Aberrant salience processing in Schizophrenia by Berk Mirza


Schizophrenia is a serious psychiatric condition which affects 1% of the population. People with schizophrenia suffer from conditions such as delusions, hallucinations and thought disorders. There have been many hypotheses to what may be causing schizophrenia. One prominent hypothesis is that the (a group of neurons that contain the dopamine neurotransmitters in the brain), which may be mediating how salient a stimulus appears to one, may be dysregulated.

 

A distinguishing feature in schizophrenia is . People who have psychosis usually have delusions and/or hallucinations. It is suggested that a dysregulated dopamine system is what causes psychosis. Evidence for this comes from antipsychotic medication studies. Although there are controversial findings, the drugs that boost dopamine levels generally worsen the psychotic symptoms in schizophrenia whereas drugs that diminish dopamine levels alleviate these symptoms.

 

The idea that dopaminergic neurons signal salience has also been applied to a much broader conception of ‘salience’. Under this hypothesis, the dopamine system responds to any stimuli that have attention grabbing properties, e.g. a novel stimuli, improbable or surprising events, observations that are informative, as well as those related to rewards and/or punishments, stimuli that have emotional value, events that align with one’s goals, stimuli that are motivating etc.

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Image credit : Modified from Pixabay

Aberrant salience hypothesis of schizophrenia establishes a benchmark for the hypotheses mentioned above, namely, the dopamine system is altered in schizophrenia such that the functions of salience processing deviates from the normal, thereby giving rise to unusual experiences and ultimately psychotic symptoms. Psychiatrist Prof. Shitij Kapur, a leader in the study of psychosis, says in his review paper (2003): “Dopamine mediates the process of salience acquisition and expression, but under normal circumstances it does not create this process. It is proposed that in psychosis there is a dysregulated dopamine transmission that leads to stimulus-independent release of dopamine. This neurochemical aberration usurps the normal process of contextually driven salience attribution and leads to aberrant assignment of salience to external objects and internal representations.

 

In our project we are investigating the aberrant salience hypothesis of schizophrenia in a visual task where certain parts of a scene become more salient because of the information they hold. This is a very simple scene categorization task that is performed with the eyes. We are hoping to use this gaze dependent task to distinguish between different behavioural phenotypes given the visual exploratory behaviour of people while performing the task.

 

References:

Kapur S. (2003). Psychosis as a state of aberrant salience: a framework linking biology, phenomenology, and pharmacology in schizophrenia. Am. J. Psychiatry 160, 13–23. 10.1176/appi.ajp.160.1.13

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