The art of magical illusion is partly exploiting people’s expectations. Our brains encode a model of how we expect the world to work. When we let go of something, it should fall to the ground. If it doesn’t, we are surprised. This also means that our behavior is predictable – we will tend to look for the object to fall to the ground, meaning the magician will know where we are going to look and can take advantage of that to do things out of our sight.

In our effort to better understand how the brain works, neuroscientists are looking at how the brain reacts to unexpected stimuli. This type of research can have a dual function – looking at the anatomical correlates of a mental phenomenon, and also validating the mental phenomenon itself (because it has an anatomical correlate). This also makes the research tricky, because the questions we ask (how we conceptualize mental phenomena) will dramatically affect the outcome.

For this reason no one study is ever going to tell a complete story. It can, at best, be one piece to a very large and complex puzzle.

The recent study, however, is looking at a fairly straightforward phenomenon – what happens in the brain when it is confronted with unexpected events? The researchers exposed subjects to visual and olfactory stimuli, pictures paired with specific odors. The odors were of food, and either sweet or savory. After being exposed to the pairs sufficiently to form a memory of the correlations, the researchers then showed the subjects a picture with the “wrong” odor. They did this while looking at their brain activity with fMRI scans. (Functional MRI scans look at blood flow in the brain, which is a good way to infer brain activity.)

What they found is that the midbrain became more active when the subject was confronted with a surprising stimuli. The midbrain is part of the brain stem, which is a very primitive part of the brain, shared with all vertebrates. For this reason it is sometimes referred to as our “lizard brain.” The brain stem is a relay center, and controls many basic functions, like breathing. The midbrain in particular is involved in relaying sensory information.

What neuroscientists have found over the years is that even the most primitive parts of the brain are highly involved in processing sensory information. Much of the basic processing of vision and sound occurs before the signals even get to the cortex. The midbrain specifically appears to be involved in filtering sensory input, and determining what we should pay attention to.

We know from psychological experiments that our brains pay particular attention to change or unexpected stimuli. Again this makes sense, once we know something and it is predictable, it becomes part of the background. We no longer expend limited cognitive energy noticing it. However, if it changes, then there is a reason to notice the change, and to update our model of the world. The current study shows that noticing the change at least involves the most basic centers in the brain that relate to sensory processing. The midbrain lights up – it is saying, this is different, pay attention to this.

But of course, in order for something to be unexpected, we need to have expectations. Expectations are a form of memory – we remember that B often follows A, so that when A occurs we expect B. When instead C occurs, this alters the midbrain.

But where is the memory that B follows A stored? Well the current study also shows that the orbitofrontal cortex lights up with unexpected stimuli. This suggests that the orbitofrontal cortex is where the expectations are being stored. Further, when an unexpected pairing occurs, this part of the brain also has to be updated. B is not always paired with A, sometimes C is. Perhaps now C will always be paired with A, or maybe A can pair with either B or C at random, or by some predictable pattern. Better pay more attention to A until this pattern becomes predictable, and we will know what to expect.

This is a pretty basic way to adapt to a changing environment, and so it makes sense that our brains would have adapted early in their evolution to do just that.

Knowing which parts of the brain are involved in this process is mainly interesting to neuroscience nerds. The more basic takeaway is that there is a lot of important processing of information that takes place at a primitive and subconscious level. In this case, we have a map of the world that tells us how it behaves. This gives us expectations about what we will see and experience, and what is likely to happen in the world. When those expectations are broken, we notice, at a fundamental neurological level. Our attention is drawn, and our brain goes into action, updating its map of the world.

It is perhaps even more important to understand what doesn’t happen when our expectations are met – we don’t notice. This has important psychological implications. We tend not to notice things that subconsciously we have determined to be not important. There may be many reasons that we determine some stimuli to be important and others to be background noise. But all this significantly biases our experience of the world, which is only a tiny slice of reality. That tiny slice can reinforce all our biases, desires, and prejudices about the world.

What we see and experience is largely determined by our internal model of reality. Still, it is a good thing that we notice change. That is highly adaptive, and gives us the opportunity to update our model of reality. It is also highly important what we do once we notice the change. We are really good at accommodating the new information without having to significantly change our belief in things we care about. If we are not invested in a fact or belief, we happily update our orbitofrontal cortex. If we are emotionally invested, we are very creative at inventing reasons to explain away the discrepancy between reality and our expectations. We notice the conflict, it causes cognitive dissonance, and then we just rationalize it away.

It takes conscious effort and discipline to confront facts that break our expectations in an open way, and not succumb to motivated reasoning. It’s worth the effort, however.