Spatio-temporal activation patterns of neuronal population evoked by optostimulation and the comparison to electrical microstimulation

Optostimulation and electrical microstimulation are well-established techniques that enable to artificially stimulate the brain. While the activation patterns evoked by microstimulation in cortical network are well characterized, much less is known for optostimulation. Specifically, the activation maps of neuronal population at the membrane potential level and direct measurements of these maps were barely reported. In addition, only a few studies compared the activation patterns evoked by microstimulation and optostimulation. In this study we addressed these issues by applying optostimulation in the barrel cortex of anesthetized rats after a short (Short(Exp)) or a long (Long(Exp)) opsin expression time and compared it to microstimulation. We measured the membrane potential of neuronal populations at high spatial (meso-scale) and temporal resolution using voltage-sensitive dye imaging. Longer optostimulation pulses evoked higher neural responses spreading over larger region relative to short pulses. Interestingly, similar optostimulation pulses evoked stronger and more prolonged population response in the Long(Exp) vs. the Short(Exp) condition. Finally, the spatial activation patterns evoked in the Long(Exp) condition showed an intermediate state, with higher resemblance to the microstimulation at the stimulation site. Therefore, short microstimulation and optostimulation can induce wide spread activation, however the effects of optostimulation depend on the opsin expression time.

Automated summary

Optostimulation and electrical microstimulation are well-established techniques for artificial brain stimulation. However, there is less known about the activation patterns evoked by optostimulation compared to microstimulation. This study applied optostimulation and microstimulation in the barrel cortex of anesthetized rats and measured the membrane potential of neuronal populations using voltage-sensitive dye imaging. The results showed that longer optostimulation pulses evoked stronger and more widespread neural responses, and the effects of optostimulation depended on the expression time of opsins. Additionally, the spatial activation patterns of optostimulation were more similar to microstimulation in the long expression time condition.