Faster bladder filling in rats reduces detrusor overactivity but worsens (i.e., decreases) bladder compliance.

The impact of bladder filling rate on cystometric outcomes remains unclear. Clinically, faster bladder filling is believed to increase the likelihood of observing detrusor overactivity (DO) in those with bladder dysfunction, although evidence of this is lacking. We executed this study to clarify how changes in bladder filling rate impacted cystometric parameters. Urethane anesthetized female CD rats (n = 19) underwent bladder filling at five different fill rates, a baseline rate scaled to have a filling phase of approximately seven minutes (in line with our previous work), and scaled rates of 1/3x, 2x, 4x, and 8x that speed. Contrary to expectations, filling at faster rates decreased the likelihood of observing detrusor overactivity, with 4x and 8x filling rates demonstrating less detrusor overactivity than the baseline (1x) rate (P = 0.0091 for 4x and P = 0.019 for 8x). However, faster filling rates did decrease bladder compliance. Filling at 4x and 8x demonstrated decreased bladder compliance compared to 1x (P = 0.032 for 4x and P < 0.0001 for 8x). Finally, increasing the filling rate led to increases in bladder capacity at 4x (P = 0.034) and 8x (P = 0.0066) relative to 1x. These results suggest that contrary to expectations, faster filling may not be more effective at eliciting detrusor overactivity (i.e., not a better diagnostic approach). As reductions in detrusor overactivity and increases in bladder capacity are critical parameters for evaluating preclinical therapeutics, faster filling may impair the ability to demonstrate further improvements.

Structural Changes in Brain White Matter Tracts Associated With Overactive Bladder Revealed by Diffusion Tensor Magnetic Resonance Imaging: Findings From a Symptoms of Lower Urinary Tract Dysfunction Research Network Cross-Sectional Case-Control Study.

PURPOSE: Our objective was to investigate structural changes in brain white matter tracts using diffusion tensor imaging (DTI) in patients with overactive bladder (OAB). MATERIALS AND METHODS: Treatment-seeking OAB patients and matched controls enrolled in the cross-sectional case-control LURN (Symptoms of Lower Urinary Tract Dysfunction Research Network) Neuroimaging Study received a brain DTI scan. Microstructural integrity of brain white matter was assessed using fractional anisotropy (FA) and mean diffusivity. OAB and urgency urinary incontinence (UUI) symptoms were assessed using the OAB Questionnaire Short-Form and International Consultation on Incontinence Questionnaire-Urinary Incontinence. The Lower Urinary Tract Symptoms Tool UUI questions and responses were correlated with FA values. RESULTS: Among 221 participants with evaluable DTI data, 146 had OAB (66 urinary urgency-only without UUI, 80 with UUI); 75 were controls. Compared with controls, participants with OAB showed decreased FA and increased mean diffusivity, representing greater microstructural abnormalities of brain white matter tracts among OAB participants. These abnormalities occurred in the corpus callosum, bilateral anterior thalamic radiation and superior longitudinal fasciculus tracts, and bilateral insula and parahippocampal region. Among participants with OAB, higher OAB Questionnaire Short-Form scores were associated with decreased FA in the left inferior fronto-occipital fasciculus, P < .0001. DTI differences between OAB and controls were driven by the urinary urgency-only (OAB-dry) but not the UUI (OAB-wet) subgroup. CONCLUSIONS: Abnormalities in microstructural integrity in specific brain white matter tracts were more frequent in OAB patients. More severe OAB symptoms were correlated with greater degree of microstructural abnormalities in brain white matter tracts in patients with OAB. TRIAL REGISTRATION: ClinicalTrials.gov: NCT02485808.

Predicting success using response after lead implantation with sacral neuromodulation for urgency incontinence.

