The Pathology of Schizophrenia: Action-Outcome Learning Impairments

By Maryna Mullerman ‘20

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Figure 1. Individuals diagnosed with schizophrenia showed a deficit in action-outcome learning, but not in reinforcement learning.

Schizophrenia is often associated with disconnections between thoughts and actions, as well as slow acquisition of adaptive behavior. Doctor Richard W. Morris and researchers from the University of New South Wales in Australia wanted to establish whether schizophrenia (SZ) patients could distinguish causal consequences from reward values. The researchers aimed to reveal action-outcome (AO) learning impairments in SZ patients.

The analysis involved 16 SZ participants and 25 healthy adults (HA). The task was to identify the best action to earn snack foods from a vending machine. The machine was operated by the button box that could tilt the machine either left or right, releasing M&Ms or crackers, respectively. The subjects were tested for reward contingency learning, with the outcome probability changing between blocks in a specific order. The contingency degradation test had equal food reward probabilities, and the machine could release a snack randomly. In the outcome devaluation test, subjects were shown a video of one of the snacks being infested with cockroaches. The people were then told that they would eat whatever food they obtained. The researchers analyzed response rates, relationships between causal learning and goal-directed actions, and participants’ medical histories.

In the reward contingency learning experiments, both HA and SZ subjects selected high-contingency action as more causal. Contingency degradation tests revealed that SZ subjects could not identify the best action. Moreover, in the outcome degradation experiments, SZ subjects were equally likely to pick both actions: to press the button that would release “cockroach infested” versions or the button that would give out a normal snack. Medical data analysis showed that AO learning was improved with decreased anxiety and disability levels.

This study showed action-outcome learning deficits in SZ patients. The researchers concluded that causal judgments of healthy people were more related to experienced contingency. The study suggested that schizophrenia was related to inabilities to encode causal outcomes of actions. The researchers omitted the mechanism of action in SZ, which could explain action-outcome learning disconnections. Future research can identify specific pathways and investigate the role of the medial prefrontal cortex, which is associated with the action-outcome mechanism in SZ patients.

 

References:

  1. R.W. Morris, et. al., Impairments in action-outcome learning in schizophrenia. Translational Psychiatry 8, (2018). doi: 10.1038/s41398-018-0103-0.
  2. Image retrieved from: https://pixabay.com/en/unordered-chaos-3192273/
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