Biology subjects

Demas, J.

Publications and source records attributed to Demas, J..

4 recordsLinked to original sources

bioRxiv2026

Large-scale volumetric two-photon calcium imaging enables cellular-resolution mesoscopic mapping of marmoset cortical areas

Primate neocortex is organized into functionally defined domains. Understanding how the functional organization within each domain emerges from single-cell tuning properties has been hampered by the lack of imaging tools that can capture large-scale activity at different depths of the scattering primate brain at cellular resolution and physiological timescales. Here, we demonstrate mesoscopic and volumetric cellular-resolution calcium imaging of entire cortical areas in the marmoset brain at multi-Hertz rates by combining fluorescence lifetime-limited temporally multiplexed two-photon recording based on Light Beads Microscopy (LBM) with optimized calcium indicator targeting. Using this approach, we perform volumetric recording of neuronal population activity within cortical volumes spanning up to 4 x 4 x 0.3 mm3 capturing the simultaneous activity of over 96,000 cells, including more than 46,000 stimulus-responsive neurons. In auditory cortex, we found fine-grain heterogeneous tuning of individual neurons to frequencies within broader tonotopic gradients. In the middle temporal area (MT) we found direction tuning along functional continua rather than discrete categories, encompassing uni-, bi-, and pandirectional tuning, where cells with similar tuning tend to cluster. Tuning direction follows a columnar organization with a lateral periodicity of [~]500 {micro}m and low variability across depth. Columns are organized by a pinwheel structure. Noise correlations between cells, revealing functional interactions, decay isotropically and monotonically with distance but remain significant even at lateral distances exceeding 3 mm and thus the scale of multiple columns. Together, these discoveries reveal the need for neurotechnologies bridging scales from single cells to multi-columnar systems. The technological advancements open the door for future large-scale, cellular-resolution investigations of functional organization and population dynamics across entire cortical areas in the primate brain.

neuroscience↗

bioRxiv2026

Fiber optical parametric amplification of low-photon-flux microscopy signals

The performance of a laser scanning microscope inevitably depends on the performance of the point detector. As laser scanning approaches aim to penetrate deeper in tissue, there is a commensurate need for detectors that can operate with high sensitivity, bandwidth, and dynamic range at near-infrared wavelengths where scattering is reduced. Here, we demonstrate that fiber optical parametric amplification can be used to boost low-power microscopy signals to levels that can be detected by near-infrared photodiodes without introducing prohibitive noise. We construct amplifiers that achieve >50 dB of parametric gain at wavelengths within the third near-infrared transparency window and have similar sensitivity to near-infrared photomultiplier tubes. Furthermore, these amplifiers outperform detection with a photodiode and subsequent electrical amplification, providing a factor of 10-100-fold improvement in sensitivity. We demonstrate amplifier bandwidths up to ~1.6 GHz, a factor of 10 faster than conventional detectors, including near-infrared photo-multiplier tubes, with sensitivity of ~8 nW (corresponding to ~20 photons/pixel). Finally, the increased performance of the optical amplifier is confirmed in diagnostic imaging experiments where >10x less power is required to achieve the same signal-to-noise ratio and contrast as images using electrical amplification. Accordingly, fiber optical parametric amplification is a new path forward for extending the performance of laser scanning microscopes in the near infrared.

biophysics↗

bioRxiv2024

Simultaneous, cortex-wide and cellular-resolution neuronal population dynamics reveal an unbounded scaling of dimensionality with neuron number

The brains remarkable properties arise from collective activity of millions of neurons. Widespread application of dimensionality reduction to multi-neuron recordings implies that neural dynamics can be approximated by low-dimensional "latent" signals reflecting neural computations. However, what would be the biological utility of such a redundant and metabolically costly encoding scheme and what is the appropriate resolution and scale of neural recording to understand brain function? Imaging the activity of one million neurons at cellular resolution and near-simultaneously across mouse cortex, we demonstrate an unbounded scaling of dimensionality with neuron number. While half of the neural variance lies within sixteen behavior-related dimensions, we find this unbounded scaling of dimensionality to correspond to an ever-increasing number of internal variables without immediate behavioral correlates. The activity patterns underlying these higher dimensions are fine-grained and cortex-wide, highlighting that large-scale recording is required to uncover the full neural substrates of internal and potentially cognitive processes.

neuroscience↗

bioRxiv2021

Volumetric Calcium Imaging of 1 Million Neurons Across Cortical Regions at Cellular Resolution Using Light Beads Microscopy

Two-photon microscopy together with genetically encodable calcium indicators has emerged as a standard tool for high-resolution imaging of neuroactivity in scattering brain tissue. However, its various realizations have not overcome the inherent tradeoffs between speed and spatiotemporal sampling in a principled manner which would be necessary to enable, amongst other applications, mesoscale volumetric recording of neuroactivity at cellular resolution and speed compatible with resolving calcium transients. Here, we introduce Light Beads Microscopy (LBM), a scalable and spatiotemporally optimal acquisition approach limited only by fluorescence life-time, where a set of axially-separated and temporally-distinct foci record the entire axial imaging range near-simultaneously, enabling volumetric recording at 1.41 x 108 voxels per second. Using LBM, we demonstrate mesoscopic and volumetric imaging at multiple scales in the mouse cortex, including cellular resolution recordings within ~3x5x0.5 mm3 volumes containing >200,000 neurons at ~5 Hz, recording of populations of ~1 million neurons within ~5.4x6x0.5 mm3 volumes at ~2Hz as well as higher-speed (9.6 Hz) sub-cellular resolution volumetric recordings. LBM provides an unprecedented opportunity for discovering the neurocomputations underlying cortex-wide encoding and processing of information in the mammalian brain.

neuroscience↗