Analytical methods for correlating electrical muscle activity with animal locomotion
Analytical methods for correlating electrical muscle activity with animal locomotion
This chapter deals with two main aspects: (i) the methodology for simultaneous recording of EMG and video on normally moving animals, and (ii) the timing and necessary conditions required to extend this methodology to quantitative biomechanics. For the application of these methods to different subjects and different experimental protocols see the study by Loeb and Gans (1986).
Operation method
Experiments on analytical methods for correlating electrical muscle activity with animal locomotion
Materials and Instruments
EMG Electrode Materials Move move Electrode program 1. Literature review: A comprehensive search of all previous literature on the neuromuscular characteristics of the area to be studied, functional anatomical knowledge, and EMG will save us a lot of unnecessary trouble in the subsequent work. Some of these works are very old, but they are very comprehensive and systematic studies. Many muscles have very complex histochemical, innervational and functional properties, which must be clearly understood in order to design rational experiments to accurately and clearly elucidate the behavioral performance of animals. 2. Necropsy: Even for experiments that you are most familiar with, we strongly recommend that you perform a necropsy at the end of the experiment to confirm the location of the surgical incision and that the muscles that are functionally involved in the production of EMG are not damaged. Record in detail where the electrodes were inserted, where they were fixed, and the route of travel. 3. Electrode design: The number of recording channels and the type of electrodes to be used should be considered during the procedure. A transparent plastic sheet should be used to make an epimysial electrode bib of the desired size, and the position of the electrode connection should be marked with a marker. As far as possible, information should be collected from larger sections of each muscle, while avoiding interference from neighboring muscles. Bipolar electrodes spaced in parallel on the nerve bundle are also often used in experiments. Recording different muscles that are segmented apart may require multiple recording channels unless these different components can clearly evoke similar responses. In order to identify possible sources of muscle interference with each other, we record all neighboring muscles if feasible, regardless of whether the neighboring muscles are behaviorally related to each other. 4. assemble the electrode implantation hardware as follows: Usually meters are used to record the activity of small superficial or thin muscles with myxoepidermal sheet electrodes, where the connectors of the bipolar electrodes are adhered to the surface of the silicone sheet. The corners of the silicone sheet are sutured to the muscle ectomysium, and the connectors of the bipolar electrodes are neatly arranged on the silicone sheet at regular intervals. The silicone sheet mainly acts as an insulating barrier to reduce interference from neighboring muscles. Two or more channels can be placed on one or both sides of the sheet to record the activity of multiple components or muscles. A blank sheet can be used to prevent interference from neighboring non-tested muscles from being transmitted along the tested muscle. As shown in Figure 28-2A, depending on the size of the muscle, the size of the sheet electrode is typically 3 to 5 mm. Note: Monkeys appear to be highly electrically resistant to the cinnamon resin sheet material, so intramuscular electrodes were used in the following experiments. (1) To make the electrode connector: Strip off a section of the insulating jacket (about 3 times the distance between the muscle and the connector location) from the wire to expose the area in contact with the electrode. (2) Cut out a piece of material of appropriate size 4 (3) Drill a hole in the sheet material with a hypodermic needle, thread the wire to the end of the needle, and have the needle guide the wire through the sheet material. (4) Place the part of the wire that has been removed from the insulating coat in the center of the sheet facing the muscular surface, and then cut off the excess part by retaining the length of the wire that extends to the other end of the sheet, which is about 3 mm. (5) Silicone adhesive is applied to four points of the sheet: the two points where the wire head passes out from the back of the sheet, and the two points where the wire travels from the sheet to the edge. (6) Autoclaving. Intramuscular hook electrodes are commonly used to record activity in large or deep muscles, and a bipolar connector is attached to a suture that guides the hook electrode to the ventral center of the muscle. A loose multi-wire connector is tied to the above suture to space the bipolar electrodes and bend them back into a hook shape to ensure that they can hang relatively securely from the muscle. A loop is made in the long end of the suture with a piece of tape that is loosely secured to its end. As shown in Fig. 28-2B, the size of the hook electrode is usually 3 to 5 mm, depending on the size of the muscle. (1) Strip off a section of the insulating jacket covering both ends of the wire, taking care not to scratch the wire. (2) Tie the two wires at a distance apart in the center of the suture as shown in Fig. 28-2B. (3) Bend the exposed wire connector. (4) Autoclave. 