The Evoked Potential Operant Conditioning System (EPOCS): A Research Tool and an Emerging Therapy for Chronic Neuromuscular Disorders

This unique protocol targets beneficial change to key places in the nervous system. This triggers much wider beneficial change. It greatly improves the behavior such as walking that has been impaired by spinal cord or brain injury.

The main advantage of the EPOCS software is that it guides the experimenter or therapist through the complex series of procedural analytical steps that the protocol requires. H-reflex operant conditioning may be able to improve recovery of locomotion and other important behaviors for people with spinal cord injury, stroke, multiple sclerosis, and other chronic neurological disorders. The protocol can be extended to H-reflexes of other leg or arm muscles to other reflex pathways, such as those responsible for cutaneous reflexes and to pathways that connect the brain to the spinal cord.

If you have never made H-reflex measurements before, contact the National Center of Neuromodulation for Rehabilitation for basic hands-on training opportunities. Tutorial materials are also available on their website. To begin, verify that the participant is set up with stimulating electrodes, bipolar EMG electrodes at the soleus muscle and tibialis anterior in a ground electrode.

Launch the EPOCS application, enter the subject ID and start a session. Ask the participant to stand naturally. Enable the stimulator and set the stimulation intensity to its minimum value, then press Start.

Warn the participant to expect stimulation and gradually increase the intensity to 10 milliamps or more until a clear H-reflex is seen. Find the stimulating location that elicits the largest H-reflex by moving the cathode a full electrode width medially, and then laterally, then a half electrode width medially and laterally, and finally, a full electrode width up and then down. Mark, note, and photograph the position of the electrodes to aid in repositioning.

Switch to the Recruitment Curve tab. Go to Settings, then EMG and configure the ranges for the target and antagonist background activity levels that will permit stimulation. Set the Background hold duration to 2 seconds to specify how long the participant must continuously keep the EMG in range to trigger each stimulus, enable the stimulator and set the intensity to a minimum value of say 5 milliamperes.

With the participant standing, press Start. Demonstrate the real-time background EMG level in the target muscle to the participant. The activity from both muscles must be within their required ranges to turn the bar from a bright red to a darker green shade and it must remain there for 2 seconds to trigger stimulation.

Press Stop at the end of the practice run. With the participant standing, press Start to measure the recruitment curve. If the H-reflex is already visible at the chosen starting intensity, gradually decrease the current until the H-reflex is no longer seen, then click Stop and again Start to begin the run.

Check the Trials Completed counter. After every 4 trials, manually increase the stimulation intensity by 2 milliamperes and make a note of the intensity. Continue until M-wave size reaches a plateau.

Press Stop when done and ask the participant to sit down to rest. Associate any written records with the run numbers shown in the top right of the window. At the end of the run, open the Log tab and enter any relevant information manually.

Press the Analysis button to open the Analysis window. In the upper panel of the analysis window, examine the stimulus-locked overlay of the target muscle signals from each trial in the previous run. Adjust the beginning and end of the green target interval and brown reference interval then click the Use marked timings button to save these settings.

In the Sequence pane in the lower half of the analysis window, assess the resulting recruitment curve. Adjust the settings to view peak-to-peak or mean rectified amplitude and to pool results from consecutive trials. Specify trials to pool at 4 and record the resulting M-max and H-max.

If this is the participant's first session, search for the optimal target muscle EMG recording location. First, move the soleus electrodes medially by a half electrode width, then gather a full recruitment curve and record the resulting M-max and H-max. Next, move the soleus electrodes the same distance laterally from their original position, and again, perform a recruitment curve measurement.

Mark, note, and photograph the electrode position that maximizes the H-max. Choose a stimulus intensity that elicits a close to maximal H-reflex, but with a visible M-wave. Ideally, aim for the rising side of the curve.

Choose a higher stimulus intensity only if necessary to ensure a distinguishable M-wave as in this case. Set this stimulus intensity value on the stimulator and note this and the corresponding M-wave size for future sessions. To measure the distribution of H-reflex sizes without giving response feedback, switch to the Control Trials tab.

With the participant standing, press Start and instruct the participant to maintain the required level of background muscle activity. For a baseline or follow-up session, perform 75 trials in succession, while for a conditioning session, perform 20 trials. After the trials, press Stop to end the run, then press Analysis.

Assess the overlay of trial-by-trial response waveforms in the upper panel, and if needed, the sequence of response sizes below. A new tab distribution is activated by default on top of the Sequence tab. Click on Log Results to append the summary statistics to the session log.

For a baseline session, repeat these steps for a total of three runs of 75 trials each and skip to the closing recruitment curve measurement. For a conditioning session, set the Target Percentile to 66. Select the corresponding criterion for down conditioning by pressing the Down-Condition button.

This action will be logged automatically and the Analysis window will close. Switch to the Training Trials tab, then press Start with the participant standing. Explain to the participant the new feedback bar in the middle of the screen showing the most recent H-reflex size relative to the shaded target range.

If the response falls within the target range, the bar will be dark green and the trial will be counted as successful. If it falls outside the range, the bar will be a brighter red and the trial will be counted as unsuccessful. Motivate the participant to perform as many successful trials as possible.

After 75 trials, press Stop to end the run, then press the Analysis button and use the Sequence tab to verify that the M-waves remained constant at the desired size. With the Distribution tab selected, use the Down-Condition button to update the operant conditioning criterion for the next run. Repeat this procedure twice for 75 trials each.

At the end of the session, perform another recruitment curve measurement. Analysis was performed following a run in Recruitment Curve mode during H-reflex operant conditioning. In the Sequence pane, stimulus intensity increases from left to right with the trial number.

H-reflex size rises then falls as a function of stimulus intensity, whereas M-wave size rises, then saturates. Analysis was done following a run performed in Control Trials or Training Trials mode during H-reflex operant conditioning. The distribution panel showed a histogram of H-reflex sizes that facilitated the selection of an appropriate criterion level for subsequent up or down conditioning.

H-reflex size and neurologically unimpaired participants plotted as a function of session numbers showed a contrasting effects of up and down conditioning. The beneficial effect of soleus H-reflex down conditioning was observed in participants with chronic lower limb impairment following incomplete spinal cord injury. Successful conditioning was associated with an improvement in walking speed and gait symmetry relative to baseline.

The effectiveness of this protocol depends on motivation and how much the subject cares about the feedback. It's important to encourage the subject to succeed in each trial as best you can, leveraging the feedback that the software provides. Absolutely, as a therapist, you might consider adding some appropriate functional or motor control exercises in tandem with operant conditioning.

For instance, you may wanna have your patient do some simple walking practice immediately following soleus H-reflex down-conditioning for best results. The development of EPOCS has allowed us to broaden the range of operant conditioning applications in treating different patient vibrations and sensory motor impairment and accelerated our efforts to maximally harness neuroplasticity to expand the possibilities of neurorehabilitation.