The Genetic Etiology of Parkinson's Disease Does Not Robustly Affect Subthalamic Physiology.

BACKGROUND: It is unknown whether Parkinson's disease (PD) genetic heterogeneity, leading to phenotypic and pathological variability, is also associated with variability in the unique PD electrophysiological signature. Such variability might have practical implications for adaptive deep brain stimulation (DBS). OBJECTIVE: The aim of our work was to study the electrophysiological activity in the subthalamic nucleus (STN) of patients with PD with pathogenic variants in different disease-causing genes. METHODS: Electrophysiological data from participants with negative genetic tests were compared with those from GBA, LRRK2, and PRKN-PD. RESULTS: We analyzed data from 93 STN trajectories (GBA-PD: 28, LRRK2-PD: 22, PARK-PD: 10, idiopathic PD: 33) of 52 individuals who underwent DBS surgery. Characteristics of ß oscillatory activity in the dorsolateral motor part of the STN were similar for patients with negative genetic tests and for patients with different forms of monogenic PD. CONCLUSIONS: The genetic heterogeneity in PD is not associated with electrophysiological differences. Therefore, similar adaptive DBS algorithms would be applicable to genetically heterogeneous patient populations. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Multicenter Validation of Individual Preoperative Motor Outcome Prediction for Deep Brain Stimulation in Parkinson's Disease.

BACKGROUND: Subthalamic nucleus deep brain stimulation (STN DBS) is an established therapy for Parkinson's disease (PD) patients suffering from motor response fluctuations despite optimal medical treatment, or severe dopaminergic side effects. Despite careful clinical selection and surgical procedures, some patients do not benefit from STN DBS. Preoperative prediction models are suggested to better predict individual motor response after STN DBS. We validate a preregistered model, DBS-PREDICT, in an external multicenter validation cohort. METHODS: DBS-PREDICT considered eleven, solely preoperative, clinical characteristics and applied a logistic regression to differentiate between weak and strong motor responders. Weak motor response was defined as no clinically relevant improvement on the Unified Parkinson's Disease Rating Scale (UPDRS) II, III, or IV, 1 year after surgery, defined as, respectively, 3, 5, and 3 points or more. Lower UPDRS III and IV scores and higher age at disease onset contributed most to weak response predictions. Individual predictions were compared with actual clinical outcomes. RESULTS: 322 PD patients treated with STN DBS from 6 different centers were included. DBS-PREDICT differentiated between weak and strong motor responders with an area under the receiver operator curve of 0.76 and an accuracy up to 77%. CONCLUSION: Proving generalizability and feasibility of preoperative STN DBS outcome prediction in an external multicenter cohort is an important step in creating clinical impact in DBS with data-driven tools. Future prospective studies are required to overcome several inherent practical and statistical limitations of including clinical decision support systems in DBS care.

Movement context modulates neuronal activity in motor and limbic-associative domains of the human parkinsonian subthalamic nucleus.

The subthalamic nucleus (STN), a preferred target for treating movement disorders, has a crucial role in inhibition and execution of movement. To better understand the mechanism of movement regulation in the STN of Parkinson's disease patients, we compared the same movement with different context, facilitation vs. inhibition context. We recorded subthalamic multiunit activity intra-operatively while parkinsonian patients (off medications, n = 43 patients, 173 recording sites) performed increasingly complex oddball paradigms with frequent and deviant tones: first, passive listening to tone series with no movement ('None-Go' task, n = 7, 28 recording sites); second, pressing a button after every tone ('All-Go' task, n = 7, 26 recording sites); and third, pressing a button only for frequent tones, thus adding inhibition of movement following deviant tones ('Go-NoGo' task, n = 29, 119 recording sites). The STN responded mainly to movement-involving tasks. In the limbic-associative STN, evoked response to the deviant tone (inhibitory cue) was not significantly different between the Go-NoGo and the All-Go task. However, the evoked response to the frequent tone (go cue) in the Go-NoGo task was significantly reduced. The reduction was mainly prominent in the negative component of the evoked response amplitude aligned to the press. Successful movement inhibition was correlated with higher baseline activity. We suggest that the STN in Parkinson's disease patients adapts to movement inhibition context by selectively decreasing the amplitude of neuronal activity. Thus, the STN enables movement inhibition not by increasing responses to the inhibitory cue but by reducing responses to the release cue. The negative component of the evoked response probably facilitates movement and a higher baseline activity enables successful inhibition of movement. These discharge modulations were found in the ventromedial, non-motor domain of the STN and therefore suggest a significant role of the limbic- associative STN domains in movement planning and in global movement regulation.

