The order and timing of II/III layer activation determine the magnitude and direction of the plastic changes in layer V of the primary motor cortex

The primary motor cortex (MO-p) is a region with a very complex and varied circuitry. It receives inputs from thalamus and other cortical regions, and its outputs goes to cortex, subcortical regions, and medulla, controlling numerous aspects of the motor behavior, as the coordination or the motor learning. The disruption of this system can lead to develop some motor diseases. It is known that glutamatergic neurons of layer II/III project to pyramidal neurons of layer V, putting the inputs and the outputs which goes to medulla and lower brainstem together. However, the plasticity of these connections is poorly understood.Here, we employed electrophysiological recordings to assess the plastic capacity of the connections between these neurons of layer II and. For this purpose, we used the Spike Timing Dependent Plasticity (STDP) paradigm, where the temporal coincidence of a pre- and post-synaptic stimulus leads to a potentiation or a depression of the synapsis. We have observed a variation of plasticity depending on the order and time of the presynaptic glutamate release and postsynaptic backpropagated action potentials, switching the response of the system to the STDP protocol. These results highlight the existence of a critical temporal window for the development of plastic changes in the MO-p.