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Background: The subcutaneous implantable cardioverter-defibrillator (ICD) is associated with fewer lead-related complications than a transvenous ICD; however, the subcutaneous ICD cannot provide bradycardia and antitachycardia pacing. Whether a modular pacing-defibrillator system comprising a leadless pacemaker in wireless communication with a subcutaneous ICD to provide antitachycardia and bradycardia pacing is safe remains unknown., Methods: We conducted a multinational, single-group study that enrolled patients at risk for sudden death from ventricular arrhythmias and followed them for 6 months after implantation of a modular pacemaker-defibrillator system. The safety end point was freedom from leadless pacemaker-related major complications, evaluated against a performance goal of 86%. The two primary performance end points were successful communication between the pacemaker and the ICD (performance goal, 88%) and a pacing threshold of up to 2.0 V at a 0.4-msec pulse width (performance goal, 80%)., Results: We enrolled 293 patients, 162 of whom were in the 6-month end-point cohort and 151 of whom completed the 6-month follow-up period. The mean age of the patients was 60 years, 16.7% were women, and the mean (±SD) left ventricular ejection fraction was 33.1±12.6%. The percentage of patients who were free from leadless pacemaker-related major complications was 97.5%, which exceeded the prespecified performance goal. Wireless-device communication was successful in 98.8% of communication tests, which exceeded the prespecified goal. Of 151 patients, 147 (97.4%) had pacing thresholds of 2.0 V or less, which exceeded the prespecified goal. The percentage of episodes of arrhythmia that were successfully terminated by antitachycardia pacing was 61.3%, and there were no episodes for which antitachycardia pacing was not delivered owing to communication failure. Of 162 patients, 8 died (4.9%); none of the deaths were deemed to be related to arrhythmias or the implantation procedure., Conclusions: The leadless pacemaker in wireless communication with a subcutaneous ICD exceeded performance goals for freedom from major complications related to the leadless pacemaker, for communication between the leadless pacemaker and subcutaneous ICD, and for the percentage of patients with a pacing threshold up to 2.0 V at a 0.4-msec pulse width at 6 months. (Funded by Boston Scientific; MODULAR ATP ClinicalTrials.gov NCT04798768.)., (Copyright © 2024 Massachusetts Medical Society.)

Background: The subcutaneous implantable cardioverter-defibrillator (S-ICD) is an accepted alternative to transvenous (TV) ICD to provide defibrillation therapy to treat life-threatening ventricular tachyarrhythmias in high-risk patients. S-ICD outcomes by age group have not been reported., Objectives: In this study, the authors sought to report S-ICD outcomes in different age groups in a multicenter S-ICD post-approval study (PAS) involving the largest cohort of patients ever reported., Methods: Patients were prospectively enrolled in the S-ICD PAS and stratified based on age: young, aged 15-34 years; adult, aged 35-69 years; and elderly, aged ≥70 years. Patient characteristics and clinical outcomes through 3 years of follow up after implantation were compared., Results: The S-ICD PAS enrolled 1,637 patients. Elderly patients were more likely to receive an S-ICD as a replacement of a TV-ICD (15.1% elderly vs 12.3% adult vs 7.4% young). Secondary prevention indication decreased with age (32.7% young vs 22.2% adult vs 20.5% elderly). Mortality rate was significantly higher in the elderly group (24.0% elderly vs 13.0% adult vs 7.4% young; P < 0.0001), whereas the complication rate did not differ significantly (12.3% young vs 11.3% adult vs 8.1% elderly). Rates of appropriate shock (12.7% young vs 13.0% adult vs 13.8% elderly) and inappropriate shock (7.8% young vs 9.1% adult vs 8.8% elderly) rates did not differ between groups (P = 0.96 and P = 0.98, respectively)., Conclusions: Implant complications and appropriate and inappropriate shock rates were similar among age groups. S-ICD for secondary prevention was more common in the young group. Replacing a TV-ICD for an S-ICD increases with age. (S-ICD System Post-Approval Study; NCT01736618)., Competing Interests: Funding Support and Author Disclosures Dr Weiss has received compensation for services from Boston Sci Advisory honoraria; Biosense Consulting and Educational Honoraria; Abbott Consulting Honoraria; S4 Travel; and Sanofi Consulting; research grants from Boston Scientific, Abbott, Biosense, and