Brain plasticity: the themes and case studies of neuro-biophysics

After a brief overview of the current status of our understanding of synaptic plasticity and sprouting in the brain, sprouting in the cat red nucleus was described in detail as a model system. As the basis of our investigations of sprouting in the RN, light and electron microscopic studies, together with computer analysis of dendritic geometry by a digital image processing system, were reported. Electrophysiology using both in vivo and in vitro preparations was described; a model study using Rall's mathematical neuron model was presented. Based on these data, lesion-induced sprouting and the formation of functional synapses at an early developmental stage were investigated. This was compared with lesion-induced sprouting in adults. The synaptic transmission of synapses newly-formed by sprouting was investigated in detail. It was also reported that sprouting takes place in the absence of lesions to central neurons, in a preparation where peripheral flexor and extensor nerves were surgically crossed (cross-innervation). Finally, an attempt to correlate cortico-rubral sprouting with behavioral plasticity, using classical conditioning, was presented.