Sep 24, 20205 min read

How Our Brain Constructs Reality

Take a look around your room. It seems easy to believe that you are experiencing your room objectively - but what if you are not?

Your brain is continually rebuilding the world around you inside your mind, with all its colours, sounds and textures. But that is not how living feels, it feels as if we experience reality as such without any obstructions. But in reality, you are essentially living in a fictional world created by your brain which mimics the world around you.

Breaking it down

This can feel like mental gymnastics so let's break down the process. Suppose you walk into a room. Your brain first predicts the sounds, light and textures in the room and creates a hallucination based on this prediction. This hallucination is what you experience as "reality".

We never actually experience reality because we have no means to. In the words of neuroscientist Professor David Eagleman, “Consider that whole beautiful world around you, with all its colours and sounds and smells and textures, your brain is not directly experiencing any of that. Instead, your brain is locked in a vault of silence and darkness inside your skull.”

How is my hallucination so accurate?

You may be thinking - if what we experience is hallucination then how do two people agree on facts about the surroundings? Though we hallucinate, it is controlled hallucination - there is a certain level of accuracy in what our brain tells us, otherwise we will be walking into doors.

Our sense organs help with the accuracy of the controlled hallucination by picking up changes around us. When they detect anything that doesn't match our prediction, it sends quick messages via electric pulses which are read by our brain - similar to how computers read codes. Our brain then actively translates this information on the reality we perceive - making us believe it is real.

This process is the reason we sometimes see things that are not there. A bunch of clothes on a chair may lead you to believe you saw a stooped man sitting in your room. You did see a man because your brain believes he should be there. When you look at it the next day, your eyes update the information thus changing the controlled hallucination you live in.

This same process is also responsible for not seeing things that are there. A series of iconic experiments had participants watch a video of people throwing a ball around. They had to count the number of times the ball was passed. Most did not notice a man in a gorilla suit walk directly into the middle of the screen, bang his chest three times, and leave after nine seconds. Other tests have confirmed we can also be ‘blind’ to auditory, touch and smell information. There is a surprising limit to how much our brains can process. Above that limit, objects are simply edited out of our hallucinated reality.

What about the colours and sounds?

We know that we live in a virtual world. For example, if a tree falls, all it does is create vibrations in the air and ground. The crash sound is created by our brain.

When you get a paper cut and your finger hurts, the pain is also an illusion. That pain is not in your finger but your brain.

Similarly, our perception of colour is the creation of our brain. The colours we see are based on the wavelengths that are detected by the three cones in our eyes.

Even sleep doesn't stop our brain's storytelling. Have you ever woken up because of a hyper-real dream? Maybe you felt like you were falling or someone was chasing you and you woke up drenched in sweat. The reason dreams seem so real is because they are made up of the same neural models we live in when we are awake.

This seems fake...

This idea does seem far fetched but it is based on studies conducted by SISSA and described in two separate papers published in Neuron and Nature.

In a study published in Neuron, researchers at SISSA investigated how the signals arriving through multiple senses are integrated. We recognise a banana through its texture, smell and taste - 3 different senses. The researchers tried to find out how the knowledge about an object (our banana) is linked to sensory inputs.

The researchers trained rats to explore a grating made of raised black and white bars. The orientation was reset randomly on each test trial and rats learned to approach the object and respond differently for two categories of orientation: horizontal and vertical. The rats were categorised into 3 groups with each group being allowed to interact either using

vision
touch
vision and touch

By comparing accuracy under the three conditions, the investigators found that rats which were allowed to use vision and touch worked more effectively than the sum of rats which were allowed only one. As the rats explored the object, the investigators also measured neuronal activity in the posterior parietal cortex (PPC), a region positioned between the primary sensory cortical areas for touch, vision and audition. Then they implemented a mathematical model to interpret the information carried by large sets of neurons. The model accurately predicted how the rat would classify the stimulus on every single trial.

Another particularly revealing discovery: while neurons varied widely in how they encoded object orientation or category, a given neuron's response was identical under the three conditions. "This means that the message of the neurons was the object itself, not the sensory modality through which the object was explored" notes Mathew Diamond, senior investigator in the research.

Sensory signals originate from real objects that have many physical attributes. Thus for efficiency, mammalian sense organs evolved to function in an intermeshed manner. Our brain integrates information from different sense organs to enhance our perception thus allowing us to relate objects to our memory irrespective of the sense organ used.

Another study, published in Nature, looks into how recent sensory memories are formed and maintained. Suppose you have misplaced your cell phone and its ringtone alerts you to an incoming call. As you search you store in memory the last ring's amplitude to compare it to the next, in this way determining whether you have moved closer or farther. But how stable is the memory of the last ring? For many years, neuroscientists have understood that as sensations fade away, their memory shifts towards the statistical mean of recent stimuli.

The researchers trained rats to compare the amplitudes of two auditory stimuli separated by a delay of several seconds similar to tracking our cell phone by comparing the current ring to the preceding one. Hundreds of such trials (each containing two stimuli) followed each other in a sequence. The behavioural data revealed that as the rat awaited the second stimulus of the trial, the memory of the first stimulus shifted towards the mean of preceding stimuli.

The experiment thus confirmed the sliding of memory towards the expected value, a phenomenon that earlier studies have termed 'contraction bias.' But how does the brain apply prior statistics to the stimulus stored in memory?

Neuronal activity in PPC revealed a trace of the memory of preceding stimuli. When researchers silenced PPC activity (through optogenetics), rats' performance improved. Why? The key is that memory of the first stimulus was not held in isolation, but instead was influenced by preceding trials.

In many situations, contraction bias offers an enormous advantage: whenever available information is not exact, the prior is on average the best guess. However, when each sensory event is independent, contraction bias reduces the accuracy of memories.

Conclusion

We live in a controlled hallucination of our brain. The only thing we will ever know is electric pulses sent by our sense organs. Our brains use these pulses to create a beautiful setting in which our life runs.

Thus confirming Leo Tolstoy’s brilliant assertion that “a real work of art destroys, in the consciousness of the receiver, the separation between himself and the artist.”