Auditory evoked potentials in the assessment of central nervous system effects of antimigraine drugs

Evaluation and Proposal for Optimization of Neurophysiological Tests In Migraine: Part 2—Neuroimaging and The Nitroglycerin Test

Neuroimaging methods have been widely used in headache and migraine research. They have provided invaluable information on brain perfusion, metabolism and structure during and outside of migraine attacks, contributing to an improved understanding of the pathophysiology of the disorder. Human models of migraine attacks are indispensable tools in pathophysiological and therapeutic research. This review of neuroimaging methods and the attack-provoking nitroglycerin test is part an initiative by a task force within the EUROHEAD project (EU Strep LSHM-CT-2004-5044837-Workpackage 9) with the objective of critically evaluating neurophysiological tests used in migraine. The first part, presented in a companion paper, is devoted to electrophysiological methods, this second part to neuroimaging methods such as functional magnetic resonance imaging, positron emission tomography and voxel-based morphometry, as well as the nitroglycerin test. For each of these methods, we summarize the results, analyse the methodological limitations and propose recommendations for improved methodology and standardization of research protocols.

Enhanced intensity dependence as a marker of low serotonergic neurotransmission in high optimistic college students

Positive psychology focuses were on the merits of individuals, such as optimism and positive attitude, and the subsequent cultivation of these virtues. Optimism or pessimism is a significant predictor of physical health outcomes. The present study examined whether optimism or pessimism is associated with the loudness dependence of auditory evoked potentials (LDAEP), a biological indicator of serotonergic neurotransmission, for the N1, P2, and N1/P2 peaks in college students. The amplitudes and amplitude-stimulus intensity function (ASF) slopes of the N1, P2, and N1/P2 peaks were determined in the 24 (10 males) high optimistic and 24 (14 males) high pessimistic individuals. Significantly higher P2 ASF slopes were found in the optimistic group relative to the pessimistic group. Concerning peaks and ASF slopes of N1 and N1/P2, no significant differences were observed. Our results suggest that the serotonergic neurotransmission of the high optimistic college students was inferior to that of the pessimistic ones. Further investigations are needed to provide sufficient support for our results.

Effects of Rizatriptan on the Contingent Negative Variation in Healthy Women

The effect of the antimigraine drug rizatriptan on the amplitude and habituation of the contingent negative variation (CNV) in healthy women was examined in a randomized, double-blind, placebo-controlled trial. The test persons were assigned either to a drug ( n = 20) or a placebo group ( n = 20). The CNV was recorded three times: before, directly after, and 24 h after drug or placebo intake. The CNV paradigm was presented in a standard, a cued and a choice version. Rizatriptan led to an increase of CNV amplitude that depended on the level of difficulty of the task. Whereas there was no drug effect in the standard version, an amplitude increase was obtained mainly in the choice task. The results are in line with the ceiling theory of migraine, which assumes a rise of CNV amplitude if the serotonin level is lowered.

Association of 5-HT1B receptor polymorphisms with the loudness dependence of auditory evoked potentials in a community-based sample of healthy volunteers

The terminal autoreceptor 5-HT1B is centrally involved in the regulation of the brain serotonergic system and in several psychiatric disorders including depression, addiction, and obsessive-compulsive disorder. The loudness dependence of the auditory evoked N1/P2-component (LDAEP; primary auditory cortex) is currently considered as one of best-validated indicators of serotonergic neurotransmission, especially for synaptically released serotonin. Since the 5-HT1B receptor is involved in the release of serotonin at terminal endings of cortical neurons, this study addressed the question whether single nucleotide polymorphism (SNP) in the gene coding for this receptor (HTR1B) are related to LDAEP of the primary auditory cortex (tangential dipole) investigating a community-based sample of 127 healthy subjects randomly selected from the general population. In this carefully recruited sample, a G-G haplotype (rs1213368-rs6296) and the respective G-alleles were found to be related to a strong LDAEP response of the left tangential dipole, indicating low serotonergic activity. Apart from the fact that this is the first study which relates HTR1B SNPs to a measure of serotonergic function, it can be speculated that LDAEP may reflect parts of the release mechanism of serotonin at cortical synapses, although the lateralized finding cannot be entirely explained. Carriers of the G-alleles may be characterized by a particularly strong feedback inhibition of serotonin release at cortical terminals in the primary auditory cortex, possibly mediated by higher sensitivity of 5-HT1B receptors associated with low serotonergic activity.

