Bo Geng

Impacts of selected stimulation patterns on the perception threshold in electrocutaneous stimulation

BackgroundConsistency is one of the most important concerns to convey stable artificially induced sensory feedback. However, the constancy of perceived sensations cannot be guaranteed, as the artificially evoked sensation is a function of the interaction of stimulation parameters. The hypothesis of this study is that the selected stimulation parameters in multi-electrode cutaneous stimulation have significant impacts on the perception threshold.MethodsThe investigated parameters included the stimulated location, the number of active electrodes, the number of pulses, and the interleaved time between a pair of electrodes. Biphasic, rectangular pulses were applied via five surface electrodes placed on the forearm of 12 healthy subjects.ResultsOur main findings were: 1) the perception thresholds at the five stimulated locations were significantly different (p < 0.0001), 2) dual-channel simultaneous stimulation lowered the perception thresholds and led to smaller variance in perception thresholds compared to single-channel stimulation, 3) the perception threshold was inversely related to the number of pulses, and 4) the perception threshold increased with increasing interleaved time when the interleaved time between two electrodes was below 500 μs.ConclusionsTo maintain a consistent perception threshold, our findings indicate that dual-channel simultaneous stimulation with at least five pulses should be used, and that the interleaved time between two electrodes should be longer than 500 μs. We believe that these findings have implications for design of reliable sensory feedback codes.

Human ability in identification of location and pulse number for electrocutaneous stimulation applied on the forearm

BackgroundThe need of a sensory feedback system that would improve users’ acceptance in prostheses is generally recognized. Feedback of hand opening and position are among the most important concerns of prosthetic users. To address the two concerns, this study investigated the human capability to identify pulse number and location when electrical stimulation applied on the forearm skin. The pulse number may potentially be used to encode the opening of prosthetic hands and stimulation location to encode finger position.MethodsTen able-bodied subjects participated in the study. Three electrodes were placed transversely across the ventral forearm spatially encoding three fingers (i.e., thumb, index, and middle finger). Five different pulse numbers (1, 4, 8, 12, and 20) encoded five levels of hand opening. The study consisted of three experiments. In the three experiments, each after a training session, the subjects were required to identify among: (a) five stimulation locations, (b) five pulse numbers, or (c) ten paired combinations of location and pulse number, respectively. The subjects’ performance in the three identification tasks was evaluated.ResultsThe main results included: 1) the overall identification rate for stimulation location was 92.2 ± 6.2%, while the success rate in two-site stimulation was lower than one-site stimulation; 2) the overall identification rate for pulse number was 90.8 ± 6.0%, and the subjects showed different performance in identification of the five pulse numbers; 3) the overall identification rate decreased to 80.2 ± 11.7% when the subjects were identifying paired parameters.ConclusionsThe results indicated that the spatial (location) and temporal (pulse number) identification performance are promising in electrocutaneous stimulation on the forearm. The performance degraded when both parameters had to be identified likely due to increased cognitive load resulting from multiple tasks. Utilizing the proposed coding strategy in practical prosthetic hands remains to be investigated for clinical evaluation of its feasibility.

Comparison of reversible-jump Markov-chain-Monte-Carlo learning approach with other methods for missing enzyme identification

Computational identification of missing enzymes plays a significant role in accurate and complete reconstruction of metabolic network for both newly sequenced and well-studied organisms. For a metabolic reaction, given a set of candidate enzymes identified according to certain biological evidences, a powerful mathematical model is required to predict the actual enzyme(s) catalyzing the reactions. In this study, several plausible predictive methods are considered for the classification problem in missing enzyme identification, and comparisons are performed with an aim to identify a method with better performance than the Bayesian model used in previous work. In particular, a regression model consisting of a linear term and a nonlinear term is proposed to apply to the problem, in which the reversible jump Markov-chain-Monte-Carlo (MCMC) learning technique (developed in [Andrieu C, Freitas Nando de, Doucet A. Robust full Bayesian learning for radial basis networks 2001;13:2359-407.]) is adopted to estimate the model order and the parameters. We evaluated the models using known reactions in Escherichia coli, Mycobacterium tuberculosis, Vibrio cholerae and Caulobacter cresentus bacteria, as well as one eukaryotic organism, Saccharomyces Cerevisiae. Although support vector regression also exhibits comparable performance in this application, it was demonstrated that the proposed model achieves favorable prediction performance, particularly sensitivity, compared with the Bayesian method.

An affordable virtual reality system for treatment of phantom limb pain

This paper describes the implementation of an affordable phantom limb pain (PLP) home treatment system using virtual reality (VR) and a motion sensor to immerse the users in a virtual environment (VE). The work is inspired by mirror therapy (MT) which is used to treat patients with PLP. This project focuses on phantom pain in amputees. Using a motion sensor, the system tracks the movement of a users hand and translates it onto the virtual hand. The system consists of exercises focusing on opening and closing the hand, rotating the hand, and finer finger movements. These exercises are conveyed in the VR as three games: (1) A bending game, where the patients have to bend a rod, (2) a box game where the patients pick up and place boxes with their hands, (3) and a button memory game where the patients have to push buttons in a given sequence. These games were tested on twelve healthy participants to see if the games encouraged similar movements as in MT. Prior to the experiment a preliminary test was conducted on an amputee with PLP to gather qualitative feedback from an end-user. The results indicated that the games did convey the exercises from the MT, although further testing is needed.

