The human brain is a fascinating structure and we are still far away from understanding how it works. In the last 3-4 months I spent some time trying to put together a website for patient education about pain. One big contribution to pain is how the brain processes the incoming information. This blog post is more about brain in general. I will leave the part about pain for another post.
One role of the brain is to help us safely navigate the environment. The brain has no direct access to the world and has to rely on information coming from the sensory organs (e.g. eyes, ears). It processes this information and tries make the best guess about what is actually happening. But how good is the best guess? Sometimes the brain makes predictable errors like optical illusions (see checker shadow illusion and table illusion). What is common to these illusions is that we expect the world to be in a certain way (illumination/orientation). Some other examples where expectations alter our perceptions: https://youtu.be/xRel1JKOEbI?t=1382 (watch until minute 25 or the whole thing if you feel like it or read the next paragraph)
A really mind blowing theory is that the brain uses predictive processing for a lot (maybe all) of its inputs. Basically, the predictive processing means that the brain predicts what the input is going to be and sends this prediction to certain areas. Then, the input sensory information (e.g. visual or auditory information) comes to the same areas. When the prediction and the input match the brain uses the prediction. When they do not match a prediction error is created. The weight of the prediction error is dependent on attention and small prediction errors may be ignored. There are few options for the brain at this point: change the prediction or change the input to match the prediction (either alter the input at the brain level or activate motor/other body functions to alter the input). The predictive processing theory is pretty well developed for almost every neuroscience field imaginable. Now I am reading the book " Surfing Uncertainty" by Andy Clark. This TED talk by Anil Seth nicely presents some of these points in a shorter talk than the link above. More resources are on this link from reddit.
The implications of seeing the brain as a predictive processing machine are quite big. There was an article in the New York Times by Lisa Feldman Barrett and Jolie Wormwood and they argue that the prediction for the brain of a police officer to see a gun in certain situations is so high that it overrides the visual input and the brain truly sees a gun. In our daily lives less dangerous examples abound. For example, recently I was helping with a simulated exam for our anesthesia residents. One hour into this somebody mentions that the small exam room I was sitting in has this huge structural pillar for the entire building. The pillar was like a foot from my chair and I had no clue it was there. The prediction of my brain for that room was without any such pillar. My visual system definitely sent the information to my brain but it was completely ignored. In the end, as long as we are aware of our limits I think we can find a way to happily live with them.