The relationship between the frequency of self-stimulation and parameters of the stimulus]

The dependence of self-stimulation frequency on stimulation parameters (current intensity, stimulation frequency, pulse duration, duration of pulse bursts) was studied in fifteen rats with monopolar electrodes implanted in the lateral hypothalamus, using rectangular current pulses for brain stimulation. All the experiments revealed qualitatively similar response surfaces to the combined change of stimulation frequency and pulse duration Self-stimulation frequency is connected in a non-linear way with the "specific charge" per unit of time, and in an approximately linear way, with the duration of the pulse burst. Regression equations are determined which precisely enough described the kind of response surface (R =0.7 to 0.95).     

Emotional manifestations in the electrical stimulation of the hypothalamic nuclei in adult and old rats

In experiments on adult (9-10 months) and old (24-26 months) white Wistar rats behavioural manifestations under electrical stimulation of the ventromedial hypothalamus nucleus and self-stimulation (SS) of the lateral hypothalamic region were studied. It has been found that with age electrical thresholds of negative emotional manifestations decrease with invariable SS thresholds. In old rats, in comparison with the adult ones, SS frequency is lower, maximum SS proceeds at lower currents, the range of currents capable to evoke an intensive SS is narrower, SS motivational component is less expressed. The obtained data testify that in old rats there exist neurophysiological preconditions for prevailing of negative emotional manifestations.     

The behavior of rats with different regimes of cerebral self stimulation]

The behaviour of rats was studied during electrical self-stimulation (SS) of the brain in a chamber with a pedal: with a fixed duration of stimuli trains (fixed SS regime), and in a self-controlled regime, where the duration of trains was set by the rat itself. As the current intensity or the duration of the trains continues to increases, the SS frequency in the fixed regime rises no longer. The duration of pressing becomes shorter than that of the trains, and the number of short pauses drops down to 50% of its total number of pauses, if at the same current intensity the duration of the train is the same or greater than that set by the rats in the self-controlled SS regime. With weak current intensities, the rats could fail to press the pedal if they received 0.1 sec. trains. But at the same current intensities the rats began SS, if they received for pressing the pedal a succession of trains of 0.1 sec. each with intervals of 0.1 divided by 0.2 sec. SS discontinued if the interval in the trains succession increased up to 0.4 sec.     

Effect of stimulation of the reticular formation on the motivational and reinforcing effects of the self stimulation zones

The influence was studied on the midbrain reticular formation (RF) on motivational and reinforcing effects of stimulation of the same selfstimulation zones (SS) of hypothalamic area. A current of gradually increasing intensity was used, by means of which three groups of functionally (behaviourally) specific reticular points were revealed: motivationaly neutral, positive and negative. The data obtained show that influences of RF on SS zones of hypothalamus differand depend on functional properties of various RF areas. Changes of motivational effects in SS zones reflex the specificity of reticular foci in a lesser degree than changes in reinforcing effects. It has been suggested that reinforcing effects of the SS hypothalamic zones possess their own activating mechanism specifically related to its "positive" link and differing from reticular mechanism of unspecific activation.     

Neuromuscular electrical stimulation for skeletal muscle function

Lack of neural innervation due to neurological damage renders muscle unable to produce force. Use of electrical stimulation is a medium in which investigators have tried to find a way to restore movement and the ability to perform activities of daily living. Different methods of applying electrical current to modify neuromuscular activity are electrical stimulation (ES), neuromuscular electrical stimulation (NMES), transcutaneous electrical nerve stimulation (TENS), and functional electrical stimulation (FES). This review covers the aspects of electrical stimulation used for rehabilitation and functional purposes. Discussed are the various parameters of electrical stimulation, including frequency, pulse width/duration, duty cycle, intensity/amplitude, ramp time, pulse pattern, program duration, program frequency, and muscle group activated, and how they affect fatigue in the stimulated muscle.     

