Links between sleep, cognition and schizophrenia

Schizophrenia is associated with wide range of symptoms including visual and auditory hallucinations, cognitive problems and motivational issues.
People with the disease have trouble with learning and memory, cognition and a compound called kynurenine.
Kynurenic acid is a neuroactive metabolite of kynurenine that is formed in the brain. People with schizophrenia have higher than normal levels of kynurenic acid in their brains.

These higher levels might be connected with a range of symptoms seen in the disease like problems with learning and memory. The mechanisms underlying the cognitive impairments in patients is not clear. An interplay between higher kynurenic acid and sleep could be responsible. There is a lot of evidence in both humans and animals that sleep dysfunction leads to problems with learning and memory. People with schizophrenia often have problems with sleep.

Researchers examined rat, they made comparisons in the behavior of rats with increased kynurenic acid in their brains to animals with normal levels of the compound. They connected the animals' brains to a device that measured the amount and quality of sleep, and found that the animals with higher levels of kynurenic acid had significantly less rapid eye movement.

This is the sleep phase in which dreams occur, and it is thought to be critical for the consolidation of previous learning.
The researchers found that the group with high kynurenic acid also had problems with learning. To test this, they place rats in a box and shine light into the box. On one side of the box there is an opening into a darker area.

Rats are nocturnal animals, and prefer the dark, so the animals typically run to the dark area. Once in this area, they receive a small electric shock. When the experiment is repeated the next day, normal animals do not run to the dark location because of the electric shock. By comparison, animals with increased levels of high kynurenic acid, and impaired sleep, do not remember the shock and run into the dark area.

Kynurenic acid disrupts sleep, which then disrupts cognition. However, disruptions in sleep may cause increased kynurenic acid, which then leads to cognitive problems. Reducing kynurenic acid could reduce problems with sleep and cognition in patients with schizophrenia. High levels of kynurenic acid are a crucial aspect of schizophrenia.
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