Theta-alpha oscillations characterize emotional subregion in the human ventral subthalamic nucleus.

BACKGROUND: Therapeutic outcomes of STN-DBS for movement and psychiatric disorders depend on electrode location within the STN. Electrophysiological and functional mapping of the STN has progressed considerably in the past years, identifying beta-band oscillatory activity in the dorsal STN as a motor biomarker. It also has been suggested that STN theta-alpha oscillations, involved in impulse control and action inhibition, have a ventral source. However, STN local field potential mapping of motor, associative, and limbic areas is often limited by poor spatial resolution. OBJECTIVES: Providing a high-resolution electrophysiological map of the motor, associative and limbic anatomical sub-areas of the subthalamic nucleus. METHODS: We have analyzed high-spatial-resolution STN microelectrode electrophysiology recordings of PD patients (n = 303) that underwent DBS surgery. The patients' STN intraoperative recordings of spiking activity (933 electrode trajectories) were combined with their imaging data (n = 83 patients, 151 trajectories). RESULTS: We found a high theta-alpha (7-10 Hz) oscillatory area, located near the STN ventromedial border in 29% of the PD patients. Theta-alpha activity in this area has higher power and lower central frequency in comparison to theta-alpha activity in more dorsal subthalamic areas. When projected on the DISTAL functional atlas, the theta-alpha oscillatory area overlaps with the STN limbic subarea. CONCLUSIONS: We suggest that theta-alpha oscillations can serve as an electrophysiological marker for the ventral subthalamic nucleus limbic subarea. Therefore, theta-alpha oscillations can guide optimal electrode placement in neuropsychiatric STN-DBS procedures and provide a reliable biomarker input for future closed-loop DBS device. © 2019 International Parkinson and Movement Disorder Society.

[DEEP BRAIN STIMULATION FOR OBSESSIVE COMPULSIVE DISORDER: CASE REPORT OF THE FIRST OCD PATIENT IN ISRAEL].

INTRODUCTION: Treatment-resistant obsessive-compulsive disorder (OCD) is considered a severe psychiatric disorder that causes severe functional decline. In the past, these patients were treated by selective ablation of neuronal pathways related to the pathophysiology of OCD. Deep brain stimulation is an effective and safe treatment alternative that enables reversible changes in neural circuits and reduces OCD symptoms. In this paper we present the outcome of a treatment-resistant OCD patient who underwent deep brain stimulation procedure for the first time in Israel. The patient has achieved a significant decline in OCD symptoms as well as improvement in personal and social functioning. The discussion focuses on methods to implement deep brain stimulation for OCD patients in Israel.

Anesthesia reduces discharge rates in the human pallidum without changing the discharge rate ratio between pallidal segments.

Classical rate models of basal ganglia circuitry associate discharge rate of the globus pallidus external and internal segments (GPe, GPi respectively) solely with dopaminergic state and predict an inverse ratio between the discharge rates of the two pallidal segments. In contrast, the effects of other rate modulators such as general anesthesia (GA) on this ratio have been ignored. To respond to this need, we recorded the neuronal activity in the GPe and GPi in awake and anesthetized human patients with dystonia (57 and 53 trajectories respectively) and in awake patients with Parkinson's disease (PD, 16 trajectories) undergoing deep brain stimulation procedures. This triad enabled us to dissociate pallidal discharge ratio from general discharge modulation. An automatic offline spike detection and isolation quality system was used to select 1560 highly isolated units for analysis. The mean discharge rate in the GPi of awake PD patients was dramatically higher than in awake dystonia patients although the firing rate in the GPe was similar. Firing rates in dystonic patients under anesthesia were lower in both nuclei. Surprisingly, in all three groups, GPe firing rates were correlated with firing rates in the ipsilateral GPi. Thus, the firing rate ratio of ipsilateral GPi/GPe pairs was similar in awake and anesthetized patients with dystonia and significantly higher in PD. We suggest that pallidal activity is modulated by at least two independent processes: dopaminergic state which changes the GPi/GPe firing rate ratio, and anesthesia which modulates firing rates in both pallidal nuclei without changing the ratio between their firing rates.

