Links between hallucinations and dopamine

Researchers at Columbia University Irving Medical Center (CUIMC) and New York State Psychiatric Institute (NYSPI) found that people with schizophrenia who experience auditory hallucinations tend to hear what they expect, an exaggerated version of a perceptual distortion that is common among other people without hallucinations.

Those with hallucinations and other psychotic symptoms are known to have elevated dopamine, the main area of focus for available treatments for psychosis, but it was unclear how this could lead to hallucinations.

The researchers found that elevated dopamine could make some patients rely more on expectations, which could then result in hallucinations. Human brain uses prior experiences to generate sensory expectations that fill in the gaps when sounds or images are distorted or unclear.

In individuals with schizophrenia, this process appears to be altered, leading to extreme perceptual distortions, such as hearing voices that are not existing. Furthermore, while such hallucinations are often successfully treated by antipsychotic drugs that block the neurotransmitter dopamine in a brain structure known as the striatum, the reason for this has been a mystery since this neurotransmitter and brain region are not typically associated with sensory processing.

The researchers designed an experiment that induces an auditory illusion in both healthy participants and participants with schizophrenia. They examined how building up or breaking down sensory expectations can modify the strength of this illusion. They also measured dopamine release before and after administering a drug that stimulates the release of dopamine.

Patients with hallucinations tended to perceive sounds in a way that was more similar to what they had been cued to expect, even when sensory expectations were less reliable and illusions weakened in healthy participants. This tendency to inflexibly hear what was expected was worsened after giving a dopamine-releasing drug, and more pronounced in participants with elevated dopamine release, and more apparent in participants with a smaller dorsal anterior cingulate (a brain region previously shown to track reliability of environmental cues). All people have some perceptual distortions, but these results suggest that excess dopamine can exacerbate human distorted perceptions
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Development of brain networks

According to new research, the brains of smart people are wired differently, it allows them to absorb important facts quickly – while blocking out irrelevant information. Scientists used MRI scans on many volunteers to shed light on the nature of intelligence. They had already identified areas of the brain that control IQ and now they have uncovered the mechanism behind it. Researchers said it is possible for people to make themselves more intelligent with brain training games.

Researchers discovered that regions interact more closely in brainy individuals – while others disconnect themselves. In more intelligent people, certain regions are clearly more strongly involved in the exchange of information between different 'sub networks' of neurons. This enables important information to be communicated faster, and more efficiently. On the other hand, the researchers also identified areas that are disconnected, or 'de-coupled', from the rest of the brain in brighter people.
They believe this results in better protection against distracting and irrelevant material.

It is possible that due to their biological predispositions, some individuals develop brain networks that favour intelligent behaviours or more challenging cognitive tasks. However, the frequent use of the brain for cognitively challenging tasks may positively influence the development of brain networks. Smart thinking requires various portions of the brain working together like different parts of an engine.

Differences in academic success and professional careers are attributed to a considerable degree to cognitive abilities. Higher level thinking are rooted in the patterns of integration among parts of the brain called functional modules.It combined the brain scans from the participants with an analysis of mathematical graphs of their networks of neurons to come up with the first neurobiological basis of human intelligence.

 The two brain regions involved in the cognitive processing of 'task relevant' information - the anterior insula and the anterior cingulate cortex - are connected more efficiently to the rest of the brain. Another brain region, the junction area between temporal and parietal cortex that has been related to the shielding of thoughts against irrelevant information, is less strongly connected to the rest of the network.

The different topological embedding of these regions into the brain network could make it easier for smarter persons to differentiate between important and irrelevant information – which would be advantageous for many cognitive challenges. This is similar to a social network which consists of multiple sub-networks, for example: families, or circles of friends. Within these sub-networks or modules, the members of one family are more strongly interconnected than they are with people from other families or circles of friends.

Human brain is functionally organised in a very similar way. There are sub-networks of brain regions – modules that are more strongly interconnected among themselves while they have weaker connections to brain regions from other modules. Researchers examined whether the role of specific brain regions for communication within and among brain modules varies with individual differences in intelligence- whether a specific brain region supports the information exchange within their more than information exchange with other families, and how this relates to individual differences in intelligence.
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