Reduced gating of middle-latency auditory evoked potentials (P50) in migraine patients: another indication of abnormal sensory processing?

Habituation disorders in auditory middle latency response of persistent postural-perceptual dizziness patients

Objectives

To study habituation disorders in auditory middle latency response (AMLR) to repetitive stimuli of persistent postural-perceptual dizziness (PPPD) patients.

Subjects

Twenty-eight PPPD (10 men and 18 women, mean 59.5 years of age, 26-81 years of age) were enrolled. For comparison, data of 13 definite vestibular migraine (VM) patients (3 men, 10 women, mean age 45.5), 13 definite unilateral Meniere's disease (MD) patients (2 men, 11 women, mean age 50.6), and 8 healthy control (HC) subjects (2 men, 6 women, mean age 37.1) in the previous study were utilized.

Methods

The electrodes were placed on the vertex and the spinal process of the fifth cervical vertebra. Clicks (0.1 msec, 70 dB nHL) were binaurally presented and averaged (800 times). Averaged responses were divided into 4 sets (S1 to S4) according to the temporal order. As peaks, Na, and Pa were identified, and relative Na-Pa amplitudes in S2-S4 to S1 were analyzed.

Results

The mean relative amplitude of PPPD patients showed lack of habituation (potentiation) as shown in VM patients, although the extent of potentiation was weaker than VM. Comparison of relative S4 amplitudes showed significant differences among the 4 groups (p = 0.0013 one-way ANOVA), Multiple comparison revealed significant differences between PPPD and MD (p = 0.0337 Dunnet's test).

Conclusion

PPPD patients showed lack of habituation (potentiation) of Na-Pa amplitude in AMLR to repetitive stimuli. Lack of habituation (potentiation) might be associated with sensory processing disorders in PPPD.

What has neurophysiology revealed about migraine and chronic migraine?

Since the first electroencephalographic recordings obtained by Golla and Winter in 1959, researchers have used a variety of neurophysiological techniques to determine the mechanisms underlying recurrent migraine attacks. Neurophysiological methods have shown that the brain during the interictal phase of an episodic migraine is characterized by a general hyperresponsiveness to sensory stimuli, a malfunction of the monoaminergic brainstem circuits, and by functional alterations of the thalamus and thalamocortical loop. All of these alterations vary plastically during the phases of the migraine cycle and interictally with the days following the attack. Both episodic migraineurs recorded during an attack and chronic migraineurs are characterized by a general increase in the cortical amplitude response to peripheral sensory stimuli; this is an electrophysiological hallmark of a central sensitization process that is further reinforced through medication overuse. Considering the large-scale functional involvement and the main roles played by the brainstem-thalamo-cortical network in selection, elaboration, and learning of relevant sensory information, future research should move from searching for one specific primary site of dysfunction at the macroscopic level, to the chronic, probably genetically determined, molecular dysfunctions at the synaptic level, responsible for short- and long-term learning mechanisms.

Sensory Inhibition Is Related to Variable Speech Perception in Noise in Adults With Normal Hearing

Purpose Speech perception in noise (SPiN) varies widely in individuals with normal hearing, which may be attributed to factors that are not reflected in the audiogram, such as inhibition. However, inhibition is involved at both sensory and cognitive stages of auditory perception, and while inhibition at the cognitive level has been shown to be a significant factor in SPiN processes, it is unknown whether sensory inhibition may also contribute to SPiN variability. Therefore, the goal of this study was to evaluate sensory inhibition in adults with normal hearing and mild SPiN impairment. Method Cortical auditory evoked potentials (CAEPs) were recorded in 49 adults via high-density electroencephalography using an auditory gating paradigm. Participants were categorized according to a median signal-to-noise ratio (SNR) loss of 1.5 dB: typical SNR loss ≤ 1.5 dB (n = 32), mild SNR loss > 1.5 dB (n = 17). CAEP gating responses were compared and correlated with SNR loss and extended high-frequency thresholds. Current density reconstructions were performed to qualitatively observe underlying cortical inhibitory networks in each group. Results In comparison to adults with typical SPiN ability, adults with mild SPiN impairment showed an absence of the gating response. A CAEP gating component (P2) reflected decreased sensory inhibition and correlated with increased SNR loss. Extended high-frequency thresholds were also found to correlate with SNR loss, but not gating function. An atypical cortical inhibitory network was observed in the mild SNR loss group, with reduced frontal and absent prefrontal activation. Conclusion Sensory inhibition appears to be atypical and related to SPiN deficits in adults with mild impairment. In addition, cortical inhibitory networks appear to be incomplete, with a possible compensatory parietal network. Further research is needed to delineate between types or levels of central inhibitory mechanisms and their contribution to SPiN processes.

