Bat eye movements resolve a long-standing question in gaze control.

Area of Science:

• Neuroscience
• Sensory Biology
• Comparative Physiology

Background:

• Eye movements are crucial for visual information gathering and gaze stabilization via optokinetic reflex (OKR) and vestibulo-ocular reflex (VOR).
• Bats were historically presumed to lack eye movements, an assumption unsupported by empirical data.
• Echolocating bats' flight agility suggests complex sensory-motor integration, yet their oculomotor capabilities remain unquantified.

Purpose of the Study:

• To quantitatively analyze eye movements in Seba's short-tailed bat (Carollia perspicillata) in response to visual and vestibular stimuli.
• To investigate the functional roles of the optokinetic reflex (OKR) and vestibulo-ocular reflex (VOR) in bats.
• To compare bat VOR pathways with those of other mammals, such as mice.

Main Methods:

• Quantitative analysis of eye movements in response to visual stimuli (OKR).
• Assessment of otolith-mediated and semicircular canal-mediated VOR during off-vertical axis rotation.
• Micro-computed tomography (Micro-CT) to reconstruct semicircular canal geometry in bats and mice.

Main Results:

• Bats demonstrate robust visually driven OKR with an oculomotor range of approximately ±10°.
• Bats exhibit strong otolith-mediated responses but minimal semicircular canal-driven angular VOR (aVOR) during passive head rotations.
• Micro-CT reveals similar semicircular canal geometry between bats and mice, suggesting functional rather than anatomical constraints on bat aVOR.

Conclusions:

• Bats possess significant eye movement capabilities, challenging previous assumptions.
• Visual and otolith-driven gaze stabilization mechanisms are prominent in bats.
• The minimal aVOR in bats may be compensated for during active flight through behavioral state-dependent modulation of vestibular pathways.