Treatment of adult attention-deficit hyperactivity disorder (ADHD) with transcranial direct current stimulation (tDCS): study protocol for a parallel, randomized, double-blinded, sham-controlled, multicenter trial (Stim-ADHD).

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation treatment used as an alternative or complementary treatment for various neuropsychiatric disorders, and could be an alternative or add-on therapy to psychostimulants in attention-deficit hyperactivity disorder (ADHD). Previous studies provided some evidence for improvements in cognition and clinical symptoms in pediatric and adult ADHD patients. However, data from multi-center randomized controlled trials (RCTs) for this condition are lacking. Thus, our aim is to evaluate short- and mid-term effects of tDCS in this multi-center, randomized, double blind, and sham-controlled, parallel group clinical trial with a 1:1 randomization ratio. Primary endpoint is the total score of DSM-IV scale of the internationally established Conners' Adult ADHD Rating Scales (German self-report screening version, CAARS-S-SR), at day 14 post-intervention (p.i.) to detect short-term lasting effects analyzed via analyses of covariance (ANCOVAs). In case of significant between-groups differences at day 14 p.i., hierarchically ordered hypotheses on mid-term lasting effects will be investigated by linear mixed models with visit (5 time points), treatment, treatment by visit interaction, and covariates as fixed categorical effects plus a patient-specific visit random effect, using an unstructured covariance structure to model the residual within-patient errors. Positive results of this clinical trial will expand the treatment options for adult ADHD patients with tDCS and provide an alternative or add-on therapy to psychostimulants with a low risk for side effects.Trial Registration The trial was registered on July 29, 2022 in the German Clinical Trials Register (DRKS00028148).

["iFightDepression" in inpatient treatment : Evaluation of a web-based, therapist-guided self-management program on a specialized ward for affective disorders]. / "iFightDepression" im stationären Setting : Evaluation eines internetbasierten, therapeutenbegleiteten Selbstmanagementprogramms auf einer Spezialstation für affektive Störungen.

BACKGROUND: E­mental health mainly plays a role in the outpatient treatment of patients with depressive disorders. The goal of this study was to implement and evaluate the web-based, therapist-guided self-management tool "iFightDepression" (iFD) to clarify if there is a benefit for inpatient use. MATERIAL AND METHODS: In this study 78 inpatients with affective disorders (ICD-10 F32.0­3, F33.0-3) or dysthymia (F34) were recruited. The intervention duration with the iFD tool went from admission until discharge, therapeutic support was granted by the ward staff. Symptom severity, intervention expectations and experience with therapy were processed in an online questionnaire before the intervention (T0) while intervention satisfaction was captured after the intervention shortly before discharge (T1) in a paper-pencil questionnaire. RESULTS: Out of 78 participating inpatients 42 used the iFD tool at least once. Moderate to high levels of expectation regarding the iFD tool and mildly above-average level of satisfaction after the intervention were observed. Of the active users 67% indicated they would continue to use the iFD tool after discharge. The main reasons for not using the iFD tool were short duration of stay, severity of disease and lack of digital literacy. CONCLUSION: An implementation of the iFD tool is feasible on principle. Active users gave positive feedback concerning the intervention and most participants claimed to continue using the iFD tool after discharge; however, low usage rates among study participants (42/78, 54%) showed barriers of implementation that have to be addressed and underline the importance of adaptations regarding the use of the intervention in a clinical setting.

[Recommendations on performing polygraphy or polysomnography in the fields of psychiatry and psychotherapy : Position paper of the working group on sleep medicine of the German Association for Psychiatry, Psychotherapy and Psychosomatics]. / Empfehlungen zur Durchführung einer Polygraphie oder Polysomnographie im Bereich Psychiatrie und Psychotherapie : Positionspapier des DGPPN-Referats Schlafmedizin.

Difficulties in falling asleep and maintaining sleep, nonrestorative sleep and decreased daytime wakefulness represent very common but relatively unspecific health complaints. Around 100 specific sleep-related disorders will be classified in their own major chap. 7 (sleep wake disorders) for the first time in the upcoming 11th version of the International Classification of Diseases (ICD 11). With respect to the disciplines of psychiatry and psychotherapy there is a bidirectional relationship between mental health and sleep wake disorders. Sleep wake disorders can be an independent risk factor for the onset of a mental disorder and have a negative influence on the course of the disease. In addition, sleep wake disorders can also precede a mental disease as an early symptom and therefore be an important indication for early recognition. Many sleep wake disorders can be diagnosed based on the anamnesis and routine clinical investigations. In special cases, examination in a specialized sleep laboratory and treatment in a sleep medicine center following a staged care approach can be mandatory. Polysomnography represents the gold standard for the differential diagnostics; however, there is no legal foundation in the field of neuropsychiatric disorders for remuneration in the German healthcare system. This review summarizes the current guidelines with respect to the criteria for an investigation in a sleep laboratory from the perspective of the disciplines of psychiatry and psychotherapy. From this the requirements for guideline-conform diagnostics and treatment are derived.