Growing enzyme gene networks by integration of gene expression, motif sequence, and metabolic information

In computational biology, gene networks are typically inferred from gene expression data alone. Incorporating multiple types of biological evidences makes it possible to improve gene network estimation. In this paper, we describe an approach for building enzyme gene networks by the integration of gene expression data, motif sequence, and metabolic information. To evaluate the approach, we apply it to a pool of E. coli genes related to aspartate pathway. The results show that integrative approach has potentials of obtaining more accurate gene networks.

Comparison of Bayesian and regression models in missing enzyme identification

Computational identification of missing enzymes is important in metabolic network reconstruction. For a metabolic reaction, given a set of candidate enzymes identified by biological evidences, a powerful predictive model is necessary to predict the actual enzyme(s) catalysing the reaction. In this study, we compare Bayesian Method, which is used in previous work, with several regression models. We apply the models to known reactions in E. coli and three other bacteria. It is shown that the proposed regression models obtain favourable performance when compared with the Bayesian method.

Comparison of Movements in a Virtual Reality Mirror Box Therapy for Treatment of Lower Limb Phantom Pain.

Many patients experience Phantom Limb Pain (PLP) after an amputation. Traditional Mirror Box Therapy (MBT) has proven efficient for some patients, but the movements in MBT are physically limited, for lower limb amputees. In this work, we investigated how anti-symmetrical mirroring compares to regular mirroring in Virtual Reality (VR) MBT for lower limb amputees, as natural leg movements are anti-symmetrical, like walking, running, and cycling. To motivate the patients, a game was developed that uses cycling and swinging movements. We implemented the required movements into a goal-oriented game where the patient must fly a gyrocopter through goal areas. The experiment was implemented as a within-subject design, where the participants had to try three versions of the game and give preferential feedback. The findings showed that the cycling version was more exhausting than the anti-symmetrical and symmetrical swinging versions. Furthermore, we discovered that the required cycling motions were too difficult and tiresome to do over a longer period of time. On the other hand, we found that it is possible to use anti-symmetrical swinging of legs in VR MBT.

Comparison of Body Positions in Virtual Reality Mirror Box Therapy for Treatment of Phantom Limb Pain in Lower Limb Amputees

This paper describes the implementation of two virtual reality (VR) games based on the traditional mirror box therapy (MBT) for lower limb amputees. The games are displayed in VR using a head mounted display (HMD) and two motion controllers attached to the intact leg. Two games were developed which both include a sitting and lying version with the purpose of testing the possibilities for enabling more freedom of leg movement. The games were tested on 8 healthy subjects to compare the sitting and lying versions. The results indicated that the lying position was preferred in one game, whereas the sitting position was preferred in the other game. This suggests that VR can enable more freedom of movement.

Discrimination of spatial and temporal parameters in electrocutaneous stimulation

This study aimed to investigate the human ability in discrimination of spatial and temporal parameters in electrocutaneous stimulation. Three surface electrodes were positioned on the ventral forearm of 14 able-bodied subjects. The subjects were instructed to discriminate between: (1) six different stimulation sites or site pairs, or (2) five different stimulation frequencies, or (3) hybrid parameters including both stimulation site and frequency, in three respective experiments. The results showed that two-site discrimination had a significantly lower success rate than one-site discrimination with a mean difference up to 12.1% (p<0.01). Temporal (frequency) discrimination appeared more challenging compared to spatial (site) discrimination. Moreover, the female subjects’ performance was noticeably better than the males in all the three discrimination tasks with the mean difference up to 11.9% (p<0.01), 15.4% (p<0.01), and 16.7% (p<0.001), respectively. The findings may provide an insight into building an effective sensory feedback strategy in relation to development of functional hand prostheses and treatment of phantom limb pain.

Gender effect on discrimination of location and frequency in surface electrical stimulation.

This work investigated the gender effect on discrimination of surface electrical stimulation applied on the human forearm. Three experiments were conducted to examine the abilty of discriminating stimulation frequency, location, or both parameters in 14 healthy subjects. The results indicated a statistically significant impact of gender on the discrimination performance in all the three experiments (p <; 0.01, p <; 0.01, and p <; 0.001, respectively). The female group performed noticeably better than the male group (i.e., mean difference 15.4%, 11.9%, and 16.7% in repective experiment). The findings may provide evidence of gender difference in perceiving and interpreting electrical stimulation. Considering the gender difference may improve the efficacy of electrically evoked sensory feedback in applications such as prosthetic use and pain relief.