Learning-induced LTP in neocortex

The hypothesis that learning occurs through long-term potentiation (LTP)- a nd long-term depression (LTD)-like mechanisms is widely held but unproven. This hypothesis makes three assumptions: Synapses are modifiable, they modi fy with learning, and they strengthen through an LTP-like mechanism. We pre viously established the ability for synaptic modification and a synaptic st rengthening with motor skill learning in horizontal connections of the rat motor cortex (MI), Here we investigated whether learning strengthened these connections through LTP. We demonstrated that synapses in the trained MI w ere near the ceiling of their modification range, compared with the untrain ed MI, but the range of synaptic modification was not affected by learning. In the trained MI, LTP was markedly reduced and LTD was enhanced. These re sults are consistent with the use of LTP to strengthen synapses during lear ning.