Primary Care Mental Health and Education

Our brains predict what is going to happen based on past experience

by Dr Alastair Dobbin GMC 2289182
Honorary Fellow, School of Clinical Sciences and Community Health, Edinburgh University
Director Foundation for Positive Mental Health

Our brains predict what is going to happen based on past experience.

The purpose of this is to avoid surprises.

Surprise represents uncertainty, which is dangerous, unpredictable, uncertain, hence the importance of prediction.

The incoming data from the outside world passes up a chain of linked brain cells in ascending levels i.e. in vision from the retina to the prefrontal cortex via the occipital areas (V1 V2 V3 etc via the superior temporal region to the prefrontal cortex. This is bottom up perception.

The prediction from the prefrontal cortex is passed down the chain from the prefrontal cortex to the retina.  This is top down perception. The data from the sense organ (say the retina) is passed up the chain to the prefrontal cortex (bottom up perception). The expectation can penetrate right down to the level of the retina and literally change what we see, by making our retina more sensitive in the areas where action is expected excluding what is not relevant to our task attention.    Or it can create a different emotional interpretation of an ambiguous face (reappraisal) from angry to very stressed, and can change our memories of traumatic events so we replay the event with a different interpretation (new paper on memory in Journal Positive Psychology is about this).

At every level the signals are compared.  There may be a discrepancy between the 2 signals, which manifests itself as a positive electrical deflection, the prediction error; the larger the deflection the larger the error. This signal is called the P(Positive) e (error) 300 (300milliseconds after the error) wave (Pe300).  This represents a level of free energy.  

The size of the electrical deflection in the Pe300 is also linked to the level of the response of the  sympathetic nervous system so it stimulates the heart rate and the skin conductance (representing the level of sweating).  These signals represent the brain attaining an appropriate alerting response which prepares the body for appropriate action.  The body also alerts the brain to the need to pay attention, to watch out for anything out of the ordinary, to be ready to respond.

Some pathways which represent important, potentially life threatening discrepancies, need to have a priority over those which are not so important, as attention is a limited resource.  The brain does this by ascribing a level of importance (precision) to each pathway .  This allows the different factors that differ from expectation to compete for attention.  In the case of more important pathways there is a mechanism (neuro modulation) which boosts the signal (or may diminish others either way controls the importance, and what is given priority).

In the case of autism (and interestingly schitzophrenia) it is proposed that there is excess neuromodulation so that instead of very important changes being given a red flag for importance so making us see it as positive and significant every event appears significant and important, hence autistics will focus on events repetitively as they try to extract the important meaning.  In adult psychosis this means that even a car numberplate is 'significant' and the way people look at you is always significant and demanding an explanation, perhaps if you feel a sense of shame this becomes the explanation, that they are after you because of your character defect.  The process of significance is also very stressful as the body fires up the SNS to constantly alert the person of importance.  Possibly this is why autistics continually repeat behaviour, trying to understand the significance.

Although I am very sceptical about 'biological' explanations for mental conditions, certainly I have no truck with anxiety and depression (and others being separate 'illnesses' - to me they are all different manifestations of distress) it does appear there is an interesting crossover between autism and schitzophrenia. However d I am sure for schizophrenia there must be some distress in the equation.

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