This paper discusses the relationship between stimulating pulse width and the threshold of electrically evoked compound action potential (ECAP). Firstly, the rheobase and chronaxy from strength-duration curve of nerve fiber was computed using the shepherd's experiment results. Secondly, based on the relationship between ECAP and the action potential of nerve fiber, a mathematical expression to describe the relationship between stimulating pulse width and ECAP threshold was proposed. Thirdly, the parameters were obtained and the feasibility was proved to the expression with the results of experiment using guinea pigs. Research result showed that with ECAP compared to the action potential of nerve fiber, their threshold function relationship with stimulating pulse width was similar, and rheobase from the former was an order smaller in the magnitude than the latter, but the chronaxy was close to each other. These findings may provide meaningful guidance to clinical ECAP measurement and studying speech processing strategies of cochlear implant.
Patch-clamp is used to study all sorts of ionic channels and their regulations with measuring pA current of cell ionic channel, but the fast capacitance (C-fast) compensation and slow capacitance (C-slow) compensation transient currents are caused by measuring objects and measuring instruments themselves which will change the properties of action potentials. The present paper firstly discusses the C-Fast transient currents affecting membrane capacitance and membrane potential, and then draws a conclusion that the changes of membrane potential affect the properties of action potential through analyzing the changes of membrane potential in H-H model. Based on this conclusion, we discuss the influence mechanisms mainly through the analysis of traditional C-fast compensation errors, and focus discussion on the shape of electrode capacitance affecting C-fast. This method can not only improve the compensation speed greatly, but also improve the compensation precision from the electrode shape as much as possible.
Neuron is the basic unit of the biological neural system. The Hodgkin-Huxley (HH) model is one of the most realistic neuron models on the electrophysiological characteristic description of neuron. Hardware implementation of neuron could provide new research ideas to clinical treatment of spinal cord injury, bionics and artificial intelligence. Based on the HH model neuron and the DSP Builder technology, in the present study, a single HH model neuron hardware implementation was completed in Field Programmable Gate Array (FPGA). The neuron implemented in FPGA was stimulated by different types of current, the action potential response characteristics were analyzed, and the correlation coefficient between numerical simulation result and hardware implementation result were calculated. The results showed that neuronal action potential response of FPGA was highly consistent with numerical simulation result. This work lays the foundation for hardware implementation of neural network.
ObjectiveTo monitor the diaphragm function of mechanical ventilated patients in the intensive care unit. MethodsA prospective study was conducted on mechanical ventilation patients who had been evaluated by ventilation weaning screening test and planning to underwent spontaneous breathing trial between May 2013 and November 2013. A newly designed multi-function esophageal electrode was used to record the phrenic nerve conduction time (PNCT),diaphragm compound muscle action potential (CMAP) and twitch transdiaphragmatic pressure (TwPdi) elicited by bilateral anterolateral magnetic phrenic nerve stimulation. Results14 patients were recruited in this study. 1 case exited because of intolerance of repetitive magnetic stimulation,2 cases had no diaphragmatic electromyographic signals nor twitch signals,1 case had diaphragmatic electromyographic signal but could not be elicited by magnetic stimulation,1 case had no available TwPdi value with PNCT of 7.2 ms and CMAP of 1.26 mV. In the rest 9 cases,the PNCT,CMAP and TwPdi were (8.5±1.5)ms,(1.01±0.35)mV,(11.2±4.7)cm H2O,respectively. ConclusionNewly designed multi-function esophageal electrode catheter combined with bilateral anterolateral magnetic phrenic nerve stimulation can be used for non-volitional comprehensive assessment of diaphragm in critically ill patients,but not suitable for all subjects.
Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive brain stimulation technique that has been paid attention to with increasing interests as a therapeutic neural rehabilitative tool. Studies confirmed that high-frequency rTMS could improve the cognitive performance in behavioral test as well as the excitability of the neuron in animals. This study aimes to investigate the effects of rTMS on the cognition and neuronal excitability of Kunming mice during the natural aging. Twelve young mice, 12 adult mice, and 12 aged mice were used, and each age group were randomly divided into rTMS group and control group. rTMS-treated groups were subjected to high-frequency rTMS treatment for 15 days, and control groups were treated with sham stimulation for 15 days. Then, novel object recognition and step-down tests were performed to examine cognition of learning and memory. Whole-cell patch clamp technique was used to record and analyze resting membrane potential, action potential (AP), and related electrical properties of AP of hippocampal dentate gyrus (DG) granule neurons. Data analysis showed that cognition of mice and neuronal excitability of DG granule neurons were degenerated significantly as the age increased. Cognitive damage and degeneration of some electrical properties were alleviated under the condition of high-frequency rTMS. It may be one of the mechanisms of rTMS to alleviate cognitive damage and improve cognitive ability by changing the electrophysiological properties of DG granule neurons and increasing neuronal excitability.
