ERP augmenting/reducing and sensation seeking: a critical review

Electrocortical correlates of hypersensitivity to large immediate rewards in sensation seeking

Sensation seeking and delay discounting are strong predictors of various risk-taking behaviors. However, the relationship between sensation seeking and delay discounting remains elusive. Here, we addressed this issue by examining how high sensation seekers (HSS; N = 40) and low sensation seekers (LSS; N = 40) evaluated immediate and delayed rewards with low and high amounts during a behavioral task and an EEG task of delay discounting. Although HSS and LSS exhibited comparable discounting preference at the behavioral level, HSS relative to LSS was associated with a greater delay discounting effect at the neural level when earned rewards were large. This abnormality of reward magnitude was further corroborated by an electrocortical hypersensitivity to large immediate rewards and a stronger neural coding of reward magnitude for HSS as compared to LSS. Our findings support both the hyperactive approach theory and the optimal arousal theory in sensation seeking and have implications for the prevention and intervention targeting sensation seeking to reduce maladaptive risk-taking behaviors.

Endogenous evoked potentials assessment in depression: a review

Over the past 15 years, researchers have shown an increasing interest in using event-related potentials (ERPs) to study depression. These studies generally fall into four classes: 1), ERPs as a means of detecting depression; 2), ERPs as a tool for distinguishing subtypes of depression; 3), ERPs as a measure of pharmacological effectiveness; 4), ERPs as indicators of defective cognitive operations in depressed subjects. Results from these heterogeneous approaches are often inconsistent and disappointing. Although some ERP components often show increased latencies and diminished amplitudes, these changes seem to reflect principally a variety of non-specific disorders affecting a wide range of cognitive functions rather than a precise and consistent deficit of a particular function. These disappointing results seem to be attributable to methodological problems (heterogeneous patient populations, disproportionate use of the odd-ball paradigm), and do not necessarily call into question the value of studying the ERPs. Furthermore, recent advances in ERP methodology have opened up new perspectives for ERP use in psychopathology.

Trait impulsivity and increased pre-attentional sensitivity to intense stimuli in bipolar disorder and controls

Impulsivity and sensation seeking are stimulus-oriented traits. Because they differ in degree of intention and planning, they may have distinct neurophysiological mechanisms. Impulsivity is prominent in bipolar disorder, and may be related to pre-attentional information filtering and stimulus-orientation. We investigated specificity of relationships between impulsivity and sensitivity to stimulus intensity in bipolar disorder and controls, using intensity-sensitivity of auditory evoked potentials. Seventy-six subjects (37 healthy controls, 39 with bipolar disorder) were administered an intensity-sensitivity paradigm. Additional measures included Barratt Impulsiveness Scale (BIS-11) and Eysenck Impulsivity and Venturesomeness scores. State-dependent rapid-response impulsivity was measured using the Immediate Memory Task. Intensity-sensitivities of the auditory evoked P1N1, N1P2, P1, N1, and P2 potentials were assessed as the slope of amplitude relative to loudness. Analyses used general linear models (GLM) with impulsivity-related measures as dependent variables and age, gender, education, and diagnosis as dependent variables. BIS-11 total, motor, and attentional impulsivity scores correlated positively with pre-attentional N1 and P1N1 intensity-sensitivity slopes in bipolar disorder, but not in controls. BIS-11 nonplanning and Eysenck Venturesomeness scores did not correlate with intensity-sensitivity. Intensity-sensitivity slopes did not correlate with rapid-response impulsivity. Correlations between N1 or P1N1 slopes and BIS-11 scores in bipolar disorder were not affected by age, education, WAIS, treatment, symptoms, or gender. Trait impulsivity in bipolar disorder may be related to poorly modulated stimulus-driven late pre-attentional responses to stimuli, potentially resulting in exaggerated responses to intense stimuli even before conscious awareness. Components of trait impulsivity are physiologically heterogenous relative to intensity-sensitivity.

More potential in statistical analyses of event-related potentials: a mixed regression approach

Despite many developments in the methods of event-related potentials (ERPs), little attention has gone out to the statistical handling of ERP data. Trials are often averaged, and univariate or repeated measures of analysis of variance (ANOVA) are used to test hypotheses. The aim of this study was to introduce mixed regression to ERP research and to demonstrate advantages associated with this method. Eighty-five healthy subjects received electrical pain stimuli with simultaneous electroencephalography (EEG) registration. Analyses first showed that results obtained with mixed regression analyses are highly comparable to those using repeated measures of ANOVA. Second, important advantages of the mixed regression technique were demonstrated by allowing the inclusion of persons with missing data, single trial analysis, non-linear time effects, time×person effects (random slope effects) and a within-subject covariate. Among others, the results showed a strong trial (habituation) effect, which contraindicates the common procedure of averaging of trials. Furthermore, the regression coefficients for intensity and trial varied significantly between persons, indicating individual differences in the effect of intensity and trial on the ERP amplitude. In conclusion, using mixed regression analysis as a statistical technique in ERP research will advance the science of unravelling mechanisms underlying ERP data.

