The Journal of Neuroscience, June 15, 2002, 22(12):5198-5203
Cognitive Slowing in Parkinson's Disease: A Behavioral
Evaluation Independent of Motor Slowing
Nobukatsu
Sawamoto1,
Manabu
Honda1, 2, 3,
Takashi
Hanakawa1,
Hidenao
Fukuyama1, and
Hiroshi
Shibasaki1
1 Department of Brain Pathophysiology, Human Brain
Research Center, Kyoto University Graduate School of Medicine,
Kyoto 606-8507, Japan, 2 Laboratory of Cerebral
Integration, National Institute for Physiological Sciences,
Okazaki 444-8585, Japan, and 3 PRESTO, Japan
Science and Technology Corporation, Kawaguchi 332-0012, Japan
Parkinson's disease (PD) is attributable primarily to depletion of
dopamine in the basal ganglia, but the full effects of this depletion
are unknown. It is well known that PD involves motor slowing, and
although it is not easy to distinguish between the motor and cognitive
components of behavior, clinical observations suggest that cognitive
processing may also be compromised. However, it remains unclear whether
such cognitive involvement exists, and if so, to what extent. Previous
studies of cognitive slowing in PD have yielded conflicting
results. This may be attributable to variations in experimental
procedures, because most of the experiments used reaction-time tasks,
which are inevitably confounded by motor components. In the present
study, we evaluated the speed of cognitive processing in patients with
PD without bradykinesia as a variable. We developed a mental-operation
task that required serial updating of mental representations in
response to a series of visual stimuli. By changing the speed of visual
presentation and evaluating performance accuracy, the speed of
cognitive processing was assessed independently of motor slowing.
Cognitive impairment in PD became evident when higher speeds of
cognitive processing (verbal more so than spatial) were required. In
addition, cognitive slowing and motor slowing were significantly
correlated. The results of the present study suggest that slowing in PD
is not restricted to the motor domain but can be generally observed in
other domains of behavior, including cognitive mental operations.
Key words:
Parkinson's disease; mental-operation task; reaction-time task; cognitive slowing; bradykinesia; cognitive-motor
interaction
Copyright © 2002 Society for Neuroscience 0270-6474/02/22125198-06$05.00/0
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