MIT engineers have developed a microscope that can record electrical activity from neurons distributed across the entire brain of a living organism at millisecond-scale speeds. The system, demonstrated in larval zebrafish, captures voltage changes from individual neurons throughout the brain rather than focusing on a small, localized region. The advance could give neuroscientists a new way to study how distant brain areas coordinate their activity to produce perception, movement, memory, and behavior. The work, published in Nature Methods, addresses a longstanding challenge in neuroscience: observing fast electrical signals across a large volume of brain tissue at the same time.
Neurons communicate by generating brief electrical impulses known as action potentials, or spikes. These signals travel along the cells and trigger communication with neighboring neurons, allowing networks of interconnected cells to process information. Conventional calcium imaging has enabled scientists to observe the activity of large numbers of neurons, but it does so indirectly. When a neuron fires, calcium ions flow into the cell, producing a chemical signal that can be detected through fluorescent indicators. Because calcium concentrations rise and fall relatively slowly, however, calcium imaging usually records activity over timescales of seconds or longer and may miss the individual spikes that carry information through neural circuits.
Voltage imaging offers a more direct alternative. Researchers can introduce genetically encoded voltage indicators into neurons, causing the cells to produce fluorescent proteins whose brightness changes when the electrical potential across the cell membrane changes. When a neuron fires, the indicator responds to the rapid shift in voltage, allowing the electrical event to be observed optically. In principle, this makes it possible to follow the timing and sequence of individual neural impulses. In practice, voltage signals are extremely brief and often faint, making it difficult to image them across a large three-dimensional brain at the speed and resolution required to distinguish individual cells.
To overcome this limitation, the MIT team modified a light-sheet microscope, an instrument designed to image large biological samples rapidly while reducing light exposure. A light sheet illuminates only a thin plane of tissue, and the microscope records the fluorescence emitted from that plane before moving through successive layers. Combining those images produces a three-dimensional representation of the sample. The researchers accelerated both parts of the process: they increased the acquisition speed of the camera and used a technique called remote refocusing to shift the imaging plane rapidly without mechanically moving the specimen or the main optical components.
The resulting instrument was able to scan the entire brain of a larval zebrafish 200 times per second, completing one full volume every five milliseconds. This rate is fast enough to capture many of the electrical events that conventional whole-brain imaging would blur or miss. The zebrafish is particularly useful for this kind of experiment because its larval brain is small and relatively transparent, allowing researchers to image neural activity throughout the organism without the need to physically remove tissue. Its nervous system also contains many of the major functional structures found in vertebrates, making it a valuable model for studying how brain-wide circuits operate.
For their demonstration, the researchers engineered larval zebrafish to express a genetically encoded voltage indicator called Positron2-Kv. The indicator did not produce usable signals in every neuron, but approximately one-quarter of the neurons showed fluorescence changes strong enough for analysis. Even this partial coverage allowed the team to observe activity across many brain regions at once. In fish that were resting, the microscope detected individual voltage spikes as well as rapid bursts of activity. These recordings provided a direct view of the timing of electrical signals and offered information that would be difficult to obtain from slower calcium measurements.
The system also revealed how activity spread through the brain after the fish received ultraviolet light. Soon after the stimulus, neurons in the optic tectum became active. This brain region receives visual information from the retina and performs early stages of visual processing. The activity then propagated across the tectum, moving from one side of the structure to the other. Because the microscope recorded the activity throughout the brain rather than in a single visual-processing area, the researchers could also observe stimulus-independent sequences in groups of neurons located in the cerebellum and hindbrain. These patterns suggest that spontaneous brain activity is organized across distributed networks, even when the animal is not responding to an obvious external signal.
The ability to observe voltage signals across a complete brain could change the way researchers formulate questions about neural computation. Brain functions rarely depend on isolated groups of neurons; instead, they emerge from interactions among circuits that may be separated by considerable anatomical distances. A neuron in a sensory region may influence cells involved in movement, attention, or internal state within milliseconds. If experiments examine only one region at a time, important participants in these network-wide processes can be overlooked. Whole-brain voltage imaging could help scientists identify coordinated activity patterns first and then investigate how specific neurons and connections contribute to them.
The new microscope is not yet a complete solution to the challenges of brain-wide recording. The researchers aim to increase the proportion of neurons that produce strong voltage-indicator signals while improving spatial resolution, imaging speed, and data analysis. Fluorescence must be collected quickly enough to distinguish a faint electrical response from background noise, and the enormous data volumes generated by high-speed three-dimensional imaging require sophisticated computational methods. The team is also exploring whether the approach can be adapted for other experimental organisms, including mice, whose larger and more complex brains present additional optical and technical obstacles.
Despite those limitations, the demonstration represents a significant step toward observing the brain as an integrated electrical network. By measuring voltage directly from neurons distributed throughout an entire organism, the method could help researchers connect rapid neural events with sensory responses, spontaneous activity, behavior, and internal mental states. Future experiments may use it to investigate how brain-wide circuits support learning, decision-making, movement, or states such as daydreaming. The broader goal is to understand not only what individual neurons do, but how thousands of cells coordinate their electrical activity to produce the unified functions of a living brain.
Subject of Research: Brain-wide voltage imaging of neuronal activity in larval zebrafish
Article Title: Voltage imaging of neurons distributed across entire brains of larval zebrafish
News Publication Date: 14-Aug-2026
Web References: https://doi.org/10.1038/s41592-026-03179-7
References: Nature Methods, DOI: 10.1038/s41592-026-03179-7
Keywords
Voltage imaging, genetically encoded voltage indicators, neurons, zebrafish, whole-brain imaging, light-sheet microscopy, neuroscience, neural networks, brain activity, Positron2-Kv