Mechanisms of impulsivity in bipolar disorder and related illness

Aims – Impulsivity is a multifaceted aspect of behavior that is prominent in psychiatric disorders and has serious behavioral consequences. This paper reviews studies integrating behavioral and physiological mechanisms in impulsivity and their role in severity and course of bipolar and related disorders. Methods – This is a review of work that used questionnaire, human behavioral laboratory, and neurophysiological measurements of impulsivity or related aspects of behavior. Subjects included individuals with bipolar disorder, substance-use disorders, antisocial personality disorder, and healthy controls. Results – Models of impulsivity include rapid-response impulsivity, with inability to reflect or to evaluate a stimulus adequately before responding, and reward-based impulsivity, with inability to delay response for a reward. In normal subjects, rapid-response impulsivity is increased by yohimbine, which increases norepinephrine release. Impulsivity is increased in bipolar disorder, whether measured by questionnaire, by measures of rapid-response impulsivity, or by measures of ability to delay reward. While affective state has differential effects on impulsivity, impulsivity is increased in bipolar disorder regardless of affective state or treatment. Impulsivity, especially rapid-response, is more severe with a highly recurrent course of illness or with comorbid substance-use disorder, and with history of medically severe suicide attempt. In antisocial personality disorder, rapid-response impulsivity is increased, but rewardbased impulsivity is not. In general, impulsivity is increased more in bipolar disorder than in antisocial personality disorder. In combined bipolar disorder and antisocial personality disorder, increased impulsivity is associated with substance-use disorders and suicide attempts. Conclusions – Impulsivity is associated with severe behavioral complications of bipolar disorder, antisocial personality disorder, and substance-use disorders.

The genetic influence on the cortical processing of experimental pain and the moderating effect of pain status

BACKGROUND

Research suggests that the COMT Val(158)Met, BDNF Val(66)Met and OPRM1 A(118)G polymorphisms moderate the experience of pain. In order to obtain experimental confirmation and extension of findings, cortical processing of experimentally-induced pain was used.

METHOD

A sample of 78 individuals with chronic low back pain complaints and 37 healthy controls underwent EEG registration. Event-Related Potentials were measured in response to electrical nociceptive stimuli and moderation by COMT Val(158)Met, BDNF Val(66)Met and OPRM1 A(118)G polymorphisms was assessed.

RESULTS

Genetic variation did not have a direct effect on cortical processing of experimental pain. However, genetic effects (COMT Val(158)Met and BDNF Val(66)Met) on experimental pain were moderated by the presence of chronic pain. In the presence of chronic pain, the COMT Met allele and the BDNF Met allele augmented cortical pain processing, whilst reducing pain processing in pain-free controls. No significant effects were found concerning the OPRM1 A(118)G polymorphism.

CONCLUSIONS

The current study suggests that chronic experience of pain enhances genetic sensitivity to experimentally induced mildly painful stimuli, possibly through a process of epigenetic modification.

Serotonergic neurotransmission in early Parkinson's disease: a pilot study to assess implications for depression in this disorder

OBJECTIVES

Depression, a disease usually accompanied by a serotonergic deficit, has been observed in about 40% of patients suffering from Parkinson's disease (PD). Thus, a serotonergic dysfunction in PD can be assumed. We aimed to investigate the interaction between serotonergic (5-HT) and dopaminergic activity in early PD. We hypothesized a serotonergic as well as a dopaminergic deficit in PD patients. We also assumed a correlation between these neurotransmitters indicating a relationship between dopaminergic and serotonergic function in PD.

METHODS

Nine unmedicated PD patients before and 12 weeks after L-dopa treatment and nine healthy subjects were examined using the loudness dependence of auditory evoked potentials (LDAEP), a promising indicator of central serotonergic function. Dopaminergic transporters (DAT) were collected using (123)I-FP-CIT and single photon emission computer tomography (SPECT). LDAEP values were correlated with (123)I-FP-CIT SPECT data.

RESULTS

A significant difference between LDAEP of controls and patients (P= 0.05) suggested lower serotonergic activity in PD. Twelve weeks after initiation of L-dopa treatment this difference was lost between patients and controls (P= 0.20). There was a trend towards a correlation between LDAEP and DAT (r= 0.65; P = 0.057) of the unmedicated patients, suggesting a low serotonergic activity may be related to a dopamine deficit in PD.

CONCLUSIONS

Our results support the hypothesis that serotonergic neurotransmission is decreased in untreated PD and suggest that a low serotonergic activity may be related to the dopamine pathology in PD. This could be related to the high prevalence of depression in PD.

Effects of stimuli intensity and frequency on auditory p50 and n100 sensory gating

Sensory gating is the brain's ability to adjust its sensitivity to incoming stimuli, i.e., to diminish its response to irrelevant or repetitive stimuli (gating out) and to increase it when a novel stimulus is presented (gating in). Most of the existing studies have investigated the gating out mechanism, giving little attention to the gating in function. Although both the P50 and N100 components of the auditory ERPs (event related potentials) show amplitude reductions to stimuli repetition, it is not clear if both components are part of a common gating system or if their sensory modulation is uncorrelated. In order to respond to these questions and to further characterize the sensory gating functions, we examined to what extent P50 and N100 are influenced by changes in the stimuli parameters and whether the sensory modulation of both components are interrelated. To this end, we obtained ERPs from 23 healthy volunteers using pairs of auditory stimuli which could be identical (S1 = S2), different in frequency (S1 = 1000 Hz; S2 = 2000 Hz) or different in intensity (S1 = 80 dB SPL; S2 = 100 dB SPL). As expected, the amplitudes of P50 and N100 decreased in response to the second stimuli of the identical pairs. With non-identical pairs, amplitude increases of P50 and N100 were observed only in pairs with different intensity, but not frequency. Thus, the results showed that both P50 and N100 are sensory modulated, showing that amplitude decreased to stimuli repetition (gating out) and increased when the two stimuli of a pair differed in intensity (gating in). A correlational analysis of the sensory gating indices (S2/S1 ratio and S1-S2 difference) obtained for P50 and N100 suggested that the sensory gating function of both components may be of a different nature. The reliability of the ratio and the difference indices of sensory gating is also discussed.

