Investigating brain waves during spinal cord stimulation

Although we will not be implanting SCS in any participant, we will be asking participants to activate their existing SCS implant in a systematic (but safe) manner that they probably would not have otherwise. Recordings will be taken in a single session, lasting approximately 90 minutes, at the Auckland Regional Pain Service. We expect the actual recording period to be about 30 minutes. With the input of the patient and a registered nurse experienced in the programming procedure (ED), we will add six experimental programs to the patient’s controller, with pulse frequencies of 15Hz, 25Hz, and 35Hz. Pulse width will be 300µs. At each frequency, stimulation amplitude will be increased in steps from zero until the patient just perceives paraesthesia, and then go several steps above that. This will give us three perceptible stimulation patterns. At each frequency we will program a non-perceptible stimulation pattern a few steps below the threshold of perceptibility, for six total experimental programs. We will program each stimulation pattern to activate for 4 seconds every 10 seconds. When the stimulation program is activated, it fires immediately. The response to the first stimulation is unlikely to be analysed (there will be no baseline beforehand), but will be for the participant to confirm that he/she wants to continue. Before each block, one of the six stimulation programs will be selected randomly by computer. This program will then be activated using the controller by the participant, and interrupted after four activations (i.e. one block), either by the experimenter or participant. The participant will have access to a deactivation button at all times, and will be encouraged to use it if they want to cease stimulation for any reason. After each block of four trials, we will ask the participant to record his/her comfort level on a visual analogue scale, give him/her an opportunity to elect to discontinue, and adjust the stimulation program in the case of continuation. We aim to collect data from 72 trials in 18 blocks, but will stop if at any point the participant requests so.