Thus far, optical recording of neuronal activity in freely behaving animals has been limited to a thin axial range. We present a head-mounted miniaturized light-field microscope (MiniLFM) capable of capturing neuronal network activity within a volume of 700 × 600 × 360 µm at 16 Hz in the hippocampus of freely moving mice. We demonstrate that neurons separated by as little as ~15 µm and at depths up to 360 µm can be discriminated.

Light-field microscopy (LFM) is a scalable approach for volumetric Ca imaging with high volumetric acquisition rates (up to 100 Hz). Although the technology has enabled whole-brain Ca imaging in semi-transparent specimens, tissue scattering has limited its application in the rodent brain. We introduce seeded iterative demixing (SID), a computational source-extraction technique that extends LFM to the mammalian cortex. SID can capture neuronal dynamics in vivo within a volume of 900 × 900 × 260 μm located as deep as 380 μm in the mouse cortex or hippocampus at a 30-Hz volume rate while discriminating signals from neurons as close as 20 μm apart, at a computational cost three orders of magnitude less than that of frame-by-frame image reconstruction. We expect that the simplicity and scalability of LFM, coupled with the performance of SID, will open up a range of applications including closed-loop experiments.

Light-field microscopy (LFM) is a scalable approach for volumetric Ca 2+ imaging with the highest volumetric acquisition rates (up to 100 Hz). While this has enabled high-speed whole-brain Ca 2+ imaging in small semi-transparent specimen, tissue scattering has limited its application in the rodent brain. Here we introduce Seeded Iterative Demixing (SID), a computational source extraction technique that extends LFM to the scattering mammalian cortex. Using GCaMP-expressing mice we demonstrate SID's ability to capture neuronal dynamics in vivo within a volume of 900×900×260µm located as deep as 380 µm in the mouse cortex and hippocampus at 30 Hz volume rate while faithfully discriminating signals from neurons as close as 20 µm, at three orders of magnitude reduced computational cost. The simplicity and scalability of LFM, coupled with the performance of SID opens up a range of new applications including closed-loop experiments and is expected to propel its wide dissemination within the neuroscience community.Understanding multi-scale integration of sensory inputs and the emergence of complex behavior from global dynamics of large neuronal populations is a fundamental problem in current neuroscience. Only recently, the combination of genetically encoded Calcium (Ca 2+ ) indicators (GECIs) 1 and new optical imaging techniques have enabled recording of neuronal population activity from entire nervous systems of small model organisms, such as C. elegans 2,3 and zebrafish larvae 4,5 , at high speed and single-cell resolution. However, single-cell resolution functional imaging of large volumes at high speed and great depth in scattering tissue, such as the mammalian neocortex, has proven more challenging.A major limitation is the fundamental trade-off between serial and parallel acquisition schemes. Serial acquisition approaches such as two-photon scanning microscopy (2PM) 6 , provide robustness to scattering, however this is achieved at the expense of temporal resolution. More recently, a number of approaches have been developed to alleviate this restriction 7 at the cost of increased complexity -by scanning faster using acousto-optic deflectors 8 , remote focusing using mechanical actuators 9 or acoustooptical lenses 10 , temporal or spatial multiplexing 11-13 , using holographic approaches 14,15 , by selectively addressing known source positions by random access scanning 16-18 , by sculpting the microscope's point spread function (PSF) in combination with a more efficient excitation scheme 19 or other PSF engineering approaches 20,21 .2 In contrast, parallel or partially parallel acquisition schemes such as wide-field epifluorescence microscopy, different variants of light-sheet microscopy 22,23,5,24,25 , widefield temporal focusing 2 and other approaches 26 can greatly improve temporal resolution. Typically, however, light scattering mixes fluorescence signals originating from distinct neurons and degrades information on their locations when a 2D array detector is used. Thus, parallel acquisition schemes have been mo...

In the version of this Brief Communication originally published online, ref. 21 included details for a conference paper (Pegard, N. C. et al. Paper presented at Novel Techniques in Microscopy: Optics in the Life Sciences, Vancouver, BC, Canada, 12-15 April 2015). The correct reference is the following: Pégard, N. C. et al. Optica 3, 517-524 (2016). This error has been corrected in the print, HTML and PDF versions of the paper.

A computational investigation of HCN → HNC isomerization in the electronic ground state by one- and few-cycle infrared pulses is presented. Starting from a vibrationally pre-excited reagent state, isomerization yields of more than 50% are obtained using single one- to five-cycle pulses. The principal mechanism includes two steps of population transfer by dipole-resonance (DR), and hence, the success of the method is closely linked to the polarity of the system and, in particular, the stepwise change of the dipole moment from reactant to transition state and on to products. The yield drops massively if the diagonal dipole matrix elements are artificially set to zero. In detail, the mechanism includes DR-induced preparation of a delocalized vibrational wavepacket, which traverses the barrier region and is finally trapped in the product well by DR-dominated de-excitation. The excitation and de-excitation steps are triggered by pulse lobes of opposite field direction. As the number of optical cycles is increased, the leading field lobes prepare a vibrational superposition state by off-resonant ladder climbing, which is then subjected to the three steps of the principal isomerization mechanism. DR excitation is more efficient from a preformed vibrational wavepacket than from a molecular eigenstate. The entire process can be loosely described as Tannor-Kosloff-Rice type transfer mechanism on a single potential surface effected by a single pulse, individual field lobes assuming the roles of pump- and dump-pulses. Pre-excitation to a transient wavepacket can be enhanced by applying a separate, comparatively weak few-cycle prepulse, in which the prepulse prepares a vibrational wavepacket. The two-pulse setup corresponds to a double Tannor-Kosloff-Rice control scheme on a single potential surface.