Sensory maps: Aligning maps of visual and auditory space

Survival, for predator or prey, may turn on the fraction of a second it takes an animal to centre its gaze on the source of a sound or movement detected in its periphery. Central to the performance of this task is a nucleus in the midbrain called, in mammals, the superior colliculus. This structure combines sensory information with signals from motor areas and computes an output to control the eye, head, body and outer-ear (pinna) movements needed to bring the animal’s attention to bear on an object of interest (see [1] for review). The superior colliculus includes topographic representations — maps — of visual and auditory space, and recent results have shed new light on the mechanisms that operate to align these two representations during an animal’s early life. Maps of sensory space in the superior colliculus Neurons in the superficial layers in each of the two superior colliculi respond to visual stimuli, whereas cells in the deeper layers respond to auditory, visual and tactile inputs. The receptive field positions for each modality are represented topographically in the superior colliculus: stimulus locations in the azimuthal (horizontal) plane are represented along the rostrocaudal axis, whereas stimulus elevation (the vertical plane) is represented along the mediolateral axis (Fig. 1). Thus, the maps are in register [2–4]. Neurons that receive inputs from motor structures are also to be found in the deep layers, as are the neurons that send control signals to a variety of motor nuclei [5]. These topographic representations may have evolved because they are computationally efficient: neighbouring regions of space that will be occupied sequentially by a moving stimulus are linked by the shortest and, therefore, the fastest connections. This arrangement will also make it easier to relate corresponding regions of space represented by the different modalities, and facilitate the organization of the motor outputs.