Brain Arousal Regulation in Carriers of Bipolar Disorder Risk Alleles.

OBJECTIVES: Recent genome-wide association studies identified a number of chromosomal risk loci for bipolar disorder (BD, 'manic-depressive illness'). According to the vigilance regulation model, the regulation of brain arousal (referred to as 'vigilance') when assessed via EEG is an emerging biomarker linked to the pathogenesis of manic and depressive episodes. On this basis, the present study aimed to assess whether carriers of BD risk alleles differ in brain arousal regulation. METHODS: Healthy participants of the population-based Leipzig Health Care Study (LIFE) underwent a 20-min eyes-closed resting EEG paradigm. Brain arousal was assessed applying the computer-based Vigilance Algorithm Leipzig (VIGALL). The primary sample (n = 540) was genotyped for ten of the most reliable BD risk variants, of which two qualified for replication (n = 509). RESULTS: Primary sample analyses revealed Bonferroni-adjusted significance for rs1006737 in CACNA1C (encoding a calcium channel subunit), with risk allele carriers exhibiting relatively steep brain arousal declines. Further, carriers of two risk alleles of rs472913 at 1p32.1 showed generally lower brain arousal levels for the duration of the resting paradigm. However, both associations failed replication. CONCLUSION: Although our initial findings are in line with the vigilance regulation model and convincing in view of the previously reported notable role of ion channelopathies in BD, our results do not provide consistent evidence for a link between BD risk variants and brain arousal regulation. Several between-sample differences may account for this inconsistency. The molecular genetics of brain arousal regulation remain to be clarified.

No evidence of structural abnormality of the substantia nigra in adult attention-deficit/hyperactivity disorder: a pilot cross-sectional cohort study.

Background: Abnormal expansion of the echogenic substantia nigra (SN+) is a common observation in Parkinson's disease (PD) and considered a potential trait marker within this context. However, SN+ was also frequently detected in children diagnosed with attention-deficit/hyperactivity disorder (ADHD), where it has been discussed as a biomarker of maturational dopaminergic dysfunction. Interestingly, ADHD was recently linked to an elevated risk of PD in epidemiological studies, particularly among individuals treated with psychostimulants. Here, we investigated the potential of SN echogenicity as a disease biomarker in adults with ADHD and its relation to psychostimulant treatment. Methods: In an exploratory cross-sectional cohort study, we performed transcranial sonography of the SN in 30 adults (mean age 33.3 ± 7.6 years, 19 males/11 females) diagnosed with ADHD according to DSM-V criteria. Results and conclusions: In this pilot study, we observed no evidence of structural abnormalities of the SN among adults diagnosed with ADHD, thus questioning the potential of SN+ as a biomarker for ADHD in this population. Moreover, we found no evidence of treatment-related SN echogenicity changes that would link therapeutic psychostimulant use to alterations in the structural integrity of the SN.

Oral Health-Related Quality of Life in Adult Patients with Depression or Attention Deficit Hyperactivity Disorder (ADHD).

The aim of this cross-sectional study was the evaluation of the oral health-related quality of life (OHRQoL) in patients with depression or attention-deficit/hyperactivity disorder (ADHD) in comparison with a group of mentally healthy individuals. Patients from the Department of Psychiatry and Psychotherapy, University of Leipzig, Germany, were recruited. A healthy comparison group (HC) was recruited from the Department of Cariology, Endodontology and Periodontology. The OHRQoL was assessed using the Oral Health Impact Profile G14 (OHIP G14). Furthermore, a questionnaire regarding oral hygiene behaviour was applied. A total of 141 patients with depression or ADHD (depression n = 94, ADHD n = 47) and 145 HC individuals with a balanced age and gender distribution were surveyed. OHIP G14 median scores were significantly higher in the overall psychiatric patient group compared to HC (5.00 vs. 0.00, p < 0.001). This was also found for the four dimensions of OHIP G14 (p < 0.001). The OHIP G14 sum score of patients with depression and ADHD was comparable (5.00 vs. 6.50, p = 0.302). A significant association among psychiatric patients between smoking, gum bleeding, professional tooth cleaning, oral health education, interdental cleaning, and elevated OHIP scores was found (p < 0.001). In conclusion, patients with depression and adults with ADHD show a reduced OHRQoL. A contradictory association between oral hygiene/oral health behaviour and OHRQoL supports the hypothesis of a changed perception of oral conditions in patients with mental diseases. Interdisciplinary collaboration between psychiatric specialists and dentists should be fostered.

