A chemical in the brain that allows messages to pass between nerve cells could shed a light on disorders – such as anxiety, post-traumatic stress disorder (PTSD), depression and schizophrenia, scientists say.
Researchers from the University of Cambridge have found that gamma-amino butyric acid (Gaba) – a neurotransmitter within the ‘memory’ region of the brain – is also responsible for suppressing unwanted thoughts as well as being a chemical messenger.
They now want to understand more about the mechanism behind how the brain inhibits unwelcome thoughts or memories in the hope that it might be able to explain why those living with mental disorders “experience persistent intrusive thoughts when these circuits go awry”.
Professor Michael Anderson, from the Medical Research Council Cognition and Brain Sciences Unit at the University of Cambridge, said: “Our ability to control our thoughts is fundamental to our wellbeing.
“When this capacity breaks down, it causes some of the most debilitating symptoms of psychiatric diseases: intrusive memories, images, hallucinations, ruminations and pathological and persistent worries.
“These are all key symptoms of mental illnesses such as PTSD, schizophrenia, depression and anxiety.”
A team of researchers led by Dr Taylor Schmitz and Professor Anderson set volunteers tasks involving memory recall and inhibition.
The participants were asked to learn to associate a series of words with a paired but otherwise unconnected word, for example ordeal/roach and moss/north.
Using the Think/No-Think procedure – a series of tasks designed to understand how the brain inhibits thoughts – the participants were asked to recall or suppress words based on colour cues.
For example, when shown ‘ordeal’ in red, the participants are asked to stare at the word but to stop themselves thinking about the associated thought ‘roach’.
Conversely, when presented with the word ‘moss’ in green, the test subjects were asked to recall the associated word ‘north’.
The researchers used a combination of functional magnetic resonance imaging (fMRI) and magnetic resonance spectroscopy to scan the brains of the participants.
They found that Gaba concentrations in the hippocampus – a region that regulates emotions and is associated with long-term memory – predicts people’s ability to block thoughts and memories from returning.
They also found that the prefrontal cortex – the brain’s command centre – acts as a “master regulator”, controlling other brain regions, which includes the hippocampus.
Professor Anderson said: “What’s exciting about this is that now we’re getting very specific.
“Where previous research has focused on the prefrontal cortex – the command centre – we’ve shown that this is an incomplete picture.
“Inhibiting unwanted thoughts is as much about the cells within the hippocampus – the ‘boots on the ground’ that receive commands from the prefrontal cortex.
“If an army’s foot-soldiers are poorly equipped, then its commanders’ orders cannot be implemented well.”
The researchers say this discovery may answer one of the long-standing questions about schizophrenia. Previous studies have shown that people affected by schizophrenia have ‘hyperactive’ hippocampi, which “correlates with intrusive symptoms such as hallucinations”.
Professor Anderson believes their findings could offer a new approach to tackling intrusive thoughts in these disorders.
He said: “Most of the focus has been on improving functioning of the prefrontal cortex.
“But our study suggests that if you could improve Gaba activity within the hippocampus, this may help people to stop unwanted and intrusive thoughts.”
The research is published in the journal Nature Communications.