IMPORTANCE: Many women report inadequate symptom control after sacral neuromodulation (SNM), despite 50% reduction in urgency incontinence episodes (UUIE) after test stimulation. OBJECTIVE: To determine the ideal percent UUIE reduction after test stimulation that predicts 24-month success. STUDY DESIGN: Using data from a multicenter SNM trial, we constructed receiver operating characteristic curves to identify an ideal threshold of percent UUIE reduction after test stimulation. We defined 24-month success as Patient Global Impression of Improvement of "very much better" to "better." We compared predictive accuracy of two models predicting success: (1) percent UUIE reduction alone and (2) with baseline characteristics. RESULTS: Of 149 women (median [IQR] baseline daily UUIE 4.7 [3.7, 6.0]), the ideal threshold for 24-month success was 72% (95% confidence interval 64,76%) UUIE reduction with accuracy 0.54 (0.42, 0.66), sensitivity 0.71 (0.56, 0.86) and specificity 0.27 (0.05, 0.55). The accuracy of the 50% reduction threshold was 0.60 (0.49, 0.71), sensitivity 0.95 (0.88, 1.0) and specificity 0.04 (0.0, 0.12). Percent reduction in UUIE was not better than chance in predicting 24-month success (concordance index [c-index] 0.47 [0.46, 0.62]); adding age, body mass index, diabetes mellitus and visual or hearing impairment the c-index was 0.68 (0.61, 0.78). CONCLUSIONS: Among women who received an internal pulse generator (IPG) due to ≥50% UUIE reduction after test stimulation, we found no ideal threshold that better predicted 24-month success. Percent reduction in UUIE after test stimulation poorly predicts 24-month success with or without clinical factors. Given this, re-evaluating how we determine who should receive an IPG is needed.

Developing a urinary incontinence primary care pathway: a mixed methods study.

BACKGROUND: While nearly 50% of adult women report at least one episode of urinary incontinence (UI), most never receive treatment. OBJECTIVE: To better integrate primary and specialty UI care, we conducted (i) an environmental scan to assess the availability of key pathway resources in primary care, (ii) interviews with primary care providers to understand barriers to care, and (iii) a pilot UI care pathway intervention. METHODS: Environmental scan: Clinic managers from all primary care clinics within a Midwestern healthcare system were invited to participate in an interview covering the availability of clinic resources. Provider interviews: Primary care providers were invited to participate in an interview covering current practices and perceived barriers to UI care. Pilot UI care pathway: Patients who screened positive for UI were provided resources for first-line behavioral management. Pilot patients completed questionnaires at baseline, 8 weeks, and 6 months. RESULTS: While many clinics had point-of-care urinalysis (17/21, 81%), most did not have a working bladder ultrasound (14/21, 67%) or on-site pelvic floor physical therapy (18/21, 86%). Providers (n = 5) described barriers to completing almost every step of diagnosis and treatment for UI. The most persistent barrier was lack of time. Patients (n = 15) reported several self-treatment strategies including avoiding bladder irritants (7/15, 47%) and performing Kegel exercises (4/15, 27%). Five patients (33%) requested follow-up care. At 6 months, patients reported small improvements in UI symptoms. CONCLUSION: Promising results from a novel UI care pathway pilot indicate that streamlining UI care may assist primary care providers in the first-line treatment of UI.

Although the majority of women will experience urine leakage at some point during their lives, most will never receive treatment. To better understand this discrepancy, we embarked on a multimodal investigation into the barriers to care and trialed a new treatment pathway in the primary care setting within a large academic medical system in the Midwest. Speaking with the clinic managers from 21 primary care clinics, we determined that many clinics lacked the tools to perform the steps outlined in the professional society guidelines for urinary incontinence diagnosis. Additionally, there was limited access to pelvic floor physical therapy, a proven treatment strategy. Interviews with five primary care providers revealed barriers, most notably lack of time during clinic visits, to almost every step of diagnosis and treatment. Finally, we trialed a care pathway for primary care providers to make it easier to provide patients with self-management education or to refer them to specialist care. Fifteen patients participated in a pilot study, about half reported trying self-management, and about 1/3 requested follow-up care. Streamlining urinary incontinence care at the primary care level may alleviate some of the barriers to patients receiving care.

