Kawasaki Disease in the Time of COVID-19 and MIS-C: The International Kawasaki Disease Registry

BACKGROUND

Patients with multisystem inflammatory syndrome in children (MIS-C) and Kawasaki disease (KD) have overlapping clinical features. We compared demographics, clinical presentation, management, and outcomes of patients according to evidence of previous SARS-CoV-2 infection.

METHODS

The International Kawasaki Disease Registry (IKDR) enrolled KD and MIS-C patients from sites in North, Central, and South America, Europe, Asia, and the Middle East. Evidence of previous infection was defined as: Positive (household contact or positive polymerase chain reaction [PCR]/serology), Possible (suggestive clinical features of MIS-C and/or KD with negative PCR or serology but not both), Negative (negative PCR and serology and no known exposure), and Unknown (incomplete testing and no known exposure).

RESULTS

Of 2345 enrolled patients SARS-CoV-2 status was Positive for 1541 (66%) patients, Possible for 89 (4%), Negative for 404 (17%) and Unknown for 311 (13%). Clinical outcomes varied significantly among the groups, with more patients in the Positive/Possible groups presenting with shock, having admission to intensive care, receiving inotropic support, and having longer hospital stays. Regarding cardiac abnormalities, patients in the Positive/Possible groups had a higher prevalence of left ventricular dysfunction, and patients in the Negative and Unknown groups had more severe coronary artery abnormalities.

CONCLUSIONS

There appears to be a spectrum of clinical features from MIS-C to KD with a great deal of heterogeneity, and one primary differentiating factor is evidence for previous acute SARS-CoV-2 infection/exposure. SARS-CoV-2 Positive/Possible patients had more severe presentations and required more intensive management, with a greater likelihood of ventricular dysfunction but less severe coronary artery adverse outcomes, in keeping with MIS-C.

Cardiac Biomarkers Aid in Differentiation of Kawasaki Disease from Multisystem Inflammatory Syndrome in Children Associated with COVID-19

Kawasaki disease (KD) and Multisystem Inflammatory Syndrome in Children (MIS-C) associated with COVID-19 show clinical overlap and both lack definitive diagnostic testing, making differentiation challenging. We sought to determine how cardiac biomarkers might differentiate KD from MIS-C. The International Kawasaki Disease Registry enrolled contemporaneous KD and MIS-C pediatric patients from 42 sites from January 2020 through June 2022. The study population included 118 KD patients who met American Heart Association KD criteria and compared them to 946 MIS-C patients who met 2020 Centers for Disease Control and Prevention case definition. All included patients had at least one measurement of amino-terminal prohormone brain natriuretic peptide (NTproBNP) or cardiac troponin I (TnI), and echocardiography. Regression analyses were used to determine associations between cardiac biomarker levels, diagnosis, and cardiac involvement. Higher NTproBNP (≥ 1500 ng/L) and TnI (≥ 20 ng/L) at presentation were associated with MIS-C versus KD with specificity of 77 and 89%, respectively. Higher biomarker levels were associated with shock and intensive care unit admission; higher NTproBNP was associated with longer hospital length of stay. Lower left ventricular ejection fraction, more pronounced for MIS-C, was also associated with higher biomarker levels. Coronary artery involvement was not associated with either biomarker. Higher NTproBNP and TnI levels are suggestive of MIS-C versus KD and may be clinically useful in their differentiation. Consideration might be given to their inclusion in the routine evaluation of both conditions.

Obesity and Outcomes of Kawasaki Disease and COVID-19-Related Multisystem Inflammatory Syndrome in Children

Importance

Obesity may affect the clinical course of Kawasaki disease (KD) in children and multisystem inflammatory syndrome in children (MIS-C) associated with COVID-19.

Objective

To compare the prevalence of obesity and associations with clinical outcomes in patients with KD or MIS-C.

Design, Setting, and Participants

In this cohort study, analysis of International Kawasaki Disease Registry (IKDR) data on contemporaneous patients was conducted between January 1, 2020, and July 31, 2022 (42 sites, 8 countries). Patients with MIS-C (defined by Centers for Disease Control and Prevention criteria) and patients with KD (defined by American Heart Association criteria) were included. Patients with KD who had evidence of a recent COVID-19 infection or missing or unknown COVID-19 status were excluded.

