Learning and memory are assumed to be supported by mechanisms that involve cholinergic transmission and hippocampal theta. Using G protein–coupled receptor-activation–based acetylcholine sensor (GRABACh3.0) with a fiber-photometric fluorescence readout in mice, we found that cholinergic signaling in the hippocampus increased in parallel with theta/gamma power during walking and REM sleep, while ACh3.0 signal reached a minimum during hippocampal sharp-wave ripples (SPW-R). Unexpectedly, memory performance was impaired in a hippocampus-dependent spontaneous alternation task by selective optogenetic stimulation of medial septal cholinergic neurons when the stimulation was applied in the delay area but not in the central (choice) arm of the maze. Parallel with the decreased performance, optogenetic stimulation decreased the incidence of SPW-Rs. These findings suggest that septo–hippocampal interactions play a task-phase–dependent dual role in the maintenance of memory performance, including not only theta mechanisms but also SPW-Rs.

We suggest a novel approach for wide-field imaging of the neural network dynamics of brain slices that uses highly sensitivity magnetometry based on nitrogen-vacancy (NV) centers in diamond. In-vitro recordings in brain slices is a proven method for the characterization of electrical neural activity and has strongly contributed to our understanding of the mechanisms that govern neural information processing. However, this traditional approach only acquires signals from a few positions, which severely limits its ability to characterize the dynamics of the underlying neural networks. We suggest to extend its scope using NV magnetometry-based imaging of the neural magnetic fields across the slice. Employing comprehensive computational simulations and theoretical analyses, we determine the spatiotemporal characteristics of the neural fields and the required key performance parameters of an NV magnetometry-based imaging setup. We investigate how the technical parameters determine the achievable spatial resolution for an optimal 2D reconstruction of neural currents from the measured field distributions. Finally, we compare the imaging of neural slice activity with that of a single planar pyramidal cell. Our results suggest that imaging of slice activity will be possible with the upcoming generation of NV magnetic field sensors, while single-shot imaging of planar cell activity remains challenging.

We demonstrate a technique for precision sensing of temperature or the magnetic field by simultaneously driving two hyperfine transitions involving distinct electronic states of the nitrogen-vacancy center in diamond. Frequency modulation of both driving fields is used with either the same or opposite phase, resulting in the immunity to fluctuations in either the magnetic field or the temperature, respectively. In this way, a sensitivity of 1.4 nT Hz −1/2 or 430 µK Hz −1/2 is demonstrated. The presented technique only requires a single frequency demodulator and enables the use of phase-sensitive camera imaging sensors. A simple extension of the method utilizing two demodulators allows for simultaneous, independent, and high-bandwidth monitoring of both the magnetic field and temperature.Negatively-charged nitrogen-vacancy (NV) color centers 1,2 have become a popular tool for precision magnetic-field sensing at the nano-to milli-meter length scales 3-6 , with a dc sensitivity in the tens of pT/Hz 1/2 range 7 and even higher ac sensitivities 8 . At room temperature, the energy-level structure of the NV ground state is sensitive also to temperature fluctuations 9,10 ; a temperature change of 1 mK causes frequency shifts equivalent to a few-nT magnetic field change. Thus, the presence of noise in one of these quantities may impact the precision of measuring the other quantity unless there is a way of discerning them, for example by temporal signatures.The temperature of the diamond can be easily read out from the optically-detected magnetic resonance (ODMR) spectrum of the NV fluorescence by sweeping a microwave (MW) frequency around 2.8 GHz. The temperature is then inferred from the positions of two opposite spin transitions corresponding to the same crystallographic orientation 9 . Thermometry using pulsed MW protocols or cw -ODMR has been demonstrated with single NVs, nanodiamonds and bulk samples [11][12][13][14] . So far, temperature sensing was demonstrated for stationary or slowly-varying conditions at timescales of many seconds to hours. Large-range (±100 K) and high bandwidth temperature sensing has been shown in Ref. 15 requiring, however, averaging of thousands of measurements. This approach is therefore only suitable for the measurement of well-controlled transients.In this article, we report on a method for recording temperature transients on millisecond timescales in a single-shot measurement while being immune to the magnetic field that induces comparable resonance shifts. The scheme can also be reversed in order to record magnetic signals that are immune to temperature variations. Such temperature transients may be due to laser and/or MW signals operated in a quasi-continuous mode. Similar concepts have been introduced for pulsed MW schemes, a magnetometer immune to temperature drifts 16 and a thermometer insensitive to magnetic fields 11 .Our approach relies on the simultaneous driving of two transitions (m S = 0 ↔ m S = ±1) using cw, frequencyor amplitude-modulated MW fields with either the same or ...

Sensitive, real-time optical magnetometry with nitrogen-vacancy centers in diamond relies on accurate imaging of small (≪10), fractional fluorescence changes across the diamond sample. We discuss the limitations on magnetic field sensitivity resulting from the limited number of photoelectrons that a camera can record in a given time. Several types of camera sensors are analyzed, and the smallest measurable magnetic field change is estimated for each type. We show that most common sensors are of a limited use in such applications, while certain highly specific cameras allow achieving nanotesla-level sensitivity in 1 s of a combined exposure. Finally, we demonstrate the results obtained with a lock-in camera that paves the way for real-time, wide-field magnetometry at the nanotesla level and with a micrometer resolution.