Flexible Depth Probes with PEDOT:PSS Microelectrodes for Chronic Recording and Stimulation

Flexible neural probes with conductive polymer electrodes present promising alternatives to rigid devices for chronic brain stimulation and recording. Organic devices, characterized by higher charge injection capabilities and better compatibility with biological tissues compared to inorganic probes, hold significant potential in this field. However, demonstrating stability and consistent physiological responses during prolonged pulsing is crucial for their practical application. Moreover, their implantation into brain tissue remains a challenge. Due to their small size and flexibility, organic devices are difficult to insert into brain tissue. This limits their widespread use for recording and deep stimulation of the brain. In this study, we fabricated plastic depth probes with PEDOT:PSS electrodes and developed a reliable protocol for their implantation into brain tissue using a stiff, removable shuttle. We implanted two identical probes into the hippocampus of an adult rat, targeting the CA1 layer with recording electrodes and Schaffer collaterals with stimulating electrodes. We demonstrated that these fabricated devices are excellent tools for recording not only the activity of the neuronal network but also individual neurons. Using microampere range electrical current pulses, we stimulated Schaffer collaterals in freely moving rats and recorded the electrophysiological responses of CA1 pyramidal cells over a 12 day period. Histological analysis of the implanted brain revealed that the lesions caused by our probes were significantly smaller than those left by metal electrodes. Thus, we demonstrated that flexible organic devices are highly effective tools for deep brain recording and stimulation.