Subthalamic nucleus input-output dynamics are correlated with Parkinson's burden and treatment efficacy.

The subthalamic nucleus (STN) is pivotal in basal ganglia function in health and disease. Micro-electrode recordings of >25,000 recording sites from 146 Parkinson's patients undergoing deep brain stimulation (DBS) allowed differentiation between subthalamic input, represented by local field potential (LFP), and output, reflected in spike discharge rate (SPK). As with many natural systems, STN neuronal activity exhibits power-law dynamics characterized by the exponent α. We, therefore, dissected STN data into aperiodic and periodic components using the Fitting Oscillations & One Over F (FOOOF) tool. STN LFP showed significantly higher aperiodic exponents than SPK. Additionally, SPK beta oscillations demonstrated a downward frequency shift compared to LFP. Finally, the STN aperiodic and spiking parameters explained a significant fraction of the variance of the burden and treatment efficacy of Parkinson's disease. The unique STN input-output dynamics may clarify its role in Parkinson's physiology and can be utilized in closed-loop DBS therapy.

Perception of emotionally incongruent cues: evidence for overreliance on body vs. face expressions in Parkinson's disease.

Individuals with Parkinson's disease (PD) may exhibit impaired emotion perception. However, research demonstrating this decline has been based almost entirely on the recognition of isolated emotional cues. In real life, emotional cues such as expressive faces are typically encountered alongside expressive bodies. The current study investigated emotion perception in individuals with PD (n = 37) using emotionally incongruent composite displays of facial and body expressions, as well as isolated face and body expressions, and congruent composite displays as a baseline. In addition to a group of healthy controls (HC) (n = 50), we also included control individuals with schizophrenia (SZ) (n = 30), who display, as in PD, similar motor symptomology and decreased emotion perception abilities. The results show that individuals with PD showed an increased tendency to categorize incongruent face-body combinations in line with the body emotion, whereas those with HC showed a tendency to classify them in line with the facial emotion. No consistent pattern for prioritizing the face or body was found in individuals with SZ. These results were not explained by the emotional recognition of the isolated cues, cognitive status, depression, or motor symptoms of individuals with PD and SZ. As real-life expressions may include inconsistent cues in the body and face, these findings may have implications for the way individuals with PD and SZ interpret the emotions of others.

Safety and Tolerability, Dose-Escalating, Double-Blind Trial of Oral Mannitol in Parkinson's Disease.

Mannitol, a natural alcoholic-sugar, was recently suggested as a potential disease-modifying agent in Parkinson's disease. In animal models of the disease, mannitol interferes with the formation of α-synuclein fibrils, inhibits the formation of α-synuclein oligomers and leads to phenotypic recovery of impaired motor functions. Parkinson's patients who consume mannitol report improvements of both motor and non-motor symptoms. Safety of long-term use of oral mannitol, tolerable dose and possible benefit, however, were never clinically studied. We studied the safety of oral mannitol in Parkinson's disease and assessed the maximal tolerable oral dose by conducting a phase IIa, randomized, double-blind, placebo-controlled, single-center, dose-escalating study (ClinicalTrials.gov Identifier: NCT03823638). The study lasted 36 weeks and included four dose escalations of oral mannitol or dextrose to a maximal dose of 18 g per day. The primary outcome was the safety of oral mannitol, as assessed by the number of adverse events and abnormal laboratory results. Clinical and biochemical efficacy measures were collected but were not statistically-powered. Fourteen patients receiving mannitol completed the trial (in addition to eight patients on placebo). Mannitol-related severe adverse events were not observed. Gastrointestinal symptoms limited dose escalation in 6/14 participants on mannitol. None of the clinical or biochemical efficacy secondary outcome measures significantly differed between groups. We concluded that long-term use of 18 g per day of oral mannitol is safe in Parkinson's disease patients but only two third of patients tolerate this maximal dose. These findings should be considered in the design of future efficacy trials.

A Real-Life Search for the Optimal Set of Conversion Factors to Levodopa-Equivalent-Dose in Parkinson's Disease Patients on Polytherapy.

