The neurobiology of motor skill learning: Structural adaptation within sensorimotor regions of the rat brain

Adaptations in neuronal connectivity are believed to mediate the adaptations in behavior that arise from experience. The following series of experiments examined how the acquisition of complex motor skill affected the structure of neurons within sensorimotor regions of the rat brain. Animals in the Acrobatic Condition (AC) were trained to traverse a complex series of obstacles that required a significant amount of motor coordination to complete. Voluntary exercise (VX) animals were housed in cages that allowed for unlimited access to a running wheel, while Motor Control (MC) animals were forced to traverse a flat, obstacle free runway equal in length to the AC task. Finally, animals in the Inactive Condition (IC) received no motor training.; Within the cerebellar cortex, AC animals had significantly more synapses/Purkinje cell than the VX, MC and IC animals. Further examination revealed that this increase was accomplished primarily through increasing the number of single parallel fiber varicosities making multiple synaptic contacts with a Purkinje cell. Further work demonstrated the stellate interneurons of the AC animals also had significantly more dendritic material than those of the MC animals. The learning dependent increase in synapse number and glial volume within the cerebellar cortex was also shown to persist for at least four weeks without continued training. Within the lateral cerebellar nucleus, motor skill learning did not lead to any significant change in the number of synapses.; A second series of studies revealed the AC animals to have significantly more synapses/neuron within layer II/III of the motor cortex than control animals and that this difference was dependent on the amount of training the animals received. Changes in synapse morphology were also observed in the AC animals that included significant increases in postsynaptic density (PSD) length, number of synapses with perforated PSDs as well as number of synapses forming multiple synaptic contacts. Finally, an examination of the gross morphology of the red nucleus revealed no significant change in neuronal density which is believed to indicate no overall change in neuronal morphology.