Sleep EEG microstructure in children and adolescents with attention deficit hyperactivity disorder: a systematic review and meta-analysis

NREM Slow-Wave Activity in Adolescents Is Differentially Associated With ADHD Levels and Normalized by Pharmacological Treatment

BACKGROUND

A compelling hypothesis about attention-deficit/hyperactivity disorder (ADHD) etiopathogenesis is that the ADHD phenotype reflects a delay in cortical maturation. Slow-wave activity (SWA) of non-rapid eye movement (NREM) sleep electroencephalogram (EEG) is an electrophysiological index of sleep intensity reflecting cortical maturation. Available data on ADHD and SWA are conflicting, and developmental differences, or the effect of pharmacological treatment, are relatively unknown.

METHODS

We examined, in samples (Mage = 16.4, SD = 1.2), of ever-medicated adolescents at risk for ADHD (n = 18; 72% boys), medication-naïve adolescents at risk for ADHD (n = 15, 67% boys), and adolescents not at risk for ADHD (n = 31, 61% boys) matched for chronological age and controlling for non-ADHD pharmacotherapy, whether ADHD pharmacotherapy modulates the association between NREM SWA and ADHD risk in home sleep.

RESULTS

Findings indicated medication-naïve adolescents at risk for ADHD exhibited greater first sleep cycle and entire night NREM SWA than both ever-medicated adolescents at risk for ADHD and adolescents not at risk for ADHD and no difference between ever-medicated, at-risk adolescents, and not at-risk adolescents.

CONCLUSIONS

Results support atypical cortical maturation in medication-naïve adolescents at risk for ADHD that appears to be normalized by ADHD pharmacotherapy in ever-medicated adolescents at risk for ADHD. Greater NREM SWA may reflect a compensatory mechanism in middle-later adolescents at risk for ADHD that normalizes an earlier occurring developmental delay.

Emotional Dysregulation and Sleep Problems: A Transdiagnostic Approach in Youth

BACKGROUND

Sleep is a complex phenomenon that affects several aspects of life, including cognitive functioning, emotional regulation, and overall well-being. Sleep disturbances, especially during adolescence, can negatively impact emotional regulation, making it a critical factor in targeting psychopathology.

METHODS

This study explores the interplay between emotional dysregulation (ED) and sleep patterns in a sample of 90 adolescent patients by means of self- and parent-rated clinical measures.

RESULTS

Our findings reveal a bidirectional relationship between ED and sleep problems. Adolescents with higher affective instability experience poorer sleep quality, while those with worse sleep quality exhibit higher internalizing problems. Additionally, emotional reactivity is associated with disrupted circadian rhythms.

CONCLUSIONS

These results emphasize the significance of addressing sleep problems in the context of psychopathology treatment, potentially leading to improved outcomes. Further research is needed to determine the most effective treatment strategies, including nonpharmacological and pharmacological interventions. Understanding the intricate relationship between sleep problems and emotion regulation offers insights for more targeted and effective treatment approaches for youths struggling with ED.

Sleep Physiology and Neurocognition Among Adolescents With Attention-Deficit/Hyperactivity Disorder

OBJECTIVE

Few studies have characterized the nature of sleep problems among adolescents with attention-deficit/hyperactivity disorder (ADHD) using polysomnography (PSG). Additionally, although adolescents with ADHD and adolescents with sleep disturbances display similar neurocognitive deficits, the role of sleep in contributing to neurocognitive impairment in adolescent ADHD is unknown. This study investigated differences in PSG-measured sleep among adolescents with ADHD compared with non-psychiatric controls and associations with neurocognition.

METHOD

Medication-free adolescents aged 13 to 17 (N = 62, n = 31 with ADHD; mean age = 15.3 years; 50% female) completed a diagnostic evaluation, 3 nights of ambulatory PSG, the Cambridge Neuropsychological Test Automated Battery, and subjective reports of sleep and executive functioning. Linear regressions covarying for age, sex, and pubertal status examined group differences in sleep indices, and partial Pearson correlations assessed relations between sleep and neurocognition.

