Although Parkinson's disease is most commonly viewed as a "movement disorder," scientists have found that the disease also causes widespread abnormalities in touch and vision - effects that have now been verified using functional magnetic resonance imaging (fMRI) of the brain.
The new findings, by scientists at Emory University School of Medicine and Zhejiang University Medical School in Hangzhou China, were presented on Oct. 17 at the Society for Neuroscience meeting in Atlanta.
Scientists studying Parkinson's disease (PD) previously have focused on the brain's motor and premotor cortex, but not the somatosensory or the visual cortex. But Emory neurologist Krish Sathian, MD, PhD, and colleagues had earlier discovered, through tests of tactile ability, that PD patients have sensory problems with touch. They designed a study using fMRI to investigate the brain changes underlying these sensory abnormalities.
Dr. Sathian's research group studied six patients with moderately advanced PD and six age-matched healthy controls. After documenting the typical movement problems of PD and ruling out dementia and nerve problems in the PD patients, they administered a common test of tactile ability to both groups, asking the participants to use their fingers to distinguish the orientation of ridges and grooves on plastic gratings. At the same time, they conducted a brain-scanning study using fMRI. This technology measures activations of neurons in different areas of the brain by means of variations in blood flow as an individual does a particular task.
The fMRI scans showed that the PD patients had much less activation of the somatosensory areas in the brain's cortex than did the healthy controls. The scientists also were surprised to find similar widespread differences in the visual cortex, although the task involved touch, not vision.
"Our finding that the visual cortex is affected in Parkinson's disease, while surprising, makes sense given that our laboratory and many others have shown previously that areas of the brain's visual cortex are intimately involved in the sense of touch," Dr. Sathian notes. "Although the reasons for this are uncertain, they may involve a process of mental visualization of the tactile stimuli and may also reflect a multisensory capability of the visual cortex."
Dr. Sathian believes the study shows that the traditional boundaries between brain systems involved in touch and vision, and between those involved in sensation and movement, are artificial constructs that break down with more in-depth study. From a practical standpoint, it shows that patients with PD and other movement disorders have considerable problems in addition to movement control.
"These problems need to be appreciated in caring for these patients and in designing newer strategies for treatment and rehabilitation," Dr. Sathian emphasizes.