Despite hundreds of millions of years of evolution, humans and fish use the same fundamental principle of brain function to perceive the world around them, an international team of scientists has found, after studying how vertebrates process information from their senses.
Researchers had long observed that the brains of fish, birds and mammals, despite their structural differences, solve similar types of problems in surprisingly similar ways. But to test this, they decided to focus on young zebrafish and conducted an experiment in which the animals, held under a microscope, were exposed to sequential flashes of light and gentle water vibrations while the activity of their entire forebrain was recorded.
The results showed that in fish, as in humans, the brain initially processes signals from different senses separately, then gradually integrates them to create a unified picture of the external world. The only significant difference is that while the thalamus plays the main role in this process in mammals, in fish this function is performed by the preglomerular complex. Yet this anatomical discrepancy does not prevent both structures from performing almost the same job.
In addition, the scientists identified specialized neurons that activated only when two different signals—for example, a light flash and a water vibration—arrived at the brain simultaneously, while those cells barely responded to individual stimuli. According to the researchers, this helps the brain recognize that those sensations belong to the same event, much as we link a flash of lightning to the sound of thunder.
The discovery further shows that evolution often prefers to reuse effective solutions rather than invent new ones each time, and this is not particularly surprising when it comes to a function vital for living organisms: the accurate perception of the environment.
Perhaps the most intriguing aspect is not so much the fact of the similarities, but how deep they run. It is not just a matter of a general principle, but of specific stages of information processing and even the types of neurons responsible for them, suggesting that this mechanism evolved very early, before the major vertebrate groups diverged.
Naturally, the question arises whether this means that the subjective experiences of fish are closer to our own feelings than we might imagine. And though science is unlikely to answer that question anytime soon, the research already forces us to look anew at questions not only about evolution, but also about the nature of consciousness.