RESULTS

Although adolescents with ADHD did not exhibit differences in PSG-measured sleep duration, awakenings, or latency (ps > .05) compared with non-psychiatric controls, they displayed lower slow wave sleep percentage (β = -.40) and non-rapid eye movement (NREM) electroencephalogram (EEG) delta power (β = -.29). They also exhibited greater stage 2 percentage (β = .41), NREM EEG sigma power (β = .41), and elevated self-reported sleep disturbances (ps < .05). Lower NREM EEG delta power, increased high-frequency power, and slower decline in NREM EEG delta power overnight were associated with poorer neurocognition among adolescents with ADHD.

CONCLUSIONS

Adolescents with ADHD reported more sleep disturbances than non-psychiatric controls and exhibited differences in sleep stage distribution and NREM sleep EEG frequency. Sleep-EEG spectral indices were associated with impaired neurocognition, suggesting that physiological sleep processes may underlie neurocognitive deficits in ADHD. Future studies may clarify whether sleep plays a causal role in neurocognitive impairments in adolescent ADHD and whether interventions normalizing sleep improve neurocognition.

CLINICAL TRIAL REGISTRATION INFORMATION

Sleep Dysfunction and Neurocognitive Outcomes in Adolescent ADHD; https://clinicaltrials.gov/; NCT02897362.

DIVERSITY & INCLUSION STATEMENT

We worked to ensure sex and gender balance in the recruitment of human participants. We worked to ensure race, ethnic, and/or other types of diversity in the recruitment of human participants. We worked to ensure that the study questionnaires were prepared in an inclusive way. One or more of the authors of this paper self-identifies as a member of one or more historically underrepresented sexual and/or gender groups in science. We actively worked to promote sex and gender balance in our author group. While citing references scientifically relevant for this work, we also actively worked to promote sex and gender balance in our reference list.

Mobile sleep EEG suggests delayed brain maturation in adolescents with ADHD: A focus on oscillatory spindle frequency

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder. Although data show ADHD is associated with sleep problems, approaches to analyze the association between ADHD and sleep electrophysiology are limited to a few methods with circumscribed foci.

AIMS

Sleep EEG was analyzed by a mixed-radix FFT routine and power spectrum parametrization in adolescents with ADHD and adolescents not at-risk for ADHD. Spectral components of sleep EEG were analyzed employing a novel, model-based approach of EEG power spectra.

METHODS AND PROCEDURES

The DREEM mobile polysomnography headband was used to record home sleep EEG from 19 medication-free adolescents with ADHD and 29 adolescents not at-risk for ADHD (overall: N = 56, age range 14-19 years) and groups were compared on characteristics of NREM sleep.

OUTCOMES AND RESULTS

Adolescents with ADHD exhibited lower frequency of spectral peaks indicating sleep spindle oscillations whereas adolescents not at-risk for ADHD showed lower spectral power in the slow sleep spindle and beta frequency ranges.

CONCLUSIONS AND IMPLICATIONS

The observed between-groups difference might indicate delayed brain maturity unraveled during sleep in ADHD.

Characteristics of ADHD Symptoms and EEG Theta/Beta Ratio in Children With Sleep Disordered Breathing

Objectives. This study aimed to explore parent-reported symptoms of attention deficit-hyperactivity disorder (ADHD) and sleep electroencephalogram (EEG) theta/beta ratio (TBR) characteristics in children with sleep disordered breathing (SDB). Methods. The parents of children (aged 6-11 years) with SDB (n = 103) and healthy controls (n = 28) completed the SNAP-IV questionnaire, and children underwent overnight polysomnography. Children with SDB were grouped according to obstructive apnea/hypopnea index: primary snoring, mild, and moderate-severe obstructive sleep apnea (OSA) groups. The TBR in non-rapid eye movement (NREM) periods in three sleep cycles was analyzed. Results. Children with SDB showed worse ADHD symptoms compared with the healthy control. There was no intergroup difference in TBR. The time-related decline in TBR observed in the control, primary snoring and mild OSA groups, which was not observed in the moderate-severe OSA group. Overnight transcutaneous oxygen saturation was negatively associated with the hyperactivity/impulsivity score of ADHD symptom. The global TBR during the NREM period in the first sleep cycle was positively correlated with inattention score. Conclusion. Children with SDB showed more ADHD inattention symptoms than the healthy control. Although we found no difference in TBR among groups, we found significant main effect for NREM period. There existed a relationship between hypoxia, TBR, and scores of ADHD symptoms. Hence, it was speculated that TBR can reflect the nocturnal electrophysiological manifestations in children with SDB, which may be related to daytime ADHD symptoms.