Main Outcomes and Measures

Patient demographic characteristics, clinical features, disease course, and outcome variables were collected from the IKDR data set. Using body mass index (BMI)/weight z score percentile equivalents, patient weight was categorized as normal weight (BMI <85th percentile), overweight (BMI ≥85th to <95th percentile), and obese (BMI ≥95th percentile). The association between adiposity category and clinical features and outcomes was determined separately for KD and MIS-C patient groups.

Results

Of 1767 children, 338 with KD (median age, 2.5 [IQR, 1.2-5.0] years; 60.4% male) and 1429 with MIS-C (median age, 8.7 [IQR, 5.3-12.4] years; 61.4% male) were contemporaneously included in the study. For patients with MIS-C vs KD, the prevalence of overweight (17.1% vs 11.5%) and obesity (23.7% vs 11.5%) was significantly higher (P < .001), with significantly higher adiposity z scores, even after adjustment for age, sex, and race and ethnicity. For patients with KD, apart from intensive care unit admission rate, adiposity category was not associated with laboratory test features or outcomes. For patients with MIS-C, higher adiposity category was associated with worse laboratory test values and outcomes, including a greater likelihood of shock, intensive care unit admission and inotrope requirement, and increased inflammatory markers, creatinine levels, and alanine aminotransferase levels. Adiposity category was not associated with coronary artery abnormalities for either MIS-C or KD.

Conclusions and Relevance

In this international cohort study, obesity was more prevalent for patients with MIS-C vs KD, and associated with more severe presentation, laboratory test features, and outcomes. These findings suggest that obesity as a comorbid factor should be considered at the clinical presentation in children with MIS-C.

ehealth technology in cardiac exercise therapeutics for pediatric patients with congenital and acquired heart conditions: a summary of evidence and future directions

Many children and adolescents with congenital and acquired heart disease (CHD) are physically inactive and participate in an insufficient amount of moderate-to-vigorous intensity exercise. Although physical activity (PA) and exercise interventions are effective at improving short- and long-term physiological and psychosocial outcomes in youth with CHD, several barriers including resource limitations, financial costs, and knowledge inhibit widespread implementation and dissemination of these beneficial programs. New and developing eHealth, mHealth, and remote monitoring technologies offer a potentially transformative and cost-effective solution to increase access to PA and exercise programs for youth with CHD, yet little has been written on this topic. In this review, a cardiac exercise therapeutics (CET) model is presented as a systematic approach to PA and exercise, with assessment and testing guiding three sequential PA and exercise intervention approaches of progressive intensity and resource requirements: (1) PA and exercise promotion within a clinical setting; (2) unsupervised exercise prescription; and (3) medically supervised fitness training intervention (i.e., cardiac rehabilitation). Using the CET model, the goal of this review is to summarize the current evidence describing the application of novel technologies within CET in populations of children and adolescents with CHD and introduce potential future applications of these technologies with an emphasis on improving equity and access to patients in low-resource settings and underserved communities.

Pediatric Cardiology Fellowship Standards for Training in Exercise Medicine and Curriculum Outline

Over the past 2 decades, fundamentals of exercise medicine, including clinical exercise testing, assessment and promotion of physical activity, exercise prescription, and supervised exercise training/rehabilitation programming have demonstrated considerable clinical value in the management of children and adolescents with congenital and acquired heart disease. Although the principles of exercise medicine have become an integral component in pediatric cardiology, there are no standardized training recommendations for exercise physiology during pediatric cardiology fellowship at this time. Thus, the Pediatric Cardiology Exercise Medicine Curriculum Committee (PCEMCC) was formed to establish core and advanced exercise physiology training recommendations for pediatric cardiology trainees. The PCEMCC includes a diverse group of pediatric cardiologists, exercise physiologists, and fellowship program directors. The expert consensus training recommendations are by no means a mandate and are summarized herein, including suggestions for achieving the minimum knowledge and training needed for general pediatric cardiology practice.

Assessment of Apple Watch Series 6 pulse oximetry and electrocardiograms in a pediatric population

BACKGROUND

Recent technologic advances have resulted in increased development and utilization of direct-to-consumer cardiac wearable devices with various functionality. This study aimed to assess Apple Watch Series 6 (AW6) pulse oximetry and electrocardiography (ECG) in a cohort of pediatric patients.

