Deep Brain Stimulation (DBS) is a surgical procedure for the treatment of motor disorders in patients with Parkinson's Disease (PD). DBS involves the application of controlled electrical stimuli to a given brain structure. The implantation of the electrodes for DBS is performed by a minimally invasive stereotactic surgery where neuroimaging and microelectrode recordings (MER) are used to locate the target brain structure. The Subthalamic Nucleus (STN) is often chosen for the implantation of stimulation electrodes in DBS therapy. During the surgery, an intraoperative validation is performed to locate the dorsolateral region of STN. Patients with PD reveal a high power in the β band (frequencies between 13 Hz and 35 Hz) in MER signal, mainly in the dorsolateral region of STN. In this work, different power spectrum density methods were analyzed with the aim of selecting one that minimizes the calculation time to be used in real time during DBS surgery. In particular, the results of three nonparametric and one parametric methods were compared, each with different sets of parameters. It was concluded that the optimum method to perform the real-time spectral estimation of beta band from MER signal is Welch with Hamming windows of 1.5 seconds and 50% overlap.
Background Myoelectric control based on hand gesture classification can be used for effective, contactless human–machine interfacing in general applications (e.g., consumer market) as well as in the clinical context. However, the accuracy of hand gesture classification can be impacted by several factors including changing wrist position. The present study aimed at investigating how channel configuration (number and placement of electrode pads) affects performance in hand gesture recognition across wrist positions, with the overall goal of reducing the number of channels without the loss of performance with respect to the benchmark (all channels). Methods Matrix electrodes (256 channels) were used to record high-density EMG from the forearm of 13 healthy subjects performing a set of 8 gestures in 3 wrist positions and 2 force levels (low and moderate). A reduced set of channels was chosen by applying sequential forward selection (SFS) and simple circumferential placement (CIRC) and used for gesture classification with linear discriminant analysis. The classification success rate and task completion rate were the main outcome measures for offline analysis across the different number of channels and online control using 8 selected channels, respectively. Results The offline analysis demonstrated that good accuracy (> 90%) can be achieved with only a few channels. However, using data from all wrist positions required more channels to reach the same performance. Despite the targeted placement (SFS) performing similarly to CIRC in the offline analysis, the task completion rate [median (lower–upper quartile)] in the online control was significantly higher for SFS [71.4% (64.8–76.2%)] compared to CIRC [57.1% (51.8–64.8%), p < 0.01], especially for low contraction levels [76.2% (66.7–84.5%) for SFS vs. 57.1% (47.6–60.7%) for CIRC, p < 0.01]. For the reduced number of electrodes, the performance with SFS was comparable to that obtained when using the full matrix, while the selected electrodes were highly subject-specific. Conclusions The present study demonstrated that the number of channels required for gesture classification with changing wrist positions could be decreased substantially without loss of performance, if those channels are placed strategically along the forearm and individually for each subject. The results also emphasize the importance of online assessment and motivate the development of configurable matrix electrodes with integrated channel selection.
Spatial information of nociceptive stimuli applied in the skin of healthy humans is integrated in the spinal cord to determine the appropriate withdrawal reflex response. Double-simultaneous stimulus applied in different skin sites are integrated, eliciting a larger reflex response. The temporal characteristics of the stimuli also modulate the reflex e.g. by temporal summation. The primary aim of this study was to investigate how the combined tempo-spatial aspects of two stimuli are integrated in the nociceptive system. This was investigated by delivering single and double simultaneous stimulation, and sequential stimulation with different inter-stimulus intervals (ISIs ranging 30-500 ms.) to the sole of the foot of fifteen healthy subjects. The primary outcome measure was the size of the nociceptive withdrawal reflex (NWR) recorded from the Tibialis Anterior (TA) and Biceps Femoris (BF) muscles. Pain intensity was measured using an NRS scale. Results showed spatial summation in both TA and BF when delivering simultaneous stimulation. Simultaneous stimulation provoked larger reflexes than sequential stimulation in TA, but not in BF. Larger ISIs elicited significantly larger reflexes in TA, while the opposite pattern occurred in BF. This differential modulation between proximal and distal muscles suggests the presence of spinal circuits eliciting a functional reflex response based on the specific tempo-spatial characteristics of a noxious stimulus. No modulation was observed in pain intensity ratings across ISIs. Absence of modulation in the pain intensity ratings argues for an integrative mechanism located within the spinal cord governed by a need for efficient withdrawal from a potentially harmful stimulus.
Many pain-related conditions are characterized by poorly localized pain areas in the body which is likely to reflect abnormal processing of spatial characteristics of the noxious phenomenon driving the condition (Gran, 2003; Graven-Nielsen & Arendt-Nielsen, 2010; Kamaleri et al., 2008; Wolfe et al., 1990). Within the spinal cord, several primary afferents converge onto spinal neurons and constitute the first relay for somatosensory integration. Electrophysiological studies in animals have shown that neurons located in this first relay play a role in
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