Mobile HomeCage with tracking capability

Mobile HomeCage allows performing precise optical and electrophysiological techniques such as two-photon imaging, patch clamp recordings, and single-cell optogenetics in the brain of non-anesthetized, head-fixed and naturally behaving mice. The motion tracker collects and displays in real time actionable data about the mouse’s movement trajectory and speed and controls the external devices in closed-loop experiments. Motion tracking allows integrating behavioral readouts with high-precision tests that require head-fixation.

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Combining neurophysiological techniques that require head-fixation with behavioral research is not simple. It requires correlating the data obtained during brain imaging or recordings with the mouse’s movement and trajectory.  It also requires integration and control of stimulation systems such as liquid reward. The Mobile HomeCage’s new motion tracking system makes it possible.

The new motion tracking is a significant leap in the Mobile HomeCage’s evolution towards a more integrated solution for behavioral research.

If you need to recap the Mobile HomeCage’s basic capabilities please refer to this this article. Otherwise read on to learn more about motion tracking in the Mobile HomeCage.

How it works

The tracking apparatus consists of a sensor board (located inside of the Mobile HomeCage’s air dispenser), a mat with magnets (placed inside the floating cage), a control unit and an open source software. Sensors detect the movement of magnets, a processor in the control unit calculates the cage coordinates in real time and streams the data to the computer software, which extrapolates the cage movements into the animal’s trajectory relative to the cage. The trajectory is displayed, along with the animal’s speed and acceleration, and stored for off-line analysis.

Why magnetic tracking?

There are many reasons why we opted for a magnetic instead of video tracking. By hiding the sensor board, the centerpiece of the tracking system, inside the air dispenser we saved space in the 2-photon set-up. Unlike video tracking, magnetic tracking works both in light and in dark conditions. Besides that: the tracker’s speed (80 fps) and resolution (1 mm) would be hard to match for most video tracking devices.

What’s next

The logical next step is adding a liquid reward system. While we are working on making it into a product, we are happy to share the DIY instructions for the liquid reward prototype.

The benefits of the Mobile HomeCage with motion tracking:

  • Actionable data on mouse’ location in the cage, its movement trajectory and velocity obtained during imaging experiments, patch-clamp recordings or optogenetic stimulation;
  • High spatial precision (1 mm) and extra-high temporal resolution (80 fps);
  • Tracking both in light and dark conditions, which cannot be achieved with camera-based tracking;
  • Compatibility with imaging equipment (magnetic tracker does not require extra space under the microscope);
  • 10+ hours of uninterrupted recording;
  • Control of external devices via TTL outputs in closed-loop experiments;
  • Dedicated open source software.

Technical specifications:

  • Dimensions, Mobile HomeCage with sensor board: 430 x 300 x 159 mm;
  • Dimensions, electronic control unit (ECU) : 92 x 100 x 40 mm;
  • Net weight: 6.8 kg;
  • Spatial resolution: 1 mm;
  • Temporal resolution: 1/80 s;
  • Data transfer interface: USB 2.0 (shielded A to B connector cable);
  • Option to connect to power supply: +5V…+12V, ≥ 5W, center positive;
  • Direct data transfer to external hardware over RS-232 interface (ASCII or binary: time stamp, x, y, angular coordinate, exact inter-frame interval, TTL’s status);
  • 2 x TTL output ports for controlling imaging, recording, reward systems;
  • 2 x TTL input ports for external control of tracking software.

Features:

  • Reusable carbon cage mats;
  • USB as primary power source (connection for an optional power supply is provided);
  • Compact size (sensor board is located inside the Mobile HomeCage’s air dispenser; tracker does not require additional space under a microscope);
  • Direct data transfer to external hardware over RS-232 interface;
  • User-defined TTL signal output to control imaging, recording, reward systems;
  • Place preference and movement visualisation;
  • Open source software.

Code:

The code for the Mobile HomeCage tracker is open source. Follow these links to Bitbucket or GitHub to access code.

Accessories:

  • Carbon cage, 180 X 70 mm, designed to roughly match the weight of the test animal for effortless movement;
  • Carbon cage, 180 X 40 mm, designed to allow better access with micromanipulators at non-vertical angles;
  • Transparent cage, 180 X 70 mm, designed to ensure compatibility with Virtual Reality systems, visual stimulation and to enable video recording from the side;
  • Carbon cage mat, 179 X 4 mm (Ø X H), designed for multiple experiments with the same animal. Magnets may be reused in other mats;
  • Head plates (selection of 12 models for various research purposes);
  • Noise reduction unit consists of a 30 mm hose with connectors and an air filter; it helps to further decrease the noise level of the Mobile HomeCage;
  • Angled clamp (10, 20, 30, 35 degrees tilt in the nodding direction, pre-set). Designed to provide for a more natural head position (when used for imaging requires a tilting microscope objective);
  • Elongated clamp designed to ensure compatibility with wide-diameter objectives;
  • Short neck (45 mm vs. standard 75 mm) designed to ensure compatibility with short objectives;
  • MultiCage Training Arena for training up to three (3) mice simultaneously.

If unsure which spare parts and accessories you need or whether the Mobile HomeCage® will fit into your experimental set-up, contact us in the online chat, send an email to mhc-support@neurotar.com or call, +358 9 428 344 56.

 

Mobile HomeCage patents: US8485133B1, EP2712500B1.