A study undertaken at the Center for Applied Medical Research of the University of Navarra, and published in the scientific journal Neuroimage, identifies the brain areas activated in a test of sensory perception. The most immediate and automatic responses of test subjects to certain tactile and auditory stimuli produce an activation of the so-called putamen. This cerebral nucleus, which regulates muscle tone and learned and automatic movements such as typewriting, is affected during the early stages of Parkinson's Disease. Therefore, the results of the study may help in diagnosing this disease in its earliest stages. The authors of the study are Dr. María A. Pastor, a neurologist at the Center for Applied Medical Research (CIMA) of the University of Navarra and the University Hospital, as well as scientists from the Institute of Neurology of University College London.

Dr. Pastor explained that if a healthy person receives two successive stimuli -such as contact on the skin, an auditory signal or the flash of a light- they may be perceived either as separate signals, or else as simultaneous if they occur within an extremely brief interval. If the time interval is very large or very small, the perception of the subject is clearer, and therefore their response is more secure. Between these two extremes, the perceptions of the test subjects are less exact. If these stimuli are presented to a subject monitored with a Functional Magnetic Resonance scanner, it is possible to visualize the brain areas involved in this kind of perception.

From 60 to 40 frames per second

According to the neurologist of the CIMA and the University Hospital, patients with Parkinson's Disease need a larger interval between the two stimuli in order to be sure that they are separate signals. "For example, a normal movie is projected at 60 frames per second. If we reduce the frame rate, normal persons will perceive it as flickering. A person who suffers from Parkinson's Disease does not perceive this difference, and can watch a movie without sensing flicker with a frame rate as slow as 40 frames per second."

The results published in Neuroimage reveal that the putamen is the area of the brain which is directly related to responses with higher certainty: very brief intervals which result in the two stimuli being perceived as a single signal, or long intervals which result in their being perceived as separate. "This test will help us to detect Parkinson's Disease during its earliest stages," concluded María A. Pastor.