Pathways and parameters of sacral neuromodulation in rats.

The stimulation paradigm for sacral neuromodulation has remained largely unchanged since its inception. We sought to determine, in rats, whether stimulation-induced increases in bladder capacity correlated with the proportion of sensory pudendal (PudS) neurons at each stimulated location (L6, S1). If supported, this finding could guide the choice of stimulation side (left/right) and level (S2, S3, S4) in humans. Unexpectedly, we observed that acute stimulation at clinically relevant (low) amplitudes [1-1.5 × motor threshold (Tm)], did not increase bladder capacity, regardless of stimulus location (L6 or S1). More importantly for the ability to test our hypothesis, there was little anatomic variation, and S1 infrequently contributed nerve fibers to the PudS nerve. During mapping studies we noticed that large increases in PudS nerve activation occurred at amplitudes exceeding 2Tm. Thus, additional cystometric studies were conducted, this time with stimulation of the L6-S1 trunk, to examine further the relationship between stimulation amplitude and cystometric parameters. Stimulation at 1Tm to 6Tm evoked increases in bladder capacity and decreases in voiding efficiency that mirrored those produced by PudS nerve stimulation. Many animal studies involving electrical stimulation of nerves of the lower urinary tract use stimulation amplitudes that exceed those used clinically (∼1Tm). Our results confirm that high amplitudes generate immediate changes in cystometric parameters; however, the relationship to low-amplitude chronic stimulation in humans remains unclear. Additional studies are needed to understand changes that occur with chronic stimulation, how these changes relate to therapeutic outcomes, and the contribution of specific nerve fibers to these changes.NEW & NOTEWORTHY Acute low-amplitude electrical stimulation of sacral nerve (sacral neuromodulation) did not increase bladder capacity in anesthetized CD, obese-prone, or obese-resistant rats. Increasing stimulation amplitude correlated with increases in bladder capacity and pudendal sensory nerve recruitment. It is unclear how the high-amplitude acute stimulation that is commonly used in animal experiments to generate immediate effects compares mechanistically to the chronic low-amplitude stimulation used clinically.

Predicting outcomes after intradetrusor onabotulinumtoxina for non-neurogenic urgency incontinence in women.

AIMS: Develop models to predict outcomes after intradetrusor injection of 100 or 200 units of onabotulinumtoxinA in women with non-neurogenic urgency urinary incontinence (UUI). METHODS: Models were developed using 307 women from two randomized trials assessing efficacy of onabotulinumtoxinA for non-neurogenic UUI. Cox, linear and logistic regression models were fit using: (1) time to recurrence over 12 months, (2) change from baseline daily UUI episodes (UUIE) at 6 months, and (3) need for self-catheterization over 6 months. Model discrimination of Cox and logistic regression models was calculated using c-index. Mean absolute error determined accuracy of the linear model. Calibration was demonstrated using calibration curves. All models were internally validated using bootstrapping. RESULTS: Median time to recurrence was 6 (interquartile range [IQR]: 2-12) months. Increasing age, 200 units of onabotulinumtoxinA, higher body mass index (BMI) and baseline UUIE were associated with decreased time to recurrence. The c-index was 0.63 (95% confidence interval [CI]: 0.59, 0.67). Median change in daily UUIE from baseline at 6 months was -3.5 (IQR: -5.0, -2.3). Increasing age, lower baseline UUIE, 200 units of onabotulinumtoxinA, higher BMI and IIQ-SF were associated with less improvement in UUIE. The mean absolute error predicting change in UUIE was accurate to 1.6 (95% CI: 1.5, 1.7) UUI episodes. The overall rate of self-catheterization was 17.6% (95% CI: 13.6%-22.4%). Lower BMI, 200 units of onabotulinumtoxinA, increased baseline postvoid residual and maximum capacity were associated with higher risk of self-catheterization. The c-index was 0.66 (95% CI: 0.61, 0.76). The three calculators are available at http://riskcalc.duke.edu. CONCLUSIONS: After external validation, these models will assist clinicians in providing more accurate estimates of expected treatment outcomes after onabotulinumtoxinA for non-neurogenic UUI in women.

