In collaboration with Nelson Totah’s lab at the University of Helsinki, we are developing tools to enable complex behavioral experiments with head-fixed, behaving rats on a treadmill/VR setup. First validated for chronic electrophysiology recordings (when Nelson was at the Max Planck Institute for Biological Cybernetics), we are now working on expanding the range of capabilities to acute electrophysiology recordings, calcium imaging and potentially, MRI compatibility for the head fixation.
Head fixation in awake mice has been revolutionary in combining state-of-the-art neuronal recordings with behavior. Rats enable more complex behaviors and higher–density neuronal recordings than mice. Yet due to their size, head fixation has so far required highly restrictive fixation methods that prevent the animal from moving, let alone running naturally in a virtual reality environment.
Head fixation system – Performance
Rat head fixation is successfully achieved by combining an innovative headplate design (patent pending) with a carefully adapted surgery protocol. Together, these advances allow an implant so stable that skull screws become unnecessary.
Developed over a period of several years, the method was thoroughly tested:
- 125 animals were implanted, with a 93% success rate
- Recordings on behaving animals could last from 3 to 8 months
Rat head fixed on a treadmill
A methods paper describing all procedures is in preparation. Data collected on behaving head-fixed rats has so far generated 2 preprints:
- Vasilev et al. Focusing perceptual attention in one modality constrains subsequent learning in another modality. bioRxiv 2022.01.22.477334; doi: https://doi.org/10.1101/2022.01.22.477334
- Vasilev et al. Brightness illusions evoke pupil constriction and a preceding primary visual cortex response in rats. bioRxiv 2022.07.13.499566; doi: https://doi.org/10.1101/2022.07.13.499566
In addition, two studies will be presented at SfN 2022:
Building a rat head fixation setup
In addition to the head fixation itself, the setup comprises several other components:
- A cylindrical treadmill with a fiberglass sandblasted surface. This provides appropriate traction for the animal’s paws. Running speed is measured by a rotary encoder.
- A liquid reward delivery system.
- A metal frame, based on an optical rail system, that can flexibly accommodate various sensors (cameras to monitor the animal and measure eye movements), actuators (sensory stimulation with sound, etc) and accessories (e.g. infrared lighting).
- A microcontroller that interfaces the various sensors, actuators and accessories using analog and digital input/output.
Setup schematic [early stage concept for illustration purposes only]
A prototype version is currently being shipped to our first adopter, a systems neuroscience lab at the University of Maryland. We’ll update this page regularly as we finalize the setup.