In order to deliver adaptive (i.e., using an algorithm based on ongoing neuronal discharge) stimulation, we constructed an experimental setup in which a copy of the recorded electrodes’ analog signal was diverted to a dedicated learn more DSP (Digital Signal Processing) chip (Figure 1A). This allowed initiation of a stimulus according to an online real-time algorithm based on a signal obtained from any of the recording electrodes. We have termed this group of stimulation paradigms “closed-loop” stimulation paradigms, since they essentially create a feedback loop between the two structures involved (e.g., Figure 1A, bottom panel). This in contrast to nonadaptive systems widely used in the treatment of
advanced PD today, in which the stimulus is delivered regardless of the ongoing activity and according to a predefined offline script http://www.selleckchem.com/products/JNJ-26481585.html (Figure 1B). The paradigm chosen in this study was to deliver a single pulse or a short train (7 pulses at 130 Hz) through a pair of GPi electrodes at a predetermined and fixed latency (80 ms) following the occurrence of an action potential recorded either from the GPi or M1. For each closed-loop stimulation session, two anatomical targets were selected. The first was the reference structure, from whose activity the trigger for stimulation was detected. In this
study, the trigger was always a spike in this reference structure, which was either M1 or the GPi. The second was the stimulated structure, to which the stimulus was
delivered, in this study always the GPi. In all trials the stimulus was applied through two electrodes located within the GPi, either regardless of the ongoing activity (open-loop Histone demethylase paradigms, e.g., standard continuous 130 Hz DBS) or after the identification of a trigger in the ongoing activity (closed-loop paradigms). Throughout this article, we use the following notation: a stimulus consisting of a train of pulses is denoted by the subscript “train”; a stimulus consisting of a single current pulse is denoted by the subscript “sp”. The full descriptions of the closed-loop paradigms therefore consist of both the anatomical targets (reference and stimulated structures) and the stimulation pattern, and are expressed as [STIMULATEDpattern|REFERENCE] (e.g., [GPtrain|M1], where GPi is the stimulated site and the M1 is the reference site). Through a number of preliminary experiments, we identified a set of successful parameters for adaptive or closed-loop stimulation paradigms. The stimulation selected was applied 80 ms after detecting a spike in the reference structure. This choice of the delay was made for several reasons. Primarily it made the stimulus coincide with the next double-tremor frequency oscillatory burst (approximately 12.5 Hz), provided the reference spike was a part of a previous burst in the GPi (when the latter was used as reference).