Direct cortical responses to electric stimulation with different frequencies in chronic experiments on dogs]

Direct cortical responses (DCR) to a series of electrical stimuli with a frequency of I to 50 per second with 10 to 20 pulses in each series were studied in chronic experiments on dogs. The nature of cortical responses differed, depending on stimulation parameters. As the stimulation frequency increased, the amplitude and number of late DCR components decreased, and with further increase of frequency, the early components decreased as well. The following types of responses were revealed: recruiting, intermittent and decremental. As the stimulation frequency increased all the three types of responses could be obtained in one and the same cortical point. Recruiting was not typical of high-amplitude and multi-component DCR with a long phase of depression of initial negativity and slightly pronounced short-term subsequent facilitation, while the intermittent type of response appeared at lower frequencies than in other dogs (5 to 10 per sec). A decremental type of response was observed in all the dogs at a stimulation frequency higher than 30 per sec. The duration of the series of after-discharges to a burst of electrical pulses depended on the pattern of the DCR to a single stimulus and on the intensity and frequency of stimulation. With similar parameters of stimulation, the greater the amplitude and the longer the duration of the slow negative DCR wave, the longer the period of after-discharges following a series of stimuli.     

Relation between the dynamics of a species-specific motor reaction and the duration of diencephalic stimulation

Species-specific reaction of thumping behaviour with the hind limbs in response to electrical stimulation of the ventromedial, dorsomedial and caudal parts of the hypothalamus was studied in chronic experiments on rabbits. Reaction of avoidance dominated during current action of various durations (1-20 s). The specific reaction under study appeared after the termination of stimulation and lasted for 30-120 s. The number of kicks in response to single stimulation depended on its duration (T). With T rising from 1 to 10 s, the number of kicks increased; with T being equal to 20 s, it decreased. The latency of the first kick after the termination of stimulation regularily increased with increase of its duration, and reaction intensity maxima shifted to the right along the axis of time. Possible mechanisms of limb kicking behaviour are discussed based on a transition of avoidance reaction during stimulus action to emotional reaction in post-stimulus period.     

Modulation of Hydra attenuata rhythmic activity. Photic stimulation.

We investigated in Hydra attenuata the possibility of altering more or less permanently and in different environmental conditions, the frequency of Contraction Pulse Trains (CPT's) associated with the rhythmic spontaneous contraction activity, by repetitive light stimuli of variable duration, frequency and amplitude. The CPT's activity of various pieces of Hydra has been also investigated in indisturbed conditions and under stimulation. The following observations have been performed. 1. A transient effect, consisting of an increase or a decrease of CPT's frequency, occurs respectively after an abrupt decrease or increase of the light level. 2. If Hydra is stimulated by repetitive light pulses of 0.5-10 sec duration, at a frequency different from the CPT's average one, the CPT's frequency modifies; if the stimulation frequency is included in a range not too much up or below that of CPT's the new CPT's frequency equals exactly that of stimulation; close to this range the CPT's frequency is a multiple or submultiple of that of stimulation. 3. No habituation to such repetitive stimulation was found. 4. The phase relation between CPT's at the new frequency and light stimuli is a function of the difference between CPT's and stimulation frequencies. 5. Stimulation with repetition of light and darkness periods of some minutes duration induces activity only or mainly during darkness. 6. Modification of CPT's frequency by means of repetitive light stimulation [of the type mentioned either in 2) or 5)] has been observed also with hypostomal preparations. 7. With cessation of the light stimulation, the new CPT's frequency of the whole animal lasts in darkness for a time (10-85 min) that is about 5-10 times longer than that necessary to obtain CPT's syncronization with stimulation. 8. The influence of the light intensity level on transient CPT's frequency variation (see 1), CPT's inhibition and stimulation, promptness of entrainment, range of entrainability, phase relation between entrained CPT's and stimuli, retention time of entrained rhythm has been examined, together with the influence of the reversal of polarity of light transitions on CPT's inhibition and entrainment.     

