Plastic changes to dendritic spines on layer V pyramidal neurons are involved in the rectifying role of the prefrontal cortex during the fast period of motor learning

Abstract

The prefrontal cortex participates in the rectification of information related to motor activity that favors motor learning. Dendritic spine plasticity is involved in the modifications of motor patterns that underlie both motor activity and motor learning. To study this association in more detail, adult male rats were trained over six days in an acrobatic motor learning paradigm and they were subjected to a behavioral evaluation on each day of training. Also, a Golgi-based morphological study was carried out to determine the spine density and the proportion of the different spine types. In the learning paradigm, the number of errors diminished as motor training progressed. Concomitantly, spine density increased on days 1 and 3 of training, particularly reflecting an increase in the proportion of thin (day 1), stubby (day 1) and branched (days 1, 2 and 5) spines. Conversely, mushroom spines were less prevalent than in the control rats on days 5 and 6, as were stubby spines on day 6, together suggesting that this plasticity might enhance motor learning. The increase in stubby spines on day 1 suggests a regulation of excitability related to the changes in synaptic input to the prefrontal cortex. The plasticity to thin spines observed during the first 3 days of training could be related to the active rectification induced by the information relayed to the prefrontal cortex -as the behavioral findings indeed showed-, which in turn could be linked to the lower proportion of mushroom and stubby spines seen in the last days of training.