Event-related modulation of alpha rhythm explains the auditory P300-evoked response in EEG.

Evoked responses and oscillations represent two major electrophysiological phenomena in the human brain yet the link between them remains rather obscure. Here we show how most frequently studied EEG signals: the P300-evoked response and alpha oscillations (8-12 Hz) can be linked with the baseline-shift mechanism. This mechanism states that oscillations generate evoked responses if oscillations have a non-zero mean and their amplitude is modulated by the stimulus. Therefore, the following predictions should hold: (1) the temporal evolution of P300 and alpha amplitude is similar, (2) spatial localisations of the P300 and alpha amplitude modulation overlap, (3) oscillations are non-zero mean, (4) P300 and alpha amplitude correlate with cognitive scores in a similar fashion. To validate these predictions, we analysed the data set of elderly participants (N=2230, 60-82 years old), using (a) resting-state EEG recordings to quantify the mean of oscillations, (b) the event-related data, to extract parameters of P300 and alpha rhythm amplitude envelope. We showed that P300 is indeed linked to alpha rhythm, according to all four predictions. Our results provide an unifying view on the interdependency of evoked responses and neuronal oscillations and suggest that P300, at least partly, is generated by the modulation of alpha oscillations.

The impact of emotional dysregulation and comorbid depressive symptoms on clinical features, brain arousal, and treatment response in adults with ADHD.

Introduction: The role of emotional dysregulation (ED) in attention-deficit/hyperactivity disorder (ADHD) has become an important issue. This study, in which we analyzed data from a predictive pharmaco-EEG-trial, aimed to examine whether symptoms of ED in adult ADHD affect ADHD symptom severity, brain arousal regulation as measured by resting EEG, and the response to stimulant medication. Methods: ED is defined as having a sex- and age-corrected T-score of >70 on the emotional lability subscale of the German version of Conners' Adult ADHD Rating Scale. A total of 115 participants were included in the study, 56 of whom had ED. Participants with ED were more impaired in terms of the severity of core ADHD symptoms, especially inattentive symptoms, comorbid depressive symptoms, interpersonal relationships, and quality of life. In addition, participants with ED were more likely to report a total score above 13 on the Beck Depression Inventory-II, which was considered to be the cutoff for mild depression. Results: No differences were found between the ED and non-ED groups in response to stimulant medication or in brain arousal regulation. In addition, there was no significant effect of ED with comorbid depressive symptoms on treatment response. There was a trend for subgroups that showed a change in brain arousal regulation associated with symptom improvement. Discussion: Our findings may support the assumption that ED may be an important feature of ADHD. The use of EEG-based brain arousal regulation as a diagnostic and predictive tool in ADHD in the presence of ED and comorbid depressive symptoms should be further investigated.

Association between Individual Norepinephrine Transporter (NET) Availability and Response to Pharmacological Therapy in Adults with Attention-Deficit/Hyperactivity Disorder (ADHD).

BACKGROUND: The role of the norepinephrine transporter (NET) has received increased focus in recent studies on the pathogenesis of attention-deficit/hyperactivity disorder (ADHD). The predictive value for pharmacological treatment and its link to other health or social limitations has been little-studied. This follow-up research on adult patients with ADHD aimed to explore whether the therapy response and health and social impairments depend on baseline individual NET availability. METHODS: Data were collected from 10 patients on personal, family and professional situations, mental and physical health and treatments received after baseline via online and telephone surveys and were compared to baseline data to evaluate treatment-related changes. RESULTS: The majority of our ADHD patients did not show therapy responses but showed improvements due to pharmacological treatment. There was no evidence of relationships between pre-treatment NET availability and therapy response or health/social limitations. CONCLUSIONS: Pharmacological monotherapy was insufficient to promote symptom remission, especially for participants with extreme insufficiency in NET availability, but improved outcomes in academic and social functioning. Psychotherapy should be considered as an add-on to the standard treatment approach due to its positive outcome in reducing social limitations. The prognostic value of individual NET availability in predicting the response to therapy needs further studies with large sample sizes.

