Perception of meaningful experiences requires that we combine multiple sensory modalities through a process called multisensory integration (MSI). Previous work on the mammalian superior colliculus has revealed the phenomenology of MSI, but little is known about the underlying biophysical mechanisms. In the Xenopus Laevis tadpole, a homologue of the superior colliculus --the optic tectum--is directly involved in MSI and is an emerging model for the study of MSI. NMDA receptors (NMDARs) can serve as coincidence detectors in neurons allowing for non-linear integration of synaptic input, so we hypothesize that NMDARs may play important roles in mediating single-neuron MSI, and thus, that blocking NMDA receptors will stunt MSI in tectal neurons. We also predict that low-intensity multisensory stimuli undergo greater MSI than high-intensity multisensory stimuli. We employed multisensory behavioral experiments and electrophysiological recordings to address these questions. Behavioral results indicate that multisensory stimuli not only result in significantly greater startle responses than unisensory stimuli, but that tadpoles use MSI to a greater extent when both stimuli are low-intensity as compared to one of the stimuli being high-intensity. Electrophysiology results indicate that low-intensity multisensory stimuli have greater signal enhancement (5.57 ± 1.01) than high-intensity multisensory stimuli (1.17 ± 0.06). Additionally, the low-intensity multisensory stimuli group has greater MSI (3.18 ± 0.68) than the NMDA-antagonist group (1.34 ± 0.34). These preliminary findings suggest that MSI is more useful for enhancing low-intensity multisensory stimuli and that the NMDA receptor is at least partially involved with MSI on a cellular level.
"Multisensory integration in the developing brain of the Xenopus laevis tadpole"
Summer Research Symposium.
Brown Digital Repository. Brown University Library.
Each year, Brown University showcases the research of its undergraduates at the Summer Research Symposium. More than half of the student-researchers are UTRA recipients, while others receive funding from a variety of Brown-administered and national programs and fellowships and go …