Vestibular Migraine Patients Show Lack of Habituation in Auditory Middle Latency Responses to Repetitive Stimuli: Comparison With Meniere's Disease Patients

Objectives: To compare habituation in auditory middle latency response (AMLR) to repetitive stimuli of vestibular migraine (VM) patients with Meniere's disease (MD) patients and healthy controls (HC) and to assess usefulness of AMLR for diagnosis of VM. Subjects: Thirteen unilateral definite MD patients (2 men, 11 women, mean age 50.6), 13 definite VM patients (3 men, 10 women, mean age 45.5), and 8 HC subjects (2 men, 6 women, mean age 37.1) were enrolled. Methods: The electrodes were placed on the vertex and the spinal process of the fifth cervical vertebra. Binaural click stimulation (0.1 ms, 70 dBnHL) was presented. A total of 800 responses were averaged. Averaged responses were divided into four sets (S1 to S4) according to the temporal order. No, Po, Na, and Pa were identified, and amplitudes and latencies were measured. Results: Concerning latencies, HC subjects showed a tendency of shorter latencies. However, there was no clear effect of repetitive stimulation. Concerning No-Po amplitudes, no significant differences were observed. Raw amplitudes of Na-Pa showed statistically significant differences in S1 and S2 among the groups (p < 0.01 one-way ANOVA). Differences were shown in MD vs. VM and HC vs. VM in S1 (smaller in VM) (p < 0.01 Bonferroni's test) and in MD vs. VM in S2 (smaller in VM) (p < 0.01 Bonferroni test). Relative amplitudes of Na-Pa to S1 showed statistically significant differences in S4 (p < 0.01 one-way ANOVA). Differences were shown in MD vs. VM and HC vs. VM (larger in VM) (p < 0.01 Bonferroni's test). Differences of Na-Pa amplitudes in S2 to S4 from Na-Pa amplitude in S1 were significant in S4 of VM patients (Dunnett's test). Conclusions: VM patients showed lack of habituation (potentiation) of Na-Pa amplitude in AMLR to repetitive stimuli while MD patients and HC subjects showed habituation. Observation of lack of habituation has high diagnostic accuracy for differential diagnosis of VM from MD.

Age Effect on Automatic Inhibitory Function of the Somatosensory and Motor Cortex: An MEG Study

Age-related deficiency in the top-down modulation of cognitive inhibition has been extensively documented, whereas the effects of age on a bottom-up or automatic operation of inhibitory function were less investigated. It is unknown that whether the older adults (OA)’ reduced behavioral performance and neural responses are due to the insufficient bottom-up processes. Compared to behavioral assessments which have been widely used to examine the top-down control of response inhibition, electrophysiological recordings are more suitable to probe the early-stage processes of automatic inhibitory function. Sensory gating (SG), a phenomenon of attenuated neural response to the second identical stimulus in a paired-pulse paradigm, is an indicator to assess automatic inhibitory function of the sensory cortex. On the other hand, electricity-induced beta rebound oscillation in a single-pulse paradigm reflects cortical inhibition of the motor cortex. From the neurophysiological perspective, SG and beta rebound oscillation are replicable indicators to examine the automatic inhibitory function of human sensorimotor cortices. Thus, the present study aimed to use a whole-head magnetoencephalography (MEG) to investigate the age-related alterations of SG function in the primary somatosensory cortex (SI) and of beta rebound oscillation in the primary motor cortex (MI) in 17 healthy younger and 15 older adults. The Stimulus 2/Stimulus 1 (S2/S1) amplitude ratio in response to the paired-pulse electrical stimulation to the left median nerve was used to evaluate the automatic inhibitory function of SI, and the beta rebound response in the single-pulse paradigm was used to evaluate the automatic inhibitory function of MI. Although there were no significant age-related differences found in the SI SG ratios, the MI beta rebound power was reduced and peak latency was prolonged in the OA. Furthermore, significant association between the SI SG ratio and the MI beta rebound power, which was seen in the younger adults (YA), was absent in the OA. In conclusion, our data suggested an age-related defect of association between sensorimotor cortices regarding automatic inhibitory function.

