Electroencephalography (EEG) has been instrumental in epilepsy research for the past century, both for basic and translational studies. Its contributions have advanced our understanding of epilepsy, shedding light on the pathophysiology and functional organization of epileptic networks, and the mechanisms underlying seizures. Here we re-examine the historical significance, ongoing relevance, and future trajectories of EEG in epilepsy research. We describe traditional approaches to record brain electrical activity and discuss novel cutting-edge, large-scale techniques using micro-electrode arrays. Contemporary EEG studies explore brain potentials beyond the traditional Berger frequencies to uncover underexplored mechanisms operating at ultra-slow and high frequencies, which have proven valuable in understanding the principles of ictogenesis, epileptogenesis, and endogenous epileptogenicity. Integrating EEG with modern techniques such as optogenetics, chemogenetics, and imaging provides a more comprehensive understanding of epilepsy. EEG has become an integral element in a powerful suite of tools for capturing epileptic network dynamics across various temporal and spatial scales, ranging from rapid pathological synchronization to the long-term processes of epileptogenesis or seizure cycles. Advancements in EEG recording techniques parallel the application of sophisticated mathematical analyses and algorithms, significantly augmenting the information yield of EEG recordings. Beyond seizures and interictal activity, EEG has been instrumental in elucidating the mechanisms underlying epilepsy-related cognitive deficits and other comorbidities. Although EEG remains a cornerstone in epilepsy research, persistent challenges such as limited spatial resolution, artifacts, and the difficulty of long-term recording highlight the ongoing need for refinement. Despite these challenges, EEG continues to be a fundamental research tool, playing a central role in unraveling disease mechanisms and drug discovery.

• Keywords
• EEG, analysis, animal models, genetic epilepsies, high‐frequency oscillations, mechanisms, preclinical,
• MeSH
• Electroencephalography * methods   MeSH
• Epilepsy * physiopathology   diagnosis   epidemiology   MeSH
• Comorbidity MeSH
• Humans MeSH
• Brain * physiopathology   MeSH
• Seizures * physiopathology   diagnosis   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH

Measuring the transduction of electrical signals within neurons is a key capability in neuroscience. Fluorescent voltage sensitive dyes (VSDs) were early tools that complemented classical electrophysiology by enabling the optical recording of membrane potential changes from many cells simultaneously. Recent advances in the VSD field have led to bright and highly sensitive sensors that can be targeted to the desired cell populations in live brain tissue. Despite this progress, recently, protein-based genetically encoded voltage indicators (GEVIs) have become the go-to tools for targeted voltage imaging in complex environments. In this Perspective, we summarize progress in developing targetable VSDs, discuss areas where these synthetic sensors are or could become relevant, and outline hurdles that need to be overcome to promote the routine use of targetable VSDs in neuroscience research.

• Keywords
• cell-selective targeting, fluorescent sensor, imaging probe, membrane potential, voltage-sensitive dye,
• MeSH
• Action Potentials * physiology   MeSH
• Fluorescent Dyes * MeSH
• Humans MeSH
• Membrane Potentials physiology   MeSH
• Brain physiology   MeSH
• Neurons * physiology   MeSH
• Voltage-Sensitive Dye Imaging * methods   trends   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Fluorescent Dyes * MeSH

The fluorescent glutamate indicator iGluSnFR enables imaging of neurotransmission with genetic and molecular specificity. However, existing iGluSnFR variants exhibit low in vivo signal-to-noise ratios, saturating activation kinetics and exclusion from postsynaptic densities. Using a multiassay screen in bacteria, soluble protein and cultured neurons, we generated variants with improved signal-to-noise ratios and kinetics. We developed surface display constructs that improve iGluSnFR's nanoscopic localization to postsynapses. The resulting indicator iGluSnFR3 exhibits rapid nonsaturating activation kinetics and reports synaptic glutamate release with decreased saturation and increased specificity versus extrasynaptic signals in cultured neurons. Simultaneous imaging and electrophysiology at individual boutons in mouse visual cortex showed that iGluSnFR3 transients report single action potentials with high specificity. In vibrissal sensory cortex layer 4, we used iGluSnFR3 to characterize distinct patterns of touch-evoked feedforward input from thalamocortical boutons and both feedforward and recurrent input onto L4 cortical neuron dendritic spines.

• MeSH
• Kinetics MeSH
• Glutamic Acid * metabolism   MeSH
• Mice MeSH
• Synaptic Transmission * MeSH
• Neurons physiology   MeSH
• Synapses physiology   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Glutamic Acid * MeSH

Neurophotonics was launched in 2014 coinciding with the launch of the BRAIN Initiative focused on development of technologies for advancement of neuroscience. For the last seven years, Neurophotonics' agenda has been well aligned with this focus on neurotechnologies featuring new optical methods and tools applicable to brain studies. While the BRAIN Initiative 2.0 is pivoting towards applications of these novel tools in the quest to understand the brain, this status report reviews an extensive and diverse toolkit of novel methods to explore brain function that have emerged from the BRAIN Initiative and related large-scale efforts for measurement and manipulation of brain structure and function. Here, we focus on neurophotonic tools mostly applicable to animal studies. A companion report, scheduled to appear later this year, will cover diffuse optical imaging methods applicable to noninvasive human studies. For each domain, we outline the current state-of-the-art of the respective technologies, identify the areas where innovation is needed, and provide an outlook for the future directions.

• Keywords
• blood flow, fluorescence, label free, molecular sensors, multimodal, optical imaging, optogenetics,
• Publication type
• Journal Article MeSH