Sleep Spindle-Related EEG Connectivity in Children with Attention-Deficit/Hyperactivity Disorder: An Exploratory Study

Attention-deficit/hyperactivity disorder (ADHD) is a neurobehavioral disorder with known brain abnormalities but no biomarkers to support clinical diagnosis. Recently, EEG analysis methods such as functional connectivity have rekindled interest in using EEG for ADHD diagnosis. Most studies have focused on resting-state EEG, while connectivity during sleep and spindle activity has been underexplored. Here we present the results of a preliminary study exploring spindle-related connectivity as a possible biomarker for ADHD. We compared sensor-space connectivity parameters in eight children with ADHD and nine age/sex-matched healthy controls during sleep, before, during, and after spindle activity in various frequency bands. All connectivity parameters were significantly different between the two groups in the delta and gamma bands, and Principal Component Analysis (PCA) in the gamma band distinguished ADHD from healthy subjects. Cluster coefficient and path length values in the sigma band were also significantly different between epochs, indicating different spindle-related brain activity in ADHD.

Patterns of polysomnography parameters in 27 neuropsychiatric diseases: an umbrella review

BACKGROUND

We provide an umbrella review of the reported polysomnographic changes in patients with neuropsychiatric diseases compared with healthy controls.

METHODS

An electronic literature search was conducted in EMBASE, MEDLINE, All EBM databases, CINAHL, and PsycINFO. Meta-analyses of case-control studies investigating the polysomnographic changes in patients with neuropsychiatric diseases were included. For each meta-analysis, we estimated the summary effect size using random effects models, the 95% confidence interval, and the 95% prediction interval. We also estimated between-study heterogeneity, evidence of excess significance bias, and evidence of small-study effects. The levels of evidence of polysomnographic changes in neuropsychiatric diseases were ranked as follows: not significant, weak, suggestive, highly suggestive, or convincing.

RESULTS

We identified 27 articles, including 465 case-control studies in 27 neuropsychiatric diseases. The levels of evidence of polysomnographic changes in neuropsychiatric diseases were highly suggestive for increased sleep latency and decreased sleep efficiency (SE) in major depressive disorder (MDD), increased N1 percentage, and decreased N2 percentage, SL and REML in narcolepsy, and decreased rapid eye movement (REM) sleep percentage in Parkinson's disease (PD). The suggestive evidence decreased REM latency in MDD, decreased total sleep time and SE in PD, and decreased SE in posttraumatic stress disorder and in narcolepsy.

CONCLUSIONS

The credibility of evidence for sleep characteristics in 27 neuropsychiatric diseases varied across polysomnographic variables and diseases. When considering the patterns of altered PSG variables, no two diseases had the same pattern of alterations, suggesting that specific sleep profiles might be important dimensions for defining distinct neuropsychiatric disorders.

The GABAA receptor modulator zolpidem augments hippocampal-prefrontal coupling during non-REM sleep

Benzodiazepines and 'Z-drugs' (including zolpidem and zopiclone) are GABAA receptor (GABAAR) positive modulators commonly prescribed as hypnotics to treat insomnia and/or anxiety. However, alongside sedation, augmenting GABAAR function may also alter coordinated neuronal activity during sleep, thereby influencing sleep-dependent processes including memory consolidation. We used simultaneous recordings of neural population activity from the medial prelimbic cortex (PrL) and CA1 of the dorsal hippocampus (dCA1) of naturally sleeping rats to detail the effects of zolpidem on network activity during the cardinal oscillations of non-REM sleep. For comparison, we also characterized the effects of diazepam and 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP/gaboxadol), which acts predominantly at extra-synaptic GABAARs. Zolpidem and THIP significantly increased the amplitudes of slow-waves, which were attenuated by diazepam. Zolpidem increased hippocampal ripple density whereas diazepam decreased both ripple density and intrinsic frequency. While none of the drugs affected thalamocortical spindles in isolation, zolpidem augmented the temporal coordination between slow-waves and spindles. At the cellular level, analyses of spiking activity from 523 PrL and 579 dCA1 neurons revealed that zolpidem significantly enhanced synchronized pauses in cortical firing during slow-wave down states, while increasing correlated activity within and between dCA1 and PrL populations. Of the drugs compared here, zolpidem was unique in augmenting coordinated activity within and between hippocampus and neocortex during non-REM sleep. Zolpidem's enhancement of hippocampal-prefrontal coupling may reflect the cellular basis of its potential to modulate offline memory processing.

