Transparent electrodes for coupling imaging and electrophysiology in the brain

High-density Electroencephalography (EEG) and single-neuron calcium imaging are two complementary techniques for studying brain computation in vivo, enabling the electric waves on the brain surface and the neuronal code of the biological networks that originate the waves to be measured. By nanofabricating dense and transparent multi-electrode arrays, EEG and single-neuron calcium activity can be simultaneously measured in the mouse visual cortex, providing a new tool to better understand cortical processing.

HFSP Cross-Disciplinary Fellow Pietro Artoni and colleagues
authored on Tue, 04 December 2018

Translational neuroscience typically runs on two parallel pathways. While clinical studies adopt noninvasive techniques such as EEG in patients, animal models can give access to both brain waves and single-neuron activity using electrophysiology and targeted optical approaches, such as fluorescent genetically encoded indicators of activity. In rodents, current genetic tools allow the study of how the activity of ensembles of cortical neurons gives rise to the resulting EEG activity. Understanding the complex relationship between single-cell activity and the waves on the brain surface in rodents has a significant translational potential. In fact, it would ultimately answer the inverse translational problem, that is: what can we infer from EEG data about neuronal activity in patients? Answering this question is crucial to the study of brain disorders, such as schizophrenia, autism, or epilepsy.

Figure: Transparent multi-electrode arrays for simultaneous EEG recording and 2-photon calcium imaging in the mouse visual cortex. Image first appeared in Science Advances, 05 Sep 2018, Vol. 4, no. 9.

Thus, electrophysiology and imaging need to take place in the same cortical area. In addition, these two pieces of information should be collected simultaneously, since brain states are continuously changing and evolving across different timescales, from milliseconds up to days or even months. A high density of electrodes is also required, since the spatial component of the brain waves carries different information from the temporal one. In principle, transparent electrodes would be the perfect candidates to carry out these measurements; the current technologies for scaling down this type of electrode, however, are limited by a decrease in performance when the electrode pads are scaled down to the micrometer level.

In collaboration with the  Fagiolini  lab at the Center for Life Science at Boston Children’s Hospital and Fang lab at the Department of Engineering of Northeastern University, we developed a new nanomaterial, consisting in a bilayer nanomesh of gold and PEDOT:PSS, which is highly conductive and acts like a “sponge for charges”. At the same time, this structure is hollow and very transparent. These electrodes can be easily scaled down to sizes that allow fine probing of the activity on the brain surface, providing fine multi-spectral EEG maps, together with a view on the activity of those neurons which, right under the electrodes, generate that activity. Pietro Artoni of Boston Children’s hospital, Yi Qiang and Kyung Jin Seo of Northeastern University are co-first authors on the paper, recently published in Science Advances.

Reference

Transparent arrays of bilayer-nanomesh microelectrodes for simultaneous electrophysiology and two-photon imaging in the brain. Yi Qiang,* Pietro Artoni,* Kyung Jin Seo,* Stanislav Culaclii, Victoria Hogan, Xuanyi Zhao, Yiding Zhong, Xun Han, Po-Min Wang, Yi-Kai Lo, Yueming Li, Henil A. Patel, Yifu Huang, Abhijeet Sambangi, Jung Soo V. Chu, Wentai Liu, Michela Fagiolini, and Hui Fang. Science Advances  05 Sep 2018, Vol. 4, no. 9, eaat0626, DOI: 10.1126/sciadv.aat0626 Science Advances (2018). *Joint first authors.

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