Restless Legs Syndrome Prevalence and Clinical Correlates Among Psychiatric Inpatients: A Multicenter Study.

Background: There are only limited reports on the prevalence of restless legs syndrome (RLS) in patients with psychiatric disorders. The present study aimed to evaluate the prevalence and clinical correlates in psychiatric inpatients in Germany and Switzerland. Methods: This is a multicenter cross-sectional study of psychiatric inpatients with an age above 18 years that were diagnosed and evaluated face-to-face using the International RLS Study Group criteria (IRLSSG) and the International RLS severity scale (IRLS). In addition to sociodemographic and biometric data, sleep quality and mood were assessed using the Pittsburgh Sleep Quality Index (PSQI), the Insomnia Severity Index (ISI), the Epworth Sleepiness Scale (ESS), and the Patient Health Questionnaire (PHQ-9). In addition to univariate statistics used to describe and statistically analyze differences in variables of interest between patients with and without RLS, a logistic model was employed to identify predictors for the occurrence of RLS. Results: The prevalence of RLS in a sample of 317 psychiatric inpatients was 16.4%, and 76.9% of these were diagnosed with RLS for the first time. RLS severity was moderate to severe (IRLS ± SD: 20.3 ± 8.4). The prevalences in women (p = 0.0036) and in first-degree relatives with RLS (p = 0.0108) as well as the body mass index (BMI, p = 0.0161) were significantly higher among patients with RLS, while alcohol consumption was significantly lower in the RLS group. With the exception of atypical antipsychotics, treatment with psychotropic drugs was not associated with RLS symptoms. Regarding subjective sleep quality and mood, scores of the PSQI (p = 0.0007), ISI (p = 0.0003), and ESS (p = 0.0005) were higher in patients with RLS, while PHQ-9 scores were not different. A logistic regression analysis identified gender (OR 2.67; 95% CI [1.25; 5.72]), first-degree relatives with RLS (OR 3.29; 95% CI [1.11; 9.73], ESS score (OR 1.09; 95% CI [1.01; 1.17]), and rare alcohol consumption (OR 0.45; 95% CI [0.22; 0.94] as predictors for RLS. Conclusions: Clinically significant RLS had a high prevalence in psychiatric patients. RLS was associated with higher BMI, impaired sleep quality, and lower alcohol consumption. A systematic assessment of restless legs symptoms might contribute to improve the treatment of psychiatric patients.

Efficacy of Augmentation of Cognitive Behavioral Therapy With Transcranial Direct Current Stimulation for Depression: A Randomized Clinical Trial.

Importance: Major depressive disorder (MDD) affects approximately 10% of the population globally. Approximately 20% to 30% of patients with MDD do not sufficiently respond to standard treatment. Therefore, there is a need to develop more effective treatment strategies. Objective: To investigate whether the efficacy of cognitive behavioral therapy (CBT) for the treatment of MDD can be enhanced by concurrent transcranial direct current stimulation (tDCS). Design, Setting, and Participants: The double-blind, placebo-controlled randomized clinical trial PsychotherapyPlus was conducted at 6 university hospitals across Germany. Enrollment took place between June 2, 2016, and March 10, 2020; follow-up was completed August 27, 2020. Adults aged 20 to 65 years with a single or recurrent depressive episode were eligible. They were either not receiving medication or were receiving a stable regimen of antidepressant medication (selective serotonin reuptake inhibitor and/or mirtazapine). A total of 148 women and men underwent randomization: 53 individuals were assigned to CBT alone (group 0), 48 to CBT plus tDCS (group 1), and 47 to CBT plus sham-tDCS (group 2). Interventions: Participants attended a 6-week group intervention comprising 12 sessions of CBT. If assigned, tDCS was applied simultaneously. Active tDCS included stimulation with an intensity of 2 mA for 30 minutes (anode over F3, cathode over F4). Main Outcomes and Measures: The primary outcome was the change in Montgomery-Åsberg Depression Rating Scale (MADRS) score from baseline to posttreatment in the intention-to-treat sample. Scores of 0 to 6 indicate no depression; 7 to 19, mild depression; 20 to 34, moderate depression; and 34 and higher, severe depression. Results: A total of 148 patients (89 women, 59 men; mean [SD] age, 41.1 [13.7] years; MADRS score at baseline, 23.0 [6.4]) were randomized. Of these, 126 patients (mean [SD] age, 41.5 [14.0] years; MADRS score at baseline, 23.0 [6.3]) completed the study. In each of the intervention groups, intervention was able to reduce MADRS scores by a mean of 6.5 points (95% CI, 3.82-9.14 points). The Cohen d value was -0.90 (95% CI, -1.43 to -0.50), indicating a significant effect over time. However, there was no significant effect of group and no significant interaction of group × time, indicating the estimated additive effects were not statistically significant. There were no severe adverse events throughout the whole trial, and there were no significant differences of self-reported adverse effects during and after stimulation between groups 1 and 2. Conclusions and Relevance: Based on MADRS score changes, this trial did not indicate superior efficacy of tDCS-enhanced CBT compared with 2 CBT control conditions. The study confirmed that concurrent group CBT and tDCS is safe and feasible. However, additional research on mechanisms of neuromodulation to complement CBT and other behavioral interventions is needed. Trial Registration: ClinicalTrials.gov Identifier: NCT02633449.