Sleep Structure in Untreated Adults With ADHD: A Retrospective Study

OBJECTIVE

Polysomnographic findings in neurodevelopmental disorders have been reported, but previous studies have had several limitations. The purpose of this study was to characterize sleep structure in untreated adults diagnosed with ADHD, excluding ADHD-related sleep disorders as determined by polysomnography and multiple sleep latency testing.

METHODS

This study included 55 patients aged 18 years or older who visited the Kurume University Hospital Sleep Clinic between April 2015 and March 2020. The diagnosis of ADHD was determined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (ADHD group, n = 28; non-ADHD, n = 27).

RESULTS

The ADHD group had significantly longer slow wave sleep (SWS) duration than the non-ADHD group (ADHD: 68.3 ± 31.0 minutes vs. non-ADHD: 43.4 ± 36.6 minutes; p = .0127).

CONCLUSIONS

The increased SWS volume observed in drug-naïve adult patients with ADHD may be related to the pathogenesis of this disorder.

Sleep disturbances in Norwegian children with fetal alcohol spectrum disorders (FASD) with and without a diagnosis of attention-deficit hyperactivity disorder or epilepsy

BACKGROUND

Fetal alcohol spectrum disorder (FASD) describes a combination of developmental, cognitive, and behavioral disabilities in children with prenatal exposure to alcohol. The literature suggests that there are higher rates of sleep disturbances in these children. Few studies have investigated sleep disturbances in relation to common comorbidities of FASD. We examined the prevalence of disturbed sleep and the relationship between parent-reported sleep problems in different FASD subgroups and comorbidities like epilepsy or attention-deficit hyperactivity disorder (ADHD) and impact on clinical functioning.

METHODS

In this prospective cross-sectional survey, caregivers of 53 children with FASD completed the Sleep Disturbance Scale for Children (SDSC). Information about comorbidities was collected, and EEG and assessment of IQ, daily-life executive and adaptive functioning were performed. Group comparisons and ANCOVA interaction models were used to test the associations between different sleep disturbances and clinical factors that could interfere with sleep.

RESULTS

An abnormal sleep score on the SDSC was very common, affecting 79% of children (n = 42) with equal prevalence in all FASD subgroups. Difficulty falling asleep was the most common sleep problem, followed by difficulty staying asleep and waking early. The incidence of epilepsy was 9.4%, with an abnormal EEG seen in 24.5%, and a diagnosis of ADHD in 47.2% of children. The distribution of these conditions was equal in all FASD subgroups. Children with signs of sleep disturbance had poorer working memory, executive function, and adaptive functioning. Children with ADHD had a greater prevalence of sleep disturbance than those without ADHD (OR 1.36; 95% CI 1.03 to 1.79).

CONCLUSION

Problems with sleep are very common in FASD children and seem independent of FASD subgroup and the presence of epilepsy or a pathological EEG finding, while those with ADHD had more sleep problems. The study underscores the importance of screening for sleep disturbances in all children with FASD as these problems may be treatable.

Owner-rated hyperactivity/impulsivity is associated with sleep efficiency in family dogs: a non-invasive EEG study

Subjective sleep disturbances are reported by humans with attention-deficit/hyperactivity disorder (ADHD). However, no consistent objective findings related to sleep disturbances led to the removal of sleep problems from ADHD diagnostic criteria. Dogs have been used as a model for human ADHD with questionnaires validated for this purpose. Also, their sleep physiology can be measured by non-invasive methods similarly to humans. In the current study, we recorded spontaneous sleep EEG in family dogs during a laboratory session. We analyzed the association of sleep macrostructure and deep sleep (NREM) slow-wave activity (SWA) with a validated owner-rated ADHD questionnaire, assessing inattention (IA), hyperactivity/impulsivity (H/I) and total (T) scores. Higher H/I and T were associated with lower sleep efficiency and longer time awake after initial drowsiness and NREM. IA showed no associations with sleep variables. Further, no association was found between ADHD scores and SWA. Our results are in line with human studies in which poor sleep quality reported by ADHD subjects is associated with some objective EEG macrostructural parameters. This suggests that natural variation in dogs' H/I is useful to gain a deeper insight of ADHD neural mechanisms.