Medtronic; and fellowship support from Boston Scientific Corporation, Abbott, Biosense, and Medtronic. Dr Knight has received consulting and speaker fees, investigator compensation, and fellowship support from Abbott, Biosense Webster, Biotronic, Boston Scientific, Medtronic, Atricure, and CVRx. Dr El-Chami has received compensation for services from Boston Scientific and Medtronic. Dr Aasbo has received consulting fees Boston Scientific and Biotronik. Dr Sadhu has received compensation for services and Speaker fees from Boston Scientific. Dr Brisben is a full-time employee of Boston Scientific. Mr Carter is a full-time employee of Boston Scientific. Dr Burke has received honoraria and research grants from Boston Scientific, Biosense Webster, and AtaCor Medical; and holds equity in AtaCor Medical. Dr Gold has received compensation for services from Boston Scientific, Medtronic, and Abbott. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2023 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: The subcutaneous implantable cardioverter-defibrillator (S-ICD) was developed to avoid complications related to transvenous implantable cardioverter-defibrillator (TV-ICD) leads. Device safety and efficacy were demonstrated previously with atypical clinical patients or limited follow-up., Objectives: The S-ICD PAS (Subcutaneous Implantable Cardioverter-Defibrillator System Post Approval Study) is a real-world, multicenter, registry of U.S. centers that was designed to assess long-term S-ICD safety and efficacy in a diverse group of patients and implantation centers., Methods: Patients were enrolled in 86 U.S. centers with standard S-ICD indications and were observed for up to 5 years. Efficacy endpoints were first and final shock efficacy. Safety endpoints were complications directly related to the S-ICD system or implantation procedure. Endpoints were assessed using prespecified performance goals., Results: A total of 1,643 patients were prospectively enrolled, with a median follow-up of 4.2 years. All prespecified safety and efficacy endpoint goals were met. Shock efficacy rates for discrete episodes of ventricular tachycardia or ventricular fibrillation were 98.4%, and they did not differ significantly across follow-up years (P = 0.68). S-ICD-related and electrode-related complication-free rates were 93.4% and 99.3%, respectively. Only 1.6% of patients had their devices replaced by a TV-ICD for a pacing need. Cumulative all-cause mortality was 21.7%., Conclusions: In the largest prospective study of the S-ICD to date, all study endpoints were met, despite a cohort with more comorbidities than in most previous trials. Complication rates were low and shock efficacy was high. These results demonstrate the 5-year S-ICD safety and efficacy for a large, diverse cohort of S-ICD recipients. (Subcutaneous Implantable Cardioverter-Defibrillator [S-ICD] System Post Approval Study [PAS]; NCT01736618)., Competing Interests: Funding Support and Author Disclosures This study was sponsored by Boston Scientific. Dr Gold has received consulting fees from Boston Scientific and Medtronic; and has participated in clinical trials with Boston Scientific, Medtronic, and Abbott. Dr El-Chami has received compensation for services from Boston Scientific and Medtronic. Dr Burke has received honoraria and research grants from AtaCor Medical, Biosense Webster, and Boston Scientific; and has held equity in AtaCor Medical. Dr Upadhyay has served on advisory boards at Abbott, BioTel, Biotronik, and Medtronic; and has served a speaker for Zoll Medical. Dr Herre has received research support from Analytics 4 Life, Boston Scientific, and EBR Systems; has received consulting fees from Medtronic; and has served as the Board Chair for LifeNet Health. Dr Kutalek has received consulting fees and compensation for services from Boston Scientific. Dr Knight has received consulting and speaker fees and investigator and/or fellowship support from Abbott, Atricure, Boston Scientific, Biosense Webster, Biotronik, CVRx, and Medtronic. Ms Leigh is a full-time employee of Boston Scientific. Ms Lucas is a full-time employee of NAMSA. Mr Carter is a full-time employee of Boston Scientific. Dr Brisben is a full-time employee of Boston Scientific. Dr Aasbo has received consulting fees from Boston Scientific and Biotronik. Dr Weiss has received compensation for services from Abbott, Boston Scientific, Biosense, Biotronik, S4, and Sanofi; has received research grants from Abbott, Boston Scientific, Biosense, and Medtronic; and has received fellowship support from Abbott, Boston Scientific, Biosense Webster, and Medtronic. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: The subcutaneous implantable cardioverter-defibrillator (S-ICD) has demonstrated safety and efficacy for the treatment of malignant ventricular arrhythmias. However, a limitation of the S-ICD lies in the inability to either pace-terminate ventricular tachycardia or provide prolonged bradycardia pacing support., Objective: The rationale and design of a prospective, single-arm, multinational trial of an intercommunicative leadless pacing system integrated with the S-ICD will be presented., Methods: A technical description of the modular cardiac rhythm management (mCRM) system (EMPOWER leadless pacemaker and EMBLEM S-ICD) and the implantation procedure is provided. MODULAR ATP (Effectiveness of the EMPOWER™ Modular Pacing System and EMBLEM™ Subcutaneous ICD to Communicate Antitachycardia Pacing) is a multicenter, international trial enrolling up to 300 patients at risk of sudden cardiac death at up to 60 centers trial design. The safety endpoint of freedom from major complications related to the mCRM system or implantation procedure at 6 months and 2 years are significantly higher than 86% and 81%, respectively, and all-cause survival is significantly >85% at 2 years., Results: Efficacy endpoints are that at 6 months mCRM communication success is significantly higher than 88% and the percentage of subjects with low and stable thresholds is significantly higher than 80%. Substudies to evaluate rate-responsive features and performance of the pacing module are also described., Conclusion: The MODULAR ATP global clinical trial will prospectively test the safety and efficacy of the first intercommunicating leadless pacing system with the S-ICD. This trial will allow for robust validation of device-device communication, pacing performance, rate responsiveness, and system safety., (© 2023 Heart Rhythm Society. Published by Elsevier Inc.)

Background: Early subcutaneous implantable cardioverter-defibrillator (S-ICD) studies included atypical cohorts of patients who were younger with fewer comorbidities. Recent S-ICD studies included patient populations with more comorbidities., Objectives: The goals of this study were to determine the incidence and predictors of S-ICD-related infection over a 3-year follow-up period and to use these results to develop an infection risk score., Methods: The S-ICD Post Approval Study is a US prospective registry of 1637 patients. Baseline demographic characteristics and outcomes with 3-year postimplantation follow-up were compared between patients with and without device-related infection. A risk score was derived from multivariable proportional hazards analysis of 22 variables., Results: Infection was observed in 55 patients (3.3%), with 69% of infections occurring within 90 days and a vast majority (92.7%) within 1 year of implantation. Late infections more likely involved device erosion; no infections occurred after year 2. The annual mortality rate postinfection was 0.6%/y. No lead extraction complications or bacteremia related to infection were observed. An infection risk score was created with diabetes, age, prior transvenous ICD implant, and ejection fraction as predictors. Patients with a risk score of ≥3 had an 8.8 hazard ratio (95% confidence interval 2.8-16.3) of infection compared with a 0 risk score., Conclusion: Infection rates in the S-ICD Post Approval Study were similar to other S-ICD populations and not associated with systemic blood-borne infections. Late infection (>1 year) is uncommon and associated with system erosion. A high-risk infection cohort can be identified that may facilitate preventive measures., (Copyright © 2022 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: Kidney disease is a risk factor for device infection in transvenous implantable cardioverter-defibrillator (TV-ICD) implants, with mechanisms that include immunodeficiency and a portal of entry for bacteria that can seed indwelling devices., Objective: The purpose of this study was to examine the impact of both kidney disease and dialysis-dependence on the incidence of device-related infection after de novo TV-ICD implantation and how the incidence changes over time in., Methods: Medicare 100% administrative and claims data were used to identify patients who underwent de novo TV-ICD implantation between July 1, 2016, and December 31, 2018. Baseline characteristics included underlying kidney disease (none, nondialysis, dialysis) plus device infection during follow-up. Patients were followed for TV-ICD infection up to 78 weeks after implantation. Piecewise