Abstract
Located within each inner ear, the vestibular apparatus supports balance, posture, and gaze stabilization via vestibulo-ocular and vestibulo-spinal reflexes, and contributes to motion perception and spatial memory. Integrated with visual and somatosensory systems, vestibular signals reach multiple cortical hubs through thalamic, hippocampal–septal, and cerebellar–thalamic routes, with access to the posterior parietal cortex. Clinical observations of vestibular disorders suggest that vestibular function may influence number representation and the spatial organisation of numerical magnitude (e.g., a mental number line), motivating experimental testing of vestibular–numerical interactions.
This thesis investigates whether acute, supra-threshold galvanic vestibular stimulation (GVS) alters numerical discrimination in a rodent model. Sixteen adult Wistar rats (8 female, 8 male) were trained over approximately 17 days on an auditory discrimination paradigm designed to dissociate number from time. Briefly, the animals were trained to accurately discriminate a small number (e.g., 2) from a big number (e.g., 8) using number-relevant signals (e.g., 2 or 8 events within 4 s) and a short duration from a long duration using time-relevant signals (4 events delivered over 2 or 8 s). Animals were then randomly assigned to either GVS or sham treatment groups and underwent testing to identify their discrimination ability using number-relevant and time-relevant cues, respectively and the influence of GVS. In the GVS group, supra-threshold stimulation was delivered prior to behavioural testing; sham animals underwent identical procedures without GVS.
Training results showed that all animals gradually acquired the discrimination, with males exhibiting faster learning than females. Males also performed better than females overall. In testing, rats used both number-relevant and time-relevant cues, demonstrating accurate discrimination from either source, however performance was stronger for time-relevant than for number-relevant cues. There was no overall difference between GVS and sham groups.
For the first time, numerical discrimination performance was compared between male and female rats, However GVS, as described here, did not affect overall numerical discrimination performance.