Timing: A Critical Factor in Multisensory Integration

Benjamin Rowland, Dept. of Neurobiology and Anatomy, Wake Forest University School of Medicine

Abstract
When cross-modal stimuli appear within the overlapping receptive fields of a multisensory superior colliculus (SC) neuron, the number of impulses evoked is typically greater than that evoked by either stimulus alone and can be greater than their predicted sum (superadditivity). This multisensory enhancement is dependent on high-level corticotectal inputs. Here we explored the temporal evolution of the multisensory response in cat SC and how it is affected by alterations in stimulus effectiveness and the interval between stimuli (SOAs). Continuous-time cumulative multisensory, unisensory, and predicted impulse counts were compared. At optimal SOAs multisensory stimuli produced shorter latency responses, with firing rates often elevated above those predicted by superposition of unisensory responses. SOA had linear effects on response latency but nonlinear effects on multisensory enhancement magnitude. Furthermore, the neurons appeared to engage in a true fusion of inputs, as the only responses evident (even at long SOAs) involved a unisensory response to the first stimulus and a fused multisensory response to the second. Enhancement was manifested at the very onset of the multisensory response. These data suggest that multisensory integration involves substantial interactions between subthreshold inputs, and coordination of multiple tectopetal inputs requiring very rapid conduction along pathways ending at the corticotectal synapse. Supported by NIH grants NS 36916, NS22543.

Not available

Back to Abstract