Dorsal surface electrical stimulation over the T9–T10 region has recently been reported to facilitate swallowing, but the underlying brainstem mechanisms and optimal stimulation sites remain unclear. In particular, it is unknown whether thoracic stimulation at different segmental levels differentially modulates ascending afferent inputs to medullary swallowing circuits. Here, we used an in situ arterially perfused brainstem–spinal cord preparation in rats, in which the brainstem swallowing central pattern generator (CPG) is preserved and its neural output can be recorded directly, to compare the effects of mid-thoracic (T8) versus lower thoracic (T12) spinal stimulation on swallowing induced by oral water infusion, and respiratory parameters. T8 stimulation is expected to recruit afferent fibers ascending from the T9–T10 region, whereas T12 stimulation is not. Therefore, comparing these two levels allowed us to assess the functional importance of inputs arising near T9–T10. T8 stimulation increased significantly the mean peak amplitudes of vagus and hypoglossal nerve activity during fictive swallowing, the number of swallow events, swallow duration, swallow-related apnea duration, and expiratory time. In contrast, none of these swallowing-related or swallow-associated respiratory measures were significantly altered by T12 stimulation. Other respiratory indices, including inspiratory time, post-inspiratory time, overall respiratory cycle duration, and mean the peak amplitudes of phrenic, vagal, and hypoglossal activity during baseline breathing, were not significantly affected by stimulation at either level. These findings demonstrate that T8-level thoracic spinal stimulation selectively and robustly facilitates medullary swallowing CPG activity and swallowing function, while largely preserving baseline respiratory rhythm apart from a prolongation of expiration. Because most swallows naturally occur during expiration, this expiratory prolongation is unlikely to be disadvantageous and may instead promote safer, more stable swallow timing. Our results highlight the importance of selecting stimulation sites within the mid-thoracic cord and support these segments as promising targets for neuromodulatory interventions to facilitate the swallowing CPG. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Kitamura et al. (Fri,) studied this question.