Mobile HomeCage with tracking capability

Mobile HomeCage allows using precise optical and electrophysiological techniques in the brain or spinal cord of awake behaving mice. The locomotion tracking device collects and displays in real-time actionable data about the mouse’s movement trajectory and speed, and controls external stimulation devices in closed-loop experiments. Locomotion 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 a liquid reward. The Mobile HomeCage’s new motion tracking system makes it possible.

The new locomotion 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 article. If you are primarily interested in spinal cord imaging or recording, navigate to the relevant section down the page. Otherwise, read on to learn more about locomotion 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 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 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.

Lick port and air puff

Since we do not recommend adding much weight to the carbon cage, our lick port and air puff assemblies attach directly to the clamp. The reward or the negative reinforcement can be administered manually or they can be controlled by the tracking device during closed-loop experiments. It is also possible to use the air puff for whisker stimulation.

The benefits of the Mobile HomeCage with locomotion 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 (such as liquid reward or air puff) via TTL outputs in closed-loop experiments;
    • Dedicated open-source software.

Using locomotion tracking for spinal cord imaging and recording

Imaging and recording stability in the spinal cord of awake mice deteriorates significantly during active locomotion. Fortunately, the tracking device allows differentiating between the idle periods and periods of active locomotion. Focusing the analysis on the data subset from the idle mice simplifies data processing and analysis.

In our recent tests, imaging stability during idle periods varied between 1.3-2.8 micrometers, while the stability was overall lower and the variation more pronounced in actively locomoting mice, 2.3-8.7 micrometers. This is illustrated by the gif image below, which is a side-by-side comparison of microglia imaging in the spinal cord of the same spinal cord area of a mouse during active locomotion and voluntary stillness:

Microglia imaging in the spinal cord of an awake mouse

Each session’s duration, as well as the overall length of the training, have a strong effect on locomotion: as the novelty subsides, mice tend to move less:

Effect of training on spinal cord imaging in awake mice

There is no need for a special training protocol aimed at teaching the mice to stay still. Instead, the locomoting tracking device allows excluding the data acquired during active locomotion, which tends to have suboptimal stability. While locomotion tracking device is optional for the spinal cord imaging and recording in the Mobile HomeCage, we strongly recommend using Neurotar’s spinal cord surgery set to achieve optimal stability.

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 a 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 the RS-232 interface;
  • User-defined TTL signal output to control imaging, recording, reward systems;
  • Place preference and movement visualization;
  • Open-source software.

Code:

The code for the Mobile HomeCage tracker is open source. Follow this link GitHub to access the 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);
  • Spinal cord surgery set (one, five or ten spinal plates and a set of instruments);
  • Standard clamp or Levelt clamp (magnetic) – specify at order, see below for pictures;
  • Tilted 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 lower lip is a part of the clamp used to ensure compatibility with wide-diameter objectives;
  • Tracking mats enable locomotion tracking in the Mobile HomeCage (6 mats are included in the Mobile HomeCage kit);
  • Adapters for mounting micromanipulators on the Mobile HomeCage bridge;
  • Lick port and air puff  for liquid reward, negative reinforcement or whisker stimulation;
  • 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.

Navigate to our references and educational webinars, support services, and distribution partners.

Mobile HomeCage patents: US8485133B1, EP2712500B1.