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Hands and knees crawling is an important motor developmental milestone but the current clinical measures of motor function during crawling stage are relatively subjective. Objective metrics using kinematics and electromyography (EMG) in infant crawling may provide more stable and accurate measures of such developmental milestone, demonstrating changes in locomotion during age span. The purpose of this paper was to determine whether joint kinematics and the underlying co-activation between flexor and extensor in infant crawling are different for arms and legs across the infant age span. Surface EMG of two pairs of flexors and extensors from arms and legs and the corresponding joint kinematic data were collected in twenty health infants (11 males and 9 females, range 8-15 months), while they were crawling on hands and knees. Co-activation index of averaged EMG was used to quantify the simultaneous contractions between flexor and extensor muscles. Coefficient of variation of joint's maximum vertical acceleration from multiple cycles was used to quantify the repeatability of kinematics during crawling. Our results indicated that the arm exhibited significantly higher co-activation and higher repeatability of joint movement than the leg, suggesting earlier development of arm compared to leg. Moreover, elder age groups, who had stronger walking ability developed, showed increased co-activation of the leg and significant increase in repeatability of the knee movement. These results were consistent with the rapid reinforcement of the leg during motor development from quadrupeds to bipedal walking. Furthermore, the EMG and kinematic parameters were significantly correlated with clinical variables. These results suggest that the EMG and kinematic analysis of infant crawling are useful in building effective assessment of infant's motor function before independent walking.

Pulsed infrared irradiation is an alternative neural stimulation with the advantages of being non-contact, spatially precise and artifact-free. Although infrared neural stimulation (INS) is well characterized in the peripheral nervous system, research has been limited in the central nervous system (CNS), especially the near infrared with wavelength around 800 nm. To establish feasibility of INS in the CNS, pulsed near infrared laser ( λ = 808 nm, pulse duration = 300–1000 μs, radiant exposure = 0.73–2.45 J/cm 2 , fiber size = 105 μm, repetition rate = 2 Hz) was used to stimulate the primary visual cortex (V1) of anesthetized Long Evans (LE) rats and the near-infrared-evoked neural activities in V1 was recorded. The impact of the duration of infrared pulse on the intensity and the latency of evoked potentials was assessed. We found that V1 was activated by 808 nm laser and the optical evoked potential (OEP) included a descending wave (D1) and an ascending wave (A1) after optical stimuli. Furthermore, with the increase of the stimulation pulse duration, both the amplitude of D1 and the latency of A1 were increased. The results from this paper will facilitate the applications of near infrared neural stimulation on central nervous system.

Pulsed near-infrared radiation has been proposed as an alternative stimulus for auditory nerve stimulation and could be potentially used in the design of cochlear implant. Although the infrared with high absorption coefficient of water (i.e., wavelength ranged from 1.8 to 2.2 μm) has been widely investigated, the lymph in the cochlea absorbs most of the infrared energies, and only a small part can arrive at the target auditory nerves. The present study is aimed to test whether the short-wavelength near-infrared irradiation with lower absorption coefficients can penetrate the lymph fluid to stimulate the auditory nerves. An 808-nm near-infrared laser was chosen to stimulate the auditory nerve in the guinea pig cochlea. The infrared pulse was delivered by an optical fiber that was surgically inserted near the round window membrane and oriented toward the spiral ganglion cells in the basal turn of the cochlea. The 2-Hz infrared pulses were used to stimulate the cochlea before and after the deafness with different pulse durations (100-1,000 μs). Optically evoked compound action potentials (oCAPs) were recorded during the infrared radiation. We successfully recorded oCAPs from both normal hearing animals and deafened animals. The oCAP amplitude increased with the infrared radiation energy. The preliminary experiment suggests that the near-infrared with lower absorption coefficients can effectively pass through the lymph filled in the cochlea and stimulate the auditory nerve. Further studies will optimize the deafness animal model and determine the optimal stimulation parameters.

Mandarin speech has four different tones and the coding mechanism underlying tone identification still remain unclear. Here in the inferior colliculus (IC) of anesthetized guinea pigs, we recorded single neuron activities to one word with four tones using tungsten electrode. Peri-stimulus time histograms (PSTHs) and inter-spike-interval (ISI) were used to evaluate the neural response. The results showed that PSTHs grouped into frequency band reflected the spectrotemporal patterns of different tones; average population PSTHs matched envelops of different tones; and the peaks of histogram of ISIs in three time segments exhibited a displacement which reflected the profile of fundamental frequency (F0). These preliminary results suggested IC neurons could encode the spectrotemporal acoustic features of different Mandarin tones.