METHODS

This single-center, prospective study enrolled pediatric patients ≥ 3kg and having an ECG and/or pulse oximetry (SpO2) as part of their planned evaluation. Exclusion criteria: 1) non-English speaking patients and 2) patients in state custody. Simultaneous tracings were obtained for SpO2 and ECG with concurrent standard pulse oximeter and 12-lead ECG. AW6 automated rhythm interpretations were compared to physician over-read and categorized as accurate, accurate with missed findings, inconclusive (automated interpretation: "inconclusive"), or inaccurate.

RESULTS

A total of 84 patients were enrolled over a 5-week period. 68 patients (81%) were placed into the SpO2 and ECG arm, with 16 patients (19%) placed into the SpO2 only arm. Pulse oximetry data was successfully collected in 71/84 (85%) patients and ECG data in 61/68 (90%). ΔSpO2 between modalities was 2.0±2.6% (r = 0.76). ΔRR was 43±44msec (r = 0.96), ΔPR 19±23msec (r = 0.79), ΔQRS 12±13msec (r = 0.78), and ΔQT 20±19msec (r = 0.9). The AW6 automated rhythm analysis yielded a 75% specificity and found: 1) 40/61 (65.6%) "accurate", 2) 6/61 (9.8%) "accurate with missed findings", 3) 14/61 (23%) "inconclusive", and 4) 1/61 (1.6%) incorrect.

CONCLUSION

The AW6 can accurately measure oxygen saturation when compared to hospital pulse oximeters in pediatric patients and provide good quality single lead ECGs that allow for accurate measurement of RR, PR, QRS, and QT intervals with manual interpretation. The AW6-automated rhythm interpretation algorithm has limitations for smaller pediatric patients and patients with abnormal ECGs.

Early preclinical experience of a mixed reality ultrasound system with active GUIDance for NEedle-based interventions: The GUIDE study

Background

Use of ultrasound (US) to facilitate vascular access has increased compared to landmark-based procedures despite ergonomic challenges and need for extrapolation of 2-dimensional images to understand needle position. The MantUS™ system (Sentiar, Inc.,) uses a mixed reality (MxR) interface to display US images and integrate real-time needle tracking.

Objective

The purpose of this prospective preclinical study was to evaluate the feasibility and usability of MantUS in a simulated environment.

Methods

Participants were recruited from pediatric cardiology and critical care. Access was obtained in 2 vascular access training models: a femoral access model and a head and neck model for a total of 4 vascular access sites under 2 conditions—conventional US and MantUS. Participants were randomized for order of completion. Videos were obtained, and quality of access including time required, repositions, number of attempts, and angle of approach were quantified.

Results

Use of MantUS resulted in an overall reduction in number of needle repositions (P = .03) and improvement in quality of access as measured by distance (P <.0001) and angle of elevation (P = .006). These findings were even more evident in the right femoral vein (RFV) access site, which was a simulated anatomic variant with a deeper more oblique vascular course. Use of MantUS resulted in faster time to access (P = .04), fewer number of both access attempts (P = .02), and number of needle repositions (P <.0001) compared to conventional US. Postparticipant survey showed high levels of usability (87%) and a belief that MantUS may decrease adverse outcomes (73%) and failed access attempts (83%).

Conclusion

Use of MantUS improved vascular access among all comers, including the quality of access. This improvement was even more notable in the vascular variant (RFV). MantUS readily benefited users by providing improved spatial understanding. Further development of MantUS will focus on improving user interface and experience, with larger clinical usage and in-human studies.

Single-Centre Case Series Assessment of Early Exercise Capacity Data Among Patients Who Received an Alterra Prestent and SAPIEN 3 Valve Placement

Previous studies have used cardiopulmonary exercise test (CPET) data to objectively assess physiological changes in patients undergoing percutaneous pulmonary valve implantation. A retrospective review was performed to assess pre- and post-CPET data among patients undergoing Alterra Adaptive Prestent and SAPIEN 3 transcatheter heart valve (Alterra) placement. Of the 7 patients eligible for the study, 5 (71%) were male. The mean age was 22 years (range: 12-49 years). CPET data showed significant (P = 0.03) improvement in ventilatory efficiency (VE/VCO2) while only 2 (29%) patients had an improvement of percent predicted peak oxygen consumption (VO2). These findings suggest favourable haemodynamic changes though further investigation is needed.