Poisson regression was used to predict the incidence of and hazard ratios for infection over time., Results: Overall, 809 of 42,200 patients (1.9%) had at least 1 device infection during mean follow-up of 66 weeks: 484 of 31,217 (1.6%) none; 202 of 9151 (2.2%) nondialysis; and 123 of 1832 (6.7%) dialysis (P <.001 via log-rank test). The incidence of infection increased during the first 8-12 weeks and declined thereafter. Hazard ratios increased over time (dialysis week 12 = 4.9/1000 patient-years; week 52 = 9.8; nondialysis week 12 = 1.4; week 52 = 2.5; all P <.05), as did the difference in cumulative incidence compared with none (dialysis week 12 = Δ11.8 and week 78 = Δ53.5; nondialysis week 12 = Δ1.4 and week 78 = Δ7.0)., Conclusion: The incidence of infection after de novo TV-ICD implantation is higher when patients have kidney disease and is substantially higher when patients are dialysis-dependent., (Copyright © 2022 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Aims: To report 5-year outcomes of EFFORTLESS registry patients with early generation subcutaneous implantable cardioverter-defibrillator (S-ICD) devices., Methods and Results: Kaplan-Meier, trend and multivariable analyses were performed for mortality and late (years 2-5) complications, appropriate shock (AS) and inappropriate shock (IAS) rates. Nine hundred and eighty-four of 994 enrolled patients with diverse diagnoses (28% female, 48 ± 17 years, body mass index 27 ± 6 kg/m2, ejection fraction 43 ± 18%) underwent S-ICD implantation. Median follow-up was 5.1 years (interquartile range 4.7-5.5 years). All-cause mortality was 9.3% (95% confidence interval 7.2-11.3%) at 5 years; 703 patients remained in follow-up on study completion, 171 withdrew including 87 (8.8%) with device explanted, and 65 (6.6%) lost to follow-up. Of the explants, only 20 (2.0%) patients needed a transvenous device for pacing indications. First and final shock efficacy for discrete ventricular arrhythmias was consistent at 90% and 98%, respectively, with storm episode final shock efficacy at 95.2%. Time to therapy remained unaltered. Overall 1- and 5-year complication rates were 8.9% and 15.2%, respectively. Early complications did not predict later complications. There were no structural lead failures. Inappropriate shock rates at 1 and 5 years were 8.7% and 16.9%, respectively. Self-terminating inappropriately sensed episodes predicted late IAS. Predictors of late AS included self-terminating appropriately sensed episodes and earlier AS., Conclusion: In this diverse S-ICD registry population, spontaneous shock efficacy was consistently high over 5 years. Very few patients underwent S-ICD replacement with a transvenous device for pacing indications. Treated and self-terminating arrhythmic episodes predict future shock events, which should encourage more personalized device optimization., (© The Author(s) 2022. Published by Oxford University Press on behalf of European Society of Cardiology.)

Background: Subcutaneous implantable cardioverter-defibrillators (S-ICDs) and leadless pacemakers (LPs) are intended to diminish transvenous lead-related complications. However, S-ICDs do not deliver antibradycardia pacing or antitachycardia pacing, and currently, there is no commercially available coordinated leadless option for patients with defibrillator and (expected) pacing needs., Objective: We evaluated the performance, safety, and potential replacement strategies of a novel modular cardiac rhythm management (mCRM) system, a wirelessly communicating antitachycardia pacing-enabled LP and S-ICD in a preclinical model., Methods: LP implantation was attempted in 68 canine subjects, and in 38 an S-ICD was implanted as well. Animals were evaluated serially up to 18 months. At all evaluations, communication thresholds (CTs) between the devices, LP electrical parameters, and system-related complications were assessed. Different replacement strategies were tested., Results: The LP was successfully implanted in 67 of 68 (98.5%) and the concomitant S-ICD in 38 of 38 (100%). mCRM communication was successful in 1022 of 1024 evaluations (99.8%). The mean CT was 2.2 ± 0.7 V at implantation and stable afterward (18 months: 1.8 ± 0.7 V). In multivariable analysis, larger LP-to-S-ICD angle and dorsal posture were associated with higher CTs. At implantation, the mean pacing capture threshold, impedance, and R-wave amplitude were 0.3 ± 0.1 V, 898.4 ± 198.9 Ω, and 26.4 ± 8.2 mV. The mean pacing capture threshold remained stable and impedance and R-wave amplitudes were within acceptable ranges throughout (0.7 ± 0.4 V, 619.1 ± 