Sensory and multisensory responses in the newborn monkey superior colliculus

Superior colliculus (SC) neurons have the ability to synthesize information from different sensory modalities, resulting in enhancements (or depressio ns) of their activity. This physiological capacity is, in turn, closely tie d to changes in overt attentive and orientation responses. The present stud y shows that, in contrast to more altricial species, many deep layer SC neu rons in the rhesus monkey are multisensory at birth. Such neurons can respo nd to stimuli from different sensory modalities, and all convergence patter ns seen in the adult are represented. Nevertheless, these neurons cannot ye t synthesize their multisensory inputs. Rather, they respond to combination s of crossmodal stimuli much like they respond to their individual modality -specific components. This immature property of multisensory neurons is in contrast to many of the surprisingly sophisticated modality-specific respon se properties of these neurons and of their modality-specific neighbors. Th us, although deep SC neurons in the newborn have longer latencies and large r receptive fields than their adult counterparts, they are already highly a ctive and are distributed in the typical adult admixture of visual, auditor y, somatosensory, and multisensory neurons. Furthermore, the receptive fiel ds of these neurons are already ordered into well organized topographic map s, and the different receptive fields of the same multisensory neurons show a good degree of cross-modal spatial register. These data, coupled with th ose from cat, suggest that the capacity to synthesize multisensory informat ion does not simply appear in SC neurons at a prescribed maturational stage but rather develops only after substantial experience with cross-modal cue s.