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

Phonophobia and brainstem excitability in migraine

Phonophobia in migraineurs may be due to lower hearing threshold (HT) and higher brainstem neuronal excitability. We report the correlation of phonophobia in migraineurs with HT, brain stem auditory evoked potential (BAEP) findings, and auditory triggers. Sixty-one migraineurs and 101 controls were included for HT, of whom 59 migraineurs and 31 controls had BAEP studies. Clinical details, migraine triggers, and headache frequency were noted. Hearing threshold was measured, and amplitudes of waves I to V of BAEP studies were measured. Migraineurs had lower HT compared with controls (41.61 ± 5.25 versus 45.39 ± 6.26 dB; p < 0.001) especially in chronic migraine (40.24 ± 4.81; p < 0.001). Hearing threshold correlated with headache frequency (p < 0.05) and auditory, visual, and tactile (p < 0.05) triggers. Hearing threshold was lower during headache (p < 0.001). Wave II, III, and IV amplitudes of BAEP were higher in migraineurs than the controls. Wave II (p < 0.05) and III (p < 0.05) amplitudes correlated with HT. Migraineurs have lower HT, especially in those having chronic migraine, ictal HT recording, and multiple sensory triggers. Higher amplitudes of BAEP waves in migraineurs and their relationship with the frequency of headache and HT suggest the sensitization of brainstem auditory neurons.

Electrically Evoked Auditory Event-Related Responses in Patients with Auditory Brainstem Implants: Morphological Characteristics, Test-Retest Reliability, Effects of Stimulation Level, and Association with Auditory Detection

OBJECTIVE

This study aimed to (1) characterize morphological characteristics of the electrically evoked cortical auditory event-related potentials (eERPs) and explore the potential association between onset eERP morphology and auditory versus nonauditory stimulation; (2) assess test-retest reliability of onset eERPs; (3) investigate effects of stimulation level on onset eERPs; and (4) explore the feasibility of using the onset eERP to estimate the lowest stimulation level that can be detected for individual stimulating electrodes in patients with auditory brainstem implants (ABIs).

DESIGN

Study participants included 5 children (S1 to S5) and 2 adults (S6 to S7) with unilateral Cochlear Nucleus 24M ABIs. Pediatric ABI recipients ranged in age from 2.6 to 10.2 years (mean: 5.2 years) at the time of testing. S6 and S7 were 21.2 and 24.6 years of age at the time of testing, respectively. S6 and S7 were diagnosed with neurofibromatosis II (NF2) and implanted with an ABI after a surgical removal of the tumors. All pediatric subjects received ABIs after being diagnosed with cochlear nerve deficiency. The lowest stimulation level that could be detected (behavioral T level) and the estimated maximum comfortable level (C level) was measured for individual electrodes using clinical procedures. For electrophysiological measures, the stimulus was a 100-msec biphasic pulse train that was delivered to individual electrodes in a monopolar-coupled stimulation mode at stimulation levels ranging from subthreshold to C levels. Electrophysiological recordings of the onset eERP were obtained in all subjects. For studies evaluating the test-retest reliability of the onset eERP, responses were measured using the same set of parameters in two test sessions. The time interval between test sessions ranged from 2 to 6 months. The lowest stimulation level that could evoke the onset eERP was defined as the objective T level.

RESULTS

Onset eERPs were recorded in all subjects tested in this study. Inter- and intrasubject variations in morphological characteristics of onset eERPs were observed. Onset eERPs with complex waveforms were recorded for electrodes that evoked nonauditory sensations, based on feedback from subjects, as well as for electrodes without any indications of nonauditory stimulations. Onset eERPs in patients with ABIs demonstrated good test-retest reliability. Increasing stimulation levels resulted in increased eERP amplitudes but showed inconsistent effects on response latencies in patients with ABIs. Objective and behavioral T levels were correlated.

CONCLUSIONS

eERPs could be recorded in both non-NF2 and NF2 patients with ABIs. eERPs in both ABI patient groups show inter- and intrasubject variations in morphological characteristics. However, onset eERPs measured within the same subject in this study tended to be stable across study sessions. The onset eERP can potentially be used to estimate behavioral T levels in patients with ABIs. Further studies with more adult ABI recipients are warranted to investigate whether the onset eERP can be used to identify electrodes with nonauditory stimulations.

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.

Transcranial magnetic stimulation reveals high test-retest reliability for phosphenes but not for suppression of visual perception

OBJECTIVE

To investigate test-retest reliability of visual cortical excitatory and inhibitory phenomena.