Sleep Power Topography in Children with Attention Deficit Hyperactivity Disorder (ADHD)

OBJECTIVE

Recent years saw an increasing interest towards sleep microstructure abnormalities in attention-deficit/hyperactivity disorder (ADHD). However, the existing literature on sleep electroencephalographic (EEG) power in ADHD is still controversial, often based on single electrode recordings, and mainly focused on slow wave activity (SWA) during NREM sleep. This study aimed to systematically investigate sleep power topography in all traditional frequency bands, in all sleep stages and across sleep cycles using high-density EEG (HD-EEG).

METHOD

Thirty drug-naïve children with ADHD (10.5 ± 2.1 years, 21 male) and 23 typically developing (TD) control participants (mean age: 10.2 ± 1.6 years, 13 male) were included in the current analysis. Signal power topography was computed in classical frequency bands during sleep, contrasted between groups and sleep cycles, and correlated with measures of ADHD severity, cognitive functioning and estimated total sleep time.

RESULTS

Compared to TD subjects, patients with ADHD consistently displayed a widespread increase in low-frequency activity (between 3 and 10 Hz) during NREM sleep, but not during REM sleep and wake before sleep onset. Such a difference involved a wide centro-posterior cluster of channels in the upper SWA range, in Theta, and low-Alpha. Between-group difference was maximal in sleep stage N3 in the first sleep cycle, and positively correlated with average total sleep time.

CONCLUSIONS

These results support the concept that children with ADHD, compared to TD peers, have a higher sleep pressure and altered sleep homeostasis, which possibly interfere with (and delay) cortical maturation.

Sleep microstructure in attention deficit hyperactivity disorder according to the underlying sleep phenotypes

The analysis of sleep microstructure in attention deficit hyperactivity disorder (ADHD) revealed an under-representation of the EEG slow component during NREM sleep. Previous studies either excluded or did not characterize objectively sleep disorders, which notoriously affect sleep architecture. The present study aimed to investigate the cyclic alternating pattern in a real clinical sample of children with ADHD, in whom sleep disorders could be considered. Twenty-seven consecutively enrolled drug-naïve children (mean age, 10.53 years; nine females) and 23 controls (mean age, 10.22 years; 11 females) underwent a full sleep investigation, including attended video-polysomnography. Visual cyclic alternating pattern analysis was performed in a blinded way. Children with ADHD had one or more sleep disorders (a narcolepsy-like phenotype was found in two cases, sleep onset insomnia in three cases, arousal disorder in one case, movement disorder phenotype in six cases and obstructive sleep apnea in 11 cases, and six children had sleep-related epileptiform discharges). Children with ADHD and normal controls showed a similar microstructure with a cyclic alternating pattern rate of about 50%. Children with obstructive sleep apnea had a significantly higher cyclic alternating pattern rate during stage N3. Despite not reaching statistical differences, a lower cyclic alternating pattern rate and A1 index were found in children without epileptic abnormalities/obstructive sleep apnea. Our analysis might allow differentiation of the "primary form" of ADHD associated with a decrease of NREM instability from those forms associated with sleep apnea and epileptic activity.

Evidence of a maturational disruption in non-rapid eye movement sleep slow wave activity in youth with attention-deficit/hyperactivity, learning and internalizing disorders

BACKGROUND

Sleep slow wave activity (SWA) peaks during childhood and declines in the transition to adolescence during typical development (TD). It remains unknown whether this trajectory differs in youth with neuropsychiatric disorders.

METHODS

We analyzed sleep EEGs of 664 subjects 6 to 21 y (449 TD, 123 unmedicated, 92 medicated) and 114 subjects 7-12 y (median 10.5 y) followed-up at 18-22 y (median 19 y). SWA (0.4-4 Hz) power was calculated during non-rapid eye movement sleep.

