Introduction 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 visual 3,4 or muscular 5,6 sensory informa- tion, 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 con- sisted of transiently eliminating the exteroceptive afferents by cooling 7 or anesthetizing 8,9 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 Chiang 13 demonstrated that standing on a soft (foam) surface reduced the ampli- tude 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 shot- gun ball platform 14 resulted in a decrease in the postural body sways. The contribution of plantar cutaneous afferents to balance control is largely evidenced by these proto- cols 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 foot 15 and of the human hand 16 and foot 17 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 mechano- receptors are able to code together the spatial origin, Cognitive Neuroscience 1111 2 3 4 5 6 7 8 9 10111 1 2 3 4 5 6 7 8 9 20111 1 2 3 4 5 6 7 8 9 30111 1 2 3 4 5 6 7 8 9 40111 1 2 3 4 5 6 7 8 9 50111 1 2 3 4 5 6111p 0959-4965 © 1998 Lippincott Williams & Wilkins Vol 9 No 14 5 October 1998 3247 THIS study investigated the role of the plantar cutaneous information in controlling human balance. We hypothesized that the cutaneous afferent messages from the main supporting zones of the feet have suffi- cient spatial relevance to inform the CNS about the body position with respect to the vertical reference and conse- quently to induce adapted regulative postural responses. Skin mechanoreceptors of anterior and/or posterior areas of one or both soles of 10 standing subjects were activated by superficial mechanical vibration with high frequency and low amplitude. Variations of the subject’s center of pressure (CoP) were recorded. Spatially oriented whole-body tilts were observed for every subject. Their direction depended on the foot areas stimulated and was always opposite to the vibration- simulated pressure increase. These responses are found to subserve a postural regulative function and we suggest that co-processing of the various cutaneous messages followed a vector addition mode. NeuroReport 9: 3247–3252 © 1998 Lippincott Williams & Wilkins. Key words: Center of pressure (CoP); Human posture; Soles; Tactile afferents; Vibration The plantar sole is a ‘dynamometric map’ for human balance control Anne Kavounoudias, CA Régine Roll and Jean-Pierre Roll Laboratoire de Neurobiologie Humaine, UMR 6562, CNRS-Université de Provence, Marseille cedex 20, France CA Corresponding Author Website publication 16 October 1998 NeuroReport 9, 3247–3252 (1998)