As part of a collaboration between several partners, including the Haesler lab and scientists at KU Leuven and imec, a new optoelectrode was designed, fabricated and tested. The optolelectrode has an integrated ultrathin neural interface with 12 optical outputs and 24 electrodes and allows for simultaneous optical stimulation and recording; and because of its small dimensions, it causes far less tissue damage than commercially available devices.
Investigating how the dynamic activity in neural circuits gives rise to perception and behavior involves the manipulation of specific neural cell types through optogenetics. To critically evaluate how these optogenetic manipulations affect neural circuits, or to identify the response of specific neural subtypes, it is necessary to illuminate the brain tissue, while simultanously monitoring the activity of many neurons. But despite great progress in the development of optogenetic interfaces, combining multi-channel recordings with multisite optical illumination at high spatial resolution remains a challenge.
Currently available interfaces which guide light of the appropriate wavelength into the brain combined with an electrophysiological modality are bulky, have low spatial resolution, dissipate heat or suffer from photovoltaic artifacts. To address these challenges, the research team set out to develop an integrated neural interface with 12 optical outputs and 24 electrodes.
The new tool is an important step forward, explains Dries Braeken (imec): "Since our device is built using established microchip technology, it can be fabricated with high reproducibility and reliability. Thanks to its small dimensions—only 30 μm thick—it also causes far less tissue damage than currently available devices."
Researchers at NERF immediately put the new optoelectrode to the test and measured the effect of localized stimulation in the anterior olfactory cortex, a brain area important for olfactory processing.
Sebastian Haesler: "We found that even very localized stimulation affects neural firing far beyond the stimulation site. This demonstrates the difficulty in predicting circuit-level effects of optogenetic manipulations and highlights the importance of closely monitoring neural activity in optogenetic experiments."
The findings resulting from this team effort have been published in the Journal of Electrophysiology.
Sarah Libbrecht, Luis Hoffman, Marleen Welkenhuysen, Chris Van den Haute, Veerle Baekelandt, Dries Braeken & Sebastian Haesler. Proximal and distal modulation of neural activity by spatially confined optogenetic activation with an integrated high-density optoelectrode. Journal of Neurophysiology 2018-03-28 epub ahead of print