Modulation of Spatial Processing By Somatosensory Inputs In The Rat

Abstract

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The generation of cognitive maps is influenced by different senses such as vision, audition or smell. However, the tactile information system -a highly developed system in the rat- and its influence on spatial processing, has hardly been studied. The availability of precise tactile information in the hippocampus (Pereira et al., 2007) is highly suggestive of a possible influence of tactile information on spatial processing. In this study we aimed to test if somatosensory information contributes to the cognitive map creation and spatial representation. The deprivation of the tactile sense without the possibility of using other senses (total darkness, homogeneous odour and uniform white noise), should then affect the coding of spatial information and could be detected as an alteration in place cell properties such as firing rate, location and/or extension of the firing fields. These types of changes would demonstrate that somatosensory inputs are involved in the cognitive map creation. To carry out this study we developed three kinds of experiments. First, we developed a paradigm (Gener et al., 2009) to temporarily deprive the tactile input using locally applied local anaesthesia (lidocaine). In a second part, we demonstrate that this deprivation was effective in the awake animal, altering the behaviour during tactile discrimination protocols and reducing successful trials from 88% to chance (48%). Finally, we applied the deprivation technique to characterise the cognitive map creation. With that purpose, we first demonstrated that place cells recorded in a controlled environment were sensitive to tactile cues, such that the rotation of the cues induce the rotation of the firing fields. Next, when tactile information was deprived, the place cells’ fields showed changes in their compactness and size. The results of this study suggest that somatosensory input information transduced by the whiskers contributes to the cognitive map creation. Those findings respond to some of the questions about hippocampus integration’s of sensory information.