As a result, stimulation causes a sparse response at antidromically activated cell bodies that can be more distant from the electrode tip. It is well established that sodium channels are mainly concentrated in axonal segments ( 10) with electrical stimulation widely viewed to be through these axonal terminals ( 7). However, more extensive work combining electrical stimulation with high spatial modalities such as two-photon (2p) imaging and functional magnetic resonance imaging has since showed that this high spatial control is not possible since a larger network of neurons are depolarized transsynaptically ( 7– 9). Early cortical stimulation models estimated that cell bodies that overlap within the radius of stimulation would be activated and the field of effect would be directly determined by current amplitude. In this case, it has been shown that the current density inside the brain shows a circular distribution around the electrode that exponentially decays as a function of distance ( 5, 6).
By leveraging surface arrays that are optically transparent with PEDOT:PSS local interconnects and integrated with depth electrodes, we are able to combine surface stimulation and recording with calcium imaging and depth recording to demonstrate these spatial limits of bidirectional communication with pyramidal neurons in mouse visual cortex both laterally and at depth from the surface.Įlectrical stimulation is often characterized by electrode current values in the range of microamperes to milliamperes stimulation is generally biphasic but monopolar. These electrodes, patterned on thin-film parylene substrate, can be subdurally implanted and adhere to the pial surface in chronic settings. Here, we demonstrate that high-density (40-μm pitch), high-capacitance (>1 nF), single neuronal resolution PEDOT:PSS electrodes can be programmed to shape the charge injection front selectively at depths approaching 300 micrometers with a lateral resolution better than 100 micrometers. Surface electrodes, in contrast, are much less invasive but are challenged by the lack of proximity to axonal processes, leading to poor resolution. Most neuromodulation approaches rely on extracellular electrical stimulation with penetrating electrodes at the cost of cortical damage.
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