Cerebral responses of healthy humans to rhythmic transcranial magnetic stimulation of different intensities

The effect of rhythmic transcranial magnetic stimulation (rTMS) of different intensities (single superthreshold rTMS more intense than 1.2 T and subthreshold one with an intensity of 70–80% of the motor threshold) of sagittal premotor cortical areas on the human functional activity was estimated in eight volunteers on the basis of combined EEG, neuropsychological, and hemodynamic examinations. The objectives of the study included the selection of the frequency of activating stimulation and revision of the objective EEG criteria of rTMS efficiency. It has been demonstrated that analysis of the EEG response to photostimulation at different frequencies is efficient in selecting the rTMS frequency. The EEG coherence is one of the most informative characteristics of the rTMS effect on central neurodynamics. The functional effects of stimulation (activating or inhibitory) have been shown to depend on the initial level of intercentral coherent relationships It has been found that rTMS of the sagittal premotor cortex causes definite changes in the functional activity of a healthy brain different from those caused by placebo. These changes are greater in the left hemisphere (in the form of intrahemispheric changes in coherence and depend on the stimulation intensity (superor subthreshold) and the initial state. The vascular factor has been shown to play an important role in the formation of cerebral responses to rTMS.     

Relationship between the tension-time area and the frequency of stimulation in motor units of the rat medial gastrocnemius muscle.

The tension-time area is an estimation of the work performed by contracting motor units. The relationship between tension and frequency of stimulation and between tension-time area and frequency have been studied on 148 single motor units of the rat medial gastrocnemius muscle, under isometric conditions. Motor units were classified as fast fatigable (FF), fast resistant to fatigue (FR) or slow (S). Trains of stimuli of increasing frequency and constant duration were used. For all motor units a half of the maximum tetanic tension corresponded to lower frequencies compared to frequencies at a half of the maximum tension-time area. Moreover, the slopes of tension-frequency and area-frequency curves (change of tension or area per 1 Hz rise in frequency) were higher for slow than for fast motor units. The tension-time area per one pulse was calculated for different frequencies of stimulation. For slow units the maximum area per pulse corresponded to significantly lower frequencies than for fast ones, especially of FF type. However, for all three types of motor units this optimal frequency corresponded to sub-fused tetani with a tension of about 75% of the maximum tension, and with the fusion index slightly over 0.90. The absolute values of the maximum tension-time area per pulse revealed that in one contraction within the tetanus, slow units are generating greater work than FR units. The work performed by FF units is nearly two times larger than for S units, although the tension of slow units is over eight times lower. The presented results reveal that the contraction of slow motor units is much more effective than was suggested based on their low tension.     

电刺激家兔迷走神经中枢端诱导的黑-伯反射中的非联合型学习现象

本文旨在研究电刺激家兔迷走神经诱导的黑-伯（Hering-Breuer,HB）反射中的学习和记忆现象。选择性电刺激家兔迷走神经中枢端（频率10～100Hz,强度20～60μA,波宽0．3ms,持续60s）,观察对膈神经放电的影响。以不同频率电刺激家兔迷走神经可模拟HB反射的两种成分,即类似肺容积增大所致抑制吸气的肺扩张反射和类似肺容积缩小所致加强吸气的肺萎陷反射。（1）长时高频（≥40Hz,60s）电刺激迷走神经可模拟呼吸频率减慢,呼气时程延长的肺扩张反射。随着刺激时间的延长,膈神经放电抑制的程度逐渐衰减,表现为呼吸频率的减慢（主要由呼气时程延长所致）在刺激过程中逐渐减弱或消失,显示为适应性或“习惯化”的现象;刺激结束时呼吸运动呈现反跳性增强,表现为一过性的呼气时程缩短,呼吸频率加快,然后才逐渐恢复正常。长时低频（〈40Hz,60s）电刺激迷走神经可模拟呼吸频率加快、呼气时程缩短的肺萎陷反射。随着刺激时间的延长,膈神经放电增强的程度逐渐衰减,同样表现出“习惯化”现象;刺激结束后,膈神经放电不是突然降低,而是继续衰减,表现为呼气时程逐渐延长,呼吸频率逐渐减慢,直至恢复到前对照水平,表现了刺激后的短时增强效应。（2）HB反射的适应性或“习惯化”程度反向依赖于刺激强度和刺激频率,表现为随着刺激强度和频率的增加,膈神经放电越远离正常基线水平,即爿惯化程度减弱。结果表明,家兔HB反射具有“习惯化”这一非联合型学习现象,反映与其有关的呼吸神经元网络具有突触功能的可翅性,呼吸的中枢调控反射具有一定的适应性。     

Battery-powered miniature implant for electrical nerve stimulation.