Somatosensory gating is altered and associated with migraine chronification: A magnetoencephalographic study

Background

Brain excitability is changed in migraine but not fully characterized yet. This study explored if somatosensory gating is altered in migraine and linked to migraine chronification.

Methods

Paired electrical stimuli were delivered to the left index fingers of 21 patients with migraine without aura (MO), 22 patients with chronic migraine (CM), and 36 controls. The first and second responses to the paired stimuli were obtained from the contralateral primary (cSI), contralateral secondary (cSII) and ipsilateral secondary (iSII) somatosensory cortices to compute the gating ratios (second vs. first response strengths).

Results

The first and second cSI responses and gating ratios differed in all groups ( p < 0.05); the responses were typically smaller in the MO and CM groups. The cSI gating ratio increased as a continuum across controls (0.73 ± 0.04, p < 0.001), MO (0.83 ± 0.04) to CM (0.97 ± 0.06) and was higher in CM vs. controls ( p < 0.001). When MO and CM were combined, cSI gating ratio was associated with headache frequency (r = 0.418, p = 0.005). Paired responses and gating ratios of cSII and iSII did not differ among the groups.

Conclusions

Somatosensory gating is altered in migraine and associated with headache chronification. Further studies must clarify if this abnormal sensory modulation is a true gating deficit independent of low preexcitation level.

Cerebrovascular Response to Repetitive Visual Stimulation in Interictal Migraine with Aura

Cortical hypersensitivity and absent habituation to different stimuli have been observed in migraine patients. These features might also be transmitted to the cerebral vasoreactivity, but results are conflicting so far. Transcranial Doppler ultrasound (TCD) was used to assess cerebral blood flow velocity (CBFV) changes in the middle (MCA) and posterior cerebral arteries (PCA) in relation to repetitive checkerboard visual stimulation. Stimulation consisted of 10 consecutive cycles, each comprising 10 s stimulation and 10 s rest. TCD recordings were analysed using stimulus-related averaging algorithm. Data of 19 interictal migraineurs with aura were compared to those of 19 headache-free healthy volunteers. The CBFV increase in PCA and in MCA during visual stimulation was significantly larger and steeper in migraineurs than in controls ( P = 0.017 and P = 0.005). The response in PCA remained stable over the 10 stimulation cycles, both in migraineurs and in controls. The response in MCA was stable only in migraineurs. In controls it decreased over the last 5 stimulation cycles compared with the first 5 cycles ( P = 0.04). Migraineurs with aura exhibit a larger cerebrovascular response to repetitive visual stimulation compared to headache-free subjects. A reduced adaptation to environmental stimuli in migraine is suggested, since there was no habituation in migraineurs in contrast to healthy controls.

Auditory Event-Related Potentials and Reaction Times in Migraine Children

Cognitive processing was investigated interictally in 18 children with migraine without aura and 18 age-matched controls by measuring event-related potentials (ERPs) and reaction times (RTs) during an acoustic oddball paradigm. Results showed that N100 amplitude evoked by frequent stimuli was significantly smaller in patients compared with controls. Habituation of target P300 amplitude was observed in patients but not in controls. Mean RTs were equivalent in the two groups, but migraine children made more errors than controls.

Central Nervous System Underpinnings of Sensory Hypersensitivity in Migraine: Insights from Neuroimaging and Electrophysiological Studies

Whereas considerable data have been generated about the pathophysiology of pain processing during migraine attacks, relatively little is known about the neural basis of sensory hypersensitivity. In migraine, the term "hypersensitivity" encompasses different and probably distinct pathophysiological aspects of sensory sensitivity. During attacks, many patients have enhanced sensitivity to visual, auditory and/or olfactory stimuli, which can enhance headache while interictally, migraineurs often report abnormal sensitivity to environmental stimuli that can cause nonpainful discomfort. In addition, sensorial stimuli can influence and trigger the onset of migraine attacks. The pathophysiological mechanisms and the origin of such sensitivity (individual predisposition to develop migraine disease or consequence of repeated migraine attacks) are ill understood. Functional neuroimaging and electrophysiological studies allow for noninvasive measures of neuronal responses to external stimuli and have contributed to our understanding of mechanisms underlying sensory hypersensitivity in migraine. The purpose of this review is to present pivotal neuroimaging and neurophysiological studies that explored the basal state of brain responsiveness to sensory stimuli in migraineurs, the alterations in habituation and attention to sensory inputs, the fluctuations of responsiveness to sensory stimuli before and during migraine attacks, and the relations between sensory hypersensitivity and clinical sensory complaints.