Effects of intravesical prostaglandin E2 on bladder function are preserved in capsaicin-desensitized rats.

Prostaglandin E2 (PGE2) instilled into the bladder generates symptoms of urinary urgency in healthy women and reduces bladder capacity and urethral pressure in both humans and female rats. Systemic capsaicin desensitization, which causes degeneration of C-fibers, prevented PGE2-mediated reductions in bladder capacity, suggesting that PGE2 acts as an irritant (Maggi CA, Giuliani S, Conte B, Furio M, Santicioli P, Meli P, Gragnani L, Meli A. Eur J Pharmacol 145: 105-112, 1988). In the present study, we instilled PGE2 in female rats after capsaicin desensitization but without the hypogastric nerve transection that was conducted in the Maggi et al. study. One week after capsaicin injection (125 mg/kg sc), rats underwent cystometric and urethral perfusion testing under urethane anesthesia with saline and 100 µM PGE2. Similar to naïve rats, capsaicin-desensitized rats exhibited a reduction in bladder capacity from 1.23 ± 0.08 mL to 0.70 ± 0.10 mL (P = 0.002, n = 9), a reduction in urethral perfusion pressure from 19.3 ± 2.1 cmH2O to 10.9 ± 1.2 cmH2O (P = 0.004, n = 9), and a reduction in bladder compliance from 0.13 ± 0.020 mL/cmH2O to 0.090 ± 0.014 mL/cmH2O (P = 0.011, n = 9). Thus, changes in bladder function following the instillation of PGE2 were not dependent on capsaicin-sensitive pathways. Further, these results suggest that urethral relaxation/weakness and/or increased detrusor pressure as a result of decreased compliance may contribute to urinary urgency and highlight potential targets for new therapies for overactive bladder.

Stimulation of the pelvic nerve increases bladder capacity in the PGE2 cat model of overactive bladder.

Selective electrical stimulation of the pudendal nerve exhibits promise as a potential therapy for treating overactive bladder (OAB) across species (rats, cats, and humans). More recently, pelvic nerve (PelN) stimulation was demonstrated to improve cystometric bladder capacity in a PGE2 rat model of OAB. However, PelN stimulation in humans or in an animal model that is more closely related to humans has not been explored. Therefore, our objective was to quantify the effects of PGE2 and PelN stimulation in the cat. Acute cystometry experiments were conducted in 14 α-chloralose-anesthetized adult, neurologically intact female cats. Intravesical PGE2 decreased bladder capacity, residual volume, threshold contraction pressure, and mean contraction pressure. PelN stimulation reversed the PGE2-induced decrease in bladder capacity and increased evoked external urethral sphincter electromyographic activity without influencing voiding efficiency. The increases in bladder capacity generated by PelN stimulation were similar in the rat and cat, but the stimulation parameters to achieve this effect differed (threshold amplitude at 10 Hz in the rat vs. twice threshold amplitude at 1 Hz in the cat). These results highlight the potential of PGE2 as a model of OAB and provide further evidence that PelN stimulation is a promising approach for the treatment of OAB symptoms.

Stimulation of the sensory pudendal nerve increases bladder capacity in the rat.

