Quantitative measures of smoothness play an important role in the assessment of sensorimotor impairment and motor learning. Traditionally, movement smoothness has been computed mainly for discrete movements, in particular arm, reaching and circle drawing, using kinematic data. There are currently very few studies investigating smoothness of rhythmic movements, and there is no systematic way of analysing the smoothness of such movements. There is also very little work on the smoothness of other movement related variables such as force, impedance etc. In this context, this paper presents the first step towards a unified framework for the analysis of smoothness of arbitrary movements and using various data. It starts with a systematic definition of movement smoothness and the different factors that influence smoothness, followed by a review of existing methods for quantifying the smoothness of discrete movements. A method is then introduced to analyse the smoothness of rhythmic movements by generalising the techniques developed for discrete movements. We finally propose recommendations for analysing smoothness of any general sensorimotor behaviour.

Background and Purpose — The goal of this study was to characterize cortical reorganization after stroke and its relation with the site of the stroke-induced lesion and degree of motor recovery using functional MRI (fMRI). Methods — Fourteen stroke patients with an affected upper limb were studied longitudinally. Three fMRI sessions were performed over a period of 1 to 6 months after stroke. Upper limb recovery, Wallerian degeneration of the pyramidal tract, and responses to transcranial magnetic stimulation were assessed. Results — Two main patterns of cortical reorganization were found. Pattern 1 was focusing, in which, after initial recruitment of additional ipsilateral and contralateral areas, activation gradually developed toward a pattern of activation restricted to the contralateral sensorimotor cortex in 9 patients. Five patients were found to have pattern 2, persistent recruitment, in which there was an initial and sustained recruitment of ipsilateral activity. Occurrence of recruitment or focusing seemed to depend mainly on whether the primary motor cortex (M1) was lesioned; persistent recruitment was observed in 3 of 4 patients with M1 injury, and focusing was seen in 8 of 10 patients with spared M1. These patterns had no relation to the degree of recovery; in particular, focusing did not imply recovery. However, there was a clear relation between the degree of recovery and the degree of Wallerian degeneration. Conclusions — These results suggest that ipsilateral recruitment after stroke corresponds to a compensatory corticocortical process related to the lesion of the contralateral M1 and that the process of compensatory recruitment will persist if M1 is lesioned; otherwise, it will be transient.

Since the late 1990s, there has been a burst of research on robotic devices for poststroke rehabilitation. Robot-mediated therapy produced improvements on recovery of motor capacity; however, so far, the use of robots has not shown qualitative benefit over classical therapist-led training sessions, performed on the same quantity of movements. Multidegree-of-freedom robots, like the modern upper-limb exoskeletons, enable a distributed interaction on the whole assisted limb and can exploit a large amount of sensory feedback data, potentially providing new capabilities within standard rehabilitation sessions. Surprisingly, most publications in the field of exoskeletons focused only on mechatronic design of the devices, while little details were given to the control aspects. On the contrary, we believe a paramount aspect for robots potentiality lies on the control side. Therefore, the aim of this review is to provide a taxonomy of currently available control strategies for exoskeletons for neurorehabilitation, in order to formulate appropriate questions toward the development of innovative and improved control strategies.

The nociceptive flexion reflex (R₁₁₁ reflex) and the concurrent subjective pain score elicited by right sural nerve stimulation at random intensities were studied in 10 healthy volunteers. A close relationship was found between the recruitment curves of the reflex and the pain score as a function of stimulus intensity. As a consequence, the threshold of the R₁₁₁ reflex (T_r) and of pain sensation (T_p) were found to be almost identical (mean: 9.8 and 11.3 mA, respectively). Similarly, the threshold for obtaining a maximal reflex response (T_mr) was found to be very close to that for intolerable pain (T_lp): 33.5 and 35.1 mA, respectively. These four parameters were studied before and during the immersion of the left hand into a heated thermoregulated waterbath at various temperatures (from 40 to 47.5° Q. While nonnociceptive temperatures (40 to 44° C) were without effect, higher conditioning temperatures induced an increase in the four thresholds. In addition, a highly significant linear relationship was observed between the increase in these thresholds and the intensity of the conditioning stimulus in the 44 to 47.5°C range. These four parameters were also studied before and during three other nociceptive conditioning stimuli: immersion of the left hand into a 6°C waterbath, 10 watts muscular exercise of the left hand performed under ischaemia and a painful (5.5 kg/cm2) pinch applied on the nasal septum. These three conditioning situations induced a very significant increase of the four thresholds considered in this study with the greatest being observed during nociceptive cold applied to the left hand. During all the conditioning situations, variations in T_r and T_p as well as in T_mr and T_ip were found to be linearly related. This indicates a close relationship between the effects of the conditioning nociceptive stimuli on the reflex and the related pain sensation. These results suggest that the modulation of pain by heterotopic nociceptive stimuli can be explained at least in part by a depression in the transmission of nociceptive messages at the spinal level. They are discussed with reference to the counterirritation phenomena and common features with 'diffuse noxious inhibitory controls' (DNIC) are underlined.

Objectives – To examine the mechanisms of alternative strategies developed by stroke patients to compensate their motor impairment and their role in recovery. Material and methods – The three‐dimen...