The Effects of Vigilance and Visual Distraction on the P50 Mid-Latency Auditory Evoked Potential

Sensory gating function has been investigated through measurement of the P50 evoked potential. However, the susceptibility of auditory P50 sensory gating to attentional modulation remains unclear. We sought to investigate the effects of vigilance (sustaining alertness across multiple recording blocks) and visual distraction (watching a muted movie versus a static fixation cross). We specifically chose a movie as the distracting stimulus because investigators sometimes show muted movies during P50 paradigms and the effects of this method were previously unknown. We recorded evoked potentials in a standard paired-click paradigm from groups watching a movie or static fixation cross; both groups completed four identical blocks of recording. Ratings of fatigue were recorded throughout the experiment. P50 and N100 amplitude showed signs of habituation, although N100’s amplitude reduction was more prominent than P50. P50 suppression did not change over the course of the recording session, despite increasing fatigue ratings. P50 suppression was significantly stronger for the participants who watched a movie during the recording. When comparing P50 gating results across studies, care should be taken to consider differing methodologies.

Altered brainstem auditory evoked potentials in a rat central sensitization model are similar to those in migraine

Migraine symptoms often include auditory discomfort. Nitroglycerin (NTG)-triggered central sensitization (CS) provides a rodent model of migraine, but auditory brainstem pathways have not yet been studied in this example. Our objective was to examine brainstem auditory evoked potentials (BAEPs) in rat CS as a measure of possible auditory abnormalities. We used four subdermal electrodes to record horizontal (h) and vertical (v) dipole channel BAEPs before and after injection of NTG or saline. We measured the peak latencies (PLs), interpeak latencies (IPLs), and amplitudes for detectable waveforms evoked by 8, 16, or 32 kHz auditory stimulation. At 8 kHz stimulation, vertical channel positive PLs of waves 4, 5, and 6 (vP4, vP5, and vP6), and related IPLs from earlier negative or positive peaks (vN1-vP4, vN1-vP5, vN1-vP6; vP3-vP4, vP3-vP6) increased significantly 2h after NTG injection compared to the saline group. However, BAEP peak amplitudes at all frequencies, PLs and IPLs from the horizontal channel at all frequencies, and the vertical channel stimulated at 16 and 32 kHz showed no significant/consistent change. For the first time in the rat CS model, we show that BAEP PLs and IPLs ranging from putative bilateral medial superior olivary nuclei (P4) to the more rostral structures such as the medial geniculate body (P6) were prolonged 2h after NTG administration. These BAEP alterations could reflect changes in neurotransmitters and/or hypoperfusion in the midbrain. The similarity of our results with previous human studies further validates the rodent CS model for future migraine research.

Altered processing of sensory stimuli in patients with migraine

Migraine is a cyclic disorder, in which functional and morphological brain changes fluctuate over time, culminating periodically in an attack. In the migrainous brain, temporal processing of external stimuli and sequential recruitment of neuronal networks are often dysfunctional. These changes reflect complex CNS dysfunction patterns. Assessment of multimodal evoked potentials and nociceptive reflex responses can reveal altered patterns of the brain's electrophysiological activity, thereby aiding our understanding of the pathophysiology of migraine. In this Review, we summarize the most important findings on temporal processing of evoked and reflex responses in migraine. Considering these data, we propose that thalamocortical dysrhythmia may be responsible for the altered synchronicity in migraine. To test this hypothesis in future research, electrophysiological recordings should be combined with neuroimaging studies so that the temporal patterns of sensory processing in patients with migraine can be correlated with the accompanying anatomical and functional changes.

A preliminary study on the relationship between central auditory processing and childhood primary headaches in the intercritical phase

BACKGROUND

Recently, an increasing number of articles have appeared on central auditory processing disorders, but in the literature there is only one study that evaluated the possible correlation between migraine in the critical phase and central auditory processing. The aim of our study was to assess the correlation between auditory processing information and childhood primary headaches in the intercritical phase.

