Head Direction Cell Activity Is Absent in Mice without the Horizontal Semicircular Canals

Area of Science:

• Neuroscience
• Spatial Navigation
• Vestibular System

Background:

• Head direction (HD) cells in the anterodorsal thalamus (ADN) encode an animal's spatial orientation.
• Vestibular information is essential for generating HD cell signals, but the specific role of semicircular canals remains unclear.

Purpose of the Study:

• To investigate the critical role of horizontal semicircular canals in generating head direction (HD) cell activity.
• To determine if the neural network for HD cells is intact in the absence of functional horizontal canals.

Main Methods:

• Recorded single-unit activity in the anterodorsal thalamus (ADN) of epstatic circler (Ecl) mice with malformed horizontal semicircular canals and control littermates.
• Analyzed cell activity patterns, including preferred firing direction and modulation by head direction.

Main Results:

• Control mice exhibited normal HD cell activity (Raleigh's r > 0.4).
• Ecl mice showed no normal HD cell activity; some cells displayed mild HD modulation (0.4 > r > 0.2).
• Ecl mice exhibited bursty neural activity, resembling HD signals but lacking a preferred direction.

Conclusions:

• The neural network underlying HD cell function remains intact in the absence of horizontal semicircular canals.
• Functional horizontal canals are necessary for the proper control and stability of the head direction (HD) signal.