Serotonin is a neurotransmitter which plays different roles in our brain, and can have effects such as sleep, arousal levels and emotion. The study was conducted by two researchers, Kasamatsu and Hirai, at Tokyo's University in 1999. The aim of the study was to find out how the sensory deprivation affects the brain and later on, the human behavior. In order to achieve their aim, the researchers examined a group of Buddhist monks who went to a religious journey to a holy mountain in Japan. This type of study is called naturalistic observation.
The monks were set to go to a 72 hour journey, during which they didn't speak to each other, had nothing to drink or eat and were exposed to the cold weather. They were supposed to be there for 72 hours, meaning 3 days, but after about 48 hours there were already some unusual findings. The monks started having hallucinations of their ancestors or simply experienced a presence by their sides. The researchers had already taken blood samples of the monks before they left for their trip, but they took another blood sample as soon as they had experienced hallucinations. The findings of the study were that the serotonin levels had increased in the brains of the monks. The higher levels of serotonin were able to activate the parts of the brain named the hypothalamus and the frontal cortex which resulted in hallucinations. The researchers concluded that the feeling of not having something, such as food or drink had caused the release of serotonin which changed the way the monks behaved and have seen the world through different eyes.
The strength of this study is that since actual people were used for the experiment, the results can be generalized for humans. If the experiment was performed on animals, it would have been harder to apply the findings to human beings. The disadvantage is that people might have had to suffer (not eat or drink) and had no contact with each other. They