id_1031. WORLD-FIXED VERSUS MONOCULAR EYE-FIXED DIRECTIONAL LIGHT BIASES ORIENTING AND INDUCES HEMISPHERIC ASYMMETRY OF LATERAL HABENULA ACTIVATION IN ALBINO RATS
Alicja Stankiewicz1, Dominika Moskal1, Martyna Marzec1,2, Tomasz Błasiak1
1 Department of Neurophysiology and Chronobiology, Institute of Zoology and Biomedical Research, Jagiellonian University, Cracow, Poland
2 Doctoral School of Exact and Natural Sciences, Jagiellonian University, Cracow, Poland
INTRODUCTION: Light can influence lateral habenula (LHb) activity via non-image-forming retinal pathways engaging retinorecipient thalamic nuclei. Because the LHb is an important regulator of midbrain dopaminergic system, hemispheric asymmetry within this pathway could translate into lateralized LHb recruitment, asymmetric dopaminergic output, and a directional bias in orienting behavior.
AIM(S): We tested whether world- vs eye-centered directional light biases orienting and drives asymmetric LHb activation.
METHOD(S): Sprague–Dawley rats were tested in darkness (no ambient illumination) on an elevated platform that constrained locomotion to orienting movements. A directional LED light stimulus (10lx at animal’s eye level; constant light; 15 minutes) was delivered in two reference frames: (i) world-centered, with the light source fixed relative to the platform, and (ii) eye-centered, with unilateral illumination aimed at the center of one eye, such that the stimulus remained stationary in the animal’s visual field. Body orientation relative to the stimulus was quantified from overhead video. After the final session, brains were collected for anti c-Fos immunohistochemistry and LHb activation was compared between hemispheres.
RESULTS: During world-centered stimulation, rats typically rotate away from the light source, shifting body orientation to side-facing or back-facing relative to the stimulus direction rather than maintaining a forward-facing orientation toward the light. In the eye-centered condition, c-Fos labeling suggested hemispheric differences in LHb activation, with c-Fos signal concentrated in the medial LHb and showing interhemispheric asymmetry.
CONCLUSIONS: These findings show that world-fixed directional illumination biases body orientation relative to the light source. The interhemispheric asymmetry in LHb activation observed with unilateral eye-centered illumination raises the possibility that hemispheric imbalance in LHb recruitment contributes to orienting bias under asymmetric sensory input.