Escitalopram is an anti-depressant drug sold under the brand name Lexapro, and researchers have discovered it affects human brains faster than once believed.

The serotonin reuptake inhibitor (SSRI) was found to create functional changes to human brains, even after a single dose. Architectural changes in connections between nerve cells in the brain were seen within three hours of consuming the drug.

"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," Julia Sacher from the Max Planck Institute for Human Cognitive and Brain Sciences, said.

Escitalopram and other SSRI's have been carefully studied by researchers, but medical investigators are still uncertain how they work. Most scientists involved in the research recognize that the drug creates changes in human brains, but these medicines were thought to take weeks to work. This new study is the first to show such short-term actions on the architecture of neural connections in the brain.

Researchers utilized a brain scanner to examine the brains of subjects as they let their minds wander for 15 minutes. Oxygen utilization was mapped in a 3D virtual diagram, in an effort to study functions within the organ. Connections between tiny blocks of neurons called voxels were examined, searching for any effect caused by the drug. Changes were pronounced in people taking SSRI's for the first time.

Connections in the cerebellum, which helps to direct motor control, and the thalamus, which is involved in both motor control and sensory perception, increased after using the drug. Other parts of the brain saw connections decreased after consumption of the medicine.

Concentrations of serotonin, a chemical in brains known to regulate moods, is increased by the use of this class of drugs, but rapid changes in the structure of brains were unexpected by researchers.

Lexapro was first released to the public in 2002, in order to treat general anxiety disorder, as well as severe depression. Side effects include headaches, insomnia, nausea and suicidal thoughts.

Future research on the drug will involve studying brains of patients who do not respond to SSRI's, to see how they differ from those who have a positive reaction from the drug.

This study "could help to better predict who will benefit from this kind of antidepressant versus some other form of therapy. 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," Sacher told the press.

Investigation of and its role in changing the structure of human brains was profiled in the journal Current Biology.