The predictive brain.

The ‘channelised’ character of experience

As human beings, we come to know the world through many filters and structures.

These range from the biological form of our sense organs to the norms in the culture where we live.

In addition, our responses to the world around us, that were once fresh and spontaneous, gradually get stuck in channels of habit. These channels get deeper through years of repetition.

A useful metaphor is a mountain landscape carved by rivers: at first water may flow in many directions, but as valleys and riverbeds deepen, the flow becomes constrained.

In the same way, repeated experiences create deep “channels” in the neural pathways of the brain.

The channelled experience then come to feel like the only possible reality, as the constraints of the channels shape our actions, thoughts, and sense of self.

Symptoms as predictions

This channelling of experience extends to symptoms.

When a new sensory signal arrives at the brain from the body, it is channelled through the neural pathways that are already set up.

If past experiences have embedded symptoms in our neural pathways, the brain may continue to generate them—even when the body itself has changed.

The brain is powerful in shaping our experiences. As long as the brain predicts the presence of a symptom, we are likely to keep experiencing it.

Why deep channels form

Of course, it is always possible for new neural pathways to be formed along which our experience can flow.

However, this will not necessarily happen. If incoming sensory information is weak or ambiguous, the brain may fail to re-route its neural pathways, prefering the predictability of the known channels.

This means we can continue to have symptoms on autopilot for years. The longer the symptom experience goes unchallenged, the deeper it becomes embedded in our brain’s learning system.

Studying problems related to this kind of subtle brain processing in real-time is challenging. However, research suggests that difficulties in updating these expectations might be at the root of some functional somatic symptoms.

In such cases, the experience of having the symptom may not be connected to what’s actually happening in the body at that moment.

In other words, persistent symptoms that no longer match present reality.
Click here to see a simplified schematic of predictive processing of sensory information.

Updating predictions

The brain needs to notice when fresh incoming information doesn’t match its predictions. A degree of ‘noise’ is overlooked. But when the brain is certain there is a mismatch, it will update its neural networks through neuroplasticity.

However, neuroplasticity is energy demanding, so the brain only updates its models when it judges this is really necessary. It uses mathematics of probability to decide whether it is more certain that the fresh information is correct, or whether it is more confident relying on its previously established model.

This can be compared to how we update our inner models that form beliefs (learn).

Imagine you usually get headaches almost every day, but recently you’ve noticed several days in a row without one.

You start to believe your headaches are finally improving.

If one mild headache happens, you might dismiss it as an exception rather than changing your belief. But if you continue to go longer stretches with fewer or no headaches, your confidence grows that things are genuinely getting better.

How many headache-free days would it take before you update your prediction that you will be likely to have a headache tomorrow?

The answer to this varies between people. Some people stick very rigidly to their longstanding beliefs. Other people are quicker to let fresh information update their predictions.