Claustrum is a thin sheet of gray matter located between external and extreme capsules of lentiform nucleus (basal ganglia). Functions of claustrum are still not clear. Positron emission tomography (PET) studies have been helpful in measuring the cerebral blood flow responses, as reflection of regional neuronal activity to various sensory stimuli. With PET it was seen that claustrum of healthy males displayed one of the highest activity with visual sexual stimuli. Bilateral activation of claustrum was seen to be involved in motivational processed, which direct behavior to a sexual goal.