Comparison of cerebral activation involved in oral and manual stereognosis.

Brain activity associated with manual stereognosis has been the focus of increasing recent research effort. However, although oral stereognosis, defined as the ability to recognize and discriminate the food bolus in the mouth, is important for mastication and swallowing, there is little information available about the neural network relating to this function. In the present study, cerebral activation associated with oral stereognosis was evaluated as compared with manual stereognosis. Brain imaging data were acquired by functional MRI (fMRI). fMRI experiments were performed on 16 healthy right-handed young adults without any history of neurological or psychiatric disorders. All subjects had all teeth without malocclusion. Ten stereognosis test shape pieces sized approximately 20 mm × 20 mm × 10 mm were fabricated for this experiment. All test pieces had a complicated form that made them difficult to recognize with ease. Subjects were instructed to assess the shape of the test piece in the mouth or hand. The ten test pieces were randomly assigned to each subject and each run. Stereognosis-specific activation was found in the primary somatosensory area, primary motor area, supramarginal gyrus, premotor area, supplementary motor area, fusiform gyrus, frontopolar area and dorsolateral prefrontal cortex. Differences in cerebral activation between oral and manual stereognosis were found in the insular cortex and visual association cortex.