An Investigation of the Role of the Corpus Callosum in the Lateralised Skilled Reaching Task

Abstract

Long-term potentiation (LTP), a long-lasting enhancement of synaptic efficacy, is believed to be the mechanism by which memory storage occurs in the brain. Several studies have shown that LTP can be induced in various neural sites, not only by electrical stimulation, but also as a result of behavioural modifications. It has previously been shown that LTP in the primary motor cortex accompanies motor skill learning. One study showed that potentiation occurred following training on a lateralised skilled reaching task. In this task, animals are trained to use only one paw to grasp a small food pellet. An interesting finding that has been uncovered from these studies is that, although only one hemisphere actively participates in the task (the trained hemisphere), the other hemisphere (untrained hemisphere) also shows potentiation. This has led to the hypothesis that the corpus callosum is involved in the transfer of information from one hemisphere to another during training on the reaching task. The nature of this communication, however, is unknown. Two possibilities were considered. The first was that the callosum transfers information that allows the animal to maintain its balance while the reaching paw is elevated. Careful observation of videorecording made while animals performed the task however, failed to reveal any deficits in balance in animals that had undergone a callosal transection. A second possibility is that the corpus callosum transfers information about the task from the trained to the untrained hemisphere such that, even though it does not actively participate in the task, the untrained paw may "know" how to perform above chance level. Analysis of the rate of successful reaching with the untrained paw revealed no advantage for normal animals over transected animals. Work is however, currently underway to increase the number of animals in the study in order to obtain a more conclusive result.