Pudendal nerve stimulation is a promising treatment approach for lower urinary tract dysfunction, including symptoms of overactive bladder. Despite some promising clinical studies, there remain many unknowns as to how best to stimulate the pudendal nerve to maximize therapeutic efficacy. We quantified changes in bladder capacity and voiding efficiency during single-fill cystometry in response to electrical stimulation of the sensory branch of the pudendal nerve in urethane-anesthetized female Wistar rats. Increases in bladder capacity were dependent on both stimulation amplitude and rate. Stimulation that produced increases in bladder capacity also led to reductions in voiding efficiency. Also, there was a stimulation carryover effect, and increases in bladder capacity persisted during several nonstimulated trials following stimulated trials. Intravesically administered PGE2 reduced bladder capacity, producing a model of overactive bladder (OAB), and sensory pudendal nerve stimulation again increased bladder capacity but also reduced voiding efficiency. This study serves as a basis for future studies that seek to maximize the therapeutic efficacy of sensory pudendal nerve stimulation for the symptoms of OAB.

OAB without an overactive bladder in the acute prostaglandin E2 rat model.

Intravesical prostaglandin E2 (PGE2) was previously used to induce overactive bladder (OAB) symptoms, as it reduces bladder capacity in rats and causes a "strong urgency sensation" in healthy women. However, the mechanism by which this occurs is unclear. To clarify how PGE2 reduces bladder capacity, 100 µM PGE2 was administered intravesically during open, single-fill cystometry with simultaneous measurement of sphincter EMG in the urethane-anesthetized female Wistar rat. PGE2 was also applied to the urethra or bladder selectively by use of a ligature at the bladder neck before (urethra) or during (bladder) closed-outlet, single-fill cystometry. Additional tests of urethral perfusion with PGE2 were made. PGE2 decreased bladder capacity, increased voiding efficiency, and increased sphincter EMG during open cystometry compared with saline controls. The number of nonvoiding contractions did not change with PGE2; however, bladder compliance decreased. During closed-outlet cystometry, PGE2 applied only to the bladder or the urethra did not decrease bladder capacity. Urethral infusion of PGE2 decreased urethral perfusion pressure. Taken together, these results suggest that intravesical PGE2 may decrease bladder capacity by targeting afferents in the proximal urethra. This may occur through urethral relaxation and decreased bladder compliance, both of which may increase activation of proximal urethra afferents from distension of the proximal urethra. This hypothesis stands in contrast to many hypotheses of urgency that focus on bladder dysfunction as the primary cause of OAB symptoms. Targeting the urethra, particularly urethral smooth muscle, may be a promising avenue for the design of drugs and devices to treat OAB.

Stimulation of the pelvic nerve increases bladder capacity in the prostaglandin E2 rat model of overactive bladder.

Overactive bladder (OAB) syndrome is a highly prevalent condition that may lead to medical complications and decreased quality of life. Emerging therapies focusing on selective electrical stimulation of peripheral nerves associated with lower urinary tract function may provide improved efficacy and reduced side effects compared with sacral neuromodulation for the treatment of OAB symptoms. Prior studies investigating the effects of pelvic nerve (PelN) stimulation on lower urinary tract function were focused on promoting bladder contractions, and it is unclear whether selective stimulation of the PelN would be beneficial for the treatment of OAB. Therefore our motivation was to test the hypothesis that PelN stimulation would increase bladder capacity in the prostaglandin E2 (PGE2) rat model of OAB. Cystometry experiments were conducted in 17 urethane-anesthetized female Sprague-Dawley rats. The effects of intravesical PGE2 vs. vehicle and PelN stimulation after intravesical PGE2 on cystometric parameters were quantified. Intravesical infusion of PGE2 resulted in decreased bladder capacity and increased voiding efficiency without a change in bladder contraction area under the curve, maximum contraction pressure, or contraction duration. Bladder capacity was also significantly decreased compared with vehicle (1% ethanol in saline) confirming that the change in bladder capacity was mediated by PGE2 PelN stimulation reversed the PGE2-induced change in bladder capacity and increased the external urethral sphincter electromyogram activity at a specific stimulation condition (amplitude of 1.0 times threshold at 10 Hz). These results confirm that the urodynamic changes reported in conscious rats are also observed under urethane anesthesia and that PelN stimulation is a novel and promising approach for the treatment of the symptoms of OAB.

