On-Chip TaO x -Based Non-volatile Resistive Memory for in vitro Neurointerfaces.

The development of highly integrated electrophysiological devices working in direct contact with living neuron tissue opens new exciting prospects in the fields of neurophysiology and medicine, but imposes tight requirements on the power dissipated by electronics. On-chip preprocessing of neuronal signals can substantially decrease the power dissipated by external data interfaces, and the addition of embedded non-volatile memory would significantly improve the performance of a co-processor in real-time processing of the incoming information stream from the neuron tissue. Here, we evaluate the parameters of TaO x -based resistive switching (RS) memory devices produced by magnetron sputtering technique and integrated with the 180-nm CMOS field-effect transistors as possible candidates for on-chip memory in the hybrid neurointerface under development. The electrical parameters of the optimized one-transistor-one-resistor (1T-1R) devices, such as the switching voltage (approx. ±1 V), uniformity of the R off/R on ratio (∼10), read/write speed (<40 ns), and the number of the writing cycles (up to 1010), are satisfactory. The energy values for writing and reading out a bit ∼30 and ∼0.1 pJ, respectively, are also suitable for the desired in vitro neurointerfaces, but are still far too high once the prospective in vivo applications are considered. Challenges arising in the course of the prospective fabrication of the proposed TaO x -based RS devices in the back-end-of-line process are identified.

Wavelet phase coherence analysis of the skin blood flow oscillations in human.

The wavelet phase coherence of oscillations in the peripheral blood flow of contralateral skin sites was studied in 20 healthy subjects. Skin perfusion was registered simultaneously on similar regions of the outer sides of the right and left forearms by the laser Doppler flowmetry technique. To estimate the reliability of the obtained wavelet phase coherence values we applied the comparative method using amplitude-adjusted Fourier transform surrogates. High median values (0.63 and 0.59) of the wavelet phase coherence were obtained for the frequency intervals of respiratory (0.145-0.6Hz) and cardiac (0.6-2Hz) rhythms in 18 and 20 participants, respectively. In all the 20 participants we detected high and reliable values (Ме=0.72) of the wavelet phase coherence for skin blood flow oscillations in the myogenic interval (0.052-0.145Hz). Additionally, we demonstrated high wavelet phase coherence in the neurogenic (0.021-0.052Hz) and endothelial (0.0095-0.021Hz) intervals in 8 and 7 participants, respectively. The corresponding medians of the reliable wavelet phase coherence values for these intervals were 0.74 and 0.82. The obtained results suggest that the microvascular blood flow possesses not only the local mechanisms of generating low-frequency blood flow oscillations, but also a central mechanism, which is likely to synchronize low-frequency oscillations throughout the whole cardiovascular system.

Analysis of heart rate variability and skin blood flow oscillations under deep controlled breathing.

The effect of deep breathing controlled in both rate (0.25, 0.16, 0.1, 0.07, 0.05 and 0.03 Hz) and amplitude on the heart rate variability (HRV) and respiration-dependent oscillations of forearm/finger skin blood flow (SBF) has been studied in 29 young healthy volunteers. The influence of sympathovagal balance on the respiratory sinus arrhythmia (RSA) amplitude and respiratory SBF oscillations has been studied. The subjects with predominant parasympathetic tonus had statistically significant higher RSA amplitudes in the breathing rate region of 0.03-0.07 Hz than the subjects with predominant sympathetic tonus. In the finger-cushion zone, having a well-developed sympathetic vascular innervations, the amplitudes of respiratory SBF oscillations at breathing rates 0.05 and 0.07 Hz were higher in the group of subjects with predominant parasympathetic tonus. In the forearm skin, where the density of sympathetic innervations is low comparatively to that in the finger skin, no statistically significant differences in the amplitude of respiratory SBF oscillations were found concerning the two groups of subjects.