5. Embedded electrodes: cut the skin to expose the recording position and fix the electrode correctly on the muscle. One electrode is inserted into the muscle fascia for use as a reference electrode. The electrode lead is threaded subcutaneously through the skin at the location of the connector. 6. Connector attachment: When more than one electrode is buried, each wire loop representing a bipolar channel can be distinguished by a different color. Multiple connectors are either firmly anchored to bone or sutured to muscle fascia (Hofferetal.1987). After applying a layer of acidic flux (10% hydrochloric acid) to the bare ends of the EMG electrodes, a layer of solder is carefully applied to the stainless steel EMG electrode heads. After soldering the electrode head to the connector header, a light coating of silicone adhesive is applied to the soldered area to prevent drying. The soldering method can also be found in Loeb et al. (1995). 7. Monitor electrode impedance. After the procedure and every day thereafter, the impedance of each electrode connector with respect to the reference electrode and each pair of bipolar electrode connectors should be monitored with an AC impedance meter. For the electrode patterns described herein, the impedance range for unipolar electrodes should be l to 10 kn, and for bipolar electrodes the range should be 70% to 90% of the sum of the impedances of the two unipolar electrodes. Under normal conditions, the impedance changes relatively slowly, with a range of ±30%. Excessive or sudden increases in impedance may indicate a broken wire joint, poor soldering or a loose joint at the connector. Low impedance may be due to fluid flow around the connector joints. 8. Animal Ethics: Execute the animal as soon as possible after the experiment and dissect it to confirm the electrode position and connections. If there is any doubt about the connection between the electrode and connector joints, it is best to test each circuit connection with a simple impedance meter. 9. Simultaneous recording of pattern data and video data: It is often necessary to simultaneously record multi-channel pattern data such as EMG and high-resolution motion information such as video signals through different instruments. Digital computers with their high speed and high capacity are fully capable of handling these two tasks simultaneously, but because of the large size of the recorded information files, it is very troublesome to handle them. In order to solve the problem of synchronization of the two recording devices, we can use a common timer suitable for both devices to solve this problem. SMPTE timer mode is synchronized with North American (NTSC, 30fmnes/s) and European (PAL, 25frames/s) cameras, which can be converted to visual signals and encoded digitally on the VCR. It would be nice to be able to control the timer with a computer. In this way, the computer can convert the pattern signal into a digital file (Figure 28-3). If a timer is not available, synchronization of multimedia recordings can be achieved by synchronized flashes of light, audible ticks, or electronic waves. 10. Selected Animal Behavior: Animal behavioral data are often inconsistent. Although sometimes only pattern data is needed or just direct motion analysis, we record animal behavior on video because we can sift through the large number of recorded animal behaviors to find the behavioral manifestations that need to be studied. VCR systems with slow play and static playback can help the experimenter to identify the start and end times of the desired data. 11. Analyze EMG: Create and browse EMG and other inverter signals by applying the temporal boundaries determined in the previous step and satisfy yourself that these signals t are free of electrical noise, stimulus artifacts, interference, and other problems with the quality of the recordings (Figure 28-3). It is important to perform these filters when initially analyzing the data because much of the information is obscured when the data are filtered and averaged.The most common method of analysis for EMG is to extract the envelope modulation (BakandLoeb1979). The analysis of EMG can be done digitally if the amplified EMG signal is digitized at high frequencies to avoid artifacts. The speed and capacity of the digitizing system can be greatly reduced by splitting the full EMG signal into different segments in advance. 12. Linking EMG signals to motion information: Detailed kinetic analysis of only a small set of EMG data is possible. A quick glance at multiple EMG records identifies the time point corresponding to a specific locus (e.g., the onset or peak of muscle activity) and then performs a detailed kinetic analysis of that point. The results of multiple recordings of the same behavior for different durations can be averaged (Fig. 28-4). The reverse dynamic analysis method requires the length, mass, rotational inertia and center of gravity of each body segment. Forward dynamic analysis methods require the mass of each muscle, fascicle length, tandem elasticity length (tendon + tendon membrane) and force arm. The effect of feathering angles less than 25° is negligible (ScottandWinter1991). Both inverse and forward dynamic analysis methods can accurately and unambiguously calculate the position of the bones of all segments and the intersegmental pinnation angles based on the position of any visible marking site. This requires a great deal of information about the relationship between the location of the marker site and the position of the center of rotation