Many studies have been developed using brain imaging methods to investigate psychological disorders. On the other hand, there are many studies that make use of virtual reality (VR) to simulate a real condition during psychological treatments. In this research, we plan to analyze brain activity during the exposure to a virtual environment related to phobias. Our first goal is to study the possibility of activating brain areas related to phobias, specifically phobias to small animals (spiders and cockroaches), using virtual reality as stimulus, while the patient is inside a functional magnetic resonance imaging (fMRI) machine. The second goal of the research is to analyze if there are differences in the activated areas after patients have followed a psychological treatment for this specific phobia. That is why two different sessions with fMRI will be performed, before and after an intensive treatment for the phobia. In the fMRI room, participants will wear special glasses to visualize the VR environments in which they have to navigate (using also a joystick adapted to fMRI). They will have to perform some tasks while being exposed to the phobic stimuli. The VR environment used in the fMRI sessions has three different conditions: first, a clean room without spiders or cockroaches; second, the same room, but dirty and disordered (giving the sensation of having small animals, although actually there are none); third, the same dirty room but having spiders and cockroaches. It is our hypothesis that the patients will get anxious in the situation in which it is possible that the animal appears and the patterns of brain activation will be different in this condition.