Depressive Symptom Clusters in Relation to Body Weight Status: Results From Two Large European Multicenter Studies.

Background: There is strong evidence for a bidirectional association between depression and obesity. Several biological, psychological, and behavior-related factors may influence this complex association. Clinical impression and preliminary evidence suggest that patients with a diagnosis of major depressive disorder may endorse very different depressive symptom patterns depending on their body weight status. Until now, little is known about potential differences in depressive symptoms in relation to body weight status. Objective: The aim of this analysis is the investigation of potential differences in depressive symptom clusters (mood symptoms, somatic/vegetative symptoms, and cognitive symptoms) in relation to body weight status. Methods: Cross-sectional baseline data were derived from two large European multicenter studies: the MooDFOOD Trial and the NESDA cohort study, including persons with overweight and obesity and normal weight reporting subthreshold depressive symptoms (assessment via Inventory of Depressive Symptomatology Self-Report, IDS-SR30). Different measures for body weight status [waist-to-hip ratio (WHR) and body mass index (BMI)] were examined. Propensity score matching was performed and multiple linear regression analyses were conducted. Results: A total of n = 504 individuals (73.0% women) were analyzed. Results show that more somatic/vegetative depressive symptoms, such as pain, change in appetite and weight, gastrointestinal symptoms, and arousal-related symptoms, were significantly associated with both a higher BMI and higher WHR, respectively. In addition, being male and older age were significantly associated with higher WHR. Mood and cognitive depressive symptoms did not yield significant associations for both body weight status measures. Conclusions: Somatic/vegetative symptoms and not mood and cognitive symptoms of depression are associated with body weight status. Thus, the results support previous findings of heterogeneous depressive symptoms in relation to body weight status. In addition to BMI, other body weight status measures for obesity should be taken into account in future studies. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT02529423.

Brain arousal regulation in adults with attention-deficit/hyperactivity disorder (ADHD).

The main aim of the current study was to test the hypothesis that adult patients with attention-deficit/hyperactivity disorder (ADHD) have less stable brain arousal regulation than healthy controls. We objectively assessed brain arousal regulation using the Vigilance Algorithm Leipzig (VIGALL 2.1) to analyze 15-min resting EEG data of thirty-three ADHD patients and thirty-five matched controls. Based on automatically classified 1-s segments we computed mean EEG-vigilance (indexing arousal level) and arousal stability score (indexing arousal regulation). Adult ADHD patients showed significantly lower arousal levels and significantly less stable brain arousal regulation than controls. Multiple regression analysis indicated that arousal regulation (i.e., arousal stability score) predicted the retrospectively-assessed severity of childhood ADHD symptoms, supporting the trait aspect of brain arousal regulation. Our findings support the arousal regulation model of ADHD, which interprets hyperactivity and sensation seeking as an autoregulatory reaction to an unstable regulation of brain arousal. EEG-based arousal parameters may be candidate biomarkers for adult ADHD.

Sleep disturbances and upregulation of brain arousal during daytime in depressed versus non-depressed elderly subjects.

