Bliem Barbara, Frombach Elke, Ragert Patrick, Knossalla Frauke, Woitalla Dirk, Tegenthoff Martin, Dinse Hubert R
Department for Neuroinformatics, Theoretical Biology, Exp. Neurobiology Lab, Ruhr-University Bochum, Bochum, Germany.
Exp Brain Res. 2007 Jul;181(1):131-7. doi: 10.1007/s00221-007-0912-5. Epub 2007 Mar 8.
As shown in animal experiments, dopaminergic mechanisms participate in N-methyl-D-aspartate (NMDA) receptor-dependent neuroplasticity. Dopamine is thought to play a similar role in humans, where it influences learning and memory. Here, we tested the dopaminergic action on learning in the tactile domain. To induce tactile non-associative learning, we applied a tactile coactivation protocol, which is known to improve tactile two-point discrimination of the stimulated finger. We studied the influence of a single oral dose of levodopa (25, 50, 100, 250 or 350 mg) administered preceding the coactivation protocol on changes in tactile performance in different groups of subjects. In addition, 3 x 100 mg levodopa was administered over a time period of 3 h in another group. Under placebo conditions, tactile two-point discrimination was improved on the coactivated index finger. Similar improvement was found when 25, 50 and 250 mg levodopa was applied. On the contrary, tactile improvement was completely eliminated by 1 x 100 and 3 x 100 mg levodopa. No drug effects were found on the left index finger indicating that the drug had no effect on performance per se. In contrast to previous findings in the motor and speech domain, we found that the administration of levodopa exerts either no or even negative effects on non-associative learning in the human somatosensory system. Whenever levodopa is used in neurorehabilitative context, it has to be kept in mind that beneficial effects in the motor or speech domain cannot be easily generalized to other systems.
动物实验表明，多巴胺能机制参与了N-甲基-D-天冬氨酸（NMDA）受体依赖性神经可塑性。多巴胺在人类中被认为起着类似的作用，它会影响学习和记忆。在此，我们测试了多巴胺能对触觉领域学习的作用。为了诱导触觉非联想学习，我们采用了一种触觉共激活方案，已知该方案可改善被刺激手指的两点辨别能力。我们研究了在共激活方案之前单次口服左旋多巴（25、50、100、250或350毫克）对不同组受试者触觉表现变化的影响。此外，另一组在3小时内服用了3×100毫克的左旋多巴。在安慰剂条件下，共激活的食指两点辨别能力得到改善。应用25、50和250毫克左旋多巴时也发现了类似的改善。相反，1×100毫克和3×100毫克的左旋多巴完全消除了触觉改善。在左手食指上未发现药物作用，表明药物本身对表现没有影响。与之前在运动和言语领域的发现相反，我们发现左旋多巴的给药对人类体感系统的非联想学习要么没有影响，甚至有负面影响。每当在神经康复环境中使用左旋多巴时，必须记住，在运动或言语领域的有益效果不能轻易推广到其他系统。
