Fish study reveals brain’s noise-cancellation feature

Ringing in the ears (tinnitus) is thought to be caused by a malfunction of the brain’s noise-cancellation mechanism against internal sounds. PHOTO | FILE

As the body carries out its functions, it produces some noise (sensory information) which is perceived by the brain. At the same time, the brain is exposed to external sensory stimuli.

How does the brain distinguish sensory stimuli from the outside world without mixing them up with stimuli from the body’s own actions?

Well, previous studies on electric fish and mice revealed that the brain has a noise cancellation mechanism, that tunes out predictable sensory information generated by an animal’s own body. By putting internal noise on the back burner, the brain can perceive and react to external stimuli. So critical is this noise-cancellation mechanism, that without it, the researchers noted that electric fish lost their ability to sense their surroundings – rendering them blind to the world around them.

“The brain constantly receives sensory information, alongside internal signals related to an animal’s own behaviour. Those internal signals clue the brain into which components are self-generated and which are not,” explained principal investigator Dr Nathaniel Sawtell.

“Over time, those internal signals form what is called a negative image in the brain. This acts as a subtraction mechanism that allows animals to focus on behaviourally important signals coming in from the outside world,” he added.

Researchers wanted to understand how creating this negative image influences the animal’s sensory experience. They focused on the elephant-nose fish which generates electricity to communicate with other fish, locate prey and sense its environment.

Neurons (nerve cells) could only respond to external signals after the brain had cancelled out the noise of internal signals i.e. after negative images of internal signals had formed.

When the fish’s noise-cancellation mechanism was interfered with, the fish could no longer distinguish between electrical signals generated by their environment and those generated by their own actions.

“This means they were essentially blind to their surroundings at the most basic level,” explained Dr Sawtell, an associate professor of neuroscience at Columbia University in the US.

The computations performed by the noise-cancellation neural circuit are essential for the fish’s ability to navigate their surroundings, added co-author Larry Abbott.

Further study will boost understanding on how humans are able to sense their surroundings without being disrupted by inner noise.

The findings published in the journal Neuron, also shed light on what happens when the system is disrupted, as in the case of tinnitus, which causes a ringing of the ears.

The ringing may be due to disruption in the brain’s ability to cancel out self-generated sounds.

 

 

Brain function mimicked

Scientists from Japan have used simplified neuromorphic circuits and devices to mimic part of the brain’s functions.

They developed neuromorphic chips which generated and transmitted spontaneous spikes to artificially replicate the neural circuits of the brain that generate and transmit nerve impulses (the work of neurons).

Neurons are nerve cells that are the core component of the brain and serve to process and transmit information. They enable the brain to adapt to the environment and learn, make ambiguous recognitions, have high recognition ability and intelligence and perform complex information processing.

Neuromorphic devices are likely to become a component of reservoir computing devices, which are poised to become the next generation of artificial intelligence.