The loudness dependence of the auditory evoked potential (LDAEP) as an in vivo biomarker of central serotonergic function in humans: rationale, evaluation and review of findings

OBJECTIVES

The loudness dependence of the auditory evoked potential (LDAEP) has been proposed as a valid means of non-invasively assessing in vivo central serotonin (5-hydroxytryptamine, 5-HT) function in humans. The specificity and sensitivity of the LDAEP to changes in 5-HT neurotransmission have recently been explored directly in a number of pharmacological and genetic studies. Subsequently, this review was undertaken in an attempt to critically evaluate the potential role of the LDAEP as a marker of the central 5-HT function.

DESIGN

Findings from clinical, experimental animal and human studies examining the relationship between the LDAEP and the 5-HT system as well as other neurochemical systems including dopaminergic, glutamatergic and the cholinergic systems were reviewed.

RESULTS

The majority of evidence for an association between the LDAEP and 5-HT has come from animal studies. Indirect studies in clinical disorders of presumed serotonergic dysfunction have been circumstantial and inconsistent with more recent investigations utilising direct genetic association studies also providing conflicting reports. Pharmacological studies in humans provide overwhelming evidence that the LDAEP is insensitive to acute changes in 5-HT function, with additional evidence outlining sensitivity to other neurotransmitter systems including the glutamatergic system.

CONCLUSIONS

The available evidence suggests that the LDAEP lacks sensitivity and specificity to acute changes in serotonergic neurotransmission. Overall the findings do not provide strong support for its utility as a marker of central 5-HT function. However the LDAEP shows more promise as a potential predictor of antidepressant treatment response and this predictive ability may provide the basis for future research involving the LDAEP.

Neural correlates of stopping and self-reported impulsivity

OBJECTIVE

To examine the relation between self-reported impulsivity, inhibitory control, and the neural correlates of stopping performance within the normal population.

METHODS

Healthy individuals scoring high and low on trait impulsivity performed an auditory stop-signal task. Stopping performance and neural correlates of stopping (i.e. N1 and stop P3) were compared between the impulsive groups as well as between participants who were slow and fast in stopping.

RESULTS

As expected, N1 and stop P3 were larger for successful relative to failed stops (i.e. N1 and stop P3 effects). Participants scoring high relative to low on impulsivity showed equal stopping performance, had larger stop P3, but similar N1 effects. Slow as compared to fast stoppers had reduced stop P3, but similar N1 effects.

CONCLUSIONS

Participants scoring high relative to low on impulsivity may need more effortful inhibitory control to yield equal stopping performance. Slow relative to fast stoppers may have weaker inhibition processes and abnormal error processing. In contrast to ADHD, both high impulsives as well as slow stoppers had an intact N1 effect.

SIGNIFICANCE

Subjective impulsivity and slow stopping in healthy individuals cannot be generalized to ADHD.

Individual Differences in Auditory, Pain, and Motor Stimulation

Abstract. Augmenting/reducing is a personality dimension related to the processing of sensory stimuli. Augmenters are assumed to augment the impact of stimuli leading to stimulation-avoidant behavior and lower pain tolerance. Reducers are assumed to attenuate sensory stimuli leading to stimulation-seeking behavior and higher pain tolerance. Augmenting/reducing can be assessed by the method of evoked potentials or - as in this study - by questionnaire. Two studies were conducted to examine associations between augmenting/reducing as assessed by questionnaire and stimulus intensity modulation. Study 1 found reducers (n = 24, 12 females) to more frequently consume psychoactive substances and to turn music on louder than augmenters (n = 25, 12 females) even after controlling for individual hearing ability. In Study 2, reducers (n = 19, 10 females) were more pain tolerant than augmenters (n = 18, 9 females) and this difference increased with increasing stimulation time. Moreover, reducers were faster than augmenters in a rapid tapping task but there was no difference in a lower-stimulation tracking task. The results suggest that differences between augmenters and reducers are most reliable when the stimulation potential is high. The clinical relevance of this construct is discussed.

Neuroticism-Anxiety, Impulsive-Sensation Seeking and autonomic responses to somatosensory stimuli

This study focused on autonomic responding in participants who scored high vs. low on the Neuroticism-Anxiety (N-Anx) and Impulsive-Sensation Seeking (Imp-SS) dimensions of the Zuckerman-Kuhlman Personality Questionnaire--Form III. Participants were presented with series of tones (standards, deviants and novels) and they received a mild electric shock (one, two or three pulses) at each 15th tone. Resting pre-stimulus skin conductance level (SCL) and heart rate (HR) level was recorded, as well as the skin conductance response (SCR) and (anticipatory) HR response to the electric stimuli. The autonomic measures differentiated between high- vs. low Imp-SS participants but failed to discriminate between high- vs. low N-Anx participants, with the exception that high N-Anx participants showed smaller SCRs on some trials compared to the low N-Anx participants. High Imp-SS had a lower pre-stimulus SCL and smaller SCRs to deviant stimuli compared to low Imp-SS participants. Additionally, their HR acceleration was smaller in anticipation of the first and the deviant tones whereas their deceleratory response was larger relative to the HR changes observed for the low Imp-SS participants. This pattern of findings was taken to suggest that high Imp-SS participants are more arousable and less prone to defensive reactions to novel or aversive stimulation.