Reliability of intensity dependence of auditory-evoked potentials

OBJECTIVE

Intensity dependence of auditory-evoked potentials (IAEP) is a suggested indicator of serotonergic neurotransmission. In contrast to its clinical renaissance, the reliability of IAEP has only been examined in a few studies, most of which are limited due to the possibly confounding effects of age and gender. Therefore, the present study examines different reliabilities of various IAEP parameterizations while controlling for age and gender.

METHODS

Auditory-evoked potentials were recorded from 166 students. Of these 37 women and 25 men were retested after three weeks.

RESULTS

Test-retest and odd-even reliabilities were remarkable at Cz in both females (r=.88/.86) and males (r=.82/.79). Reliabilities were higher in women, higher with linear than median slopes and best at Cz. Bisection of sweep number, split-half reliability, the second run, and lower intensities revealed lower reliabilities.

CONCLUSIONS

Reliabilities at Cz can reach the same level as previously reported by dipole-source-localization methods, if sufficient sweep number and linear slopes are applied.

SIGNIFICANCE

Based on theoretical arguments and current data, the continued use of the easy and rapidly done single-channel IAEP is suggested, although ideally in combination with multi-channel source-localization methods. This would be seminal for a drafted program standardizing IAEP to further improve its clinical utility.

Evaluation and proposal for optimalization of neurophysiological tests in migraine: part 1--electrophysiological tests

Neurophysiological testing has become a valuable tool for investigating brain excitability and nociceptive systems in headache disorders. Previous reviews have suggested that most neurophysiological tests have limited value for headache diagnosis, but a vast potential for exploring the pathophysiology of headaches, the central effects of certain pharmacological treatments and phenotype-genotype correlations. Many protocols, however, lack standardization. This meta-analytical review of neurophysiological methods in migraine was initiated by a task force within the EUROHEAD project (EU Strep LSHM-CT-2004-5044837-Workpackage 9). Most of the neurophysiological approaches that have been used in headache patients are reviewed, i.e. evoked potentials, nociception-specific blink reflex, single-fibre electromyography, neuroimaging methods (functional MRI, PET, and voxel-based morphometry) and the nitroglycerin attack-provoking test. For each of them, we summarize the results, analyse the methodological limitations and propose recommendations for improved methodology and standardization of research protocols. The first part is devoted to electrophysiological methods, the second to neuroimaging techniques and the NTG test.

An electrophysiological endophenotype of hypomanic and hyperthymic personality

BACKGROUND

Hyperthymic Temperament (HYT) and a closely related trait, Hypomanic Personality (HYP), have both been related to bipolar affective disorder (BAD). Intensity dependence of auditory evoked potentials (IAEP) is a suggested inverse indicator of serotonergic neurotransmission and has been found to be elevated in BAD. Therefore the present study explored for the first time whether subclinical variance of HYT/HYP is also associated with IAEP in a healthy sample. As several traits from biological personality research are correlated with HYT/HYP and also with BAD, the specificity of results against these traits was further analyzed by calculating multiple regression analyses.

METHODS

Evoked potentials were recorded from a sample (N=87) homogenous for confounding variables influencing IAEP. For this reason, only 19 to 27-year-old non-smoker psychiatrically healthy male students were included.

RESULTS

Significant correlations were found between IAEP and both HYP and HYT. Including Sensation or Novelty Seeking and Extraversion in Regression Analyses did not weaken the associations of HYP with IAEP much, but did affect those of HYT. However, these competing biological personality traits were hardly able to predict IAEP themselves. Impulsivity, though, was able to reduce the predictive power of HYP and HYT and to explain unique IAEP-variance. This was even more the case for Behavioral-Activation-System-Sensitivity (BAS) subscale Fun Seeking clearly dominating all regression analyses.

LIMITATIONS

Homogeneity of sample.

CONCLUSIONS

The impact of BAS is in agreement with the assumption that heightened BAS-sensitivity is an underlying biological cause for HYP/HYT and for BAD. Future studies on BAD should include BAS and Impulsivity besides HYP/HYT to further explore uniqueness of the latter and to develop questionnaires based on those items of a hyperthymic-hypomanic-impulsive-funseeking item pool, which possess the most external validity.

Prediction of clinical response to antidepressants in patients with depression: neurophysiology in clinical practice

Brain monoaminergic neurotransmission is involved in the pathophysiology of various psychiatric disorders including depression. Reliable indicators of central monoaminergic activity might be helpful to specifically identify and differentiate dysfunctions in individual patients in order to selectively adjust medication and predict clinical response. In patients with depression, predictors of treatment response to serotonergic versus non-serotonergic (e.g., noradrenergic) antidepressants could be of considerable clinical relevance by avoiding unfavorable factors such as a prolonged duration of the disorder, risk of suicidality and therapy-resistance. Consequently, these tools might help to decrease direct and indirect costs of treatment. The loudness dependence of the N1/P2 component of auditory evoked potentials (LD) has been proposed as a noninvasive neurophysiological indicator of central serotonergic function. This review focuses on recent studies providing evidence for the validity of LD as an indirect serotonergic marker and highlights data on the clinical application in terms of prediction of treatment response in patients with depression.