of the joint. If there is a tendency for the surface of the skin to slide toward the bones below it, then it is necessary to transdermally attach the epidermal marking site directly to the bones below, or to apply trigonometry to calculate the position of some joints. Muscle lengths and velocities can be calculated from joint angles between skeletal segments and from morphometric data. Particularly for joints with greater degrees of freedom and for muscles that span more than one joint, there has been an increased effort to 'census' the variation in muscle length corresponding to different joint angles, rather than using the method of calculating the force arm from the attachment points of muscles and tendons on the bone. This 'census' results in the transformation of the joint angle into a 'path length' for each muscle, which is often further decomposed, when required, into the length of a muscle bundle and the non-contractile tandem elastic component of the tendon and tendon membrane. In muscles with relatively long tandem elastic components, altering muscle force causes a significant length change in the contractile component due to stretching or shortening of the tandem elastic component. EMG data can reasonably represent the level of activity of the contractile component, and the "envelope" characteristic of the EMG signal amplitude explains the rise and fall times of this activity, which are dependent on the type of fiber involved in the activity. It is necessary to classify the EMG amplitude into divisions that represent the activity of the total muscle cross-section area. It is useful to record the behavioral performance of a muscle when it is maximally activated. The strength of a whole muscle can be derived from the activation, length and velocity of the contractible component (Brownetal.1996). When the force arm of the muscle at each angle of the joint is known, the torque of the joint can be deduced from the strength of the muscle. The angular acceleration can be calculated by differentiating the kinetic data at the skeletal positions twice, and from the angular acceleration the torque to overcome inertia can be calculated according to Newton's laws of motion (Hoyand Zernicke 1985;Hoyetal.1985b Noise in the kinetic data at the individual labeled positions in the process can be very headache-inducing. Some additional influences to note are external forces at gravity joints, internal inhibitors such as elastic ligaments and bones limiting the amplitude of motion, and intersegmental coriolis effects.KnowledgeRevolutionInc. provides a working model software package that is very helpful in building 2D and 3D systems with desirable segmentation and connectivity features. It is theoretically possible to sum the torques calculated for each muscle by applying forward dynamics and to reconcile the results with the net torque calculated by analyzing the motion with reverse dynamics. In practice, however, this is hardly feasible, as it requires full data and very accurate modeling of all muscles through all joints.$ Nevertheless, it is very useful in testing whether the available EMG data can explain the biomechanical principles of a given task. Figures 28-3 to 28-4 show typical EMG results recorded at different stages of analysis. The curves in the figures were plotted by software for processing spreadsheets on a Macintosh computer. Many commercially available data acquisition and analysis software packages are available for this type of analysis. Figure 28-3 shows the results of analyzing a multichannel EMG data that was digitally transformed after a 3.3-ms intersampling interval by integrating the entire EMG recorded image into 3.3-ms bins synchronized with the digital processor (BakandLoeb 1979). The scale next to the recorded image signal represents a scale that takes into account amplifier gain and bandwidth; if the bin width is doubled, the integrated EMG amplitude is doubled, and the voltage scale connected to the scale bar is halved. The established bin-integrated EMG amplitude is equivalent to 10 times the original signal. Experimentally, we know that the starting SMPTE time point of the digitized file, the sampling interval, is the same step as the 8kHz SMPTE time encoder carrier. Both of these make it possible to place a pointer on the data curve to mark the time point of the cut. If a time curve is added above the recording curve, which is labeled with the average time (indicated by large dots) and the individual video frames and the 10th frame (indicated by small and large hooks). This would facilitate the selection of the range of video recordings for static analysis in order to extract the kinematic parameters corresponding to the limb movements. Figure 28-4 shows a more advanced analysis method. Multiple loop recordings with similar durations were segmented into multiple individual recordings based on video analysis of limb postural positions. For each EMG channel, the EMG data were digitally filtered and inserted into each phase in order to obtain the same number of samples for each loop. The graph of the time-stamped loops was plotted as a raster pattern curve according to the actual f loop times, with loops with large variations in time filtered out. The curve above then shows the range of EMG values throughout the cycle, expressed in terms of the standard error of the mean. For more product details, please visit Aladdin Scientific website.
Dacron Reinforced silicone perimembrane Artificial cinnamon resin rubber adhesive Non-absorbable sutures