METHODS

This is an observational study. We enrolled 54 patients, 30 with primary headache (migraine and tension headache) and 24 normal controls, matched for sex and age. The mean age at first observation was 9 years 10 months; the duration of observational follow-up was 2 years. Both groups had normal audiological and neurological profiles, normal peripheral hearing acuity and normal cognitive and behavioral skills. We excluded patients who had undergone pharmacological prophylactic treatment for headaches in the 6 months preceding the study and subjects with a frequency of headache lower than one every two months. After enrolment, both groups were analyzed with a computerized test battery for Speech Perception Tests in silence and in noise background to assess speech perception disabilities. In addition, with a test battery of Speech Perception Tests, we compared patients with migraines and tension-type headaches. The non-parametric χ2 test, the Mann-Whitney U-test and the Wilcoxon signed ranks test were used for statistical analysis. P-values <0.05 were considered significant and STATA 10 software was used for statistical analyses.

RESULTS

Our results showed that patients with primary headache (migraine and tension-type headache), had a deficit of auditory processing in noisy background compared to control cases, but we found no significant differences when we compared patients with migraine and tension-type headache.

CONCLUSIONS

This is a work in progress and further studies are needed to assess the relationship between the impairment of auditory processing and primary headache, not only to improve the diagnostic approach to primary headache, but also to improve therapeutic intervention.

Functional and effective connectivity in EEG alpha and beta bands during intermittent flash stimulation in migraine with and without aura

Objectives:

This research was a case-control study to evaluate functional and effective connectivity patterns in ongoing electroencephalography (EEG) under repetitive photic stimulation in the interictal phase of migraine patients with and without aura compared to nonmigraine controls.

Methods:

EEG was recorded by six scalp electrodes from 19 migraine without aura patients (MO), 19 migraine with aura patients (MA) and 11 healthy subjects (control group (N)). Flash stimuli were presented at 9–27 Hz frequencies. Phase synchronization after Hilbert transform and Granger causality were evaluated filtering the EEG in alpha and beta bands.

Results:

Phase synchronization increased in alpha band in MO, and decreased in beta band in MA, with respect to controls. The intensity of directed interactions in beta band, revealed by Granger causality, increased in MA compared to both MO patients and controls.

Discussion:

There were clear differences in ongoing EEG under visual stimulation, which emerged between the two forms of migraine, probably subtended by increased cortical activation in migraine with aura, and compensatory phenomena of reduced connectivity and functional networks segregation, occurring in patients not experiencing aura symptoms. Further investigation may confirm whether the clinical manifestation of aura symptoms is subtended by a peculiar neuronal connectivity pattern.

Aging-related decline in somatosensory inhibition of the human cerebral cortex

Primary somatosensory (SI) cortical inhibition to repetitive stimuli tends to decline with increasing age. However, aging effects on the inhibition mechanism of secondary somatosensory cortex (SII) remain elusive. We aimed to study the aging-related changes of cortical inhibition in the human somatosensory system. Neuromagnetic responses to paired-pulse electrical stimulation to the median nerve were recorded in 21 young and 20 elderly male adults. Paired-pulse suppression (PPS) of SI and SII activities was estimated by the ratio of the response to Stimulus 2 to the response to Stimulus 1. Based on equivalent current dipole modeling, PPS ratios of the contralateral (SIIc) and ipsilateral (SIIi) secondary somatosensory cortices were higher in elderly than in young subjects (p < 0.001 in SIIc and p = 0.034 in SIIi). At an individual basis, a higher PPS ratio in SIIc than in SI was found in 16 (80 %) out of the 20 elderly participants; in contrast, the PPS ratios of SIIc and SI cortices were similar in young participants (p = 0.031). In conclusion, a larger PPS ratio in elderly suggests an aging-related decline in somatosensory cortical inhibition. Furthermore, compared to SI, the electrophysiological responses of SII cortex are especially vulnerable to aging in terms of cortical inhibition to repetitive stimulation.

Bandpass filter settings differentially affect measurement of P50 sensory gating in children and adults

OBJECTIVE

This study investigated the effect of four different bandpass filter settings on measures of the P50 component and the signal-to-noise ratios (SNR) of averaged ERPs obtained from a sensory gating paradigm employing paired-click stimuli.

METHODS

Participants were adults (n=18) 20-55years old and children (n=25) 5-10years old who were free of neurological disorders.

