Neuroscience Letters 480 (2010) 178–181 Contents lists available at ScienceDirect Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet Does somatosensory loss induce adaptation of the gait initiation process? M. Vinti a,∗ , A. Couillandre b , P. Thoumie a,c a Laboratoire du service de rééducation neuro-orthopédique, APHP et UPMC Paris-6, Hôpital Rothschild, 21 passage Gatbois, F-75012 Paris, France b EA 2931, UFR STAPS, Université Paris Ouest Nanterre La Défense, France c CMP EA 4042 UFR STAPS, Université Paris-Sud 11 F-91405 Orsay, France article info Article history: Received 16 November 2009 Received in revised form 4 June 2010 Accepted 6 June 2010 Keywords: Initiation of movement Ataxia Center of gravity and foot pressure abstract Gait initiation (GI) is the transient period between posture and movement. Its central programming takes into account the environmental constraints as well as the constraints induced by the body itself. Patients with peripheral sensory neuropathies display a severe proprioceptive deficit leading to balance and gait impairments and rely on a variety of compensatory mechanisms and are known to be dependent on vision. GI was studied on eight healthy subjects and five patients in order to assess the effect of somatosensory loss on the different phases of GI, combined with a manipulation of the visual inputs. Our main hypothesis is that the proprioceptive deficit would induce an adaptation of the GI process, especially when modifying the lower part of peripheral vision. The results show that the pathology induces some adaptations of the GI process, characterized by a decrease of the motor performance (assessed by the maximal anteroposterior velocity of the center of gravity at the end of the first step), a decrease in the spatial parameters (assessed by the peak amplitude of the backward shift of the center of foot pressure during the anticipation phase and the length of the first step), and a non-modification of the temporal parameters (assessed by the duration of the anticipation phase and of the first step). The suppression of the lower part of peripheral vision has no effect on the GI process. The role of the lower part of peripheral vision seems therefore to be less critical for GI, than for balance and locomotion. © 2010 Elsevier Ireland Ltd. All rights reserved. Chronic neuropathies with ataxia are debilitating diseases charac- terized by the predominance of sensory disorders affecting large myelinated fibers leading to major handicaps. They are charac- terized by sensory-motor deficits that predominantly affect the lower limbs and are associated with balance and gait impairments. Peripheral neuropathy patients have problems maintaining a sta- ble posture [30,19] and this impairment seems to be correlated with the severity of the disease [6]. Consequently, they develop compensatory strategies based on available sensory inputs in order to maintain balance. Thus, postural instability may be reduced by a gentle fingertip touch [16]. Similarly, in case of profound sen- sory loss, auditory stimulation may facilitate the onset of adapted postural responses during an anteroposterior imbalance, especially when the latter is performed with closed eyes [18]. Furthermore, vision appears to be crucial for the maintenance of equilibrium [19]. These patients are usually described as vision dependent. Vision enables those patients to maintain the execution of fine and precise movements [2]. Whereas many studies have been conducted on the regulation of movement in the presence of a somatosensory loss, to our knowl- edge no study has investigated movement initiation, that is why we have chosen the experimental paradigm of gait initiation. ∗ Corresponding author. Tel.: +33 6 74 21 73 04. E-mail address: maria.vinti@neuf.fr (M. Vinti). Gait initiation is a particularly interesting situation in order to study gait programming because it enables a better understanding of the central and peripheral mechanisms involved in this pro- cess. As a model in the interactions between posture, equilibrium and voluntary movement, gait initiation analyzes the postural and dynamic needs that have to be satisfied prior to walking and also enables to identify adaptations in the motor command performed by the CNS if occurs an impairment. In addition, this experimen- tal paradigm is of significant clinical interest because compared to conventional walking tests, its implementation is easier, especially for patients displaying a great fatigability. The gait initiation phase corresponds to the transient period between two stable states, the initial posture and steady state gait, during which the postural synergy disappears and the locomotor synergy appears [9]. It is included between the onset of the first mechanical phenomena and the time when the maximum veloc- ity of the center of gravity (CG) in the sagittal plane is reached, i.e. at the end of the first step. It consists of two distinct phases: an early postural phase characterized by its anticipatory postural adjustments (APA) and an execution phase, the separation between these two phases being at the time of the swing limb heel-off. It begins with a body forward fall allowing the release of gravita- tional forces initially neutralized by the activity of the Soleus [9,15]. The APA phase is characterized by a CG forward shift towards the stance foot and a backward shift of the center of foot pressure (COP) towards the swing foot [7]. In the sagittal plane, the amplitude of 0304-3940/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2010.06.017