Study finds drug hurts memory

University researchers discovered this summer that your brain, like the rest of your body, can have too much of a good thing. The drug bromocriptine is known to improve cognitive abilities in patients with brain damage, but a recent study at the Hospital of the University of Pennsylvania found that the substance can actually hinder a healthy subject's performance on memory tests. The fickle drug works by masquerading as the neurotransmitter dopamine, a molecule in the brain which can affect behavior and memory. Dopamine is one of the substances linked to cocaine addiction. "As far as [brain] receptors are concerned, bromocriptine looks like dopamine," said Dan Kimberg, a postdoctoral fellow in neurology and the lead author of an article on the research appearing in the November issue of NeuroReport. The more dopamine you have in your brain, the better you're likely to do on a wide array of tests which measure working memory -- but only to a point. "After running a couple of pilot studies we noticed that subjects who did better on a reading memory test scored worse when performing the test a few hours after taking bromocriptine," Kimberg said in a written statement. He added that working memory "means very, very short-term," explaining that the ability to recall academic material or a birthday is associated with long-term memory, which resides in another area of the brain. The memory tests were administered on Macintosh computers and measured a subject's ability to remember simple visual stimuli, like the location of a black dot on a screen or the last word in a sentence. The results of the study suggest that given tasks require some ideal amount of dopamine, although the exact amounts have not yet been determined. "I think the response of the drug is dependent upon particular task parameters," Kimberg said. But don't start asking for prescriptions quite yet. "Nothing in this research has direct clinical applications," he stressed. Bromocriptine, a drug best known for its use in patients suffering from Parkinson's disease, causes several adverse side effects such as nausea and vomiting. "The effects of the drug are short-lived," Kimberg added, explaining that bromocriptine usually wears off completely after about 10 hours. Now, Kimberg and HUP neurologist Mark D'Esposito are testing how bromocriptine affects blood flow to different areas of the brain. The researchers are using a special type of MRI scanner, which allows them to observe certain features of the brain while the subject performs memory-related tasks. Kimberg's team is also examining the effects of another dopamine-like drug which reaches a broader range of receptors in the brain than bromocriptine. "It's going to be a big, ugly study," he said, explaining that each subject will take part in a series of 14 tests of working memory.