The range of application of implantable stimulators in functional electrical stimulation (FES) for therapeutic purposes and for the restoration of lost or damaged functions has steadily grown within the last 20 years. Each time a clinically used method is improved, a new field of FES application explored or basic research conducted, animal experiments are needed to check and evaluate the findings and results. It is precisely for this use that the stimulation system described in this paper was developed. The battery-powered single-channel stimulator can be used for the excitation of motor and sensory nerves with monophasic or biphasic impulses. All parameters and functions are programmable via the bidirectional telemetry circuit. Implant programming is achieved by a laptop computer, supported by a graphical user interface, instead of by a specially designed programmer. The maximum settings of the stimulation parameters are: frequency 100 Hz, monophasic pulse duration 0.8 ms, biphasic pulse duration 1.6 ms, stimulation current 3 mA. The implant volume was reduced to 2 cm3 (length 23 mm, width 13 mm, height 7.5 mm), lowering the weight to 3.6 g. Due to this small volume the implant can be used in small animals. The power supply via battery obviates the need for transcutaneous tunneling or permanent external high-frequency senders and facilitates the keeping of the animals.     

Electromyostimulation--a systematic review of the influence of training regimens and stimulation parameters on effectiveness in electromyostimulation training of selected strength parameters

Our first review from our 2-part series investigated the effects of percutaneous electromyostimulation (EMS) on maximal strength, speed strength, jumping and sprinting ability, and power, revealing the effectiveness of different EMS methods for the enhancement of strength parameters. On the basis of these results, this second study systematically reviews training regimens and stimulation parameters to determine their influence on the effectiveness of strength training with EMS. Out of about 200 studies, 89 trials were selected according to predefined criteria: subject age (<35 years), subject health (unimpaired), EMS type (percutaneus stimulation), and study duration (>7 days). To evaluate these trials, we first defined appropriate categories according to the type of EMS (local or whole-body) and type of muscle contraction (isometric, dynamic, isokinetic). Unlike former reviews, this study differentiates between 3 categories of subjects based on their level of fitness (untrained subjects, trained subjects, and elite athletes) and on the types of EMS methods used (local, whole-body, combination). Special focus was on trained and elite athletes. Untrained subjects were investigated for comparison purposes. The primary purpose of this study was to point out the preconditions for producing a stimulus above the training threshold with EMS that activates strength adaptations to give guidelines for implementing EMS effectively in strength training especially in high-performance sports. As a result, the analysis reveals a significant relationship (p < 0.05) between a stimulation intensity of ≥50% maximum voluntary contraction (MVC; 63.2 ± 19.8%) and significant strength gains. To generate this level of MVC, it was possible to identify guidelines for effectively combining training regimens (4.4 ± 1.5 weeks, 3.2 ± 0.9 sessions per week, 17.7 ± 10.9 minutes per session, 6.0 ± 2.4 seconds per contraction with 20.3 ± 9.0% duty cycle) with relevant stimulation parameters (impulse width 306.9 ± 105.1 microseconds, impulse frequency 76.4 ± 20.9 Hz, impulse intensity 63.7 ± 15.9 mA) to optimize training for systematically developing strength abilities (maximal strength, speed strength, jumping and sprinting ability, power).     

Phase-Dependent Effects of Transcutaneous Spinal Cord Stimulation on Regulation of Kinematics of Human Stepping Motions