METHODS

Transcranial magnetic stimulation (TMS) was applied over occipital cortex twice in 22 healthy young adults with at least a one-month interval between both measurements. The test-retest reliability of the phosphenes and TMS-induced suppression of visual perception was assessed using correlation and calculation of the repeatability coefficient.

RESULTS

Both analyses revealed a high reliability for phosphenes but not for the suppression of visual perception.

CONCLUSIONS

It seems likely that the phosphenes may be better used than the TMS-induced suppression of visual perception in experiments which need repeated measurements (e.g., longitudinal studies or studies with pharmacological and non-pharmacological interventions).

SIGNIFICANCE

The study demonstrates a rather limited value of the TMS-induced suppression of visual perception for studies with repeated measurements.

Clinical symptoms of major depression are associated with the intensity dependence of auditory event-related potential components

The intensity (loudness) dependent amplitude change (IDAP) of the auditory event-related potential (ERP) has been shown to be associated with the outcome of treatment with selective serotonin reuptake inhibitors in major depression. The purpose of the present study is to evaluate associations between clinical symptoms of major depression and the IDAP as an indirect indicator of cortical serotonergic function. We assessed 40 in-patients suffering from a major depressive episode (DSM-IV) prior to antidepressant treatment. Psychometric characteristics of depression were assessed by means of psychiatric rating scales (CGI, HDRS, HAMA, STAI and BDI) and evaluated for associations with auditory evoked P1, N1, P2 as well as P1/N1 and N1/P2 peak to peak amplitude slopes. Our data revealed a positive correlation of the intensity dependent N1 amplitude slope with the degree of certain somatic symptoms of depression: loss of appetite and weight, insomnia, and sexual dysfunction. The results of our study might contribute to a more specific clinical basis in the differential indication of serotonergic versus noradrenergic antidepressants.

Treatment effects of serotonergic and noradrenergic antidepressants on the intensity dependence of auditory ERP components in major depression

The intensity dependent amplitude change of auditory evoked potentials (IDAP), an assumed indicator of the level of central nervous serotonergic neurotransmission, was measured in major depressive disorder (MDD, DSM-IV: 296.2, 296.3; APA 1994) before and after treatment with either a selective serotonin reuptake inhibitor or a selective noradrenaline reuptake inhibitor antidepressant and compared with the results of a healthy control group. Auditory evoked P1, N1, P2, P1/N1 and N1/P2 peak-to-peak amplitudes were evaluated in 26 in-patients with MDD prior to and after antidepressant treatment with citalopram (24 days, n=14) or reboxetine (25 days, n=12), and in 43 healthy control subjects. Clinical symptoms of MDD were assessed by means of standardized psychiatric rating scales (CGI, HDRS, HAMA and BDI). The IDAP within the control group remained stable over 24 days (N1 amplitude slope retest ANOVA p=.79). Neither applied antidepressants nor decrease of HDRS total score during treatment had a significant effect on the IDAP in the patients' sample. The conclusion that the IDAP does not reflect the temporary depressive state in MDD is discussed.

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.

The intensity dependence of auditory ERP components in unmedicated patients with major depression and healthy controls. An analysis of group differences

BACKGROUND

The intensity dependent amplitude change (IDAP) of auditory evoked Event Related Potential (ERP) components has been found to correlate with the level of central serotonergic neurotransmission and to be associated with response to certain antidepressants. However, it is currently unknown whether there is a general abnormality of the IDAP in patients with major depression. Therefore, the purpose of the present study was to compare the IDAP in unmedicated depressed patients with that of healthy control subjects.

METHODS

We report the results of a study evaluating the change of auditory evoked P1, N1, P2 as well as P1/N1 and N1/P2 peak to peak amplitudes in 34 in-patients with major depressive episode prior to antidepressant treatment, and 44 healthy control subjects. Clinical symptoms of depression were assessed by means of standardized psychiatric rating scales (CGI, HDRS, HAMA and BDI).

RESULTS

In multivariate analyses of variance we found no group differences in the intensity dependent increase neither of the P1, N1, and P2 nor of the P1/N1 and N1/P2 peak to peak amplitudes between patients and controls.

CONCLUSIONS

Our data revealed no general abnormality of the IDAP in patients with major depression in comparison to healthy control subjects. This result suggests that specific alterations of the IDAP are not to be expected in major depression in general, these may be confined to subgroups of depressed patients.

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.

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.