90.6 Ω, and 20.1 ± 8.4 mV at 18 months). Different replacement strategies seem feasible., Conclusion: This first mCRM system demonstrated excellent performance up to 18 months in a preclinical model., (Copyright © 2022 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: The subcutaneous (S) implantable cardioverter-defibrillator (ICD) is safe and effective for sudden cardiac death prevention. However, patients in previous S-ICD studies had fewer comorbidities, had less left ventricular dysfunction, and received more inappropriate shocks (IAS) than in typical transvenous ICD trials. The UNTOUCHED trial (Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction) was designed to evaluate the IAS rate in a more typical, contemporary ICD patient population implanted with the S-ICD using standardized programming and enhanced discrimination algorithms., Methods: Primary prevention patients with left ventricular ejection fraction ≤35% and no pacing indications were included. Generation 2 or 3 S-ICD devices were implanted and programmed with rate-based therapy delivery for rates ≥250 beats per minute and morphology discrimination for rates ≥200 and <250 beats per minute. Patients were followed for 18 months. The primary end point was the IAS-free rate compared with a 91.6% performance goal, derived from the results for the ICD-only patients in the MADIT-RIT study (Multicenter Automatic Defibrillator Implantation Trial-Reduce Inappropriate Therapy). Kaplan-Meier analyses were performed to evaluate event-free rates for IAS, all-cause shock, and complications. Multivariable proportional hazard analysis was performed to determine predictors of end points., Results: S-ICD implant was attempted in 1116 patients, and 1111 patients were included in postimplant follow-up analysis. The cohort had a mean age of 55.8±12.4 years, 25.6% were women, 23.4% were Black, 53.5% had ischemic heart disease, 87.7% had symptomatic heart failure, and the mean left ventricular ejection fraction was 26.4±5.8%. Eighteen-month freedom from IAS was 95.9% (lower confidence limit, 94.8%). Predictors of reduced incidence of IAS were implanting the most recent generation of device, using the 3-incision technique, no history of atrial fibrillation, and ischemic cause. The 18-month all-cause shock-free rate was 90.6% (lower confidence limit, 89.0%), meeting the prespecified performance goal of 85.8%. Conversion success rate for appropriate, discrete episodes was 98.4%. Complication-free rate at 18 months was 92.7%., Conclusions: This study demonstrates high efficacy and safety with contemporary S-ICD devices and programming despite the relatively high incidence of comorbidities in comparison with earlier S-ICD trials. The inappropriate shock rate (3.1% at 1 year) is the lowest reported for the S-ICD and lower than many transvenous ICD studies using contemporary programming to reduce IAS. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02433379.

Introduction: The third-generation subcutaneous implantable cardioverter-defibrillator (S-ICD) (EMBLEM™ A219, Boston Scientific) contains a new diagnostic tool to detect atrial fibrillation (AF) in S-ICD patients, without the use of an intracardiac lead. This is the first study to evaluate the performance of the S-ICD AF monitor (AFM)., Methods: The AFM algorithm analyzes a subcutaneous signal for the presence of AF, similar to the signals collected by implantable and wearable diagnostic devices. The AFM algorithm combines heart rate (HR) scatter analysis with an HR histogram. The algorithm was tested against publicly available electrocardiogram databases (simulated performance). Real-world performance of the algorithm was evaluated by using the S-ICD LATITUDE remote monitoring (RM) database., Results: The simulated performance of the AFM algorithm resulted in a sensitivity of 95.0%, specificity of 100.0%, and positive predictive value (PPV) of 100.0%. To evaluate the real-world performance of the AFM, 7744 S-ICD devices were followed for up to 30 months by RM, whereof 99.5% had the AFM enabled. A total of 387 AF episodes were randomly chosen for adjudication, resulting in a PPV of 67.7%. The main cause of misclassification was atrial and ventricular ectopy., Conclusion: The AFM exhibited a very high sensitivity and specificity in a simulated setting, designed to maximize PPV in order to minimize the clinical burden of reviewing falsely detected AF events. The real-world performance of the AFM, enabled in 99.5% of S-ICD patients, is a PPV of 67.7%., (© 2020 The Authors. Pacing and Clinical Electrophysiology published by Wiley Periodicals LLC.)

