You may know that low levels of the brain chemical serotonin are often associated with depression. However, it's been difficult for scientists to measure its natural fluctuations. A recent study provides the first glimpse at monitoring serotonin in humans in real-time. Several patients scheduled for brain surgery without full anesthesia volunteered to have a special microelectrode inserted during their procedure. The device tracked their serotonin levels while they performed a psychological test following the movement of a random dot. In addition to providing a breakthrough in measuring serotonin, this study by neuroscientists at University College London produced several other important findings. It confirmed serotonin's involvement in a wide range of cognitive functions and showed how it affects different parts of the brain. These findings could help create more effective treatments for many conditions, including depression and Parkinson's Disease.