A Single-center Experience Comparing First- Versus Second-generation Insertable Cardiac Monitors in Pediatric Patients

Insertable cardiac monitors (ICMs) have undergone advancements in size and functionality over the past decade, resulting in the introduction of small, easily insertable devices capable of long-term remote monitoring. We define first-generation ICMs as implantable cardiac monitoring devices that require an incision and surgical creation of a subcutaneous pocket and second-generation ICMs as devices implanted using a custom-made tool for subcutaneous insertion, respectively. The aim of this study was to understand the differences between first- and second-generation pediatric ICM implants, implant indications, and time to diagnosis. We performed a retrospective, single-center chart review of patients who underwent ICM implantation from 2009–2019, spanning a 5-year course of first-generation ICM implantations and 5-year course of second-generation ICM implantations. Demographic data, past medical history, implant indication, and time to diagnosis were obtained. A total of 208 patients were identified over the 10-year time period, including 38 (18%) who underwent implantation with a first-generation device and 170 (82%) who underwent implantation with a second-generation device. Implant indications for first-generation ICMs included syncope (71%), palpitations (16%), inherited arrhythmia syndrome (IAS) management (5%), and premature ventricular contractions/ventricular tachycardia (VT) (8%); implant indications for second-generation ICMs included syncope (48%), palpitations (19%), IAS management (40%), premature ventricular contractions/VT (11%), atrial fibrillation (2%), tachycardia (3%), and heart block (0.5%). The average time to diagnosis was 38 weeks for patients with first-generation devices and 55 weeks for those with second-generation devices. With innovations in ICM technologies, there are expanding indications for ICM implantation in pediatric patients for long-term monitoring, specifically regarding the management of IAS patients.

Incorporation of the CardioMEMS™ System During an Exercise Physiology Test in a Pediatric Congenital Heart Disease Patient Contributing to Medical Decision-Making

Exercise testing among the pediatric congenital heart disease population continues to transform and expand the way patients are evaluated and managed. We describe a case where a stress echocardiogram was performed while successfully collecting data from a previously implanted CardioMEMS™ HF system which helped guide decision-making.

EKG Abnormalities in a Youth Athlete Following COVID-19: It's Not Always Myocarditis!

COVID-19 associated myocarditis following mild infections is rare while incidental findings may be more common. A young athlete fully recovered from a mild COVID-19 infection presented with inferolateral T-wave inversions and left ventricular hypertrophy on imaging. Exercise testing aided in correctly diagnosing the patient with masked systolic hypertension.

A unique cardiovascular presentation of pheochromocytoma

We describe a unique presentation of a pheochromocytoma in a normotensive teenager, who presented with symptoms of headache, neck pain, and palpitations. Holter and event monitor tracings revealed intermittent junctional rhythm causing electromechanical dyssynchrony between atrial and ventricular contraction resulting in reported symptoms. Exercise stress testing helped correlate symptomatic junctional rhythm events to episodic hypertension which led to the eventual diagnosis of pheochromocytoma. The exercise test provided insight into the physiologic coupling that the sympathetic and parasympathetic autonomic nervous systems have on the cardiovascular system during exercise and exaggerated hypertension. The patient was found to have MEN2A and partial adrenalectomy resulted in complete resolution of symptoms and arrhythmia. This unusual presentation illustrates the benefit of a comprehensive clinical evaluation, which led to the eventual diagnosis.

Institutional experience of healthy pediatric patients presenting with atrial fibrillation who had an electrophysiology study

INTRODUCTION

Atrial fibrillation (AF) is a very common tachyarrhythmia with increasing prevalence with age, but uncommon in the pediatric population. Understanding that AF increases comorbidities make the need for investigation and potential elimination of alternate etiologies in pediatric AF patients critical. The objective of this study was to review our institutional data and compare our findings with previously documented adult AF risk factors to pediatric patients while also identifying which patients had alternate electrophysiology diagnoses amenable to transcatheter ablation.

METHODS

A retrospective chart review was performed identifying AF patients who were less than 21 years old, had no significant congenital cardiovascular anomalies, a documented episode of AF on electrocardiogram and underwent invasive electrophysiology study (EPS).

