Effects Of Stimulation Parameters Research Articles

Interpreting the Effect of Stimulus Parameters on the Electrically Evoked Compound Action Potential and on Neural Health Estimates

Variations in the condition of the neural population along the length of the cochlea can degrade the spectral and temporal representation of sounds conveyed by CIs, thereby limiting speech perception. One measurement that has been proposed as an estimate of neural survival (the number of remaining functional neurons) or neural health (the health of those remaining neurons) is the effect of stimulation parameters, such as the interphase gap (IPG), on the amplitude growth function (AGF) of the electrically evoked compound action potential (ECAP). The extent to which such measures reflect neural factors, rather than non-neural factors (e.g. electrode orientation, electrode-modiolus distance, and impedance), depends crucially upon how the AGF data are analysed. However, there is currently no consensus in the literature for the correct method to interpret changes in the ECAP AGF due to changes in stimulation parameters. We present a simple theoretical model for the effect of IPG on ECAP AGFs, along with a re-analysis of both animal and human data that measured the IPG effect. Both the theoretical model and the re-analysis of the animal data suggest that the IPG effect on ECAP AGF slope (IPG slope effect), measured using either a linear or logarithmic input-output scale, does not successfully control for the effects of non-neural factors. Both the model and the data suggest that the appropriate method to estimate neural health is by measuring the IPG offset effect, defined as the dB offset between the linear portions of ECAP AGFs for two stimuli differing only in IPG.

150 Effect of Stimulation Parameters on Visual Percepts Elicited by Stimulation of a Visual Cortical Prosthesis for the Blind

Abstract INTRODUCTION Stimulation of human visual cortex is known to elicit visual percepts (phosphenes) which makes it a suitable candidate for generating artificial vision for blind. Although there have been a few attempts to build visual cortical prostheses, a greater understanding of the physiology of stimulation is required to generate useful perceptions. This study aims to characterize the phosphenes elicited by a neurostimulation device and explore the effects of stimulation parameters (amplitude, frequency, pulse-width and burst duration) on the quality of these percepts. METHODS A 30-year-old volunteer with an 8-year history of bare light perception secondary to Voght-Koaynagi-Harada Syndrome participated in this study. Two parallel cortical strip leads (each with four contacts) were implanted over the right medial occipital lobe. Phosphene characteristics were assessed postoperatively using subject's drawings of on a touch screen as well as subjective description of the percepts intensity and color. The stimulus parameters for eliciting a well-defined phosphene were obtained by varying the stimulus parameters for each contact at the beginning of each session during the eight months' period of the study. RESULTS >Stimulation of each of the eight contacts elicited phosphenes with a consistent shape and location in the visual field. The stimulus parameters for generating a well-defined phosphene were stable for six contacts and had to be adjusted for two over the period of the study. Increasing the amplitude and frequency resulted in more intense perceptions and the subject indicated seeing colored phosphenes for certain amplitudes. Simultaneous stimulation of multiple contacts was perceived as a summation of percepts elicited by stimulating the contacts individually. Sequential stimulation of two contacts generated two phosphenes and the subject was able to identify them in order. CONCLUSION Visual cortical prostheses are feasible candidates for creating artificial sight due to reproducibility of the perceptions and consistency of the stimulation parameters required to generate basic visual perceptions.

The Duration of Motor Responses Evoked with Intracortical Microstimulation in Rats Is Primarily Modulated by Stimulus Amplitude and Train Duration.