Event-related potentials in psychiatry

Electrophysiological assessments of psychiatric disorders have produced a number of promising, highly replicable findings and thus carry the potential of becoming clinically utilizable in the diagnostic or prognostic evaluation of psychopathological conditions. The procedures involved are rather complex technically and the interpretation of the findings require a combined neurophysiological and clinical expertise. On the other hand, electrophysiological techniques are in general non-invasive and relatively inexpensive, and neurophysiology laboratories are widely available in the clinical setting. Among these techniques, event-related potentials (ERPs) are of major interest in psychiatry, particularly since these tools can indicate cortical neuronal dysfunctions, which play a major role in various neuropsychiatric disorders.

Intensity dependence of auditory evoked dipole source activity in polydrug ecstasy users: evidence from an 18 months longitudinal study

Numerous animal studies have been able to demonstrate neurotoxic damage to central serotonergic systems after exposure to 3,4-methylenedioxymethamphetamine (MDMA, ecstasy). It has been suggested that a high loudness dependence of auditory evoked potentials (LDAEP) and, particularly, of the tangential N1/P2 source activity is associated with a low functioning of serotonergic activity. Therefore, the LDAEP may be used as a non-invasive indicator for a possible neurotoxic damage caused by the long-term use of ecstasy in recreational users. We recorded auditory evoked potentials (AEP) with a passive listening paradigm in 18 polydrug ecstasy users at baseline (t1) and after 18 months (t2). Several aspects of ecstasy use, such as frequency of use, cumulative lifetime dose or period of abstinence were associated with the LDAEP for several tangential dipoles at both measuring times. However, we failed to demonstrate any significant relationship between drug use reported at follow-up and AEP changes from baseline to follow-up. Despite some incertitude these data suggest, yet do not unambiguously con.rm, the hypothesis that abstinent ecstasy users present with diminished central serotonergic activity. This feature of information processing is potentially related to the neurotoxic potential of ecstasy. However, alternative interpretations of these data refer to possible preexisting traits and the potential impact of other illicit drugs, particularly amphetamine, since ecstasy users typically exhibit polydrug use patterns. Thus, further research with larger sample sizes and prospective study designs are needed to definitively establish a causative link between ecstasy use and neurotoxicity-related dysfunctions in sensory processing.

Neurotoxicity of methylenedioxyamphetamines (MDMA; ecstasy) in humans: how strong is the evidence for persistent brain damage?

BACKGROUND

The popular dance drug ecstasy (3,4-methylenedioxymethamphetamine: MDMA and some analogues) causes selective and persistent neurotoxic damage of central serotonergic neurones in laboratory animals. Serotonin plays a role in numerous functional systems in the central nervous system (CNS). Consequently, various abnormalities including psychiatric, vegetative, neuroendocrine and cognitive disorders could be expected in humans following MDMA-induced neurotoxic brain damage.

AIMS

In recent years, the question of ecstasy-induced neurotoxicity and possible functional sequelae has been addressed in several studies with drug users. The aim of this paper was to review this literature and weigh the strength of the evidence for persistent brain damage in ecstasy users.

METHODS

We used Medline to view all available publications on 'ecstasy' or 'MDMA'. All available studies dealing with ecstasy users entered this analysis.

FINDINGS AND CONCLUSIONS

Despite large methodological problems the bulk of evidence suggests residual alterations of serotonergic transmission in MDMA users, although at least partial restitution may occur after long-term abstinence. However, functional sequelae may persist even after longer periods of abstinence. To date, the most consistent findings associate subtle cognitive, particularly memory, impairments with heavy ecstasy use. However, the evidence cannot be considered definite and the issues of possible pre-existing traits or the effects of polydrug use are not resolved.

RECOMMENDATIONS

Questions about the neurotoxic effects of ecstasy on the brain remain highly topical in light of its popularity among young people. More longitudinal and prospective studies are clearly needed in order to obtain a better understanding of the possible long-term sequelae of ecstasy use in humans.

Cerebral information processing in personality disorders: I. Intensity dependence of auditory evoked potentials

Patients with personality disorders such as the histrionic type exaggerate their responses when receiving external social or environmental stimuli. We speculated that they might also show an augmenting pattern of the auditory evoked potential N1-P2 component in response to stimuli with increasing levels of intensity, a response pattern that is thought to be inversely correlated with cerebral serotonin (5-HT) activity. To test this hypothesis, we collected auditory evoked potentials in 191 patients with personality disorders (19 patients with the paranoid type, 12 schizoid, 14 schizotypal, 18 antisocial, 15 borderline, 13 histrionic, 17 narcissistic, 25 avoidant, 30 dependent and 28 obsessive-compulsive) and 26 healthy volunteers. Their personality traits were measured using the Dimensional Assessment of Personality Pathology-Basic Questionnaire (DAPP-BQ). Compared with healthy subjects and other patient groups, the histrionic group scored higher on the basic traits Affective Instability, Stimulus Seeking, Rejection and Narcissism, and on the higher traits Emotional Dysregulation and Dissocial, than the other groups, and the schizoid group scored lower on most of the DAPP-BQ basic and higher traits. In addition, the histrionic group showed steeper amplitude/stimulus intensity function (ASF) slopes at three midline scalp electrodes than the healthy controls or the other patient groups. The ASF slopes were not correlated with any DAPP-BQ traits in the total sample of 217 subjects. However, the DAPP-BQ basic trait Rejection was positively correlated with the ASF slopes at all three electrode sites in the histrionic group. The increased intensity dependence of the auditory N1-P2 component might indicate that cerebral 5-HT neuronal activity is, on average, weak in the histrionic patients.

