Using a simple approach, the researchers introduced unexpected changes in a series of sounds to observe how neurons reacted. They unexpectedly omitted a sound from a predictable sequence of auditory cues and made interesting observations.
The brain detects absence of a sound
Firstly, they discover that a specific group of neurons responded precisely at the anticipated moment when the omitted sound should have occurred. This finding not only confirms that the brain detects the absence of a sound but also highlights its ability to predict when the sound should be present.
Interestingly, the researchers noticed that the brain’s response to the missing sound was much more pronounced when the subject was awake compared to when under anesthesia. This suggest that a higher level of consciousness plays a role in the brain’s predictive mechanisms.
Furthermore, the scientists found that the response in the auditory cortex, a higher-level region of the brain, was significantly greater than in the inferior colliculus, a more basic brain region responsible for initial sound processing.
These results are particularly intriguing as they focus on how the brain generates predictions. This contrasts with situations where predictions are violated by the introduction of an alternative sound, where a response is expected but its magnitude remains uncertain. In the case of a missing sound, however, in a non-predictive system, no response would typically be expected.
These findings provide direct evidence at the level of individual neurons, supporting the theory of predictive coding. This theory proposes that the brain's predictive abilities play a crucial role in interpreting and understanding the activities that occur within our minds. The research study, a collaboration with Prof. Manuel Malmierca, and is published in the esteemed journal Science Advances.
Englitz is already thinking about building upon these results: “We are not only looking at single neurons but different types of neurons as well. We are getting closer to the building parts of the brains and how they interact between different layers and regions. It is exciting to unravel a new level of understanding about how our brains anticipate and react to missing sounds. “