Background: Post-stroke gait is limited by compromised volitional joint control that results from muscle weakness, excessive tone, and poor synergist control. About one third of all patients are left with gait deficits after physical therapy and may benefit from assistance during gait. Peroneal nerve stimulators and ankle foot orthoses provide benefit for patients affected by dropfoot, but patients with more severe deficits require additional assistance. Therapeutic and neuroprosthetic effects of a fully implanted pulse generator (IPG) for multi-joint control to assist walking after stroke were evaluated in this case study. Methods: The participant was a 64 year old male who suffered a hemorrhagic stroke 2 years prior to inclusion in the study. His gait was limited by a combination of muscle weakness, limited independent joint movement, and mild hypertonia. He was a household ambulator with contact guard assistance, but used a wheelchair in the community. He was implanted with an 8-channel IPG and intramuscular electrodes targeting the following muscles: tensor fasciae latae, sartorius, gluteus maximus, short head of biceps femoris, quadriceps, and tibialis anterior (two electrodes). After implantation, a stimulation pattern was tuned to assist with hip, knee, and ankle control. A heel switch in the sole of the shoe on the affected side was used as a trigger to initiate swing and stance phase stimulation. He underwent home exercise with electrical stimulation and stimulation assisted gait training in the laboratory. Outcome measures included the 10m walk to assess gait speed, 6 minute timed walk to evaluate fatigue, and maximum walk to measure endurance. Assessments were repeated under three conditions: 1) volitional walking at baseline, 2) volitional walking after training, and 3) walking with stimulation after training. Comparisons include evaluating the 1) therapeutic effect (baseline volitional vs. volitional after training), 2) neuroprosthetic effect (volitional after training vs. stimulation after training), and 3) total effect (baseline volitional vs. stimulation after training). Results: After gait training with stimulation, the participant demonstrated both therapeutic and neuroprosthetic benefits. Therapeutic effects increased walking speed from 0.26m/s to 0.31m/s (p<0.05) while neuroprosthetic effects increased walking speed from 0.31m/s to 0.59m/s (p<0.05) and total effects increased walking speed from 0.26m/s to 0.59m/s (p<0.05). The neuroprosthetic and total effects had a clinically relevant effect size on walking speed of greater than 0.2m/s. Maximum walk distance after training increased from 301m without stimulation to 1418m with stimulation. Discussion: Multi-joint control by means of an IPG provides a clinically relevant neuroprosthetic effect on walking speed and distance. In addition, there was a trend in therapeutic benefits on walking speed and distance. These data provide proof of concept that a multi-joint IPG control can provide clinically relevant improvements in gait after stroke. O3: Changes in Synaptic Function and Excitability in Single Neurons Following Transcranial Magnetic Stimulation N A Matheson, J B H Shemmell, P W Brownjohn, J N J Reynolds University of Otago, Dunedin, New Zealand Repetitive transcranial magnetic stimulation, (rTMS) can non-invasively alter the activity of neural circuits for a time outlasting the stimulation XXX10.1177/1545968315625245Neurorehabilitation and Neural Repair research-article2015 Abstracts from the 2015 Annual Meetings from the 2015 Annual Meeting 2 Neurorehabilitation and Neural Repair period. This has been demonstrated in some studies examining changes in peripheral motor-evoked potentials (MEPs) following application of various rTMS protocols. These prolonged changes have been attributed to the induction of synaptic plasticity. At a single neuron level however, the effects of rTMS are not well understood and the induction of synaptic plasticity or prolonged changes in cellular excitability have not been demonstrated. Using a rat model we investigated the effects of TMS on activity characteristics of single pyramidal neurons. In vivo intracellular sharpelectrode electrophysiological recordings were made from single cortical neurons in urethane-anaesthetized Wistar rats, during the application of TMS. Spontaneous neuron activity was recorded in response to single pulse and rTMS. In addition, post-synaptic potentials (PSPs) elicited using electrical or magnetic stimulation of the ipsilateral hemisphere were investigated both pre and post rTMS. Action potentials and PSPs were reliably obtained following single pulse TMS, delivered at intensities much lower than those used in many clinical settings. During rTMS trains, spontaneous rhythmical neuronal activity was disrupted and in some cases, neuronal firing was induced. Following rTMS, neuronal excitability was altered as indicated by lasting changes in rheobase current and spontaneous activity. Furthermore, both long term potentiation (LTP) and long term depression (LTD) were observed following particular combinations of rTMS protocols. These results provide the first indication of the effects that both single pulse and repetitive TMS have on cortical neuron excitability and synaptic plasticity. With a better understanding of these effects it is hoped rTMS protocols may be more effectively targeted to specific neural circuits, in order to optimize clinical treatment of neurological disorders. O4: Enhancing Cortical Representational Plasticity with Non-Invasive Direct Current Stimulation to Accelerate Upper Limb Recovery in Quadriplegia Kelsey Potter-Baker, Daniel Janini, Nicole Varnerin, David Cunningham, Vishwanath Sankarasubramanian, Ken Sakaie, Frederick Frost, Ela Plow Cleveland Clinic Foundation, Cleveland, OH, USA Current published work suggests that a minimum of 9 months of rehabilitation is required to elicit significant improvement in upper limb function following incomplete spinal cord injury (iSCI). With over 12,500 new cases and a prevalence of 337,000 in the U.S. alone, however, such extensive rehabilitation programs are impractical. Here, we tested the hypothesis that the brain and its residual descending pathways represent the most spared, and hence ideal, innovative targets for maximizing and accelerating upper limb recovery in iSCI. In particular, since loss of representation of weaker muscles in the motor cortex exaggerates muscle weakness and limits recovery following iSCI, we aimed to boost inherent adaptive plasticity of weak representations using transcranial direct current stimulation (tDCS). We hypothesized that tDCS would accelerate increases in weak muscle cortical representational plasticity while also enhancing excitability of their descending pathways to paretic limbs to ultimately maximize functional outcomes following rehabilitation. To test our hypothesis, eight patients with chronic iSCI received either upper limb rehabilitation with tDCS (2 mA anodal) to motor cortical representations of weak muscles or rehabilitation alone. Representational plasticity was measured using TMS before and after treatment and diffusion tensor magnetic resonance imaging (DTI) quantified sparing of descending tracts. Functional recovery and muscle strength was assessed before and after treatment. We found that patients who received tDCS plus rehabilitation demonstrated significant focal increases in the cortical representation of their weaker muscle, where its excitability increased by 60% (p<0.05). Representational plasticity changes were associated with gains in motor function and muscle strength. In addition, level of recovery was related to cortical tract integrity, wherein patients that demonstrated the most recovery had greatest tract sparing following their iSCI (r=0.97; p<0.0001). Our results suggest that long-term pairing with tDCS applied to the motor cortex could result in significant functional improvements by facilitating more permanent plasticity of weaker cortical representations. Further, descending tract integrity, as measured with DTI, may serve as a valuable prognostic marker of impairment and functional recovery potential. O5: Detection and Predictive Value of Fractional Anisotropy Abnormalities in the Acute Stroke Patients Jasmine Wang, Gottfried Schlaug Beth Israel Deaconess Medical Center and Harvard Medical School, Boston,