Anxiety disorder is a common emotional handicap, which seriously affects the normal life of patients and endangers their physical and mental health. The prefrontal cortex is a key brain region which is responsible for anxiety. Action potential and behavioral data of rats in the elevated plus maze (EPM) during anxiety (an innate anxiety paradigm) can be obtained simultaneously by using the in vivo and in conscious animal multi-channel microelectrode array recording technique. Based on maximum likelihood estimation (MLE), the action potential causal network was established, network connectivity strength and global efficiency were calculated, and action potential causal network connectivity pattern of the medial prefrontal cortex was quantitatively characterized. We found that the entries (44.13±6.99) and residence period (439.76±50.43) s of rats in the closed arm of the elevated plus maze were obviously higher than those in the open arm [16.50±3.25, P<0.001; (160.23±48.22) s, P<0.001], respectively. The action potential causal network connectivity strength (0.017 3±0.003 6) and the global efficiency (0.044 2±0.012 8) in the closed arm were both higher than those in the open arm (0.010 4±0.003 2, P<0.01; 0.034 8±0.011 4, P<0.001), respectively. The results suggest that the changes of action potential causal network in the medial prefrontal cortex are related to anxiety state. These data could provide support for the study of the brain network mechanism in prefrontal cortex during anxiety.
Spinal cord stimulation (SCS) for pain is usually implanted as an open loop system using unchanged parameters. To avoid the under and over stimulation caused by lead migration, evoked compound action potentials (ECAP) is used as feedback signal to change the stimulating parameters. This study established a simulation model of ECAP recording to investigate the relationship between ECAP component and dorsal column (DC) fiber recruitment. Finite element model of SCS and multi-compartment model of sensory fiber were coupled to calculate the single fiber action potential (SFAP) caused by single fiber in different spinal cord regions. The synthetized ECAP, superimposition of SFAP, could be considered as an index of DC fiber excitation degree, because the position of crests and amplitude of ECAP corresponds to different fiber diameters. When 10% or less DC fibers were excited, the crests corresponded to fibers with large diameters. When 20% or more DC fibers were excited, ECAP showed a slow conduction crest, which corresponded to fibers with small diameters. The amplitude of this slow conduction crest increased as the stimulating intensity increased while the amplitude of the fast conduction crest almost remained unchanged. Therefore, the simulated ECAP signal in this paper could be used to evaluate the degree of excitation of DC fibers. This SCS-ECAP model may provide theoretical basis for future clinical application of close loop SCS base on ECAP.
As a noninvasive neuromodulation technique, transcranial magnetic stimulation (TMS) is widely used in the clinical treatment of neurological and psychiatric diseases, but the mechanism of its action is still unclear. The purpose of this paper is to investigate the effects of different frequencies of magnetic stimulation (MS) on neuronal excitability and voltage-gated potassium channels in the in vitro brain slices from the electrophysiological perspective of neurons. The experiment was divided into stimulus groups and control group, and acute isolated mice brain slices were applied to MS with the same intensity (0.3 T) at different frequencies (20 Hz and 0.5 Hz, 500 pulses) respectively in the stimulus groups. The whole-cell patch clamp technique was used to record the resting membrane potential (RMP), action potential (AP), voltage-gated potassium channels current of hippocampal dentate gyrus (DG) granule cells. The results showed that 20 Hz MS significantly increased the number of APs released and the maximum slope of a single AP, reduced the threshold of AP, half width and time to AP peak amplitude, and improved the excitability of hippocampal neurons. The peak currents of potassium channels were decreased, the inactivation curve of transient outward potassium channels shifted to the left significantly, and the time constant of recovery after inactivation increased significantly. 0.5 Hz MS significantly inhibited neuronal excitability and increased the peak currents of potassium channels, but the dynamic characteristics of potassium channels had little change. The results suggest that the dynamic characteristics of voltage-gated potassium channels and the excitability of hippocampal DG granule neurons may be one of the potential mechanisms of neuromodulation by MS.