HOW DO YOU SEE THE WORLD?
Do you like the world-famous Korean band BTS? In the case of the band, BTS stands Bang Tan Sonyeondan, but in neuroscience, it could also stand for brain transfer stimulus, which is a crucial brain function. The brain recognises what your eyes see and can interpret those visual information or stimulus, so you can understand what you are reading or seeing. A stimulus is anything that captures your attention. When we are talking about vision, you detect visual stimuli, such as light. For instance, when you are at a BTS concert, you see powerful lights flashing with various colours, but this does not surprise you. The brain receives these visual stimuli and processes them with other visual information, so that you know the lights come from the stage. In other words, your brain helps you to recognise things, such as stage lights and a singer at a concert.

HOW DOES YOUR BRAIN HELP YOU SEE?
Have you ever wondered how your eyes allow you to see? For instance, when you are at a concert, how can you spot a friend in the huge crowd? Even though you see with your eyes, a part of the brain called the visual cortex is also responsible for vision, as it processes any visual information from the eyes. This brain region contains several levels for analysing information. Let us think of the visual cortex as a fabulous, multi-layered cake. On the bottom, you have the primary visual cortex (V1), which interprets dots or any forms without shapes. Surprisingly, it only takes 70 milliseconds (msec, 0.07 seconds) to move signals from the eyes to V1.

Next, the secondary visual cortex (V2) recognises more detailed visual representation than V1, such as geometric shapes. You can think of it this way: as you move up in cake layers, the levels of the visual cortex interpret more complex visual information [2]. With higher levels of visual cortex, you can see different colours or movements. It takes longer to transmit signals from the eyes to “higher” levels of the visual cortex. It takes 100 msec (0.1 seconds) to move from the eyes to V2, about 120 msec (0.12 seconds) from the eyes to V3.

In other words, visual information moves from the eyes through the levels of the visual cortex in a very short amount of time (Figure 1). This explains how you can quickly recognise a friend at a concert. Also, as you are reading this article, you can understand the meaning of each word in a sentence, instead of seeing just a jumble of words. Your brain and eyes work as a team to process visual information.

HOW DO WE KNOW HOW THE HUMAN BRAIN WORKS?
The human brain has billions of cells called neurones. Neurones connect with each other to form networks, and they communicate using tiny electrical signals. If the networks of neurones in the brain are damaged, neurones cannot receive electrical signals from each other. This can negatively affect brain functions, leading to disorders like memory impairment and dementia.

Since we cannot see the inside of the brain, how do we know if there is an issue with brain networks? Scientists and doctors have several ways to analyse the brain! Since neurones communicate using electrical signals, we can measure the brain’s electrical activity using small, non-metallic devices called electrodes (Figure 2A).

Electrodes help us to see brain waves made from the electrical activities of neurones. Just like waves in the ocean, the brain waves look like wavy lines moving up and down. However, if a person has brain damage, the electrodes might show slow and unusual patterns of brain waves. The ability to accurately read brain waves is important in neuroscience because it helps us to identify brain abnormalities or disorders.

To record the brain activity of patients in our study, we placed electrodes into the visual cortex during surgery, and then showed patients pictures of various shapes and patterns. As patients looked at these visual stimuli, the electrodes recorded their brain waves, so we could examine which brain regions became activated and how the brain responded to each shape and pattern (Figure 2B). For simple visual responses like dots or a flash of lights, V1 regions were activated. For intermediate visual responses, like geometric shapes, such as triangles, circles, V2 areas were activated, and for complex visual responses like visual fantasy or an illusion with mixed colours, V3/V3+ areas were activated.

There are other ways to measure brain activity that do not require surgery, such as electroencephalography (EEG). In EEG, electrodes can be harmlessly placed on the patient’s scalp. EEG is widely used to look at brain activity and identify brain disorders. Today, computers also help us to understand brain abnormalities. Using artificial intelligence (AI), computers can mimic the networks of neurones in the human brain (Figure 3), which allows these computers to function similarly to the brain. For instance, AI-based computerised “vision” allows computers to recognise and interpret visual stimuli, kind of like they are “seeing”. This computer-based “seeing” is similar to human vision, but computers can identify things more quickly and accurately. Thus, whenever we have difficulties in finding brain disorders in patients, we can use AI networks to gain more insight into disorders and treat patients more efficiently.

SUMMARY
In this article, we told you about how the visual cortex functions in vision and how scientists and doctors can monitor brain activities by measuring brain waves. Now you know that the brain must work with the eyes to allow you to see! Networks of brain cells in the visual cortex communicate to process “levels” of visual information, from simple to complex. When brain networks do not work properly, brain disorders like memory impairment and dementia can result. Computerised neural networks, like those used by AI, can help scientists to understand what goes wrong in brain disorders. With our work, we hope to inspire many bright young scientists to show interest in neuroscience and help to answer more fascinating questions about vision someday!