Hierarchical Neural Process to Detect Moving Tactile Stimuli in the postcentral Oral Representation of Conscious Macaque Monkeys

The representation of the oral structures in the postcentral somatosensory cortex (areas 3b, 1 and 2) was studied in conscious Japanese monkeys (Macaca fuscata) by recording single neuronal activity. Neuronal receptive fields (RFs) were examined by manually applying simple tactile stimuli such as light touching or pressing, and moving tactile stimuli. A large body of data was collected from eight hemispheres of six male animals. A total of 3,435 neurons responded to tactile stimuli. Most of them (96%, 3,297/3,435) responded to simple tactile stimuli (simple tactile neurons), whereas the rest (4%, 138/3,435) responded exclusively to moving tactile stimuli (movement-specific neurons). The relative incidences of movement-specific neurons among the total sample were 1.2% in area 3b and increased gradually with statistical significance upon moving caudally toward area 1 (4.4%) and area 2 (7.2%). Ninety percent of the neurons had ordinary uninterrupted RFs (continuous RFs) and the remaining 10% had RFs composed of several discrete RF-portions, e. g., the tongue dorsum and palate (discontinuous RFs). The relative incidences of neurons with discontinuous RFs in area 3b or 2 were significantly higher in movement-specific neurons than in simple tactile neurons. This suggests that the spatiotemporal integration to represent motion proceeds across the postcentral oral region and tends to be accompanied by the convergence of inputs from discrete but functionally related oral portions.