SummaryWe report a noninvasive strategy for electrically stimulating neurons at depth. By delivering to the brain multiple electric fields at frequencies too high to recruit neural firing, but which differ by a frequency within the dynamic range of neural firing, we can electrically stimulate neurons throughout a region where interference between the multiple fields results in a prominent electric field envelope modulated at the difference frequency. We validated this temporal interference (TI) concept via modeling and physics experiments, and verified that neurons in the living mouse brain could follow the electric field envelope. We demonstrate the utility of TI stimulation by stimulating neurons in the hippocampus of living mice without recruiting neurons of the overlying cortex. Finally, we show that by altering the currents delivered to a set of immobile electrodes, we can steerably evoke different motor patterns in living mice.

Highlights d Auditory gamma entrainment using sensory stimuli (GENUS) boosts hippocampal function d GENUS affects microglia, astrocytes, and vasculature in auditory cortex and hippocampus d Auditory plus visual GENUS induces microglia clustering around plaques d Auditory plus visual GENUS reduces amyloid pathology throughout neocortex

Particle manipulation based on dielectrophoresis (DEP) can be a versatile and useful tool in lab-on-chip systems for a wide range of cell patterning and tissue engineering applications. Even though there are extensive reports on the use of DEP for cell patterning applications, the development of approaches that make DEP even more affordable and common place is still desirable. In this study, we present the use of interdigitated electrodes on a printed circuit board (PCB) that can be reused to manipulate and position HeLa cells and polystyrene particles over 100 microm thick glass cover slips using DEP. An open-well or a closed microfluidic channel, both made of PDMS, was placed on the glass coverslip, which was then placed directly over the PCB. An AC voltage was applied to the electrodes on the PCB to induce DEP on the particles through the thin glass coverslip. The HeLa cells patterned with DEP were subsequently grown to confirm the lack of any adverse affects from the electric fields. This alternative and reusable platform for DEP particle manipulation can provide a convenient and rapid method for prototyping a DEP-based lab-on-chip system, cost-sensitive lab-on-chip applications, and a wide range of tissue engineering applications.

Several series of near-infrared (NIR) fluorescent proteins (FPs) were recently engineered from bacterial phytochromes but were not systematically compared in neurons. To fluoresce, NIR FPs utilize an enzymatic derivative of heme, the linear tetrapyrrole biliverdin, as a chromophore whose level in neurons is poorly studied. Here, we evaluated NIR FPs of the iRFP protein family, which were reported to be the brightest in non-neuronal mammalian cells, in primary neuronal culture, in brain slices of mouse and monkey, and in mouse brain in vivo. We applied several fluorescence imaging modes, such as wide-field and confocal one-photon and two-photon microscopy, to compare photochemical and biophysical properties of various iRFPs. The iRFP682 and iRFP670 proteins exhibited the highest brightness and photostability under one-photon and two-photon excitation modes, respectively. All studied iRFPs exhibited efficient binding of the endogenous biliverdin chromophore in cultured neurons and in the mammalian brain and can be readily applied to neuroimaging.

SUMMARY Targeted patch clamp recording is a powerful method for characterizing visually identified cells in intact neural circuits, but it requires skill to perform. We previously developed an algorithm that automates “blind” patching in vivo, but full automation of visually guided, targeted in vivo patching has not been demonstrated, with currently available approaches requiring human intervention to compensate for cell movement as a patch pipette approaches a targeted neuron. Here we present a closed-loop real-time imaging strategy that automatically compensates for cell movement by tracking cell position and adjusting pipette motion while approaching a target. We demonstrate our system’s ability to adaptively patch, under continuous two-photon imaging and real-time analysis, fluorophore-expressing neurons of multiple types in the living mouse cortex, without human intervention, with yields comparable to skilled human experimenters. Our “imagepatching” robot is easy to implement, and will help enable scalable characterization of identified cell types in intact neural circuits.

In our original Figure 1B, the appearance of Figures 1Bii and 1Biii incorrectly made it look like the pipette descended into the brain in the downward direction (implying that it would cause brain damage), and furthermore in the original Figure 1Biv the black arrows incorrectly implied that the pipette descends into the brain further downward. In reality, the pipette enters the brain at a diagonal angle, along the axis of the pipette, and furthermore as the pipette approaches the cell, it does so in staggered downward and lateral steps that simulate diagonal movement. We have now corrected Figure 1B to reflect the real configuration of the system. In particular, the pipette enters into the brain (Figure 1Biii) at a diagonal, and toward the end of the process, the pipette moves in staggered downward and lateral steps to approach the cell (we have removed the downward black arrows from Figure 1Biv, so that the lower left of Figure 1B provides the full explanation of the final stages of pipette movement). The figure has now been corrected online. The authors apologize for any confusion this error may have caused.

We report the electric field and pH sensitivity of fluid gated metal-semiconductor hybrid (MSH) Schottky structures consisting of a Titanium layer on n-type GaAs. Compared to standard field-effect sensors, the MSH Schottky structures are 21 times more sensitive to electric field of -46.6 V/cm and show about six times larger resistance change as pH of the solution is decreased from 8.17 to 5.54. The potential change at the fluidic gate and passivation layer interface by bias voltages and pH are mirrored by the metal shunt, resulting in larger depletion widths under the Schottky junction and resistance change as compared to sensors with no Schottky junction. 2D numerical simulation results are in good agreement with the measured data and suggest thinner mesa with lower doping density can further increase device sensitivity.