Long-lasting changes in muscle activation and step cycle variables induced by repetitive sensory stimulation to discrete areas of the foot sole during walking

We examined whether repetitive electrical stimulation to discrete foot sole regions that is phase-locked to the step cycle modulates activity patterns of ankle muscles and induces neuronal adaptation during human walking. Non-noxious repetitive foot sole stimulation (STIM; 67 pulses @333 Hz) was given to the medial forefoot (f-M) or heel (HL) regions at (1) the stance-to-swing transition, (2) swing-to-stance transition, or (3) mid-stance, during every step cycle for 10 min. Stance, but not swing, durations were prolonged f-M STIM delivered at stance-to-swing transition, and these changes remained for up to 20-30 min after the intervention. Electromyographic (EMG) burst durations and amplitudes in the ankle extensors were also prolonged and persisted for 20 min after the intervention. Interestingly, STIM to HL was ineffective at inducing modulation, suggesting stimulation location-specific adaptation. In contrast, STIM to HL (but not f-M), at the swing-to-stance phase transition, shortened the step cycle by premature termination of swing. Furthermore, the onset of EMG bursts in the ankle extensors appeared earlier than in the control condition. STIM delivered during the mid-stance phase was ineffective at modulating the step cycle, highlighting phase-dependent adaptation. These effects were absent when STIM was applied while mimicking static postures for each walking phase during standing. Our findings suggest that the combination of walking-related neuronal activity with repetitive sensory inputs from the foot can generate short-term adaptation that is phase-dependent and localized to the site of STIM.

The Babinski sign in Renaissance paintings—a reappraisal of the toe phenomenon in representations of the Christ Child: observational analysis

Objective To investigate systematically the presence of the Babinski sign in paintings of the Christ Child by the greatest painters of the Renaissance. Design Observational analysis. Setting Large collection of paintings depicting the Christ Child from Flemish, Rhenish, and Italian schools between 1400 and 1550 CE, searched using published catalogues and Google. Study sample 302 Renaissance paintings (by 19 painters) depicting the Christ Child. Main outcome measure Babinski sign, defined as a hallux extension with an amplitude greater than 30°. The presence of foot sole stimulation was also noted. Results An unquestionable upgoing toe was apparent in 90 (30%) of the 302 paintings. The Babinski sign was present in more than 60% of Christ Child paintings by Rogier van der Weyden, Hans Memling, Martin Schongauer, and Matthias Grünewald. A bilateral Babinski sign was observed in three paintings. Stimulation of the sole was noted in 48/90 (53%) paintings and was always present in paintings by Andrea del Verrocchio, Leonardo da Vinci, and Giorgione. No association existed between the presence of the Babinski sign and the period during which the painter was active. Conclusions Four main factors were noted in relation to the representation of the Babinski sign in paintings of the Christ Child: the physiological toe phenomenon in infants, the representation of the nudity of the Christ by painters during the 15th century to demonstrate the incarnation, Renaissance painters’ need for precise observation of anatomy, and the desire of some Rhenish and Flemish painters to depict very realistic details. Italian Renaissance painters, whether Mannerist or not, tended to idealise the beauty of human body, and they often did not reproduce the Babinski sign.

Plantar Cutaneous Afferents Normalize the Reflex Modulation Patterns During Stepping in Chronic Human Spinal Cord Injury

Plantar cutaneous afferent transmission is critical for recovery of locomotion in spinalized animals, whereas a phase-dependent reflex modulation is apparent during fictive or real locomotion. In nine people with a chronic spinal cord injury (SCI) the effects of foot sole stimulation on the soleus H-reflex and tibialis anterior (TA) flexion reflex modulation patterns during assisted stepping were established on different days. The soleus H-reflex was elicited by posterior tibial nerve stimulation followed by a supramaximal stimulus 100 ms after the test H-reflex to control for movement of recording electrodes. The flexion reflex was evoked by sural nerve stimulation with a 30-ms pulse train, recorded from the ipsilateral TA muscle, and elicited at 1.2- to twofold the reflex threshold. During assisted stepping, spinal reflexes were conditioned by percutaneous stimulation of the ipsilateral metatarsals at threefold perceptual threshold with a 20-ms pulse train delivered at 9- to 11-ms conditioning-test intervals. Stimuli were randomly dispersed across the step cycle, which was divided into 16 equal bins. The conditioned soleus H-reflex was significantly facilitated at midstance and depressed during midswing when compared with the unconditioned soleus H-reflex recorded during stepping. Foot sole stimulation induced a significant facilitation of the long-latency TA flexion reflex before, during, and after stance-to-swing transition when compared with the unconditioned long-latency TA flexion reflex during stepping. This study provides evidence that plantar cutaneous afferents remarkably influence the soleus H-reflex and TA flexion reflex modulation patterns during stepping and support that actions of plantar cutaneous afferents onto spinal interneuronal circuits engaged in locomotion are manifested in a phase-dependent manner in chronic SCI subjects.