The effect of transcutaneous electrical spinal cord stimulation on the kinematic parameters of movement of the ipsilateral and contralateral legs in healthy subjects during treadmill walking at speeds of 1.5 to 1.7 km/h has been studied. The stimulation electrodes were placed 2.5 cm lateral from the right and left sides of the spinal midline at L1 and T11 levels. During the stance phase, stimulation was administered at L1 level at a frequency of 15 Hz; during the swing phase the stimuli was delivered to T11 at a frequency of 30 Hz, followed by alternating stimulation at L1 and T11. The stimulation during the swing phase (T11) was more effective than that during the stance phase (L1); the most impressive changes in kinematic parameters were observed when combined delivery of stimulations to L1 and T11 was performed. With unilateral spinal stimulation, the amplitude of the angles in the hip, knee and/or ankle joints, the length of the transfer, and the height of the leg elevation increased in the ipsilateral leg. Similar but less pronounced changes were observed in the contralateral leg. A 10% increase in the duration of stimulation in the swing phase caused a change in the kinematic stepping parameters both in ipsilateral and contralateral legs. The maximum effect was observed when bilateral alternating stimulation was used. These data show that phasic transcutaneous electrical spinal cord stimulation, using a wide range of natural walking speeds, can be applied to control kinematic movement parameters.

     

Synchronization of respiratory frequency by somatic afferent stimulation.

In cats anesthetized with chloralose-urethan, vagotomized, paralyzed, and artifically ventilated, superficial radial (cutaneous) and hamstring (muscle) nerve afferents were stimulated while phrenic nerve electrical activity was recorded. The results obtained with both types of nerves were similar. Stimulation in mid and late expiration advanced the onset of the next inspiration, shortening its duration. Stimulation in early inspiration advanced, while that in late inspiration delayed, the onset of the next expiration. These effects were often accompanied by changes in phrenic motoneuron firing patterns (earlier recruitment, increased discharge frequency, increased slope of integrated phrenic neurogram). Repetitive somatic afferent stimulation produced sustained increases in respiratory frequency in all cats and in half of them entrainment of respiratory frequency to the frequency of stimulation occurred at ratios such as 4:3, 4:5, 1:2, 1:3, 1:4, and 1:7. The lowest stimulus intensity required for evoking these phase shifts was between 5 and 10T (threshold of most excitable fibers) for muscle afferents and between 1 and 2T for cutaneous afferents. These results demonstrate the existence of a reflex mechanism capable of locking respiratory frequency to that of a periodic somatic afferent input. They also provide an experimental basis for the hypothesis that reflexes are resposible for the observed locking between step or pedal frequency and respiratory rate during exercise in man.     

Morphological and electrophysiological changes produced by electrical stimulation in cultured neuroblastoma cells.

Electric fields, which were equivalent to those generated by medical devices, were applied to cultured neuroblastoma cells (mouse and human) to test for morphological damage and to establish damage thresholds. Each of two methods of applying fields permitted flow of electrical current and minimized exposure of cells to electrode-breakdown products. One method consisted of a pair of parallel wires in a Petri dish by which current was delivered within a fixed volume of flowing tissue-culture media. With the other method, the cells were held in a confined geometrical chamber and current was applied via agar bridges. Under a given set of stimulation parameters, damage was found to be variable from cell to cell. By changing the strength of the electric field (frequency and duration of stimulation held constant), thresholds of several V/cm were found above which cell damage could be reliably produced. Depending on the intensity of the field, damage took the form of cell lysis or damage to neurites. Intracellular recordings from the mouse neuroblastoma cells revealed a correlation between a decline in resting transmembrane potential and stimulus intensity. Human neuroblastoma cells were less susceptible to damage than were the mouse neuroblastoma cells, given the same strength of applied electric fields.     

Sinusoidal galvanic stimulation of the labyrinths and postural responses

We studied the effect of sinusoidal stimulation of the labyrinths on postural reflexes in man, using a 0.3 Hz current of alternating polarity and +/- 1 mA intensity for stimulation. The test subjects were tested binaurally by the bipolar method (BB), with two electrodes on the mastoid processes, and binaurally by the monopolar method (BM), with electrodes localized bilaterally on the mastoid process and the hand. Stabilographic postural parameters were measured in 22 subjects in five experimental situations. Each situation lasted 60 s. Body sway, detected by astabilometer, was recorded on a Philips FM tape-recorder and then analysed off-line on a PDP-11/34 computer. On BB stimulation of the labyrinths, the variance of body sway in the left-right (LR) direction increased more than in the anteroposterior (AP) direction. In BM stimulation, only the variance of LR sway increased. Other posturographic parameters displayed a similar effect. From the aspect of body sway frequency, BB stimulation produced a peak in the course of the power spectral density of the lateral stabilogram at 0.3 Hz. In this experimental situation, a habituation effect was manifested, depending on the subject. It can be stated that binaural bipolar (BB) stimulation of the labyrinths selectively influences lateral body sway, while the increase in AP body sway in this situation is merely a concomitant phenomenon.     

