Researchers of the University of Barcelona have found, in humans, a gen involved in sound processing, an essential function for human communication. The study, published in the Journal of Neuroscience, has detected genetic differences in the efficacy with which the inferior colliculus, a subcortical structure of the brain, codifies auditory signals. These results will be used to focus on the understanding of the auditory system and the different pathologies related to the codification of language such as dyslexia, autism or the central auditory processing disorder.
The research is led by Carles Escera, director of the Institute of Neurosciences of the University of Barcelona, and professor of Cognitive Neuroscience at the Department of Clinical Psychology and Psychobiology, from the Faculty of Psychology. The study is also signed by the researchers from Brainlab- Research Group on Cognitive Neuroscience of the UB Lenka Selinger –first author of the article- Katarzyna Zarnowiec, Marc Via and Immaculada C. Clemente.
Aiming to discover this correlation in humans, the researchers studied the genotype of 58 volunteers to analyse the presence of 5-HTTLPR, a genetic polymorphism that shapes the serotonin in the synaptic cleft. The participants were then exposed to a repeated stimulus, the syllable /ba/- and an electrode helmet registered the response from the neurones of the inferior colliculus. "This is the registration of a specific response, called frequency following response. That is, when a stimulus with a characteristic frequency within a specific rang is shown –in this case the syllable /ba/-, the neurones in the inferior colliculus react and synchronize their physiological response to the stimulus’", says Lenka Selinger.
The more serotonin, the better signal codification
The results show that neurones in people with the 5-HTTLPR short variable, and thus with a bigger availability for serotonin in synaptic cleft, were synchronized with more precision to the stimulus than the other participants. "These data show that people with more serotonin in the inferior colliculus are able to analyse the stimulus more properly and take the signal in the same context, as if neurones were a Wi-Fi antenna with more coverage. This is actually the first time such a big genetic difference is found in sound encoding", says Carles Escera.
The challenge researchers are now facing is to discover which functional consequences has this clarity in sound encoding and whether it could serve as an indicator for several speech disorders. "If we find a correlation between sound encoding and perception, the genotype could help us detect people who have more probabilities of having problems due to a deficient sound encoding, such as the central auditory processing disorder, and design personalized treatments", says Lenka Selinger.
The study shows for the first time, genetic differences in human auditory signal processing.
Selinger, L.; Zarnowiec, K.; Vila, M.; Clemente, I. C. i Escera. C. «Involvement of the serotonin transporter gene in accurate subcortical speech encoding». Journal of Neuroscience, October 2016.