Microstimulation of brain tissue plays a key role in a variety of sensory prosthetics, clinical therapies and research applications, however the effects of stimulation parameters on the responses they evoke remain widely unknown. In particular, the effects of parameters when delivered in the form of a stimulus train as opposed to a single pulse are not well understood despite the prevalence of stimulus train use. We aimed to investigate the contribution of each parameter of a stimulus train to the duration of the motor responses they evoke in forelimb muscles. We used constant-current, biphasic, square wave pulse trains in acute terminal experiments under ketamine anaesthesia. Stimulation parameters were systematically tested in a pair-wise fashion in the caudal forelimb region of the motor cortex in 7 Sprague-Dawley rats while motor evoked potential (MEP) recordings from the forelimb were used to quantify the influence of each parameter in the train. Stimulus amplitude and train duration were shown to be the dominant parameters responsible for increasing the total duration of the MEP, while interphase interval had no effect. Increasing stimulus frequency from 100–200 Hz or pulse duration from 0.18–0.34 ms were also effective methods of extending response durations. Response duration was strongly correlated with peak time and amplitude. Our findings suggest that motor cortex intracortical microstimulations are often conducted at a higher frequency rate and longer train duration than necessary to evoke maximal response duration. We demonstrated that the temporal properties of the evoked response can be both predicted by certain response metrics and modulated via alterations to the stimulation signal parameters.

Intracortical Microstimulation Parameters Dictate the Amplitude and Latency of Evoked Responses.

Microstimulation of brain tissue plays a key role in a variety of sensory prosthetics, clinical therapies and research applications. However, the effects of stimulation parameters on the responses they evoke remain widely unknown. We aimed to investigate the contribution of each stimulation parameter to the response and identify interactions existing between parameters. Parameters of the constant-current, biphasic square waveform were examined in acute terminal experiments under ketamine anaesthesia. The motor cortex of 7 Sprague-Dawley rats was stimulated while recording motor evoked potentials (MEP) from the forelimb. Intracortical microstimulation (ICMS) parameters were systematically tested in a pair-wise fashion to observe the influence of each parameter on the amplitude and latency of the MEP. The amplitude of the MEP increased continually with stimulus amplitude (p < 0.001) and pulse duration (p = 0.001) throughout the range tested. Increases were also observed when stimuli were raised from low to moderate values of frequency (p = 0.022) and train duration (p = 0.045), after which no further excitation occurs. The latency of MEP initiation decreased when stimulus amplitude (p = 0.037) and frequency (p = 0.001) were raised from low to moderate values, after which the responses plateaued. MEP latencies were further reduced by increasing the pulse duration (p = 0.011), but train duration had no effect. Our data indicate that MEP amplitude and onset latency can be modulated by alterations to a number of stimulus parameters, even in restrictive paradigms, and suggest that the parameters of the standard ICMS signal used for evoking movements from the motor cortex can be further optimized.

The Effects of Stimulation Parameters on Clinical Outcomes in Patients With Vagus Nerve Stimulation Implants With Major Depression

Stimulation techniques, such as vagus nerve stimulation, are a promising new approach for treatment-resistant depression. Most international studies have used fixed stimulation parameters or have varied the stimulation frequencies. Our retrospective examination of 2 parallel groups of 10 patients each compared low-strength/high-frequency vagus nerve stimulation parameters (≤1.5 mA, 20 Hz) with high-strength/low-frequency ( >1.5 mA, 15 Hz) parameters. We found a significant decrease in the Hamilton Rating Scale for Depression scores in patients who were treated using the low-strength/high-frequency stimulation parameters. In contrast, the scores of the patients treated with high-strength/low-frequency stimulation did not change.

Effects of stimulation parameters and electrode location on thresholds for epidural stimulation of cat motor cortex

Epidural electrical stimulation (ECS) of the motor cortex is a developing therapy for neurological disorders. Both placement and programming of ECS systems may affect the therapeutic outcome, but the treatment parameters that will maximize therapeutic outcomes and minimize side effects are not known. We delivered ECS to the motor cortex of anesthetized cats and investigated the effects of electrode placement and stimulation parameters on thresholds for evoking motor responses in the contralateral forelimb. Thresholds were inversely related to stimulation frequency and the number of pulses per stimulus train. Thresholds were lower over the forelimb representation in motor cortex (primary site) than surrounding sites (secondary sites), and thresholds at sites <4 mm away from the primary site were significantly lower than at sites >4 mm away. Electrode location and montage influenced the effects of polarity on thresholds: monopolar anodic and cathodic thresholds were not significantly different over the primary site, cathodic thresholds were significantly lower than anodic thresholds over secondary sites and bipolar thresholds were significantly lower with the anode over the primary site than with the cathode over the primary site. A majority of bipolar thresholds were either between or equal to the respective monopolar thresholds, but several bipolar thresholds were greater than or less than the monopolar thresholds of both the anode and cathode. During bipolar stimulation, thresholds were influenced by both electric field superposition and indirect, synaptically mediated interactions. These results demonstrate the influence of stimulation parameters and electrode location during cortical stimulation, and these effects should be considered during the programming of systems for therapeutic cortical stimulation.

