The intensity of brain activity can be measured by the colors. The most activity is the red, followed by yellow, green, and finally blue. The depressed brain is in a very low activity state almost like hibernation. You can see why mental concentration is not very good in someone who is depressed. The PET scanner is used mainly in research and not specific or sensitive enough to be used in everyday medical practices.
Antidepressants work by increasing the amount of neurotransmitters available at the synapse.
This ultimately results in improved communication between the neurons. Diagnosis Unfortunately, there is no specific blood test to detect a deficiency of seratonin in the brain. Several blood and urine tests have been tested, but have not proven useful thus far. PET scanning is being done at research centers, but is not widely available. Depression actually causes a decrease in the metabolic activity of the brain.