BACKGROUND: A wide variety of conversion factors for a levodopa-equivalent-dose (LED) have been proposed for each Parkinson's disease (PD) medication. The currently-used set of conversion factors is based on studies that relied on subjective experience or theoretical assumptions. This set was never validated in patients receiving polytherapy. OBJECTIVES: To use real-life data to identify an optimal set of conversion factors independent of prior assumptions regarding clinical efficacy of different medications. METHODS: Retrospective analysis of data from 206 cognitively-preserved patients with advanced PD receiving polytherapy before deep brain stimulation (DBS) surgery. A nonlinear automated problem solver was used to find a set of conversion factors that, when applied, minimized the coefficient of variation of LEDs in a relatively homogenous cohort of patients. RESULTS: Independent and model-free evaluation of a wide range of possible sets of conversion factors to LED suggested a set of normalized conversion factors for immediate release levodopa (1.00), controlled release levodopa (0.88), and amantadine (1.23). A minimal clinical benefit of entacapone was observed for patients with motor fluctuations. Our analysis could not detect conversion factors for dopamine agonists and MAO-B inhibitors, possibly because their clinical contribution when added to levodopa is limited. CONCLUSIONS: Independent from previous studies and prior assumptions we show that the currently-used LED conversion factors for immediate release levodopa, controlled release levodopa and amantadine are largely correct and that dopamine agonists, MAO-B inhibitors and entacapone, given in addition to levodopa, have little additional clinical value for PD patients with motor fluctuations.

Independently together: subthalamic theta and beta opposite roles in predicting Parkinson's tremor.

Tremor is a core feature of Parkinson's disease and the most easily recognized Parkinsonian sign. Nonetheless, its pathophysiology remains poorly understood. Here, we show that multispectral spiking activity in the posterior-dorso-lateral oscillatory (motor) region of the subthalamic nucleus distinguishes resting tremor from the other Parkinsonian motor signs and strongly correlates with its severity. We evaluated microelectrode-spiking activity from the subthalamic dorsolateral oscillatory region of 70 Parkinson's disease patients who underwent deep brain stimulation surgery (114 subthalamic nuclei, 166 electrode trajectories). We then investigated the relationship between patients' clinical Unified Parkinson's Disease Rating Scale score and their peak theta (4-7 Hz) and beta (13-30 Hz) powers. We found a positive correlation between resting tremor and theta activity (r = 0.41, P < 0.01) and a non-significant negative correlation with beta activity (r = -0.2, P = 0.5). Hypothesizing that the two neuronal frequencies mask each other's relationship with resting tremor, we created a non-linear model of their proportional spectral powers and investigated its relationship with resting tremor. As hypothesized, patients' proportional scores correlated better than either theta or beta alone (r = 0.54, P < 0.001). However, theta and beta oscillations were frequently temporally correlated (38/70 patients manifested significant positive temporal correlations and 1/70 exhibited significant negative correlation between the two frequency bands). When comparing theta and beta temporal relationship (r θ ß) to patients' resting tremor scores, we found a significant negative correlation between the two (r = -0.38, P < 0.01). Patients manifesting a positive correlation between the two bands (i.e. theta and beta were likely to appear simultaneously) were found to have lower resting tremor scores than those with near-zero correlation values (i.e. theta and beta were likely to appear separately). We therefore created a new model incorporating patients' proportional theta-beta power and r θ ßscores to obtain an improved neural correlate of resting tremor (r = 0.62, P < 0.001). We then used the Akaike and Bayesian information criteria for model selection and found the multispectral model, incorporating theta-beta proportional power and their correlation, to be the best fitting model, with 0.96 and 0.89 probabilities, respectively. Here we found that as theta increases, beta decreases and the two appear separately-resting tremor is worsened. Our results therefore show that theta and beta convey information about resting tremor in opposite ways. Furthermore, the finding that theta and beta coactivity is negatively correlated with resting tremor suggests that theta-beta non-linear scale may be a valuable biomarker for Parkinson's resting tremor in future adaptive deep brain stimulation techniques.

Subthalamic theta activity: a novel human subcortical biomarker for obsessive compulsive disorder.

