However, this is not the only consequence of consuming the drug. Researchers have found that MDMA has affects on the cognitive processes – such as thinking and memory. Studies have confirmed that MDMA users suffer poorer memory and impaired thought processes, compared with people who haven't tried the drug (Morgan, 2000). It has also been found to interfere with processes such as sleep cycles (Allen et al, 1993). However, the problem with ascribing these effects to ecstasy is that people who take MDMA, it can not be ruled out that these people frequently stay up all night dancing and may also take other drugs. To investigate the isolated effects of ecstasy, Ricaurte et al (2002), gave squirrel monkeys and baboons doses of the drug that they claimed were similar to those taken by some clubbers in a single night. This dose administrated to the animals was found to completely destroy neurons that produce the neurotransmitter dopamine, and led to a condition similar to Parkinson's disease. Furthermore, 2 out of the ten animals died. Ricaurte et al (2002) conclude that "A young individual who sustains injury to these dopamine cells and depletes their reserve may be at greater risk of parkinsonism." It is widely-accepted from literature reviews that brain dopamine declines with age; therefore, taking the drug Ecstasy aids to speed up the aging process and susceptibility for developing diseases such a Parkinson’s.