Subject of study
In the course of the experiment, the mice were forced to run on the simulator, while the sounds of their steps were replaced by a sound that was significantly different in timbre from it. It is known that the source of noise can be both the external environment and the actions of the individual, for example, steps, speech and breathing.
In humans, as in animals, in the process of evolution, the ability to suppress background noises has developed, distinguishing them from external auditory stimuli. In other words, we prefer not to constantly hear the noise of our breathing, but rather we will listen to the fact that for an unknown byaka rises from the external environment, whether it can eat us or, on the contrary, will be good for food.
This ability has become one of the basic foundations of our hearing. Today, the neural circuits in the auditory cortex, which learn to recognize external and self sounds, as well as mask and compensate for them in perception, remain poorly understood, if not worse, practically unknown to neuroscientists.
Experiment
Scientists used 11 laboratory mice, forming an association of extraneous sound with their steps. For this, a kind of virtual reality was created, but not visual, but acoustic. The animals were fixed with their heads and placed on a miniature treadmill. In time with the steps, a recording of special sounds was played, which were assigned as a sound accompaniment to the movements. The sound was fundamentally new and not like natural noise. In this case, the new stimulus from the auditory stimulus was constantly monitored by recording changes in the local field potential (LFP).
Over time, the cortex stopped responding to the stimulus, and the stimulus with a changed frequency (a change of half an octave) was sufficiently suppressed and did not cause such a pronounced excitation of the nervous tissue as at the start of the experiment. The effect was clearly related to mouse movement and was not observed in its absence. At rest, sensory neurons of the auditory zone reacted to test sound stimuli in the same way as to other external sounds. The sensors also recorded that the test sounds produced stronger changes in the infra-granular part of the cortex than in the supra-granular part. This localization of the response indicates that it is precisely the neurons of the auditory cortex that participate in noise suppression, and suppression occurs outside of cognitive processes, as suggested in some hypotheses earlier.
Pavlov confirmation and evolutionary patterns
Several more experiments were carried out to verify the results. The mice were trained to search for a reward, which had to start after two different beeps. As in the first experiment, one of the test sound stimuli was associated associatively with motor activity.
It was noted that the signal associated with movement was recognized by the brain worse than the one that was not associated with them. At the same time, in a state of relative rest, they recognized both signals equally well.
The study further mentions the evolutionary importance of self-noise suppression. Especially for mice, which are potential victims of various predators, and sound is one of the most important sensory indicators of danger. Numerous studies confirm that auditory markers of danger are also extremely significant for humans, which is noted in a study on the psychoacoustic effect of low frequencies, works on the localization of sound sources in space, etc.
The system of neural noise suppression in humans, obviously, also performs more complex functions that are already tied to higher nervous activity, such as mastering oral speech, as well as mastering the performance of musical instruments. The fact is that this seemingly simple mechanism is directly related to musical memory, which, in turn, has a mechanism for representative prediction of sounds and ways of extracting them. It is this mechanism that makes it possible to link hearing, perception, memory and motor responses in such complex complex processes.
According to Schneider, “In the process of speech training and performance skills, we predict the sounds that we intend to hear. For example, before pressing a piano key. In the future (author's note) we compare them with the result in reality. We use the discrepancy between expectations and reality to adjust performance. Over time, we get better and better as the brain tends to reduce the number of errors. "
As a conclusion
Research by Schneider and his colleagues demonstrates a direct relationship between the neurobiological capabilities of hearing in humans and animals with evolutionary mechanisms that influence their development. I believe that a close study of such phenomena and relationships is the key to the deepest understanding of the phenomena and phenomena associated with human hearing.
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