Further evidence for an association of 5-HTTLPR with intensity dependence of auditory-evoked potentials

Intensity dependence of auditory-evoked potentials (IAEP) has been suggested as an indicator of central serotonergic neurotransmission. Two recent studies investigated a possible association of IAEP with a functional polymorphism in the transcriptional control region of the serotonin transporter gene (5-HTTLPR) that has a short (s) and a long (l) variant. Although both studies found an association between 5-HTTLPR and IAEP, Gallinat et al found l/l individuals to exhibit lower IAEP, whereas Strobel et al observed stronger IAEP in l/l individuals. These conflicting results require further evaluation and more attention needs to be paid to variables that are known to be confounded with the effects of IAEP and 5-HTTLPR. Using a paradigm comparable to Strobel et al, the present study analyzes the effect of 5-HTTLPR on IAEP in a healthy male student sample (N=91; age=23 years, SD=1.9) that was homogenous for most significant confounding variables. A stronger IAEP was shown in l/l individuals, irrespective of the method of IAEP parametrization. This also held at retest after 3 weeks in a subsample (N=18). Given the successful replication of Strobel et al, several possible reasons for conflicting results with regard to Gallinat et al are discussed. It is argued that the most significant difference between Gallinat et al on the one hand, and Strobel et al and this study on the other, is that different intensity ranges are used which impact IAEP. Therefore, this study encourages further analysis of dose dependence of results.

Physiological Parameters as Biomarkers of Migraine

We review physical signs and measurements from neurophysiological research, which may be considered biomarkers of migraine. Most studies show that information processing is abnormal in migraineurs. Studies of trigeminal nociception are in line with a central sensitization during the attack. The best documented abnormality is an interictal lack of habituation in migraineurs, with a normalization during the headache state, which has been shown using evoked and event-related potentials. Together with a diminished energy reserve found in MR-spectroscopy studies, these results suggest a possible role of increased energy consumption in attack generation. Importantly, to date, no neurophysiological marker has a high enough sensitivity and specificity to point out the single migraine patient. Therefore, these biomarkers are to be understood as tools for research and are not to be used for diagnostic purposes.

Event related potentials and fMRI in neuropsychopharmacology

Event related potentials (ERP) are important clinical and research instruments in neuropsychiatry, particularly due to their strategic role for the investigation of brain function. These techniques are often underutilized in the evaluation of neurological and psychiatric disorders, but nevertheless they can be most useful and highly effective in the diagnostic workup of a wide range of neuropsychiatric disorders as well as in monitoring the course of the disorders and the prediction of treatment responses. ERP are noninvasive instruments that directly reflect cortical neuronal activity. Cortical neuronal dysfunction plays a major role in variable neuropsychiatric disorders, and a change in cortical activity under medication might reflect treatment response and could be useful for monitoring drug effects. ERP are the only methods with a sufficiently high time resolution for the analysis of the dynamic patterns of neuronal brain activity, e.g., synchronization and desynchronization, oscillations, coherence, gamma band activity, latency of event related activity, etc., which are crucial for a deeper understanding of functional (neurophysiological) correlates of cognitive, emotional and behavioral disturbances in neuropsychiatric patients. Methodological advances have further improved and strengthened the position of ERP concerning research and clinical application. The usefulness and applicability of ERP in determining and monitoring clinico-pharmacological effects will be summarized mainly by focussing on the auditory evoked P300 and the N1/P2 component of auditory evoked potentials. Owing to important recent developments in the field of brain functional diagnostics the combination of neurophysiological techniques and functional magnetic resonance imaging (fMRI) will be included.

