Cutaneous and muscular afferents from the foot and sensory fusion processing: Physiology and pathology in neuropathies

Abstract

The foot-sole cutaneous receptors (section 2), their function in stance control (sway minimisation, exploratory role) (2.1), and the modulation of their effects by gait pattern and intended behaviour (2.2) are reviewed. Experimental manipulations (anaesthesia, temperature) (2.3 and 2.4) have shown that information from foot sole has widespread influence on balance. Foot-sole stimulation (2.5) appears to be a promising approach for rehabilitation. Proprioceptive information (3) has a pre-eminent role in balance and gait. Reflex responses to balance perturbations are produced by both leg and foot muscle stretch (3.1) and show complex interactions with skin input at both spinal and supra-spinal levels (3.2), where sensory feedback is modulated by posture, locomotion and vision. Other muscles, notably of neck and trunk, contribute to kinaesthesia and sense of orientation in space (3.3). The effects of age-related decline of afferent input are variable under different foot-contact and visual conditions (3.4). Muscle force diminishes with age and sarcopenia, affecting intrinsic foot muscles relaying relevant feedback (3.5). In neuropathy (4), reduction in cutaneous sensation accompanies the diminished density of viable receptors (4.1). Loss of footsole input goes along with large-fibre dysfunction in intrinsic foot muscles. Diabetic patients have an elevated risk of falling, and vision and vestibular compensation strategies may be inadequate (4.2). From Charcot-Marie-Tooth 1A disease (4.3) we have become aware of the role of spindle group II fibres and of the anatomical feet conditions in balance control. Lastly (5) we touch on the effects of nerve stimulation onto cortical and spinal excitability, which may participate in plasticity processes, and on exercise interventions to reduce the impact of neuropathy.

Specific Posture-Stabilising Effects of Vision and Touch Are Revealed by Distinct Changes of Body Oscillation Frequencies

“…Analogously, it seems simplistic to posit that the proprioceptive system is disturbed, or its contribution attenuated or invalidated when standing on foam ( 43 , 159 , 160 ). Sway while on foam compared to solid BoS may be less useful for “exploration” of the support base ( 161 ) and for “resetting” of the input from the adapting receptors of the foot sole ( 40 ). Whereas, pelvis and trunk movements may be more important in getting information about body segments' orientation in space when task difficulty increases ( 134 , 162 ).…”

“…Proprioception is crucial in the control of body stability and orientation in space (32)(33)(34)(35), and various manoeuvres have been put in place to clarify its role, including muscle vibration as a tool for activating the spindles (36) or leg ischemia by compression to attenuate the transmission of their firing (37,38). However, the contribution of the spindles to standing posture may not have been completely elucidated, not to speak of the role of the information from the foot sole and from the intrinsic foot muscles (39)(40)(41). These inputs under a quiet stance on the firm ground would play a limited function because the information originating in the primary spindle terminations, which are mainly sensitive to the velocity of muscle stretch (42), may not be crucial in the absence of rapid changes in muscle length.…”

“…When vision and touch are available, sway can further decrease compared to either information alone (63,74). On the other hand, removal of peripheral sensation, as by anaesthesia or cooling of the skin of the foot sole, increases body oscillations (40). It might be supposed that integration of multiple inputs, as from the eye, the skin, the proprioceptors, or the graviceptors, can afford excellent body stabilisation (reduction of CoP sway) in accordance with the assumption that "more is better."…”

“…When vision and touch are available, sway can further decrease compared to either information alone ( 63 , 74 ). On the other hand, removal of peripheral sensation, as by anaesthesia or cooling of the skin of the foot sole, increases body oscillations ( 40 ). It might be supposed that integration of multiple inputs, as from the eye, the skin, the proprioceptors, or the graviceptors, can afford excellent body stabilisation (reduction of CoP sway) in accordance with the assumption that “more is better.” This view would implicitly assume the existence of one posture-controlling centre able to integrate the sensory inputs and produce the adequate motor commands, which are evidently optimally designed when the centre receives the best possible amount of information.…”

Influence of pregnancy related anthropometric changes on plantar pressure distribution during gait—A follow-up study

“…However, to our knowledge, there were no longitudinal studies on the relationship between anthropometric changes following foetus growth and plantar pressure distribution pattern during gait. Given that even small changes in the foot deformation and feedback from the foot cutaneous and muscular receptors affect both posture and gait [21,22], longitudinal studies may further contribute to understanding important changes or adaptations in the gait pattern and stability that occur throughout pregnancy. Considering a reported high number of falls that occur in gestation period [6], it is of great importance to find out more about influencing factors.…”