Decreased cerebrospinal fluid acetylcholinesterase in patients with subcortical ischemic vascular dementia

The main objective was to investigate the acetylcholinesterase E (AChE) activity in the cerebrospinal fluid (CSF) of patients with three common dementia disorders. We also wanted to investigate the influence of apolipoprotein E (ApoE) epsilon4 allele possession and CSF-tau level on the CSF-AChE activity in these patients. The study included 17 consecutive patients with subcortical vascular dementia (SVD), 39 with Alzheimer's disease (AD), 14 with frontotemporal dementia (FTD) and 12 controls. CSF was obtained by lumbar puncture and CSF-AChE activity was measured by an enzyme antigen immunoassay. CSF-AchE activity was significantly decreased compared to controls only in the SVD group (p = 0.010). The CSF-tau level was increased in the AD group compared to the control (p < 0.01) and FTD groups (p < 0.05). No influence of ApoE epsilon4 allele possession on CSF-AChE activity was found. It is suggested that abnormal CSF-AChE activity in patients with SVD reflects a disturbance in the cholinergic system.

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.

A neural network model of sensitization of evoked cortical responses in migraine

Migraine patients show abnormalities of cerebral electrophysiology that manifest themselves mainly during the attack interval. Cortical-evoked potentials of migraineurs fail to habituate to repetitive presentations of visual stimuli, and the amplitude of components of their auditory cortical-evoked potentials have a higher dependence on the stimulus intensities than in healthy subjects. A computer model of a neural hetwork has been developed that is able to reproduce both these neurophysiological dysfunctions. It predicts a positive correlation between the magnitudes of both these dysfunctions. The model also offers an explanation of why mutations in the same ion channel gene with opposite consequences on channel function, e.g. P/Q Ca2+ channels in migraine, may lead to similar electrophysiological abnormalities.

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.

Habituation of visual and intensity dependence of auditory evoked cortical potentials tends to normalize just before and during the migraine attack

Between attacks, migraine with (MO) or without aura (MA) patients show deficient habituation of pattern-reversal visual evoked potentials (PR-VEP) and a strong intensity dependence of auditory evoked cortical potentials (IDAP). Clinical observations of migraine prodromes and previously published electrophysiological studies suggest that cortical information processing may vary in close temporal relationship to the attack. We studied PR-VEP and IDAP just before (11 MO pts), during (23 MO, 3 MA), 1 day following (27 MO, 1 MA) and 2 days following (14 MO) a migraine attack. The results were compared with a large group of MO patients recorded at a distance of at least 3 days from an attack (n = 66 for IDAP; n = 39 for VEP). Patients recorded the day before the attack had on average an habituation of -13.6+/-20.5% (mean +/- SD) between the 5th and 1st block of 100 averaged VEP responses and a flat (0.38+/-1.06 microV/10 dB) amplitude-stimulus intensity function (ASF) slope of the auditory evoked cortical potential. Both values were significantly different from those obtained in the attack interval (P=0.003; P=0.020). During the attack, VEP habituation was less pronounced (-0.17+/-26.2%) and ASF slopes remained flat (0.32+/-1.44 microV/10 dB; P=0.002 compared to interval). During the 2 days following the attack, VEP habituation was replaced by potentiation (+0.09+/-29.1% the 1st day; 19.5+/-45.7% the 2nd day) and ASF slopes increased markedly (0.87+/-1.39 and 1.14+/-1.12 microV/10 dB). The normalization of evoked cortical responses just before and during the attack, might reflect an increase in the cortical preactivation level due to enhanced activity in raphe-cortical serotonergic pathways.

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

Because the "intensity dependence" of cortical auditory evoked potentials (IDAP) is under serotonergic control, it can be used to assess central antimigraine effects of 5HT1B/1D agonists. We measured IDAP before and 2 h after naratriptan (5 mg, n = 19) and zolmitriptan (5 mg, n = 19) in healthy volunteers. IDAP was expressed as the amplitude-stimulus intensity function ("ASF slope"). Naratriptan tended to increase ASF slope (mean difference 0.23 +/- 0.62 microV/10 dB, p = 0.06) while zolmitriptan (0.08 +/- 0.95 microV/10 dB, p = 0.35) did not. We assessed the suitability of IDAP for measuring central antimigraine drug effects using repeatability data (see companion paper). We calculated the trade-off between the size of the expected drug effects (ASF slope difference) and the necessary sample size. Because of poor repeatability 36 to 80 subjects are required to detect ASF slope changes in the 0.25-0.5 microV/10 dB range. These data can be used to design trials using IDAP.