Electrophysiological substrates of impulsiveness: potential effects on aggressive behavior

Previous investigations attempting to examine impulsiveness as a personality construct are likely confounded with a high incidence of aggressive and antisocial behavior. The present study assessed electroencephalographic activity at rest and during photic stimulation in two groups: (1) an impulsive group (n=10) scoring high on the Barratt Impulsiveness Scale (BIS-11) and reporting no indication of impulsive aggressive behavior; and (2) a non-aggressive control group (n=14) scoring within the normal range on the BIS-11. All subjects completed a brief battery of personality measures related to impulsivity and aggression. Resting EEG was recorded at 9 electrode sites. Photic stimulation was administered at three frequency levels. The primary findings were consistently lower frontal delta and theta activity in the impulsive group as well as a different topographical pattern of beta activity between the groups. These differences appeared to be independent of photic stimulation. Personality analyses indicated significantly greater hostility and lifetime history of aggression in the impulsive group. Taken together, the personality and EEG results suggest some similarity between the present impulsive group and research on groups regularly exhibiting premeditated aggression. These results provide unique insight into the construct of impulsivity and its role in the expression of specific subtypes of aggressive behavior.

Is auditory evoked potential augmenting/reducing affected by acute tryptophan depletion?

Several lines of evidence suggest that the auditory evoked potential (AEP) augmenting/reducing slope may serve as a biological marker of central serotonergic activity. According to Hegerl and Juckel (Biol. Psychiatry, 33, 1993, 173), reduced serotonergic activity is hypothesized to increase the slope of the AEP amplitude stimulus intensity function (ASF-slope). Hints for this hypothesis were investigated by employing the acute tryptophan depletion paradigm in 18 healthy females. A within-subject, placebo controlled double-blind cross over design was used for that purpose. Subjects ingested both a 50 g amino-acid drink with (placebo condition) and without tryptophan (depletion condition). With respect to the N1/P2-slope, test-retest reliability of a 1 week interval ranged between r=0.56 and 0.58 for the pre-ingestion baseline recording sessions. Affect was not altered by tryptophan depletion and not related to the ASF-slope. The comparison between placebo and depletion conditions did not reveal significant alterations of the ASF-slope, neither after 5 nor 6 h post-ingestion. Thus, the results do not support the assumption of the ASF-slope reflecting central serotonergic function.

Electrophysiological indication for a link between serotonergic neurotransmission and personality in alcoholism

The serotonergic neurotransmission seems to be involved in the neuropsychobiology of alcoholism. The intensity dependence of the N1/P2 component of auditory-evoked potentials is discussed as an indicator of the central serotonergic neurotransmission in healthy subjects. The aim of this study was to verify this correlation between intensity dependence and serotonergic neurotransmission, as indicated by the personality trait "harm avoidance" (HA) within the Temperament and Character Inventory (TCI) in alcohol-dependent patients. The intensity dependence was measured in 25 alcohol-dependent patients, 10 and 40 days after detoxification. The personality trait HA was assessed, which is supposed to reflect the serotonergic neurotransmission. The intensity dependence was negatively correlated with the temperament trait HA of the TCI (r = - .55, P<.01) at Day 40, but neither on Day 10 nor with the other personality dimensions. We conclude, that the intensity dependence reflects the serotonergic neurotransmission in withdrawn alcohol-dependent patients.

Event-related potentials. Do they reflect central serotonergic neurotransmission and do they predict clinical response to serotonin agonists?

The increasing knowledge concerning anatomical structures and cellular processes underlying event-related potentials (ERP) as well as methodological advances in ERP data analysis (e.g. dipole source analysis) begin to bridge the gap between ERP and neurochemical aspects. Reliable indicators of the serotonin system are urgently needed because of its role in pathophysiology and as target of pharmacotherapeutic interventions in psychiatric disorders. Converging arguments from preclinical and clinical studies support the hypothesis that the loudness dependence of the auditory evoked N1/P2-response (LDAEP) is regulated by the level of central serotonergic neurotransmission. Dipole source analysis represents an important methodological advance in this context, because the two N1/P2-subcomponents, generated by the primary and secondary auditory cortex known to be differentially innervated by serotonergic fibers, can be separated. A pronounced LDAEP of primary auditory cortices is supposed to reflect low central serotonergic neurotransmission, and vice versa. LDAEP is a parameter with potential clinical value since subgroups of patients with a serotonergic dysfunction can be identified and can be treated more specifically. In depressed patients, a significant relationship between strong LDAEP, indicating low serotonergic function, and a favorable response to SSRI has been found. Additionally, there is evidence from several studies with patients with affective disorders implicating a strong LDAEP as a predictor of favorable response to a preventive lithium treatment.