RESULTS

Nineteen patients were identified over a 9-year period of time finding a male predominance (74%), the average age of 14.95 ± 4.17 years, the average weight of 78.5 ± 31.4 kg, and average body mass index of 26.8 ± 6.87 kg/m² . Preprocedural left atrial volumes made on echocardiograms demonstrated a mean of 33.96 ± 16.35 mL/m² (Z-scores -0.81 ± 1.50), indicating no dilation. Five of nineteen patients (26%) had additional electrophysiologic diagnoses during EPS, including atrioventricular reentrant tachycardia (n = 2, 10%) and atrioventricular nodal reentrant tachycardia (n = 3, 16%). Four patients underwent successful ablation with no documented or clinical AF recurrence.

CONCLUSIONS

Adult risk factors of male predominance and obesity were seen in pediatric AF patients, while left atrial enlargement was not. Twenty-one percent of the pediatric AF patients who had additional electrophysiologic substrates and successful ablations resulted in no further clinical episodes of AF. This suggests that pediatric patients presenting with AF might benefit from an EPS as part of a complete evaluation.

Recanalization of an atretic intramural left main coronary artery after bypass surgery in a pediatric patient with anomalous aortic origin of the left main coronary artery arising from the right sinus of Valsalva

We report a pediatric patient with nonatherosclerotic chronic total occlusion (CTO) of the left main coronary artery (LMCA) leading to complete LMCA atresia which was successfully recanalized via retrograde techniques through a previous internal mammary bypass graft. After the CTO was treated, the artery was found to be anomalous off the right cusp with an intramural coarse and slit-like orifice. The patient's ischemic symptoms resolved after Percutaneous Coronary Intervention (PCI), and she has continued to do well.

Clinicians' judgement of capacity of nursing home patients to give informed consent

OBJECTIVE

The study determined the rate of incapacity to give informed consent for medical treatment among patients admitted to a nursing home and assessed whether clinical staff members recognized this incapacity and whether they used alternative means to provide surrogate decision making for their patients' treatment.

METHODS

After 44 patients admitted to a nursing home affiliated with a major teaching hospital gave oral consent, two standardized tests, the Hopkins Competency Assessment Test (HCAT) and the Mini Mental State Examination (MMSE) were administered to them. Later a researcher blind to the test results reviewed subjects' clinical records to determine whether staff recognized any incapacity in giving informed consent for medical treatment.

RESULTS

Twenty of 44 subjects were identified by the HCAT as incompetent to give informed consent for medical treatment. Clinical staff had identified 13 of those subjects as clinically incompetent. None of the subjects whom clinical staff identified as clinically incompetent was provided with surrogate decision makers in accordance with procedures outlined in state law.

CONCLUSIONS

The prevalence of incapacity to give informed consent in the nursing home population was high. Clinical screening by staff did not identify all clinically incompetent patients, and staff had unresolved conflicting opinions about individual patients' capacity to give informed consent. Even when staff recognized a patient's incapacity to give informed consent, proper legal procedures for appointing surrogate decision makers were not followed.

Evidence for two functionally distinct subpopulations of neurons within the rat striatum

Type I and Type II extracellular action potential waveforms were recorded from the rat striatum and studied with respect to their dependence on recording conditions, response to paired impulse stimulation of the corticostriatal pathway, and iontophoretic application of dopamine (DA). Results showed that the distinguishing characteristics of Type I and Type II waveforms are relatively independent of the degree of filtering, distance of the electrode tip from the target neuron, type of recording electrode, and firing rate of the neuron. Very low impedance electrodes, however, were found to mask the difference in spike shape. Electrical stimulation of cortical afferents results in excitation of both action potential waveforms, though the Type II class exhibits a significantly shorter latency than the Type I class. Paired impulse analyses revealed that both waveforms exhibit variation in the probability of discharge (facilitation or inhibition) to the second impulse of each impulse pair that are a function of the interimpulse interval. Most importantly, however, the probabilities of discharge of Type I and Type II neurons to the second impulse are inversely related, i.e., when one cell type exhibits facilitation, the other displays inhibition. These data demonstrate that Type I and Type II waveforms represent the activity of functionally different subpopulations of striatal neurons. Moreover, Type II neurons are found much more often than Type I cells, suggesting that the 2 cell classes may be represented with different frequencies within striatum. Finally, Type II neurons display at least a 5 times greater sensitivity to iontophoretically applied DA than Type I cells, suggesting that the 2 cell populations also are affected differentially by dopaminergic input from the substantia nigra.