S1806 Central Neuronal Mechanisms of GES and Effects of Stimulation Parameters and Locations in Regular and Diet-Induced Obese Rats

S1806 Central Neuronal Mechanisms of GES and Effects of Stimulation Parameters and Locations in Regular and Diet-Induced Obese Rats

Cognitive Outcomes after Deep Brain Stimulation for Parkinson's Disease: A Review of Initial Studies and Recommendations for Future Research

Modern ablative surgery for movement disorders probably results in less frequent and severe cognitive morbidity than seen in early surgical series. Nonetheless, recent studies indicate that neurobehavioral functions commonly compromised in Parkinson's disease (PD) (e.g., executive functions, verbal fluency, and memory) are negatively impacted in some patients by lesion placement. The potential reversibility of cognitive dysfunction after chronic electrical deep brain stimulation (DBS) for PD has lead some to favor this treatment modality over ablation. This paper reviews the initial studies of the cognitive effects of thalamic, pallidal, and subthalamic DBS. These studies suggest that DBS is relatively safe from a cognitive standpoint and that the benefits of motor improvements probably outweigh the cost of minimal cognitive morbidity. This conclusion must be offered with caution, however, given the small numbers of studies to date and their methodological limitations. Neurobehavioral research has yet to adequately address (1) outcome relative to appropriate control groups; (2) effects of electrode placement versus stimulation; (3) laterality- and site-specific effects of DBS; (4) long-term effects of DBS; (5) effects of stimulation parameters; (6) risk factors for cognitive dysfunction with DBS; (7) whether cognitive dysfunction associated with DBS is reversible; and (8) comparative neurobehavioral outcome after DBS and ablation. DBS affords an exciting opportunity to clarify the neurobehavioral role of the basal ganglia.

ACh release from horse airway cholinergic nerves: effects of stimulation intensity and muscle preload.

This study was conducted to determine the effects of stimulation parameters and muscle preload on acetylcholine (ACh) release induced by electrical field stimulation (EFS) of horse airway cholinergic nerves. Trachealis strip bundles were prepared and suspended in 2-ml tissue baths. The tissues were stimulated three to five times for 30 min each. Increasing frequency (0.5-16 Hz) and voltage (5-20 V) increased ACh release; increasing pulse duration (0.5-3 ms) had only a minor effect. Alterations in muscle preload (2-20 g) had no effect on ACh release. ACh release was fairly constant for up to five repeated stimulation periods with the same EFS parameters. Stimulation of the tissues for 15 min released the same amount of ACh as 30 min if the amount was expressed as picomoles per gram per minute, suggesting that ACh release rate was constant during the 30-min period of stimulation. Atropine (10(-6) M) potentiated the release of ACh four- to fivefold, presumably by removing the autoinhibitory effect of ACh on the cholinergic nerves. Tetrodotoxin (10(-6) M) abolished the EFS-induced ACh release.

Discrimination between aversive brain stimulations: Effect of stimulation parameters

Rats placed in a T maze were shown to be able to discriminate between two stimulations applied to one and the same brain site and inducing aversive effects of different magnitude. Discrimination occurred irrespective of whether the two stimulations differed in either intensity or frequency, and irrespective of whether they were applied to a medial hypothalamic or to a mesencephalic central gray site. Generalization experiments were performed in which either the stimulation parameter used to establish the discrimination or another parameter was varied. The results show that the animal's choice cannot be predicted on the sole basis of either the electrical charge/second applied or the escape latency induced.