Obsessive-compulsive disorder (OCD) is a common and serious psychiatric disorder. Although subthalamic nucleus deep brain stimulation (DBS) has been studied as a treatment for OCD patients the underlying mechanism of this treatment and the optimal method of stimulation are unknown. To study the neural basis of subthalamic nucleus DBS in OCD patients we used a novel, implantable DBS system with long-term local field potential sensing capability. We focus our analysis on two patients with OCD who experienced severe treatment-resistant symptoms and were implanted with subthalamic nucleus DBS systems. We studied them for a year at rest and during provocation of OCD symptoms (46 recording sessions) and compared them to four Parkinson's disease (PD) patients implanted with subthalamic nucleus DBS systems (69 recording sessions). We show that the dorsal (motor) area of the subthalamic nucleus in OCD patients displays a beta (25-35 Hz) oscillatory activity similar to PD patients whereas the ventral (limbic-cognitive) area of the subthalamic nucleus displays distinct theta (6.5-8 Hz) oscillatory activity only in OCD patients. The subthalamic nucleus theta oscillatory activity decreases with provocation of OCD symptoms and is inversely correlated with symptoms severity over time. We conclude that beta oscillations at the dorsal subthalamic nucleus in OCD patients challenge their pathophysiologic association with movement disorders. Furthermore, theta oscillations at the ventral subthalamic nucleus in OCD patients suggest a new physiological target for OCD therapy as well as a promising input signal for future emotional-cognitive closed-loop DBS.

CSF analysis of IgH gene rearrangement in CNS lymphoma: relationship to the disease course.

PURPOSE: To assess whether clonal IgH genes in CSF of patients with CNS lymphoma correlates with the disease course. BACKGROUND: It has been shown that the PCR technique, which offers a sensitive test for diagnosis of systemic lymphoproliferative malignancies, can be applied to the CSF. METHODS: Seventy-three CSF specimens from 32 patients (27 with primary CNS lymphoma and 5 with an isolated parenchymal CNS relapse of systemic lymphoma) were examined. The results were evaluated retrospectively and compared to conventional cytology, clinical and imaging data, and course of the disease. CNS disease was defined as active when leptomeningeal and/or parenchymal brain involvement was evident on neuroimaging. Patients were considered to have a complete response when imaging confirmed absence of a tumor mass or leptomeningeal seeding. RESULTS: Sixty-three of 73 samples had adequate genetic material for testing. Of the 63, 15 (24%) were positive for clonal IgH rearrangement. In nine (60%) of the 15 patients with active disease, PCR results were positive, while negative results were observed in 19 (95%) of the 20 patients showing clear response to treatment. The sensitivity and specificity of the PCR evaluation were 54% and 97%, respectively. The predictive values of positive and negative tests were 93% and 74%, respectively. CONCLUSIONS: The integrated results of both PCR and cytology evaluations increase the sensitivity of CSF analysis. The PCR study has high specificity and positive results are indicative for the presence of active disease, even when the tumor seems confined to the brain parenchyma.

Early clinical heterogeneity in choreoacanthocytosis.

BACKGROUND: Choreoacanthocytosis (CHAC) is a slowly progressive multisystem disorder with involuntary movements, cognitive decline, behavioral changes, seizures, and polyneuropathy caused by mutations in the VPS13A gene. OBJECTIVE: To describe the early clinical features and possible genotype-phenotype correlation in CHAC. DESIGN AND SETTING: Case series in a tertiary care center. PATIENTS AND MAIN OUTCOME METHODS: Choreoacanthocytosis was diagnosed in 3 patients of Jewish origin from 3 unrelated families. We reviewed their medical histories and performed molecular analysis by screening all 73 exons of VPS13A. RESULTS: Trichotillomania, hypertrophic cardiomyopathy, and idiopathic hyperCKemia, in 1 patient each, preceded the development of the full clinical spectrum of CHAC by 2 to 20 years. At diagnosis, 2 patients manifested signs of overt neuromuscular involvement and were homozygous for the 6059delC mutation, whereas 1 patient had only hyporeflexia and was homozygous for the EX23del mutation. Because only 1 of the 2 patients with 6059delC had cardiomyopathy, its relevance to CHAC is unclear. CONCLUSIONS: These findings extend the knowledge of significant early clinical heterogeneity in CHAC and suggest a possible genotype-phenotype correlation. Awareness of the early manifestations may prevent misdiagnosis and enable appropriate genetic counseling.

