Santa Cruz
FOR neuroscientists, it is like learning that the Pope is a protestant.
American researchers claim to have overturned the century-old belief that the
area of the brain called the cerebellum coordinates muscle movements. They argue
that the cerebellum, tucked away at the back of the brain, processes sensory
information.
Patients with cerebellar damage show no obvious sensory impairment, but their
movements become awkward. But movement control needs sensory information, says
Lawrence Parsons of the University of Texas Health Science Center in San
Antonio. And most studies cannot tell which of the two tasks the cerebellum is
doing.
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Parsons and his colleagues used functional magnetic resonance imaging鈥攁
technique that detects changes in blood flow in the brain, and hence brain
activity鈥攁s human volunteers performed a variety of tasks. A purely
sensory task鈥攄etecting sandpaper rubbed across the subject鈥檚
hand鈥攍ed to a mild increase in blood flow in the cerebellum鈥檚 dentate
nucleus, the region that funnels information to the rest of the brain.
In contrast, a simple motor task鈥攑icking up a small ball鈥攑roduced
no significant activation. However, when the subject was asked to pick up a ball
in each hand and judge whether the two were identical, the dentate nucleus
sprang into vigorous action (Science, vol 272, p 545).
This suggests that the cerebellum鈥檚 main role is in processing sensory
information. But Farrel Robinson of the University of Washington in Seattle
notes that the comparative task involved muscle movements and high-level thought
processes. He argues that Parsons鈥� team has still not fully teased apart the
tangle. 鈥淚t looks like the cerebellum may be dedicated to more than pure
movement,鈥� says Robinson. 鈥淏ut the question is, to what?鈥