What actually happens to an impulse after reaching the brain?

The photons of the light which fall on the object are reflected by it and are incident on the retina. The retina senses the frequency and wavelengths of these photons. The retina can sense the wavelength between 400–700 Nano-meters.

Just to give a quick comparison, if electromagnetic waves belonging to various ranges of wavelength are compared to the distance from Kanyakumari to Leh in the Himalayas, the range that is perceived by the human retina (400–700 nm) is equivalent to the size of a room. We can now imagine how insignificant little of the existing universe we actually perceive!

The rods and cones are stimulated by photons and a chemical signal is released. The chemical signal is converted into an electrical signal which becomes a brain wave inside the brain. The brain wave is indeed an electrical wave created by the action of neurons.

A million dollar question is, who reads these brain waves, how they are read, and what is the reason behind this reading.

Nobody knows the answer.

Similarly, the electrical signals generated by the neurons after sound input will also become waves in the brain.

All five sensory inputs become electrical signals and they become waves in the brain. Of course, there are filters on their way to their final destinations.

The function of the brain is to create electrical waves by the neurons of the brain. Different patterns of electrical waves are created and the neurons group together to generate particular types of waves. They are also stored as memories. Whenever a new pattern of wave is generated, it is immediately cross matched with the memorized bits of information and the actual meaning of that input is deciphered.

It all depends on what type of waves we have stored as memory. Any fresh input is observed and understood with the bias of previous existing memory. It is like wearing red glass spectacles and looking at the world!

We actually do not know what this external world really looks like! Our brain works on its matching proficiency and describes the external world according to its memorized data. The external world looks different for a nocturnal bat, a cat, a dog, or any other animal. The world is read differently by different animals depending upon the design of their brain!

Reference: RN Sreenathan