Machine Learning for Urodynamic Detection of Detrusor Overactivity.

OBJECTIVE: To develop a machine learning algorithm that identifies detrusor overactivity (DO) in Urodynamic Studies (UDS) in the spina bifida population. UDS plays a key role in assessment of neurogenic bladder in patients with spina bifida. Due to significant variability in individual interpretations of UDS data, there is a need to standardize UDS interpretation. MATERIALS AND METHODS: Patients who underwent UDS at a single pediatric urology clinic between May 2012 and September 2020 were included. UDS files were analyzed in both time and frequency domains, varying inclusion of vesical, abdominal, and detrusor pressure channels. A machine learning pipeline was constructed using data windowing, dimensionality reduction, and support vector machines. Models were designed to detect clinician identified detrusor overactivity. RESULTS: Data were extracted from 805 UDS testing files from 546 unique patients. The generated models achieved good performance metrics in detecting DO agreement with the clinician, in both time- and frequency-based approaches. Incorporation of multiple channels and data windowing improved performance. The time-based model with all 3 channels had the highest area under the curve (AUC) (91.9 ± 1.3%; sensitivity: 84.2 ± 3.8%; specificity: 86.4 ± 1.3%). The 3-channel frequency-based model had the highest specificity (AUC: 90.5 ± 1.9%; sensitivity: 68.3 ± 5.3%; specificity: 92.9 ± 1.1%). CONCLUSION: We developed a promising proof-of-concept machine learning pipeline that identifies DO in UDS. Machine-learning-based predictive modeling algorithms may be employed to standardize UDS interpretation and could potentially augment shared decision-making and improve patient care.

Noncancerous Genitourinary Conditions as a Public Health Priority: Conceptualizing the Hidden Burden.

OBJECTIVE: To provide a conceptual framework to guide investigations into burdens of noncancerous genitourinary conditions (NCGUCs), which are extensive and poorly understood. METHODS: The National Institute of Diabetes and Digestive and Kidney Diseases convened a workshop of diverse, interdisciplinary researchers and health professionals to identify known and hidden burdens of NCGUCs that must be measured to estimate the comprehensive burden. Following the meeting, a subgroup of attendees (authors of this article) continued to meet to conceptualize burden. RESULTS: The Hidden Burden of Noncancerous Genitourinary Conditions Framework includes impacts across multiple levels of well-being and social ecology, including individual (ie, biologic factors, lived experience, behaviors), interpersonal (eg, romantic partners, family members), organizational/institutional (eg, schools, workplaces), community (eg, public restroom infrastructure), societal (eg, health care and insurance systems, national workforce/economic output), and ecosystem (eg, landfill waste) effects. The framework acknowledges that NCGUCs can be a manifestation of underlying biological dysfunction, while also leading to biological impacts (generation and exacerbation of health conditions, treatment side effects). CONCLUSION: NCGUCs confer a large, poorly understood burden to individuals and society. An evidence-base to describe the comprehensive burden is needed. Measurement of NCGUC burdens should incorporate multiple levels of well-being and social ecology, a life course perspective, and potential interactions between NCGUCs and genetics, sex, race, and gender. This approach would elucidate accumulated impacts and potential health inequities in experienced burdens. Uncovering the hidden burden of NCGUCs may draw attention and resources (eg, new research and improved treatments) to this important domain of health.

State-dependent bioelectronic interface to control bladder function.

