The plantar sole is a

In addition to the central postural program, multiple sensory modalities are involved in the organization and control of human erect posture. Numerous studies have focused on the specific role of vestibular,1,2 visual3,4 or muscular5,6 sensory information, but little is known about the role of cutaneous information from the soles. Because they are at the boundary between the body and the ground, the cutaneous mechanoreceptors of the soles might play an important role in controlling balance. Data supporting this view were obtained through two experimental approaches. A first method consisted of transiently eliminating the exteroceptive afferents by cooling7 or anesthetizing8,9 the plantar soles. In all cases, suppressing these inputs increased the postural instability. The body sways induced by sinusoidal low frequency (0.3 Hz) displacement of the supporting surface were also increased when an ischemic block of afferent fibers was applied above the ankles.10,11 In addition, this loss of foot sensitivity resulted in a new strategy to compensate the body disequilibrium, that is, an increased hip strategy instead of the ankle strategy generally used under normal conditions.12 The ischemic blocking method, however, does not selectively exclude the tactile afferences since it also eliminates all the somatosensory inputs from the feet, including the proprioceptive ones. The second method generally used to study the role of plantar cutaneous messages in postural control consisted of changing the characteristics of the supporting surface on which the subject is standing. In fact, by recording the pressure distribution under the soles, Wu and Chiang13 demonstrated that standing on a soft (foam) surface reduced the amplitude of the maximal plantar pressures and increased the contact area between the sole and the support. The resulting ankle muscle responses induced by a sudden toes-up rotation of this supporting surface were then delayed. Conversely, standing on a shotgun ball platform14 resulted in a decrease in the postural body sways. The contribution of plantar cutaneous afferents to balance control is largely evidenced by these protocols excluding or stimulating all of these afferents. However, how the plantar mechanoreceptors are functionally involved in balance control remains unclear. Studies focusing on the mechanoreceptors of the glabrous skin of the rat foot15 and of the human hand16 and foot17 have shown there are different types of mechanoreceptors, whose distribution and density vary according to the skin areas considered. Because of their specific functional properties, the mechanoreceptors are able to code together the spatial origin, Cognitive Neuroscience