FlatMux captures electrical activity optically from nearly 200 genetically defined neurons across new depths in brain circuits, revealing how signals flow, cells connect, and computations emerge in a living mouse brain, according to research published in Nature Methods by the Vaziri lab.
Two-Photon Imaging Platform Captures 200 Neurons Simultaneously
Researchers have developed a custom two-photon imaging platform called FlatMux that records electrical activity from almost 200 neurons at once. According to Alipasha Vaziri, head of the Laboratory of Neurotechnology and Biophysics at Rockefeller, traditional methods often focus on individual neuron response properties. The new system instead investigates how brain functions emerge from a highly interconnected system where computation is distributed across a large network of neurons.
The platform achieves depths up to 500 micrometers and frame rates of up to 2,000 per second. By scanning laser pulses across samples at a rate of 150 million samples per second, the tool sets new performance benchmarks in neuroscience imaging.
Overcoming Limitations of Calcium Imaging and GEVIs
Existing optical tools have faced significant technical hurdles. Scientists have long relied on calcium imaging to track calcium surges tied to neural firing, but these signals provide only an indirect measurement of electrical activity. Calcium signals are also much slower than the millisecond electrical impulses neurons use to communicate, causing techniques to miss sub-threshold responses that shape activity before a neuron fires.
More recently, researchers adopted genetically encoded voltage indicators, or GEVIs, which are fluorescent sensors embedded in cell membranes that report voltage directly. However, GEVIs produce faint signals that are roughly 100 times faster than calcium signals and extremely difficult to capture deep inside living tissue. Traditional two-photon systems lack the efficiency needed to record large neuronal populations without risking tissue heating or sensor degradation.
Rethinking Light Delivery with an Optical Cavity
To address these physical limits, the Rockefeller research team built FlatMux using an optical cavity. According to the study, the platform splits a laser beam into many precisely timed pulses delivered to distinct, non-overlapping points in the tissue. This coordinated approach replaces mechanical sweeping, which typically results in laser pulses oversampling each scan region.
The design maximizes fluorescent photon output for every excitation photon put in, generating stronger signals from less light while reducing tissue heating. Furthermore, the scalable architecture means that as GEVIs improve, FlatMux can reallocate energetic resources to record larger neuronal populations at identical speeds without increasing power consumption.
Testing FlatMux in Awake Mice on Treadmills
To evaluate the platform under realistic conditions, the research team tested the system in awake mice running on a treadmill while exposed to whisker stimulation. According to study findings, the system successfully captured faint voltage signals during both whisker stimulation and spontaneous behavior.
The platform recorded almost 200 neurons simultaneously across two cortical layers at once, allowing researchers to observe how signals move through layered cortical circuitry in real time. In high-sensitivity mode, the system also detected weak signals crucial for identifying synaptically coupled neurons.
Frequently Asked Questions
What is FlatMux?
FlatMux is a custom two-photon imaging platform described in Nature Methods that captures electrical activity optically from nearly 200 genetically defined neurons simultaneously across cortical layers.
How deep can FlatMux image into brain tissue?
The platform reaches depths up to 500 micrometers while operating at frame rates of up to 2,000 per second.
Why is direct electrical imaging better than traditional calcium imaging?
Unlike calcium imaging, which provides slow and indirect measurements of neural firing, direct optical imaging via fluorescence captures fast millisecond electrical events and sub-threshold responses.
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