Predicting events in the ever-changing environment is a fundamental survival function intrinsic to the physiology of sensory systems. But what’s happening in the brain to help us do this? When a deviant stimulus is presented inserted in a sequence of coherent ones, the brain produces a negative response called mismatch negativity (MMN), usually followed by a positive component named P3a. Because these happen so quickly, it’s often registered without us even thinking about it. Such components of human response and how the brain detects and adapts to environmental irregularities is always of research interest.
It has been reported that there is a significant individual variation in the skill for detecting deviant sound, and that presumably depends on neurophysiology, biology, and genetics. Even though it is established that genetic heritage is a major source of such individual variations in cognitive processes, no studies are tracking down the brain’s auditory predictive processes to genetic mutations. The catechol-O-methyltransferase (COMT) gene is one of the genes that has been reported to be involved in the auditory predictive processing in the human brain. Specifically, the COMT enzyme breaks down dopamine with a degradation rate 40% faster in people with GG genotype than people with AA genotype, leading to lower dopamine levels in the brain in people with GG genotype than AA genotype. Dopamine is a well-known neurotransmitter in the brain involved in high-level attention and memory processes.
To explore this idea, researchers examined the neurophysiological responses to deviant stimuli recorded with magnetoencephalography (MEG) in 108 healthy participants carrying different variants of Val158Met (rs4680) within the COMT gene. The deviant stimuli were inserted in a sequence of coherent piano tones. The musical key (12 major and 12 minor) of the presentation changed in pseudorandom order by replacing it with a deviant of one of six types: pitch, timbre, location, intensity, slide, and rhythm. For example, the pitch deviant was defined as the sound 24 cents lower than standard, and “old-time radio” filter was used for timbre deviant. The MEG results showed carriers of heterozygotes (AG genotype) of rs4680 responded to all deviants stronger than homozygous (AA/GG) carriers.
The rs4680, with findings reporting a higher cognitive performance for the Met homozygotes (AA genotype) and the Val homozygotes (GG genotypes). Thus, researchers decided to adopt a grouping strategy that could best describe balanced dopamine levels suggested by the inverted-U shape theory. This theory may explain why genotypes may have a stronger response to specific sounds.
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