Electrical stimulation therapies to promote bladder filling and prevent incontinence deliver continuous inhibitory stimulation, even during bladder emptying. However, continuous inhibitory stimulation that increases bladder capacity (BC) can reduce the efficiency of subsequent voiding (VE). Here we demonstrate that state-dependent stimulation, with different electrical stimulation parameters delivered during filling and emptying can increase both BC and VE relative to continuous stimulation in rats and cats of both sexes. We show that continuous 10 Hz pudendal nerve stimulation increased BC (120-180% of control) but decreased VE (12-71%, relative to control). In addition to increasing BC, state-dependent stimulation in both rats and cats increased VE (280-759% relative to continuous stimulation); motor bursting in cats increased VE beyond the control (no stimulation) condition (males: 323%; females: 161%). These results suggest that a bioelectronic bladder pacemaker can treat complex voiding disorders, including both incontinence and retention, which paradoxically are often present in the same individual.

Effects of Synchronous Electrode Pulses on Neural Recruitment During Multichannel Microstimulation.

The recent proliferation of high-density microelectrode arrays has inspired several new applications of electrical microstimulation, including restoration of sensory functions in the visual, auditory, and somatosensory systems. In each case, the goal is to achieve precisely targeted activation of neurons, while patterning the location and timing of stimulation across the array to mimic naturalistic patterns of neural activity. However, when two or more electrodes deliver stimulation pulses at the same time, the electric fields created by each electrode interact. The effects of field interactions on neuronal recruitment depend on several factors, which have been studied extensively at the macro-scale but have been overlooked in the case of high density arrays. Here, we report that field interactions can significantly affect neural recruitment, even with low amplitude stimulation. We created a computational model of peripheral nerve axons to estimate stimulation parameters sufficient to generate neural recruitment during synchronous and asynchronous stimulation on two microelectrodes located within the peripheral nerve. Across a range of stimulus amplitudes, the model predicted that synchronous stimulation on adjacent electrodes (400 µm separation), would recruit 2-3 times more neurons than during asynchronous stimulation. Our results suggest that field interactions should not be ignored when designing multichannel microstimulation paradigms, even at threshold-level stimulus amplitudes.

Detection of Bladder Contractions From the Activity of the External Urethral Sphincter in Rats Using Sparse Regression.

Bladder overactivity and incontinence and dysfunction can be mitigated by electrical stimulation of the pudendal nerve applied at the onset of a bladder contraction. Thus, it is important to predict accurately both bladder pressure and the onset of bladder contractions. We propose a novel method for prediction of bladder pressure using a time-dependent spectrogram representation of external urethral sphincter electromyographic (EUS EMG) activity and a least absolute shrinkage and selection operator regression model. There was a statistically significant improvement in prediction of bladder pressure compared with methods based on the firing rate of EUS EMG activity. This approach enabled prediction of the onset of bladder contractions with 91% specificity and 96% sensitivity and may be suitable for closed-loop control of bladder continence.

Effects of spatial and temporal parameters of primary afferent microstimulation on neural responses evoked in primary somatosensory cortex of an anesthetized cat.

Patterned microstimulation of muscle and cutaneous afferent neurons may provide tactile and proprioceptive feedback to users of advanced prosthetic limbs. However, it is unclear what types of stimulation patterns will be effective, and the parameter space for creating these patterns is prohibitively large to explore systematically using only psychophysics paradigms. In this study, we used an array of microelectrodes in primary somatosensory cortex (S1) of an isoflurane anesthetized cat to measure responses in a population of neurons evoked by various patterns of primary afferent microstimulation delivered to the L6 and L7 dorsal root ganglia (DRG). Each pattern consisted of a 300 ms train of microstimulation pulses having a fixed amplitude, pulse rate, and location in the array of DRG electrodes. Evoked responses were detectable on many S1 channels at the lowest amplitude tested (5 µA) and pulse rate (10 pulses per second). Increasing the pulse rate lowered the threshold amplitude for evoking a response on some S1 channels. Location effects were also observed. Adjacent stimulation sites evoked discriminable responses at low but not high (20 µA) amplitudes. In summary, we observed interactions between stimulation pulse rate, pulse amplitude, and location. Such interactions must be considered when designing stimulation patterns for transmitting sensory feedback by primary afferent microstimulation.