Preclinical neuropharmacology of naratriptan

The basic CNS neuropharmacology of naratriptan is reviewed here. Naratriptan is a second-generation triptan antimigraine drug, developed at a time when CNS activity was thought not to be relevant to its therapeutic effect in migraine. It was, however, developed to be a more lipid-soluble, more readily absorbed and less readily metabolized variant on preexisting triptans and these variations conferred on it a higher CNS profile. Naratriptan is a 5-HT(1B/1D) receptor agonist with a highly selective action on migraine pain and nausea, without significant effect on other pain or even other trigeminal pain. Probable sites of therapeutic action of naratriptan include any or all of: the cranial vasculature; the peripheral terminations of trigeminovascular sensory nerves; the first-order synapses of the trigeminovascular sensory system; the descending pain control system; and the nuclei of the thalamus. Naratriptan may prevent painful dilatation of intracranial vessels or reverse such painful dilatation. Naratriptan can prevent the release of sensory peptides and inhibit painful neurogenic vasodilatation of intracranial blood vessels. At the first order synapse of the trigeminal sensory system, naratriptan can selectively suppress neurotransmission from sensory fibers from dural and vascular tissue, while sparing transmission from other trigeminal fibers, probably through inhibition of neuropeptide transmitter release. In the periaqueductal gray matter and in the nucleus raphe magnus, naratriptan selectively activates inhibitory neurons which project to the trigeminal nucleus and spinal cord and which exert inhibitory influences on trigeminovascular sensory input. Naratriptan has also a therapeutic effect on the nausea of migraine, possibly exerting its action at the level of the nucleus tractus solitarius via the same mechanisms by which it inhibits trigeminovascular nociceptive input. The incidence of naratriptan-induced adverse effects in the CNS is low and it is not an analgesic for pain other than that of vascular headache. In patients receiving selective serotonin uptake inhibitors (SSRIs) naratriptan may cause serotonin syndrome-like behavioral side effects. The mechanism of action involved in the production of behavioral and other CNS side effects of naratriptan is unknown.

Impact of Antimigraine Compounds on Cognitive Processing: A Placebo‐Controlled Crossover Study

OBJECTIVE

To evaluate potential cognitive impairment caused by acute antimigraine drugs.

METHODS

We conducted a placebo-controlled, double-blind, crossover study to detect the short-term impact of sumatriptan, zolmitriptan, and ergotamine tartrate on cognitive processing as measured by event-related potentials and a d2 test. Sixteen healthy subjects were enrolled in the study and given placebo, sumatriptan 100 mg, zolmitriptan 2.5 mg, and ergotamine tartrate 2 mg on different days and in random order. Before and 2 hours after drug administration, visually evoked event-related potentials and a d2 test were measured.

RESULTS

The N2 latency was significantly increased after ergotamine intake. No other significant differences could be observed in all other event-related potential parameters. In the d2 test, the GZ value was unchanged after ingestion of zolmitriptan and ergotamine, but improved significantly after taking placebo and sumatriptan. The number of relative errors and the concentration value did not change significantly. All results fell within the reference values for the d2 test in all examinations.

CONCLUSION

Our data suggest that there may be a slight cognitive decline 2 hours after ingestion of ergotamine tartrate and, to an even lesser extent, zolmitriptan, but not after ingestion of sumatriptan or placebo. All changes recorded were very mild and unlikely to be clinically relevant.

Electrophysiological studies in migraine: a comprehensive review of their interest and limitations

Electrophysiological methods may help to unravel some of the pathophysiological mechanisms of migraine. Lack of habituation is the principal and most reproducible interictal abnormality in sensory processing in migraineurs. It is found in evoked potential (EP) studies for every stimulation modality including nociceptive stimuli, and it is likely to be responsible for the increased intensity dependence of EP. We have hypothesized that deficient EP habituation in migraine could be due to a reduced preactivation level of sensory cortices because of hypofunctioning subcortico-cortical aminergic pathways. This is not in keeping with simple hyperexcitability of the cortex, which has been suggested by some, but not all, studies of transcranial magnetic stimulation (TMS). A recent study of the effects of repetitive TMS on visual EP strongly supports the hypothesis that migraine is characterized by interictal cortical hypoexcitability. With regard to pain mechanisms in migraine, electrophysiological studies of trigeminal pathways using nociceptive blink and corneal reflexes have confirmed that sensitization of central trigeminal nociceptors occurs during migraine attacks.