Total and Proteinase K-Resistant α-Synuclein Levels in Erythrocytes, Determined by their Ability to Bind Phospholipids, Associate with Parkinson's Disease.

A marker for diagnosis of Parkinson's disease (PD), which reflects on the occurrence of peripheral pathogenic mechanisms, would potentially improve therapy. The significance of α-Synuclein (α-Syn) expression in red blood cells (RBC) is currently unclear. Here we investigated whether RBC's-expressed α-Syn may associate with PD. To this aim, we determined the levels of total and proteinase K-resistant α-Syn in samples of packed red blood cells (PRBCs). Twenty-one individuals with PD at various disease stages and 15 healthy controls, with similar demographic features, were recruited to this study. α-Syn levels were determined by their biochemical property to bind phospholipids, using a phospholipid-ELISA assay. A significantly lower ratio of total-to-proteinase K-resistant α-Syn levels was detected in PD patients than in the healthy control group. However, there was considerable overlap between the two groups. Suggesting a need for additional markers to be tested in combination with α-Syn levels. To the best of our knowledge, this is the first evidence for an association between RBCs-expressed α-Syn and pathogenic mechanisms involved in PD.

Asymmetric right/left encoding of emotions in the human subthalamic nucleus.

Emotional processing is lateralized to the non-dominant brain hemisphere. However, there is no clear spatial model for lateralization of emotional domains in the basal ganglia. The subthalamic nucleus (STN), an input structure in the basal ganglia network, plays a major role in the pathophysiology of Parkinson's disease (PD). This role is probably not limited only to the motor deficits of PD, but may also span the emotional and cognitive deficits commonly observed in PD patients. Beta oscillations (12-30 Hz), the electrophysiological signature of PD, are restricted to the dorsolateral part of the STN that corresponds to the anatomically defined sensorimotor STN. The more medial, more anterior and more ventral parts of the STN are thought to correspond to the anatomically defined limbic and associative territories of the STN. Surprisingly, little is known about the electrophysiological properties of the non-motor domains of the STN, nor about electrophysiological differences between right and left STNs. In this study, microelectrodes were utilized to record the STN spontaneous spiking activity and responses to vocal non-verbal emotional stimuli during deep brain stimulation (DBS) surgeries in human PD patients. The oscillation properties of the STN neurons were used to map the dorsal oscillatory and the ventral non-oscillatory regions of the STN. Emotive auditory stimulation evoked activity in the ventral non-oscillatory region of the right STN. These responses were not observed in the left ventral STN or in the dorsal regions of either the right or left STN. Therefore, our results suggest that the ventral non-oscillatory regions are asymmetrically associated with non-motor functions, with the right ventral STN associated with emotional processing. These results suggest that DBS of the right ventral STN may be associated with beneficial or adverse emotional effects observed in PD patients and may relieve mental symptoms in other neurological and psychiatric diseases.

Phase I/II trial of intravenous NDV-HUJ oncolytic virus in recurrent glioblastoma multiforme.

We undertook a Phase I/II trial in patients with apparent recurrent glioblastoma multiforme (GBM) based on imaging studies to determine the safety and tumor response of repetitive intravenous administration of NDV-HUJ, the oncolytic HUJ strain of Newcastle disease virus. The first part of the study utilized an accelerated intrapatient dose-escalation protocol with one-cycle dosage steps of 0.1, 0.32, 0.93, 5.9, and 11 billion infectious units (BIU) of NDV-HUJ (1 BIU = 1 x 10(9) EID(50) 50% egg infectious dose) followed by three cycles of 55 BIU. Virus was administered by intravenous infusion over 15 min. In the second part, patients received three cycles of 11 BIU. All patients without progressive disease were maintained with two doses of 11 BIU iv weekly. Eleven of the 14 enrolled patients (11-58 years, Karnofsky performance scale 50-90%) received treatment. Toxicity was minimal with Grade I/II constitutional fever being seen in 5 patients. Maximum tolerated dose was not achieved. Anti-NDV hemagglutinin antibodies appeared within 5-29 days. NDV-HUJ was recovered from blood, saliva, and urine samples and one tumor biopsy. One patient achieved a complete response. Intravenous NDV-HUJ is well tolerated. The findings of good tolerability and encouraging responses warrant the continued evaluation of NDV-HUJ in GBM, as well as other cancers.