Electrical- and optical stimulation of neuronal networks

Neuroprosthesis depend on precise stimulation of neurons, both spatially and in the time domain. A new paradigm, optical stimulation with laser pulses, has the potential to achieve much higher spatial resolution compared to electrical stimulation, because light can be focused down to a spot-size in the micrometer range. We have prepared laser systems and developed optical elements to couple the laser into the optical path of our microscope. The establishment of neuronal cultures extracted from neonatal mouse brains on MEAs is ongoing and we expect first experiments will be possible within a few weeks. We have also started to model the electrical excitation of neurons in an implanted inner ear. Comparison of the transmitted information and automatic speech recognition results with our model of the intact inner ear will provide us new insights into the limitations of the coding strategies, especially in noise. We also strive to improve coding strategies for cochlear implants with the main goal to encode the temporal fine structure of auditory signals. For this purpose we derive electrical stimulation trains for cochlear implant electrodes from our auditory model of the human ear. This coding strategy overcomes the limitations imposed by fixed stimulation rate schemes and provides phase-locking on the temporal fine structure of the sound signals. To evaluate these strategies, we have started to conduct first measurements with cochlear implant patients at the ENT-hospital using a research interface, which allows us to deliver electrical stimuli directly to the implant.

Cortical neurons (mouse) cultivated on a multi-electrode array (MEA) chip. On MEAs, neurons are accessible for optical stimulation with a laser coupled into the microscope and for electrical stimulation with a recording electrode or a dedicated stimulation electrode.