RESULTS

TD and unmedicated youth showed cubic central and frontal SWA trajectories from 6 to 21 y (p-cubic<0.05), with TD youth showing peaks in central SWA at 6.8 y and frontal at 8.2 y. Unmedicated attention-deficit/hyperactivity (ADHD) and/or learning disorders (LD) showed peak central SWA 2 y later (at 9.6 y, coinciding with peak frontal SWA) than TD, followed by a 67% steeper slope by 19 y. Frontal SWA peak and slope in unmedicated ADHD/LD, and that of central and frontal in internalizing disorders (ID), were similar to TD. Unmedicated ADHD/LD did not differ in the longitudinal SWA percent change by 18-22 y; unmedicated ID showed a lower longitudinal change in frontal SWA than TD. Medicated youth showed a linear decline in central and frontal SWA from 6 to 21 y (p-linear<0.05).

CONCLUSIONS

ADHD/LD youth show a maturational delay and potential topographical disruption in SWA during childhood and steeper decline throughout adolescence, suggesting faster synaptic pruning. Youth with ID experience less changes in frontal SWA by late adolescence. Psychotropic medications may impact the maturational trajectory of SWA, but not the magnitude of developmental decline by late adolescence.

Three-dimensional analysis of upper airway and craniofacial morphology in orthodontic adolescents with Attention Deficit Hyperactivity Disorder (ADHD): A comparative retrospective study

PURPOSE

The aim of this study is to evaluate craniofacial characteristics and upper airway morphology in adolescents with Attention Deficit Disorder with Hyperactivity (ADHD) compared to controls (CON).

MATERIALS AND METHODS

Records from July 2014 to May 2018 of patients who were seeking orthodontic treatment at a single institute and had full pre-treatment orthodontic records including cone-beam computed tomography (CBCT) were reviewed. Comprehensive cephalometric variables were measured to determine craniofacial morphology. Upper airway volume (UAV), minimum cross-sectional area (MCA), and linear measurements were calculated at multiple planes.

RESULTS

A total of 87 adolescents (ADHD, 29; CON, 58) were included in the study. Overall, UAV and MCA in ADHA group were smaller than CON. Statistical significance was evident in airway widths at planes A (P=0.002), C (P=0.042), and D (P<0.001), and airway area at plane D (lower hypopharynx) (P<0.001), with the ADHD group showing narrower widths and area compared to CON. The most common skeletal classification in the ADHD group was sequenced as Class II, Class I then Class III, with percentages of (58.6%), (31%) and (10.3%), respectively. No significant differences were found between the groups for any of the skeletal, dental, and soft tissue cephalometric variables.

CONCLUSIONS

ADHD affected adolescents have similar craniofacial characteristics, but narrower upper airway dimensions compared to controls. Further investigations with larger samples are warranted to further elucidate the relationship between SDB and ADHD.

A systematic review and meta-analysis of the cyclic alternating pattern across the lifespan

BACKGROUND

Cyclic alternating pattern (CAP) is the electroencephalogram (EEG) pattern described as a marker of sleep instability and assessed by NREM transient episodes in sleep EEG. It has been associated with brain maturation. The aim of this review was to evaluate the normative data of CAP parameters according to the aging process in healthy subjects through a systematic review and meta-analysis.

METHODS

Two authors independently searched databases using PRISMA guidelines. Discrepancies were reconciled by a third reviewer. Subgroup analysis and tests for heterogeneity were conducted.

RESULTS

Of 286 studies, 10 submitted a total of 168 healthy individuals to CAP analysis. Scoring of CAP can begin at 3 months of life, when K-complexes, delta bursts, or spindles can be recognized. Rate of CAP increased with age, mainly during the first 2 years of life, then decreased in adolescence, and increased in the elderly. The A1 CAP subtype and CAP rate were high in school-aged children during slow-wave sleep (SWS). A1 CAP subtypes were significantly more numerous in adolescents compared with other groups, while the elderly showed the highest amounts of A2 and A3 CAP subtypes. Our meta-analysis registered the lowest CAP rate in infants younger than 2 years old and the highest in the elderly.

CONCLUSIONS

This review summarized the normative data of CAP in NREM sleep during the aging process. The CAP rate increased with age and sleep depth, especially during SWS. Parameters of CAP may reflect gender hormonal effects and neuroplasticity. More reports on CAP subtypes are needed for their reference values establishment.