Wednesday, January 24, 2007

Early Experience Determines How the Senses Will Interact

This is the title of a fascinating article by Wallace and Stein in the January issue of the Journal of Neurophysiology. They reared cats "in an altered sensory environment in which visual and auditory stimuli were temporally coupled but originated from different locations. Neurons in the superior colliculus (SC) developed a seemingly anomalous form of multisensory integration in which spatially disparate visual-auditory stimuli were integrated in the same way that neurons in normally reared animals integrated visual-auditory stimuli from the same location. The data suggest that the principles governing multisensory integration are highly plastic and that there is no a priori spatial relationship between stimuli from different senses that is required for their integration. Rather, these principles appear to be established early in life based on the specific features of an animal's environment to best adapt it to deal with that environment later in life."

Andrew King writes an essay in the same issue giving more context for these experiments and relating them to studies on humans, where plasticity of multisensory processing has also been shown to occur. One definition clip from the essay: "for each sensory modality, stimulus location is represented topographically in the SC to form overlapping maps of space. In principle, this allows the different sensory cues associated with a common source to activate a specific region of the SC motor map and therefore be transformed into motor commands that result in a change in gaze direction....many of the neurons found in the deeper layers of this midbrain structure receive converging inputs from two or more sensory systems and generate higher spike discharge rates—and it is likely, in turn, more accurate orienting responses—when combinations of stimuli are delivered in close temporal and spatial proximity."

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