Auditory Prostheses Research with Multiple Channel Intracochlear Stimulation in Man

Although single-channel electrode arrays implanted in the scala tympani of deaf patients are useful as an aid to lip reading and for distinguishing some environmental sounds, they do not transmit intelligible speech. However, multichannel electrode arrays, which take advantage of the cochlea's tonotopic organization, may be capable of generating the complex patterns of neural activity necessary for speech discrimination. In this study, multichannel electrodes were implanted in the cochleas of four volunteers, with access to the connecting wires made through the skin via a percutaneous connector. The major portion of the data presented is from two of these subjects: one has been bilaterally deaf since birth and the other has been unilaterally deaf for 15 years. Preliminary results of experiments with two more recently implanted subjects are described as well as experiments with a fifth volunteer who was implanted with five electrodes by House in 1969. Data on pitch and loudness discrimination as well as the effects of stimulation parameters on threshold, impedance, and electrode interaction are presented. Place pitch and periodicity pitch were observed in all five volunteers. The results of pitch-matching experiments with the unilaterally deaf volunteer were consistent with tonotopic maps of the cochlea, and experiments indicated that a pitch continuum may be achieved by combining place and periodicity pitch modulation. Preliminary experiments in tune recognition with one subject demonstrate his ability to recognize simple melodies based on periodicity pitch cues. These results, coupled with the finding that subjective sensations remain stable over the long-term, support the feasibility of providing artificial hearing with a multichannel cochlear stimulation system.

Effects of stimulation parameters on behavior elicited by stimulation of the hypothalamic defense area.

Effects of stimulation parameters on behavior elicited by stimulation of the hypothalamic defense area.

Psychosomatic aspects of Parkinsonism

Modern ablative surgery for movement disorders probably results in less frequent and severe cognitive morbidity than seen in early surgical series. Nonetheless, recent studies indicate that neurobehavioral functions commonly compromised in Parkinson's disease (PD) (e.g., executive functions, verbal fluency, and memory) are negatively impacted in some patients by lesion placement. The potential reversibility of cognitive dysfunction after chronic electrical deep brain stimulation (DBS) for PD has lead some to favor this treatment modality over ablation. This paper reviews the initial studies of the cognitive effects of thalamic, pallidal, and subthalamic DBS. These studies suggest that DBS is relatively safe from a cognitive standpoint and that the benefits of motor improvements probably outweigh the cost of minimal cognitive morbidity. This conclusion must be offered with caution, however, given the small numbers of studies to date and their methodological limitations. Neurobehavioral research has yet to adequately address (1) outcome relative to appropriate control groups; (2) effects of electrode placement versus stimulation; (3) laterality- and site-specific effects of DBS; (4) long-term effects of DBS; (5) effects of stimulation parameters; (6) risk factors for cognitive dysfunction with DBS; (7) whether cognitive dysfunction associated with DBS is reversible; and (8) comparative neurobehavioral outcome after DBS and ablation. DBS affords an exciting opportunity to clarify the neurobehavioral role of the basal ganglia.

Constancy of hippocampal afterdischarge under various conditions of stimulation

The effect of stimulation parameters on duration of afterdischarge (AD) evoked from the dorsal hippocampus has been studied in the non-anaesthetized rabbit. Repeated hippocampal stimulation of an animal on a single day frequently resulted in prolongation of AD in spite of constant conditions of stimulation. Within short series of stimulations, in which the response remained constant, the following observations were made: 1. 1. Variation of the frequency of stimulation from 10–100 c/sec resulted in AD of the same duration. 2. 2. Increase in voltage, beyond the threshold, did not substantially influence the duration of AD. 3. 3. Hippocampal discharge is observed during stimulation. Under prolonged stimulation, hippocampal discharge comes to an end while stimulation continues. The period from the beginning of stimulation to the end of the hippocampal discharge is constant and not dependent on duration of stimulation. 4. 4. In a given animal AD evoked from different points of both dorsal hippocampi i of the same duration. 5. 5. The duration of hippocampal AD appears to be independent of stimulation parameters over a wide range. It is suggested that this may be a general characteristic of epileptic afterdischarge.