Two-photon calcium imaging of neuronal activity

Abstract

other to generate movements, emotions or cognition is a central goal of neuroscience, requiring tools to record neuronal activity. For most of the twentieth century, electrophysiology was the only method available to neuroscientists to record neural activity. Although electro physiology remains the gold standard to accurately record action potentials and sub-threshold changes in membrane potential, it suffers from important shortcomings. Electrodes must be inserted into brain tissue, which causes trauma and, potentially, triggers irritability of neurons. Furthermore, the number of neurons that can be recorded simultaneously is limited, and their identity cannot be readily identified -neurons are almost always targeted blindly, and therefore there is a bias towards very active neurons. Recent advances in silicon probe technology, which now allow for multiple probes to be inserted into the brain (each with hundreds of contact sites), have expanded the number of neurons and brain regions that can be sampled with electrophysiology, but with greater invasiveness, higher cost and the same limitations compared with single-neuron electrode recordings.Optical probing of neural activity, especially calcium imaging, has become a popular alternative to electrophysiology. Recording neural activity with fluorescence probes -primarily calcium and voltage sensors -has become mainstream in neuroscience 1,2 . In particular, calcium imaging with two-photon (2P) microscopy has become the preferred method for recording neuronal ensemble dynamics in the intact brain over the past two decades 3,4 , because it offers several advantages over in vivo electrophysiology. Principles of calcium imagingThe ability to conduct calcium imaging experiments with rigour and reproducibility requires an in-depth knowledge of what signal is being measured and how. This requires, in turn, a basic understanding of the experimental techniques and equipment necessary to detect that signal, and of the computational pipelines to analyse and interpret the signal. In general terms, calcium imaging relies on the detection of changes in intracellular calcium concentration ([Ca 2+ ] i ) using fluorescent calcium indicators. Calcium contributes to a range of complex signals within neurons, from triggering neurotransmitter release to long-lasting synaptic plasticity in dendritic branches and spines. Importantly, the [Ca 2+ ] i regulates these processes over vastly different timescales, from a few microseconds to several hours. Thus, the time course, the amplitude or the site of its action in distinct cellular compartments are all essential determinants for the function of intraneuronal calcium signals. However, when discussing calcium imaging as a means of probing neural activity, which is the principal focus of this Primer, we are referring to Ca 2+ ions entering the cell body (the soma) through voltage-gated calcium channels when a neuron fires an action potential (FiG. 1a). Therefore, because the [Ca 2+ ] i in the soma correlates with action potential firing, so...

Efficient inference of synaptic plasticity rule with Gaussian process regression

“…In the case of indirect inference from network activities, two-photon calcium imaging can be used because stable imaging over consecutive days and weeks enables tracing learning-related changes in vivo. 32 , 51 , 52 Also, recent technical advancement allows cortex-wide monitoring of neuronal circuits at a cellular resolution. 53 , 54 Thus, tracing pre- and postsynaptic activities together during learning might be available in the near future, and our method to infer plasticity rules from network activities can be applied.…”

High fidelity sensory-evoked responses in neocortex after intravenous injection of genetically encoded calcium sensors

“…For example, in the auditory and visual cortex, there have been reports of highly variable trial-by-trial responses to sensory stimulation during two-photon calcium imaging in anesthetized mice (Bandyopadhyay et al, 2010; Jia et al, 2010; Chen et al, 2011b). The type of anesthesia, the experimental preparation quality and sensor performance can all heavily impact the fidelity of responses (Bandyopadhyay et al, 2010; Grienberger et al, 2022). Even in visual cortical brain slices, monosynaptic activation of spiny stellate neurons in layer 4 can evoke responses with a wide range of trial-by-trial variability (Stratford et al, 1996).…”

Enhanced detection sensitivity of neuronal activity patterns using CaMPARI1 vs. CaMPARI2

“…Over the past two decades, extensive efforts have been invested in designing and optimizing protein-based sensors to record from neurons inside the living brain. The development of genetically encoded calcium indicators (GECIs) especially benefitted from these efforts, with the engineering of multiple GECI variants excited by different wavelengths and utilizing different mechanisms to translate changes in intracellular Ca 2+ concentration into fluorescence signal ( Looger and Griesbeck, 2012 ; Rodriguez et al, 2017 ; Grienberger et al, 2022 ). For example, the ongoing optimization of the GCaMP sensors ( Nakai et al, 2001 ; Tian et al, 2009 ; Akerboom et al, 2012 ; Chen et al, 2013 ; Dana et al, 2019 ; Inoue et al, 2019 ; Zhang et al, 2021 ) enabled the extension of earlier in vitro experiments into in vivo recordings under multiple experimental conditions and using various animal models.…”