Evoked potentials and transcranial magnetic stimulation in migraine: published data and viewpoint on their pathophysiologic significance

Migraine is a disorder in which central nervous sytem dysfunction might play a pivotal role. Electroneurophysiology seems thus particularly suited to study its pathophysiology. We have extensively reviewed evoked potential and transcranial magnetic stimulation studies performed in migraineurs in order to identify their pathophysiologic significance. Publications available to us were completed by a Medline search. Retrieved and personal data were compared with respect to methodology and interpreted according to present knowledge on cortical information processing. Results are in part contradictory which appears to be method-, patient- and disease- related. Nonetheless, both evoked potential and transcranial magnetic stimulation studies demonstrate that the cerebral cortex, and possibly subcortical structures, are dysfunctioning interictally in both migraine with and without aura. These electrophysiologic abnormalities tend to normalise just before and during an attack and some of them seem to have a clear familial and predisposing character. Besides the studies of magnetophosphenes which have yielded contrasting results, chiefly because the method is not sufficiently reliable, most recent electrophysiologic investigations of cortical activities in migraine favour deficient habituation and decreased preactivation cortical excitability as the predominant interictal dysfunctions. We propose that the former is a consequence of the latter and that it could favour both interictal cognitive disturbances as well as a cerebral metabolic disequilibrium that may play a role in migraine pathogenesis. To summarize, electrophysiologic studies demonstrate in migraine between attacks a cortical, and possibly subcortical, dysfunction of which the hallmark is deficient habituation.

The electrophysiology of migraine

Migraine is currently regarded as a neurovascular disorder of trigeminal sensory processing, generated centrally, probably at the level of the brainstem. In the past, electrophysiological techniques have drawn no definite conclusions on either interictal or ictal changes in migraineurs compared with controls, largely because of methodological differences. Recently, two findings have been shown consistently: an interictal increasing lack of habituation of evoked potentials with a normalization at the start of the attack and strong intensity dependence of auditory evoked potentials. These findings substantiate migraine sufferers as having an abnormal trait interictally, with the attack characterized by a change in the state of central processing. Exploitation of these differences may be a useful tool to study the mechanism of action of drugs used for the treatment of migraine.

Visual, long-latency auditory and brainstem auditory evoked potentials in migraine: relation to pattern size, stimulus intensity, sound and light discomfort thresholds and pre-attack state

We aimed to estimate primary sensory evoked potential (EP) amplitude, amplitude-intensity functions and habituation in migraine patients compared with healthy control subjects and to investigate the possible relation to check size, sound and light discomfort thresholds, and the time to the next attack. Amplitudes of cortical visual evoked potentials (VEP, check size 8' and 33'), cortical long latency auditory evoked potential (AEP NIP1; 40, 55 and 70 dB SL tones) and brainstem auditory evoked potential (BAEP wave IV-V; 40, 55 and 65 dB SL clicks) were recorded and analysed in a blind and balanced design. The difference between the response to the first and the second half of the stimulus sequence was used as a measure of habituation. Twenty-one migraine patients (16 women and five men, mean age 39.3 years, six with aura, 15 without aura) and 22 sex- and age-matched healthy control subjects were studied (18 women and four men, mean age 39.5 years). Low sound discomfort threshold correlated significantly with low levels of BAEP wave IV-V amplitude habituation (r = -0.30, P = 0.05). VEP an AEP amplitudes, habituation, and amplitude-intensity function (ASF) slopes did not differ between groups when ANOVA main factors were considered. Control group VEP habituation was found for small check stimuli (P = 0.04), while potentiation was observed for medium sized checks (P = 0.02). The eight migraine patients who experienced headache within 24 h after the test tended to have increased BAEP wave IV-V ASF slopes (P = 0.08). This subgroup did also have a significant VEP habituation to small checks (P = 0.04). No correlation was found between different modalities. These results suggest that: (i) VEP habituation/potentiation state and brainstem activatio state may depend on the attack-interval cycle in migraine; (ii) VEP habituation/ potentiation may depend on spatial stimulus frequency; (iii) phonophobia (and possibly photophobia) may depend more on subcortical (brainstem) function than on cortical mechanisms; (iv) low cortical preactivation in migraine could not be confirmed; (v) EP habituation and ASF analysis may reflect sensory modality-specific, not generalized, central nervous system states in migraine and healthy control subjects.

Repeatability of the intensity dependence of cortical auditory evoked potentials in the assessment of cortical information processing

Data on repeatability and optimal settings are needed when studying the influence of drugs on the intensity dependence of auditory evoked cortical potentials (IDAP). IDAP was recorded at intervals of 1, 2, and 24 h at two centers in 22 healthy volunteers. Settings were modified to compare fixed versus randomly varied stimulus repetition rate, as well as 30 Hz and 100 Hz low pass filters. Repeatability was assessed for different intervals and different settings. Group means did not differ between centers, the 2-h or 24-h retest, or when using different settings. We observed an order effect for the 1 h retest. Fixed repetition rate and the 30 Hz filter improved repeatability with still high intraindividual variability. IDAP group means can be compared between centers for retest intervals of 2 h and 24 h and different settings. Variability is too large to compare individuals.