Magnetic control of cortical pyramidal neuron activity using a micro-coil

Transcranial magnetic stimulation (TMS) is a noninvasive method that modulates neural activity in the central nervous systems. It has been widely used both to study basic structure and function of the nervous system as well as to treat neurological diseases, i.e. clinical depression. However, ongoing advancements have been hampered by a lack of understanding as to the mechanisms by which TMS modulates neural activity. Here, we report responses from two distinct types of cortical pyramidal neurons to magnetic stimulation arising from a sub-millimeter coil. Cell attached patch clamps were used to record neural activity of layer 5 pyramidal neurons of the prefrontal cortex (PFC) in the in vitro mouse brain slice preparation. We found that both types of L5 pyramidal neurons were strongly excited by 10 Hz repetitive simulation when the coil was positioned on distal apical dendrites (i.e. layer 1-4). However, the excitation switched into strong inhibition when the coil was positioned close to the soma (i.e. close to layer 5) for one type of neuron, but not for the other type. These results suggest that responses of the L5 pyramidal neurons of the PFC are heterogeneous depending on the cell-type, and further, that this type of approach may be useful for studying the cellular level mechanisms underlying repetitive TMS.