Recent studies have provided evidence that training, differential use and alterations
in behavior cause plastic reorganizational changes in the human central nervous system.
However, no report addressed the issue of how immobilization and thereby sensorimotor
restriction caused tactile behavioral changes besides the previously described neural
changes in the human motor system. To investigate the implication of a several-week
immobilization induced by wearing a cast due to bone fractures of the hand, we tested
spatial 2-point discrimination abilities of the healthy and immobilized hand during
immobilization. To study the reversibility of the observed behavioral effects, subjects
were additionally tested 2 weeks after removal of the cast. Here we found that, in
spite of large variations in age and duration of immobilization, the thresholds measured
for the index finger of the affected hand were significantly higher than the thresholds
of the intact hand, indicating impaired discrimination abilities on the affected hand.
Based on these findings, we then asked whether enforced disuse of the affected hand
accompanied by restricted tactile acuity in cast patients is closely related to the
duration of wearing a cast. We therefore correlated side-to-side differences between
both IF with the individual duration of immobilization revealing a strong positive
correlation. Accordingly, little impairment of discrimination abilities was associated
with short-term immobilization. On the other hand, those subjects with long-term immobilization
also had the highest discrimination thresholds and therefore the highest restriction
of their affected hand. Retesting of discrimination behavior 2 weeks after removal
of the cast indicated the reversibility of the observed effects. We conclude that
enforced disuse over several weeks impairs discrimination abilities, whereby the impairment
was reversible within 2 weeks. Moreover, functional MRI was performed in cast patients
to test not only behavioral but also cortical changes within primary somatosensory
cortex (SI) due to several weeks of immobilization.