Background: The subcutaneous implantable cardioverter-defibrillator (S-ICD) has shown favorable outcomes in large registries with broad inclusion criteria. The cohorts reported had less heart disease and fewer comorbidities than standard ICD populations., Objective: The purpose of this study is to characterize acute performance for primary prevention patients with a left ventricular ejection fraction (LVEF) ≤35% (primary prevention ≤35%)., Methods: Primary prevention ≤35% patients with no prior documented sustained ventricular tachycardia (VT), pacing indication, end-stage heart failure, or advanced renal failure were prospectively enrolled. Analyses included descriptive statistics, Kaplan-Meier time to event, and multivariable linear and logistic regression., Results: In 1112 of 1116 patients, an S-ICD was successfully implanted (99.6%). Predictors for longer procedure time included 3-incision technique, higher body mass index (BMI), performing defibrillation testing (DFT), imaging, younger age, black race, and European vs North American centers. Patients undergoing DFT (82%) were successfully converted (99.2%; 93.5% converting at ≤65 J). Higher BMI was predictive of failing DFT at ≤65 J. The rate of 30-day freedom from complications was 95.8%. Most complications involved postoperative healing (45%) or interventions after DFT or impedance check (19%)., Conclusion: The procedural outcome data of UNTOUCHED reinforce that S-ICD therapy has low perioperative complication rates and high conversion efficacy of induced ventricular fibrillation, even in a higher-risk cohort with low LVEF and more comorbidities than previous S-ICD studies. Higher BMI warrants more careful attention to implant technique., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Introduction: The subcutaneous ICD system (S-ICD) has been shown to be a safe and effective treatment for patients at risk for sudden cardiac death. This device reliably detects ventricular tachyarrhythmias with a low incidence of inappropriate shocks for supraventricular arrhythmias. However, T-wave oversensing (TWOS) is more common with the S-ICD compared with transvenous systems. We developed a novel discrimination algorithm to reduce TWOS without compromising tachyarrhythmia discrimination., Methods and Results: The algorithm was developed using a database of recorded episodes, including 244 appropriate therapies for ventricular arrhythmias and 133 episodes with an inappropriate detection due to TWOS, and using a computer model that simulates the S-ICD system. An independent set of data of 161 TWOS episodes, 137 ventricular and 328 supraventricular episodes, was used to validate the algorithm on actual device hardware. The S-ICD performance with the new algorithm was compared with the S-ICD without the new algorithm. Development results showed a decrease in inappropriate charge due to TWOS by 30.7 ± 18%. All ventricular arrhythmias were appropriately detected and the time to appropriate charge initiation was not increased. System validation showed that the new algorithm avoided an inappropriate charge due to TWOS by 39.8 ± 11.4%. No decrease in ventricular arrhythmia sensitivity and no significant change in supraventricular specificity were observed., Conclusions: A new algorithm that uses correlation of the existing complex to previous complexes reduced TWOS episodes by approximately 40%. The algorithm has potential for a clinically meaningful decrease in inappropriate shocks., (© 2015 Wiley Periodicals, Inc.)

This paper describes a project using telecommunication and robotics to develop a system that addresses developmental goals for children with disabilities. A user-centered design was employed to meet the needs of the end users: children with disabilities, therapists, educators, and parents. The design team developed the prototype robot system for therapy, education, and play. The robot system is an adaptable, programmable robot, designed to address a wide range of disabilities, interests, and developmental goals. The production design will include data collection and remote monitoring capabilities. The steps leading to the prototype and its evaluation are described, including identification of user needs and system requirements to satisfy these needs.

To address several fundamental questions regarding how multiwhisker tactile stimuli are integrated and processed by the trigeminal somatosensory system, a novel behavioral task was developed that required rats to discriminate the width of either a wide or narrow aperture using only their large mystacial vibrissae. Rats quickly acquired this task and could accurately discriminate between apertures of very similar width. Accurate discriminations required a large number of intact facial whiskers. Systematic removal of individual whiskers caused a decrease in performance that was directly proportional to the number of whiskers removed, indicating that tactile information from multiple whiskers is integrated as rats gauge aperture width. In different groups of rats, different sets of whiskers were removed in patterns that preferentially left whisker rows or whisker arcs intact. These different whisker removals caused similar decreases in performance, indicating that individual whiskers within the vibrissal array are functionally equivalent during performance of this task. Lesions of the barrel cortex abolished the ability of rats to discriminate, demonstrating that this region is critically involved in this tactile behavior. Interestingly, sectioning the facial nerve, which abolished whisker movements, did not affect the ability to perform accurate discriminations, indicating that active whisker movements are not necessary for accurate performance of the task. Collectively, these results indicate that the trigeminal somatosensory system forms internal representations of external stimuli (in this case, aperture width) by integrating tactile input from many functionally equivalent facial whiskers and that the vibrissal array can function as a fine-grained distance detector without active whisker movements.