Effects of dopamine depletion on the spontaneous activity of type I striatal neurons: relation to local dopamine concentration and motor behavior

The relation between the electrophysiological activity of Type I striatal neurons, local dopamine (DA) concentration, and motor behavior in rats was investigated using intraventricular administration of the neurotoxin 6-hydroxydopamine (6-HDA) and extracellular single-unit recording. Results are compared with findings of past experiments in which the activity of Type II striatal neurons was examined after comparable 6-HDA-induced lesions. Several differences between the present observations and the earlier results were found. First, although large depletions (greater than 50%) of DA local to the site of the recording were required before the spontaneous firing rate of either cell type was increased, the levels necessary for this effect were found to be less for Type I cells than for Type II neurons. Second, although DA depletions of greater than 50% always were associated with increased Type I cell activity, depletions of greater than 95% resulted in spontaneous firing rates that were lower than those observed after depletions of approximately 90%. Thus, the relation between extent of dopaminergic depletion and Type I cell firing rate was biphasic, whereas that relation previously was found to be monophasic for Type II neurons. Finally, whereas increased Type I cell activity in the lateral striatum was associated with the aphagia, adipsia, and akinesia induced by large DA-depleting brain lesions, increased Type II cell activity in the medial striatum was found to be associated with these impairments. Because accumulating evidence suggests that the functioning of the lateral striatum is more critical for these behaviors, however, it is proposed that the substrate of the behavioral dysfunctions resulting from DA depletion is the Type I cell population in lateral striatum.

Lesions of the retrosplenial cortex produce deficits in reversal learning of the rabbit nictitating membrane response: implications for potential interactions between hippocampal and cerebellar brain systems

The effect of bilateral lesions of the retrosplenial cortex on discrimination reversal learning of the rabbit nictitating membrane response was examined. Results showed that animals with such lesions were not impaired in their ability to acquire a cross-modality discrimination, but were severely impaired in their ability to reverse the discrimination once it was learned. All animals failed at the reversal phase of the task because they displayed high levels of conditioned responding to both the CS+ and the CS-. Thus bilateral damage to the retrosplenial cortex results in deficits in reversal learning that are highly similar to those observed after bilateral hippocampectomy. These findings are interpreted within a conceptual framework that characterizes multisynaptic projections from the hippocampus to the retrosplenial cortex, and ultimately to the cerebellum, as responsible for the behavioral expression of learning-related changes in hippocampal pyramidal cell activity.

Short-term effects of dopamine-depleting brain lesions on spontaneous activity of striatal neurons: relation to local dopamine concentration and behavior

The spontaneous activity of striatal neurons was measured after dopamine (DA)-depleting brain lesions were produced in rats by the neurotoxin 6-hydroxydopamine. The extent of DA depletion was determined using tissue punches from the same regions of striatum in which cell activity was recorded. Results showed that the spontaneous activity of Type II neurons in either the medial or lateral striatum increased only when local DA depletions exceeded 90%; when local depletions were less than 90%, spontaneous firing rates of Type II neurons were equivalent to control values. This finding was consistent with additional observations that ingestive and motor behaviors of the same animals were not disrupted until striatal DA depletions exceeded 90%. It also was found that spontaneous firing rates of neurons in the lateral but not the medial striatum could be at control levels in animals clearly exhibiting aphagia, adipsia and akinesia.

Lesions of the retrosplenial cortex produce deficits in reversal learning of the rabbit nictitating membrane response: Implications for potential interactions between hippocampal and cerebellar brain systems

The effect of bilateral lesions of the retrosplenial cortex on discrimination reversal learning of the rabbit nictitating membrane response was examined. Results showed that animals with such lesions were not impaired in their ability to acquire a cross-modality discrimination, but were severely impaired in their ability to reverse the discrimination once it was learned. All animals failed at the reversal phase of the task because they displayed high levels of conditioned responding to both the CS+ and the CS-. Thus bilateral damage to the retrosplenial cortex results in deficits in reversal learning that are highly similar to those observed after bilateral hippocampectomy. These findings are interpreted within a conceptual framework that characterizes multisynaptic projections from the hippocampus to the retrosplenial cortex, and ultimately to the cerebellum, as responsible for the behavioral expression of learning-related changes in hippocampal pyramidal cell activity.

