Calcium imaging is a versatile experimental approach capable of resolving single neurons with single-cell spatial resolution in the brain. Electrophysiological recordings provide high temporal, but limited spatial resolution, due to the geometrical inaccessibility of the brain. An approach that integrates the advantages of both techniques could provide new insights into functions of neural circuits. Here, we report a transparent, flexible neural electrode technology based on graphene, which enables simultaneous optical imaging and electrophysiological recording. We demonstrate that hippocampal slices can be imaged through transparent graphene electrodes by both confocal and two-photon microscopy without causing any light-induced artifacts in the electrical recordings. Graphene electrodes record high frequency bursting activity and slow synaptic potentials that are hard to resolve by multi-cellular calcium imaging. This transparent electrode technology may pave the way for high spatio-temporal resolution electrooptic mapping of the dynamic neuronal activity.

a b s t r a c tIntroduction: As cutaneous head and neck malignancies are highly prevalent especially in older patients, the risk of surgical complications is substantial in this potentially vulnerable population. The objective of this study was to evaluate the value of geriatric assessment of this population with respect to postoperative complications. Methods: Patients were prospectively included in OncoLifeS, a databiobank. Before surgery, patients underwent a geriatric assessment including multiple validated screening tools for frailty, comorbidity, polypharmacy, nutrition, functional status, social support, cognition and psychological status. Postoperatively, complications (Clavien-Dindo grade II) were registered. Uni-and multivariable logistic regression analyses were performed yielding odds ratios (ORs) and 95% confidence intervals (95%CIs). Results: 151 patients undergoing surgery for cutaneous head and neck malignancies were included in this study (mean age 78.9 years, 73.5% male). In a multivariable analysis, frailty measured by the Geriatric 8 (G8) (OR ¼ 6.34; 95%CI:1.73e23.25) was the strongest independent predictor of postoperative complications, among other predictors such as major treatment intensity (OR ¼ 2.73; 95%CI:1.19e6.26) and general anesthesia (OR ¼ 4.74; 95%CI:1.02e22.17), adjusted for age and sex. Conclusion: Frailty, measured by G8, is the strongest predictor of postoperative complications in patients undergoing surgery for cutaneous head and neck malignancies in addition to treatment intensity and type of anesthesia. Geriatric screening on multiple domains is recommended for patients with cutaneous malignancies undergoing head and neck surgery is recommended, as this population includes old patients and frequently suffers postoperative complications.

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