Development of multisensory integration from the perspective of the individual neuron

Key Points The brain is able to maximize its detection and evaluation of external events by the process of multisensory integration, whereby information from different senses is synthesized and used in concert. Studies of single neurons in animals have revealed that this process is not present at birth, and studies of multisensory neurons in the superior colliculus have provided a developmental model by which the maturation of these neurons can be understood. This integrative capability gradually develops during postnatal life as the underlying neural circuit matures and as the brain acquires experience with cross-modal events. Disruptions of an essential cortical input or the absence of experience with cross-modal events does not preclude the development of multisensory neurons in the superior colliculus. However, it does interfere with the development of a multisensory neuron's capacity to integrate its sensory inputs. Experience also helps to craft the principles by which multisensory integration is instantiated in order to adapt the system to the environment in which it will be used. Thus, abnormal cross-modal experience can alter the principles that normally govern this process. Although multisensory integration capability is most rapidly developed in the young brain, under the proper circumstances even a brain deprived of cross-modal experience early in life can later develop this capability, albeit less efficiently. Superior colliculus neurons develop the ability to integrate information from different senses postnatally based on experience with cross-modal events. In this Review, Stein et al . discuss how this experience-dependent process ensures that this multisensory circuit and the behaviours it mediates are adapted to the environment in which they will operate. The ability to use cues from multiple senses in concert is a fundamental aspect of brain function. It maximizes the brain's use of the information available to it at any given moment and enhances the physiological salience of external events. Because each sense conveys a unique perspective of the external world, synthesizing information across senses affords computational benefits that cannot otherwise be achieved. Multisensory integration not only has substantial survival value but can also create unique experiences that emerge when signals from different sensory channels are bound together. However, neurons in a newborn's brain are not capable of multisensory integration, and studies i