On the Reliability of Augmenting/Reducing

Abstract To investigate the impact of several methodological variations in the assessment of augmenting/reducing, auditory evoked potentials to 1000 Hz tones with varying stimulus intensity (59, 71, 79, 88, 92, 96 dB (SPL)) were recorded at 19 EEG sites in 24 participants during two separate recording sessions. The internal consistency analysis revealed only weak correlations for linear regression slopes based on high intensity levels when compared to slopes based on low intensity levels. For base-to-peak and peak-to-peak ERP component measurements, acceptable internal consistency and temporal stability were confirmed for the N1/P2-based slope, and partly for the P2 slope, whereas P1, N1, and P1/N1 slopes were not reliable. After submitting auditory evoked potentials to a covariance-based principal component analysis (PCA), followed by unscaled varimax rotation, temporal stability of slope measures for the corresponding factor scores substantially increased. The findings suggest that at least five to six intensity-levels are required over a relatively broad range to yield a reliable measure of auditory evoked augmenting/reducing. If measured reliably, P2 slopes may reflect stimulus intensity changes more precisely than N1/P2 slopes, and should therefore be evaluated in future studies of individual differences in augmenting/reducing.

Identifying psychiatric patients with serotonergic dysfunctions by event-related potentials

The increasing knowledge concerning anatomical structures and cellular processes underlying event-related potentials (ERP) as well as methodological advances in ERP data analysis (e.g. dipole source analysis) is beginning to bridge the gap between ERP and neurochemical aspects. Reliable indicators of the serotonin system are urgently needed because of its role in pathophysiology and as target of pharmacotherapeutic interventions in psychiatric disorders. Converging arguments from preclinical and clinical studies support the hypothesis that the loudness dependence of the auditory evoked N1/P2-response (LDAEP) is regulated by the level of central serotonergic neurotransmission. Dipole source analysis represents an important methodological advance in this context, because the two N1/P2-subcomponents, generated by the primary and secondary auditory cortex known to be differentially innervated by serotonergic fibres, can be separated. A pronounced LDAEP of primary auditory cortices is supposed to reflect low central serotonergic neurotransmission, and vice versa. LDAEP is a parameter with potential clinical value since subgroups of patients with a serotonergic dysfunction can be identified and can be treated more specifically. In depressed patients, a significant relationship between strong LDAEP, indicating low serotonergic function, and a favourable response to SSRI has been found. Additionally, there is evidence from several studies with patients with affective disorders that a strong LDAEP predicts favourable response to a preventive lithium treatment.

Intensity dependence of auditory evoked cortical potentials in migraine families

Intensity dependence of auditory evoked cortical potentials is abnormal in migraine. This study investigated intensity dependence in migraine and healthy families using group comparisons and analysis of individual differences. Migraineurs were characterized by a steeper amplitude/stimulus function slope and more pronounced difference between the amplitudes of N1-P2 on the more and the less intensive tones than healthy age matched subjects. Apart from migraine, the age of the participants was an important predictive variable of intensity dependence. Analysis of individual differences revealed low sensitivity and moderate specificity of intensity dependence for migraine. Familial prevalence of intensity dependence among first-degree relatives in migraine families was equal to that in healthy families. These findings support the assumption that high-intensity dependence reflects a functional CNS trait which is more pronounced and prevalent in migraine, but may also be found in healthy individuals and in other neuropsychiatric disorders. Increased intensity dependence is only one of several factors contributing to the risk for this form of headache.

Augmenter vs. Reducer: Kortikale und autonome Reaktivität auf Reize unterschiedlicher Intensität

Zusammenfassung: Ziel dieser Studie war es, Unterschiede zwischen anhand der Reducer-Augmenter Skala als extrem eingestuften Augmentern (N = 19, Petrie Reducer) und Reducern in elektrokortikalen (EEG), peripher-physiologischen (EDA, EKG) und subjektiven Reaktionen (EMI) auf weißes Rauschen (65 bis 105 dB; ISI 15-25s) sowie in einer Reaktionszeitaufgabe zu prüfen. In der P1-N1-Amplitude unterschieden sich die Gruppen nicht. Entgegen der Erwartung reagierten die Reducer (Petrie Augmenter) in den N1-P2-Amplituden, der Hautleitfähigkeit und tendenziell auch der Herzrate stärker als die Augmenter. Reducer gaben an, nervöser und weniger optimistisch zu sein als die Augmenter. Die Geräusche beurteilten sie als lauter. In der Reaktionszeitaufgabe wiesen sie längere Reaktionszeiten auf als die Augmenter. Die Ergebnisse sprechen für eine generell erhöhte Reaktivität der Reducer (Petrie-Augmenter) und stehen damit in Übereinstimmung mit der ursprünglichen Konzeption von Augmenting-Reducing nach Petrie .

Effects of intensity and order of stimuli presentation on AEPs: an analysis of the consistency of EP augmenting/reducing in the auditory modality

OBJECTIVES

(1) To achieve a better understanding of the intensity dependence function of AEPs recorded at fronto-central and temporal electrode sites; (2) To assess the possible influence of the order of stimuli presentation on this function; and (3) To investigate if a subject's AEPs augmenting or reducing (A/R) tendency is consistent throughout two intra-session runs.

METHODS

Two sequences of 288 stimuli of different intensities (60, 80, 90 and 110 dB SPL) were delivered to 29 psychology students. In the first run, stimuli were presented in 4 consecutive blocks of 72 tones of each intensity, either in an ascendant (from lowest to loudest stimuli) or descendent (from loudest to lowest) way. In the second run, a pseudo-randomized sequence of stimuli of the 4 intensities was presented.