Hippocampectomy disrupts the topography of conditioned nictitating membrane responses during reversal learning

The effects of bilateral hippocampectomy on the topography, or shape, of conditioned nictitating membrane (NM) responses were examined during four learning tasks: one-tone delay conditioning, unpaired extinction, two-tone discrimination, and reversal of two-tone discrimination. Results showed that hippocampal ablation altered conditioned NM response topography only during reversal learning and not during the other training paradigms. In addition, the shapes of learning curves for hippocampectomized animals were different from those of control animals during reversal conditioning but not during the other paradigms. The implications of these findings with respect to unit-recording studies of hippocampal cellular activity during classical conditioning of the NM response are discussed.

Hippocampectomy disrupts the topography of conditioned nictitating membrane responses during reversal learning

The effects of bilateral hippocampectomy on the topography, or shape, of conditioned nictitating membrane (NM) responses were examined during four learning tasks: one-tone delay conditioning, unpaired extinction, two-tone discrimination, and reversal of two-tone discrimination. Results showed that hippocampal ablation altered conditioned NM response topography only during reversal learning and not during the other training paradigms. In addition, the shapes of learning curves for hippocampectomized animals were different from those of control animals during reversal conditioning but not during the other paradigms. The implications of these findings with respect to unit-recording studies of hippocampal cellular activity during classical conditioning of the NM response are discussed.

Hippocampectomy disrupts acquisition and retention of learned conditional responding

The effects of bilateral hippocampal and neocortical lesions were examined on acquisition and retention of classically conditioned responses based on (a) simple associations, (b) a nonconditional discrimination, and (c) a conditional discrimination in the same subjects. Results showed that combined hippocampal and neocortical damage permanently prevented (within the limits tested) both acquisition and retention of learned behavior based on the conditional discrimination but had no effect on behaviors based on the nonconditional discrimination or simple associations. Neocortical lesions alone had no effect on either conditional or nonconditional discriminative responding, but they did temporarily disrupt acquisition and retention of behavior dependent on CS-CS (two conditioned stimuli) associations. Neither lesion affected learned behaviors mediated by CS-US (conditioned stimulus and unconditioned stimulus) associations. Thus, results showed that hippocampal damage selectively disrupted learned conditional behaviors and also revealed that central nervous system control of conditional discrimination performance, within-compound associations, and CS-US associations is mediated by different neural mechanisms.

Hippocampectomy disrupts acquisition and retention of learned conditional responding

The effects of bilateral hippocampal and neocortical lesions were examined on acquisition and retention of classically conditioned responses based on (a) simple associations, (b) a nonconditional discrimination, and (c) a conditional discrimination in the same subjects. Results showed that combined hippocampal and neocortical damage permanently prevented (within the limits tested) both acquisition and retention of learned behavior based on the conditional discrimination but had no effect on behaviors based on the nonconditional discrimination or simple associations. Neocortical lesions alone had no effect on either conditional or nonconditional discriminative responding, but they did temporarily disrupt acquisition and retention of behavior dependent on CS-CS (two conditioned stimuli) associations. Neither lesion affected learned behaviors mediated by CS-US (conditioned stimulus and unconditioned stimulus) associations. Thus, results showed that hippocampal damage selectively disrupted learned conditional behaviors and also revealed that central nervous system control of conditional discrimination performance, within-compound associations, and CS-US associations is mediated by different neural mechanisms.

Hippocampectomy selectively disrupts discrimination reversal conditioning of the rabbit nictitating membrane response

The effects of hippocampal lesions were tested on two-tone discrimination reversal conditioning of the rabbit nictitating membrane response. Results showed that hippocampectomized animals learned the initial two-tone discrimination at rates equivalent to operated control animals and animals with neocortical lesions. During reversal conditioning, however, animals with hippocampal lesions were severely impaired relative to both other groups. Neocortical lesions were without effect on reversal learning. An additional study revealed that the hippocampectomized animals' failure at reversal could not be attributed to a lesion-induced increased resistance to extinction. Results are discussed with respect to several theories of hippocampal function, and with respect to changes in the activity of hippocampal pyramidal neurons which occur during classical conditioning of the nictitating membrane response.