Turning on the central contribution to contractions evoked by neuromuscular electrical stimulation.

Neuromuscular electrical stimulation can generate contractions through peripheral and central mechanisms. Direct activation of motor axons (peripheral mechanism) recruits motor units in an unnatural order, with fatigable muscle fibers often activated early in contractions. The activation of sensory axons can produce contractions through a central mechanism, providing excitatory synaptic input to spinal neurons that recruit motor units in the natural order. Presently, we quantified the effect of stimulation frequency (10-100 Hz), duration (0.25-2 s of high-frequency bursts, or 20 s of constant-frequency stimulation), and intensity [1-5% maximal voluntary contraction (MVC) torque generated by a brief 100-Hz train] on the torque generated centrally. Electrical stimulation (1-ms pulses) was delivered over the triceps surae in eight subjects, and plantar flexion torque was recorded. Stimulation frequency, duration, and intensity all influenced the magnitude of the central contribution to torque. Central torque did not develop at frequencies < or = 20 Hz, and it was maximal at frequencies > or = 80 Hz. Increasing the duration of high-frequency stimulation increased the central contribution to torque, as central torque developed over 11 s. Central torque was greatest at a relatively low contraction intensity. The largest amount of central torque was produced by a 20-s, 100-Hz train (10.7 +/- 5.5 %MVC) and by repeated 2-s bursts of 80- or 100-Hz stimulation (9.2 +/- 4.8 and 10.2 +/- 8.1% MVC, respectively). Therefore, central torque was maximized by applying high-frequency, long-duration stimulation while avoiding antidromic block by stimulating at a relatively low intensity. If, as hypothesized, the central mechanism primarily activates fatigue-resistant muscle fibers, generating muscle contractions through this pathway may improve rehabilitation applications.     

Resistance and facilitation gradient in synchronized cardiac stimulation in the dog]

Electrical stimulation synchronized on spontaneous or paced cardiac rhythms demonstrates, in dogs : 1) phenomena of intermittent capture (I.C.), and intermittent loss (I.L.) of control, at all moments in the idastole ; 2) constant lowering of Excitability Threshold (E.T.) and Pacing Threshold (P.T.). These experiments confirm the existence of Resistance Gradients (including I.C. and I.L. phenomena) and Facilitation Gradients (measuring E.T. and P.T. lowerings). These gradients -- that we previously described in human pacing -- are parameters of the cardiac excitability.     

Is maximum stimulation intensity required in the assessment of muscle activation capacity?

Voluntary activation assessment using the interpolation twitch technique (ITT) has almost invariably been done using maximal stimulation intensity, i.e., an intensity beyond which no additional joint moment or external force is produced by increasing further the intensity of stimulation. The aim of the study was to identify the minimum stimulation intensity at which percutaneous ITT yields valid results. Maximal stimulation intensity and the force produced at that intensity were identified for the quadriceps muscle using percutaneous electrodes in eight active men. The stimulation intensities producing 10–90% (in 10% increments) of that force were determined and subsequently applied during isometric contractions at 90% of maximum voluntary contraction (MVC) via twitch doublets. Muscle activation was calculated with the ITT and pain scores were obtained for each stimulation intensity and compared to the respective values at maximum stimulation intensity. Muscle activation at maximal stimulation intensity was 91.6 (2.5)%. The lowest stimulation intensity yielding comparable muscle activation results to maximal stimulation was 50% (88.8 (3.9)%, p < 0.05). Pain score at maximal stimulation intensity was 6.6 (1.5) cm and it was significantly reduced at 60% stimulation intensity (3.7 (1.5) cm, p < 0.05) compared to maximal stimulation intensity. Submaximal stimulation can produce valid ITT results while reducing the discomfort obtained by the subjects, widening the assessment of ITT to situations where discomfort may otherwise impede maximal electrostimulation.