| These results suggest that effort sensation critically involves the basal ganglia. This signal
and/or the integration of sensory feed-back which generates what is experienced as the sense of effort, would be altered in
HD. |
In this study, we investigated sensation of effort in Huntington
disease (HD). We tested the hypothesis that the basal ganglia are involved in processing effort sensation.
The experimental
paradigm consisted in a contralateral matching procedure where normal subjects (N=6) and HD patients (N=6) were required to
lift a reference weight with their non-dominant index, and then compare the target-weight with variable weights lifted by
the dominant index.
Two kinds of sequences were administered:
(1) increasing, where the first weight was lighter than the
reference weight and progressively increased in 20g steps,
(2) decreasing, where trials started with a heavier weight and
progressively decreased.
We calculated the discrimination threshold (DT) across sequences
as the weight for which the subject's response changed
sign.
The difference between the higher and the lower threshold was
defined as "uncertain area". |
We predicted that controls should over-estimate the reference
weight lifted by their non-dominant hand because the same effort produces more force when applied to stronger muscles.
If the basal ganglia mediates sensation of
effort, patients'
capability to discriminate weights should be degraded.
As expected, normal subjects overestimated the reference weight
lifted by their non-dominant index and showed a restricted uncertain area, thus, indicating that were able to discriminate
minimal differences in generated forces.
By contrast, patients with HD under-estimated the reference weight lifted
by their non-dominant hand and showed a broad uncertain area, thus, demonstrating that they could detect only important differences
in the matched efforts.
These results suggest that effort sensation critically involves the basal ganglia. In normal
conditions, in parallel with the efferent command of force, an efferent copy reflecting the magnitude of the voluntary motor
command is transmitted to sensory centres.
This signal and/or the integration of sensory feedback which
generates what is exper-ienced as the sense of effort, would be altered in HD.
|