A system is described that delivers complex, biologically realistic, tactile stimuli to the rat's facial whisker pad by independently stimulating up to 16 individual facial whiskers in a flexible yet highly controlled and repeatable manner. The system is technically simple and inexpensive to construct. The system consists of an array of 16 miniature-solenoid driven actuators that are attached to 16 individual facial whiskers via very small (130 microm dia.) Teflon-coated stainless steel wires. When individual solenoids are energized, the wire is rapidly retracted, resulting in a deflection of individual whiskers. The rise time of deflection is approx. 1 mm/ms. Repeatable stimulation of individual whiskers can be achieved without touching adjacent whiskers, thereby allowing a very high density of stimulators to be attached within the spatially restricted region of the facial whisker pad. Complex patterns of whisker stimulation (designed to mimic biologically realistic stimuli) are delivered to the whisker pad by activating individual solenoid actuators in precisely controlled temporal patterns. These stimulations can be combined with multi-electrode single-unit ensemble recordings at multiple sites within the rat trigeminal somatosensory system. Analysis of neuronal population responses to these complex stimuli is intended to examine how the trigeminal somatosensory system encodes and processes spatiotemporally complex stimuli.

We recorded action potentials from three RA fibers innervating primate fingerpad, while applying electrotactile (electrocutaneous) stimulation. Negative pulses required 1.3-1.5 times more current than positive ones for entrainment. The strength-duration time constant was approximately 151 micros. Suprathreshold sinusoidal vibration synchronized to 30-Hz electrotactile pulses changed the electrotactile entrainment current slightly, indicating a possible electrical-mechanical transduction interaction.

A tool or probe often functions as an extension of the hand, transmitting vibrations to the hand to produce a percept of the object contacting the tool or probe. This paper reports the psychophysical results of a combined psychophysical and neurophysiological study of the perception of vibration transmitted through a cylinder grasped in the hand. In the first part of the psychophysical study, 19 subjects grasped a cylinder, 32 mm diam, with an embedded motor that caused vibration parallel to the axis of the cylinder. The relationship between threshold and frequency was the traditional U-shaped function with a minimum between 150 and 200 Hz. Except a study by Békésy in which subjects grasped a rod that vibrated parallel to the skin surface, thresholds above 20 Hz were lower and the slopes were steeper than any reported previously. Thresholds were <0.01 microm in some subjects. Data from both the psychophysical and the neurophysiological studies suggest that detection performance at frequencies >20 Hz was based on activity in Pacinian afferents. The extreme sensitivity compared with previous reports may have resulted from differences in contact area, direction of vibration, contact force, and the shape of the stimulus probe. The effects of each of these variables were studied. At 40 and 300 Hz (frequencies near the lower and upper end of the Pacinian range) thresholds were 9.8 and 18.5 dB (68 and 88%) lower, respectively, when subjects grasped the cylinder than when a 1-mm-diam probe vibrated perpendicular to the skin. These differences were accounted for as follows: 1) thresholds at a single fingerpad obtained with the large cylindrical surface were, on average, 20 and 60% lower, respectively, than thresholds with the punctate probe; 2) thresholds at the palm were, on average, 15 and 40% lower, respectively, than at the fingerpads; 3) thresholds obtained when the subjects grasped the cylinder averaged 40 and 20% less, respectively, than when the cylinder contacted only the palm; 4) thresholds with the cylinder contacting two fingers were 10 and 30% lower, respectively, than thresholds with the cylinder contacting a single finger; and 5) thresholds with vibration parallel to the skin surface were, on average, 10 and 30% lower, respectively, than thresholds with vibration perpendicular to the skin. Contact force, which was varied from 0.05 to 1.0 N, had no effect.