Although infrared laser was proven to be an alternative approach for neural stimulation, there is very little known about the neural response to infrared laser irradiation in visual cortex. This study is to investigate the effect of near-infrared laser irradiation on neural activities at the cortex level. A 850-nm pigtailed diode laser was applied to stimulate the rat primary visual cortex while the horizontal black and white stripe pattern was used as standard visual stimulation to evoke visual-evoked potential (VEP). Both amplitude and latency of VEP P100 was measured with or without infrared pulse stimulation applied in rat primary visual cortex. Paired t test and one-way analysis of variance were used to evaluate the impact of infrared irradiation and its pulse width on the amplitudes and latencies of P100, respectively. The results from our preliminary study revealed that, the pulsed near-infrared laser depressed the VEP amplitude and shortened the latency of P100; with the increment of pulse width of infrared irradiation, further decline of VEP amplitude and much shortened latency of P100 were observed. The present work suggests that near-infrared laser irradiation can alter the neural activities in primary visual cortex transiently, and could provide a novel contactless artificial neural stimulus to brain cortex with high spatial selectivity.

Multitendoned extrinsic muscles of the human hand can be divided into several neuromuscular compartments (NMCs), each of which contributes to the ability of human finger to produce independent finger movements or force. The aim of this study was to investigate the changes in the spatial activation of flexor digitorum superficialis (FDS) during the fingertip force production with non-invasive multichannel surface electromyography (sEMG) technique. 7 healthy Subjects were instructed to match the target force level for 5s using individual index finger (I), individual middle finger (M) and the combination of the index and middle finger (IM) respectively. Simultaneously, a 2 × 6 electrode array was employed to record multichannel sEMG from FDS as finger force was produced. The entropy and center of gravity of the sEMG root mean square (RMS) map were computed to assess the spatial inhomogeneity in muscle activation and the change in spatial distribution of EMG amplitude related to the force generation of specific task finger. The results showed that the area and intensity of high amplitude region increased with force production, and the entropy increased with force level under the same task finger. The findings indicate that the change of spatial distribution of multitendoned extrinsic hand muscle activation is correlated to specific biomechanical functions.

This study aimed to explore if the red light irradiation can affect the electrophysiology performance of flexor digitorum superficialis (FDS) and fatigue recovery. Four healthy volunteers were randomly divided into two groups. In the designed force-tracking tasks, all subjects performed the four fingertip isometric force production except thumb with a load of 30% of the maximum voluntary contraction (MVC) force until exhaustion. Subsequently, for the red light group, red light irradiation (640 nm wavelength, 0.23J/cm 2 , 20 min) was used on the right forearm; for the control group, the subjects relaxed without red light irradiation. Then subjects were required to perform fatigue trail again, and sEMG signal was collected simultaneously from FDS during finger force production. Average rectified value (ARV) and median frequency (MF) of sEMG were calculated. Compared to the control group, the red light irradiation induced more smoother value of ARV between 30% and 40%, and the value of MF was obviously large and smooth. The above electrophysiological markers indicated that recovery from muscle fatigue may be positively affected by the red light irradiation, suggesting that sEMG would become a power tool for exploring the effect of red light irradiation on local muscle fatigue.

Quantizing the relationship between finger force and multitendoned extrinsic hand muscles could be useful for understanding the control strategies that underlie the coordination of finger movements and forces. The objective of this study is to explore the relationship of fingertip force production and total power of surface electromyography (sEMG) recorded on extrinsic hand muscles under isometric voluntary contraction. Thirteen healthy volunteers were recruited to participate in this study. In the designed force-tracking tasks, all volunteers were required to produce a certain force with either index finger or middle finger to match the target force for 5 s. Meanwhile, the sEMG signals were acquired from two extrinsic hand muscles: extensor digitorum (ED) and flexor digitorum superficialis (FDS). For each trial, sEMG of the effective force segment was extracted; then, the power spectrum was estimated based on autoregressive (AR) model and from which the corresponding total power of sEMG was computed. The experimental results reveal that the total power of sEMG linearly increases with force level regardless of the task finger and extrinsic hand muscle. It is also found that the total power obtained from index finger is significantly less than that of middle finger for FDS at the same force level (p < 0.05), while this kind of statistical significance cannot be found for ED. However, with respect to the measurement of total power, the type of extrinsic hand muscle has not exhibited significantly different contribution to the task finger under a certain fingertip force level. The findings of this study indicate that the total power of the extrinsic hand muscle's sEMG can be used to characterize finger's activities.