It is widely believed that patients using antidepressants need to take the medication for around 4-6 weeks before they notice any improvement in depressive symptoms, but a new study claims a single dose can trigger significant changes in the brain within hours.

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Researchers say a single dose of SSRI triggered brain changes in healthy participants within 3 hours.

The research team, including co-author Dr. Julia Sacher of the Max Planck Institute for Human Cognitive and Brain Sciences in Germany, publish their findings in the journal Current Biology.

Around 1 in 10 adults report some form of depression, and 1 in 10 people with depression aged 12 years or older take antidepressants for the condition.

Selective serotonin reuptake inhibitors (SSRIs) are some of the most commonly prescribed antidepressants. Brand names of such drugs include Prozac, Zoloft and Lexapro. The drugs are believed to alter brain connectivity and boost production of a neurotransmitter called serotonin, which is believed to play a role in maintaining mood balance.

“However,” the researchers say, “the full scope of serotonergic action on functional connectivity in the human brain has not been explored.”

For their study, Dr. Sacher and colleagues set out to see how SSRIs worked in the brains of 22 healthy participants.

Each subject underwent a 15-minute brain scan that measured the oxygenation of blood flow in the brain. They were then given a single dose of an SSRI known as escitalopram (Lexapro), before undergoing another brain scan a few hours later.

The team then measured the number of connections between voxels in the brain – the equivalent to pixels in an image – to create a 3D image of each brain. The 3D images of brain scans before and after SSRI usage were compared.

When analyzing the network of the whole brain, the researchers found that the SSRI reduced intrinsic connectivity levels in most areas of the brain within 3 hours. However, it increased connectivity in two specific brain regions – the cerebellum (involved in voluntary movement) and the thalamus (involved in sensory perception and motor function).

“We were not expecting the SSRI to have such a prominent effect on such a short timescale or for the resulting signal to encompass the entire brain,” says Dr. Sacher. These findings, the researchers say, suggest that SSRIs may reorganize the brain early to reduce depressive symptoms later.

Talking to Medical News Today, Dr. Sacher said:

Our findings reveal that SSRIs affect brain connectivity right away and that these changes encompass the entire brain. It is possible that these connectivity changes are the first step in remodeling the brain, as there is evidence from other experiments that such functional connectivity changes can reflect neuroplastic change. However, additional research will be required to further unravel these mechanisms of neuroplasticity.”

Such findings may lead to a better understanding of which patients with depression respond to SSRIs and which do not, Dr. Sacher says, adding:

“The hope that we have is that ultimately our work will help to guide better treatment decisions and tailor individualized therapy for patients suffering from depression.”

The team now plans to move toward clinical trials and hopes to compare the brain connectivity of depression patients who have responded to treatment with those who have not.

“We would like to compare the acute, subacute and chronic effects of SSRIs on the functional architecture of the brain in health and disease,” Dr. Sacher told us. “Ideally, we would also like to include more diverse antidepressant treatment strategies in our studies, such as cognitive therapy, sleep deprivation or light-therapy, and investigate whether we can identify characteristic patterns in functional connectivity for each treatment option.”

Medical News Today recently reported on a study published in the journal Science, in which scientists claim they have identified an area of the brain that controls mood disorders.