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Sensory maps are areas of the brain which respond to sensory stimulation, and are spatially organized according to some feature of the sensory stimulation. In some cases the sensory map is simply a topographic representation of a sensory surface such as the skin, cochlea, or retina. In other cases it represents other stimulus properties resulting from neuronal computation and is generally ordered in a manner that reflects the periphery. An example is the somatosensory map which is a projection of the skin's surface in the brain that arranges the processing of tactile sensation. This type of somatotopic map is the most common, possibly because it allows for physically neighboring areas of the brain to react to physically similar stimuli in the periphery or because it allows for greater motor control. The somatosensory cortex is adjacent to the primary motor cortex which is similarly mapped. Sensory maps may play an important role in facilitating motor responses. Other examples of sensory map organization may be that adjacent brain regions are related through proximity of the receptors that they process as in the map of the cochlea in the brain, or that similar features are processed as in the map of the feature detectors or the retinotopic map, or that time codes are used in organization as in the maps of an owl's sense of direction via interaural time difference between ears. These examples exist in contrast to non-mapped or randomly distributed patterns of processing. An example of a non-mapped sensory processing system is the olfactory system where unrelated odorants are processed side-by-side in the olfactory bulb. In addition to non-mapped and mapped processing, stimuli may be processed under multiple maps as in the human visual system. ==Functions== Mapped sensory processing areas are a complex phenomenon and must therefore serve an adaptive advantage as it is highly unlikely for complex phenomena to appear otherwise. Sensory maps are also very old in evolutionary history as they are nearly ubiquitous in all species of animals and are found for nearly all sensory systems. Some advantages of sensory maps have been elucidated by scientific exploration: # Filling In: When sensory stimulation is organized in the brain in some form of topographic pattern, then the animal might be able to “fill in” information that is missing using neighboring regions of the map since they will usually be activated together when all information is present. Loss of signal from one area can be filled in from adjacent areas of the brain if those areas are for physically related parts of the periphery. This is evident in animal studies where the neurons bordering a lesioned, or damaged, brain area (which used to process the sense of touch in a hand) to recover processing of that sensory region because they process information from adjacent hand areas.〔Jain, N., Qi, H.X., Collins, C.E., and Kass, J.H. (1989), Large-Scale Reorganization in the Somatosensory Cortex and Thalamus after Sensory Loss in Macaque Monkeys. Journal of Neuroscience. Vol 28(43): 11042–11060〕 # Lateral Inhibition: Lateral inhibition is an organizing principle, it allows contrast in many systems from the visual to the somatosensory. This means that if adjacent areas inhibit one another then stimulation which activates one brain region can simultaneously inhibit the adjoining brain regions to create a sharper resolution between stimuli. This is evident in the visual system of humans where sharp lines can be detected between bright and dark regions because of simple cells which inhibit their neighbors. # Summation: Organization also allows related stimuli to be summed in the neural assessment of sensory information. Examples of this are found in the summation of tactile inputs neurally or visual inputs under low light 〔Laughlin, S. (1989), The Role of Sensory Adaptation in the Retina. Journal of Experimental Biology. 146, 39-6〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「sensory maps」の詳細全文を読む スポンサード リンク
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