OBJECTIVES: Although patients with depression often suffer from sleep disturbances, most of them are not sleepy. Upregulation of brain arousal has been proposed as pathophysiological mechanism explaining sleep disturbances, inner tension, autonomic hyperarousal and anhedonia in depression. The aim of the current study was to examine the association between night-time sleep disturbances and brain arousal regulation the next day in depressed versus non-depressed subjects. METHODS: Twenty-eight elderly subjects (21 female; age = 70.5 ± 4.4 years) with depressive syndromes without psychotropic medication, and 28 controls (22 female; age = 70.9 ± 4.5 years), underwent a 15-min resting electroencephalogram; the Vigilance Algorithm Leipzig (VIGALL 2.1) provided an objective measure of brain arousal regulation. Sleep disturbances were assessed by a validated and self-rated sleep questionnaire. RESULTS: In the depressive group, but not in controls, more sleep disturbances were associated with a higher brain arousal stability score (high score corresponds to upregulation) the next day (sleep onset latency: rs = 0.69, P < .0001; sleep quality: rs = -0.59, P < .001). CONCLUSIONS: The data confirm the hypothesis that in persons with depressive syndromes sleep disturbances are related to upregulation of brain arousal the next day. This finding is in line with the concept that dysregulation of brain arousal is a central pathophysiological aspect in depression.

Time to wake up: No impact of COMT Val158Met gene variation on circadian preferences, arousal regulation and sleep.

Dopamine has been implicated in the regulation of sleep-wake states and the circadian rhythm. However, there is no consensus on the impact of two established dopaminergic gene variants: the catechol-O-methyltransferase Val158Met (COMT Val158Met; rs4680) and the dopamine D4 receptor Exon III variable-number-of-tandem-repeat polymorphism (DRD4 VNTR). Pursuing a multi-method approach, we examined their potential effects on circadian preferences, arousal regulation and sleep. Subjects underwent a 7-day actigraphy assessment (SenseWear Pro3), a 20-minute resting EEG (analyzed using VIGALL 2.0) and a body mass index (BMI) assessment. Further, they completed the Morningness-Eveningness Questionnaire (MEQ), the Epworth Sleepiness Scale (ESS) and the Pittsburgh Sleep Quality Index (PSQI). The sample comprised 4625 subjects (19-82 years) genotyped for COMT Val158Met, and 689 elderly subjects (64-82 years) genotyped for DRD4 VNTR. The number of subjects varied across phenotypes. Power calculations revealed a minimum required phenotypic variance explained by genotype ranging between 0.5% and 1.5% for COMT Val158Met and between 3.3% and 6.0% for DRD4 VNTR. Analyses did not reveal significant genotype effects on MEQ, ESS, PSQI, BMI, actigraphy and EEG variables. Additionally, we found no compelling evidence in sex- and age-stratified subsamples. Few associations surpassed the threshold of nominal significance (p < .05), providing some indication for a link between DRD4 VNTR and daytime sleepiness. Taken together, in light of the statistical power obtained in the present study, our data particularly suggest no impact of the COMT Val158Met polymorphism on circadian preferences, arousal regulation and sleep. The suggestive link between DRD4 VNTR and daytime sleepiness, on the other hand, might be worth investigation in a sample enriched with younger adults.

Tobacco use is associated with reduced amplitude and intensity dependence of the cortical auditory evoked N1-P2 component.

RATIONALE: Tobacco use is linked to cerebral atrophy and reduced cognitive performance in later life. However, smoking-related long-term effects on brain function remain largely uncertain. Previous studies suggest that nicotine affects serotonergic signaling, and the intensity dependence (alias loudness dependence) of the auditory evoked N1-P2 potential has been proposed as a marker of serotonergic neurotransmission. OBJECTIVE: In the present study, we assesed the effects of chronic smoking on amplitude and intensity dependence of the auditory evoked N1-P2 potential. METHODS: Subjects underwent a 15-min intensity dependence of auditory evoked potentials (IAEP) paradigm. From N = 1739 eligible subjects (40-79 years), we systematically matched current smokers, ex-smokers, and never-smokers by sex, age, alcohol and caffeine consumption, and socioeconomic status. Between-group differences and potential dose-dependencies were evaluated. RESULTS: Analyses revealed higher N1-P2 amplitudes and intensity dependencies in never-smokers relative to ex- and current smokers, with ex-smokers exhibiting intermediate intensity dependencies. Moreover, we observed pack years and number of cigarettes consumed per day to be inversely correlated with amplitudes in current smokers. CONCLUSIONS: According to the IAEP serotonin hypothesis, our results suggest serotonin activity to be highest in current smokers, intermediate in ex-smokers, and lowest in never-smokers. To our knowledge, the present study is the first providing evidence for a dose-dependent reduction in N1-P2 amplitudes. Further, we extend prior research by showing reduced amplitudes and intensity dependencies in ex-smokers even 25 years, on average, after cessation. While we can rule out several smoking-related confounders to bias observed associations, causal inferences remain to be established by future longitudinal studies.