RESULTS

(1) AEPs recorded at fronto-central electrodes showed a stronger intensity dependence than those recorded at temporal leads; (2) The delivery of tones of different intensities in an aleatory sequence provoked higher amplitudes at Fz and Cz - especially for the loudest tones - but not at temporal leads; (3) The individual's AEP responses to stimuli of increasing intensity are highly consistent throughout two intra-session runs.

CONCLUSIONS

The different findings obtained for the fronto-central N1P2 and the T complex in relation to the effect of intensity and order of stimuli presentation may be explained in terms of the cortical origin of those components. The higher amplitudes found with an aleatory sequence, especially for the highest intensity stimuli, may reflect that these stimuli capture the subject's attention and provoke an enhancement of the N1 component. The implications of the present results for investigation into A/R and the clinical relevance of this phenomenon are discussed.

Intensity dependence of auditory evoked potentials in behaving cats

The intensity dependence of auditory evoked potentials (AEPs) recorded epidurally over the primary (AI) and secondary (AII) areas of the auditory cortex was studied in behaving cats during wakefulness, sleep and anesthesia. Four kHz tones of 50, 60, 70, and 80 dB SPL, presented in random order every 2 +/- 0.2 s by a bone conductor, elicited clear changes of the AEP amplitudes with increasing stimulus intensity, but individual components displayed different response curves. AEP components from the AI region showed saturation of their amplitude with stimulus intensity (P13, P34) or no amplitude increase (N19), while amplitude and intensity were linearly related in the AII area. The intensity dependence of the first positive component (P12/P13) was consistently stronger for the AEP recorded from the AI than from the AII area, while later components exhibited no difference between AI and AII. During slow wave sleep, the intensity dependence of this first positive component increased in the two areas, while that of later components decreased. Pentobarbital anesthesia abolished almost all later components and depressed the intensity dependence of the first positive component both in the AI and AII area. These results indicate that (I) clear intensity dependence of AEP exists in the cat auditory cortex and (2) this intensity dependence, especially that of the first positive AEP component, shares functional similarities to the human augmenting/reducing phenomenon in the auditory modality concerning regional differences and sleep-waking cycle.

Serotonergic ethanol effects and auditory evoked dipole activity in alcoholic and healthy subjects

Ethanol has central serotonergic effects that may be of pathogenetic importance in a subgroup of alcohol-dependent patients with a central serotonergic hypofunction. Recent results indicate that pronounced amplitude increases of auditory evoked responses (tangential dipoles, N1/P2 component) with increasing stimulus intensity (loudness) may be an indicator of such a low serotonergic neurotransmission. Because of its serotonin-agonistic effects, ethanol can be expected to decrease this intensity dependence. Twenty-eight alcoholic patients were studied both in the intoxication phase and after 1 week of withdrawal. A reduced intensity dependence of the tangential dipole activity was observed in the intoxicated state. Correspondingly, a reduction of this parameter was found in 14 healthy subjects after an ethanol load (1 g/kg, p.o.).

Psychobiology of novelty seeking and drug seeking behavior

There is considerable evidence that high novelty seekers are at increased risk for using drugs of abuse relative to low novelty seekers. This review examines the potential biological mechanism that may help explain the relationship between novelty seeking and drug seeking behavior. Evidence is summarized to suggest that exposure to novelty activates, at least in part, the same neural substrate that mediates the rewarding effects of drugs of abuse. It is argued that individual differences in response to novelty and drugs may relate to individual differences in the mesolimbic dopamine (DA) system of the brain. Individual differences in both novelty seeking and drug seeking behavior, while under some degree of genetic control, appear to be modifiable by early development experiences and this modification may relate to alterations in activity of the mesolimbic DA system. Within the context of this biological formulation, implications for the prevention and treatment of drug abuse are discussed.

Auditory event-related potentials while ignoring tone stimuli: attentional differences reflected in stimulus intensity and latency responses in low and highly hypnotizable persons

Effect of hypnotic susceptibility level on auditory event-related potentials (AERPs) was studied as subjects were instructed to ignore tones while reading a novel or counting one's pulse. Assessed previously on two hypnotic susceptibility scales [Harvard Group Scale of Hypnotic Susceptibility; Stanford Hypnotic Susceptibility Scale, Form C (SHSSC)], subjects were 12 low (lows; SHSSC 0-2) and 12 highly (highs; SHSSC 9-12) hypnotizable, right-handed college students. AERPs were recorded at C3, C4, and Cz to 50 ms 1.961 tone pips 50, 60, 70 and 80 dB intensities, pseudorandomly presented at 1.5 intervals. As predicted, highs had significantly smaller N1 and P2 amplitudes than did lows when ignoring tones. As stimuli intensities increased, N1 latencies decreased for lows while N1 latencies increased for highs. N1 latency slopes across the 50 to 80 dB intensities were significantly more negative for lows than highs; slopes correlated significantly with both hypnotizability and absorption (Tellegen Absorption Scale). Thus, the highs appeared to divert greater attentional processing to the tasks at hand, particularly as the tones increased in intensity, and were slower to respond to not-to-be-attended stimuli. These results are interpreted as further evidence for hypnotic susceptibility being associated with efficient attentional processing such that highs can more effectively partition attention towards relevant stimuli and away from irrelevant stimuli than can low hypnotizables.

