. This data in aging mice strongly suggests that topical or oral nicotine or nicotine-like substances may be profoundly beneficial for aging humans with central auditory processing disruptions.
Khaleel A. Razak, Ph.D., is a 2009 and 2018 Emerging Research Grants scientist. His 2018 grant was generously funded by Royal Arch Research Assistance. Razak is a professor of psychology and the director of the graduate neuroscience program at the University of California, Riverside. This is adapted from the paper in Neurobiology of Aging.
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