Sensory cortical processing and the biological basis of personality

Action-oriented personality traits such as sensation seeking, extraversion, and impulsivity have been related to a pronounced amplitude increase of auditory evoked scalp potentials with increasing stimulus intensity. Dipole source analysis represents a crucial methodological progress in this context, because overlapping subcomponents of the scalp potentials can be separated and can be related to their generating cortical structures. In a study on 40 healthy subjects, it was found that sensation seeking is clearly related to the auditory evoked response pattern (N1/P2-component, stimulus intensities: 60, 70, 80, 90, 100 dB SPL) of the superior temporal plane including primary auditory cortex, but not to that of secondary auditory areas in the lateral temporal cortex. These results support the concept that the serotonergic brain system, which is supposed to modulate sensory processing in primary auditory cortices, is an important factor underlying individual differences in sensation seeking.

The Tridimensional Personality Questionnaire and the intensity dependence of auditory evoked dipole source activity

The relationship between the tridimensional personality questionnaire's (TPQ) dimensions "novelty seeking," "harm avoidance," and "reward dependence" and the intensity dependence of the auditory evoked N1/P2-component was investigated in healthy subjects. Using dipole source analysis, evoked activity of the primary auditory cortex (tangential dipole) could be analyzed at least in part separately from that of secondary auditory areas (radial dipole). It was found that the intensity dependence of the tangential dipole was positively correlated to the TPQ dimension "novelty seeking," but not to "harm avoidance" and "reward dependence." This is in line with findings concerning similar personality traits like "sensation seeking," "impulsivity," or "extraversion." It is therefore concluded that a strong intensity dependence may characterize subjects with an action-oriented and extroverted personality style. The results are discussed within the concept that a low central serotonergic neurotransmission is underlying both an impulsive personality type and a strong intensity dependence of the tangential dipole.

Antisocial tendencies and cortical sensory-evoked responses in alcoholism

Alcohol-dependent patients with antisocial, aggressive, and impulsive behaviors form a subgroup, in which a dysfunction of the brain serotonin system is discussed as a pathogenetic factor. Early onset and a transmission from fathers to sons (type II alcoholism; Cloninger, 1987) are supposedly further characteristics of this subgroup. The response pattern of primary auditory cortices to auditory stimuli with different intensities is discussed as a noninvasive indicator of the level of central serotonergic neurotransmission. A strong intensity dependence of these responses is supposed to indicate low serotonergic neurotransmission and vice versa. A strong intensity dependence is therefore expected to characterize patients with antisocial tendencies. Auditory-evoked potentials (N1/P2 component) to stimuli in five different intensities were recorded in 53 hospitalized patients after 1 week of withdrawal. Dipole source analysis was performed to separate responses of primary and secondary auditory cortices. Patients with antisocial tendencies showed a significantly stronger intensity dependence of their evoked responses of primary auditory cortices (tangential dipoles). Age at onset and family history were not related to the intensity dependence of the evoked responses. The results support the notion that alcohol-dependent patients with strong intensity dependence and antisocial tendencies form a subgroup with a serotonergic hypofunction. These patients may respond favorably to a relapse prevention with serotonergic drugs.

Intensity dependence of auditory evoked dipole source activity

The spatio-temporal approach of dipole source analysis represents a crucial methodological progress in research on individual differences in the dependence of auditory evoked potential amplitude on stimulus intensity (augmenting/reducing) because overlapping subcomponents of the N1/P2-component can be separated and can be related to their generating cortical structures. Basic aspects of the intensity dependence of auditory evoked dipole source activity were analysed in 40 healthy subjects. The evoked responses to binaural 1000-Hz tones at five levels of intensity (60, 70, 80, 90, 100 dB sound pressure level) were recorded at 33 sites across the scalp. The dipole source analysis of the grand average data confirms the reports in the literature that the N1/P2 potentials at the scalp can be explained by two dipoles per hemisphere: a tangential dipole, representing activity of the superior temporal cortex (including primary auditory cortex), and a radial dipole, representing activity of the lateral temporal cortex (secondary auditory areas). The intensity dependence of the tangential dipole activity was significantly more pronounced than that of the radial dipoles, supporting the assumption that radial and tangential dipoles represent different physiological processes. A high reliability of the intensity dependence of the tangential dipole (Pearson correlation: r = 0.88) was found when retesting the subjects after three weeks. Age was negatively correlated with the intensity dependence of the tangential dipole. Dipole source analysis proved to be a reliable method which allows, at least in part, to study separately the intensity dependence of the evoked responses from primary and secondary auditory cortices. This is of importance with regard to the hypothesis that the central serotonergic system modulates the intensity dependence of the evoked N1/P2-response of primary auditory cortex.

Intensity dependence of auditory evoked potentials as an indicator of central serotonergic neurotransmission: a new hypothesis

Because of the increasing importance of the central serotonergic neurotransmission for pathogenetic concepts and its role as a target of pharmacotherapeutic interventions in psychiatry, reliable indicators of this system are needed. It is proposed that the stimulus intensity dependence of auditory evoked N1/P2-component, which is probably modulated by cortical serotonergic innervation, may be a useful and noninvasive indicator of behaviorally relevant aspects of serotonergic activity. Converging evidence from our own studies as well as from the literature suggests that a pronounced intensity dependence of auditory evoked N1/P2-component reflects low central serotonergic neurotransmission. Recent findings concerning general functional aspects of the brain serotonin system reveal that this system is well qualified for adjusting individual levels of sensory processing ("set the tone"), especially in the primary auditory cortex in which the N1/P2-component is mainly generated. Dipole source analysis represents an important methodological advance in this context because it allows the separation of N1/P2-subcomponents generated in the primary auditory cortex from those generated in secondary auditory areas.