RESULTS

Results show that the filter settings (0.23-75Hz, 10-50Hz, 10-75Hz, and 10-200Hz) differentially affected the P50 amplitude, noise power and SNR measures of the conditioning and test clicks, and P50 T/C ratios.

CONCLUSIONS

The 10-50Hz filter setting may be optimal in studies that include only adults as these settings resulted in the smallest mean P50 T/C ratio, a reasonable standard deviation (SD) for the ratio, and the highest SNRs. The 10-200Hz filter may be the best for studying young children as this setting had the smallest mean and SD of P50 T/C ratios for these participants.

SIGNIFICANCE

In studies that include both adults and children investigators are advised to use the 10-200Hz filter setting because the smaller variability of sensory gating in the child group helps ensure better homogeneity of variance measures between the groups.

Enhanced auditory brainstem response and parental bonding style in children with gastrointestinal symptoms

BACKGROUND

The electrophysiological properties of the brain and influence of parental bonding in childhood irritable bowel syndrome (IBS) are unclear. We hypothesized that children with chronic gastrointestinal (GI) symptoms like IBS may show exaggerated brainstem auditory evoked potential (BAEP) responses and receive more inadequate parental bonding.

METHODOLOGY/PRINCIPAL FINDINGS

Children aged seven and their mothers (141 pairs) participated. BAEP was measured by summation of 1,000 waves of the electroencephalogram triggered by 75 dB click sounds. The mothers completed their Children's Somatization Inventory (CSI) and Parental Bonding Instrument (PBI). CSI results revealed 66 (42%) children without GI symptoms (controls) and 75 (58%) children with one or more GI symptoms (GI group). The III wave in the GI group (median 4.10 interquartile range [3.95-4.24] ms right, 4.04 [3.90-4.18] ms left) had a significantly shorter peak latency than controls (4.18 [4.06-4.34] ms right, p = 0.032, 4.13 [4.02-4.24] ms left, p = 0.018). The female GI group showed a significantly shorter peak latency of the III wave (4.00 [3.90-4.18] ms) than controls (4.18 [3.97-4.31] ms, p = 0.034) in the right side. BAEP in the male GI group did not significantly differ from that in controls. GI scores showed a significant correlation with the peak latency of the III wave in the left side (rho = -0.192, p = 0.025). The maternal care PBI scores in the GI group (29 [26]-[33]) were significantly lower than controls (31 [28.5-33], p = 0.010), while the maternal over-protection PBI scores were significantly higher in the GI group (16 [12]-[17]) than controls (13 [10.5-16], p = 0.024). Multiple regression analysis in females also supported these findings.

CONCLUSIONS

It is suggested that children with chronic GI symptoms have exaggerated brainstem responses to environmental stimuli and inadequate parental behaviors aggravate these symptoms.

Where does a migraine attack originate? In the brainstem

Migraine is a common, paroxysmal, highly disabling primary headache disorder. The origin of migraine attacks is enigmatic. Numerous clinical and experimental results suggest that the activation of distinct brainstem nuclei is crucial in its pathogenesis, but the primary cause of this activation is not fully understood. We conclude that the initialization of a migraine attack can be explained as an altered function of the neuronal elements of the brainstem nuclei. In light of our findings and the literature data, we can assume that migraine is a subcortical disorder of a specific brainstem area.

Pattern of P50 suppression deficit in patients with epilepsy and individuals with schizophrenia

OBJECTIVE

To identify P50 suppression in patients with epilepsy, to investigate the effect of seizure control on P50 suppression, and to compare epilepsy patients with individuals with schizophrenia and healthy volunteers.

METHOD

P50 evoked potential parameters and P50 suppression were studied crossectionally in patients with uncontrolled or controlled epilepsy, in individuals with schizophrenia and in healthy volunteers.

RESULTS

Individuals with schizophrenia had significantly smaller conditioning stimulus (S1) amplitude, and patients with epilepsy had larger test stimulus (S2) amplitude. Mean S2/S1 ratio was 0.71 ± 0.33 for patients with uncontrolled epilepsy; 0.68 ± 0.36 for patients with controlled epilepsy; 0.96 ± 0.47 for individuals with schizophrenia, and 0.42 ± 0.24 for healthy volunteers.

CONCLUSION

The sensory filter of patients with epilepsy is altered, and this alteration is not associated with seizure control. Also, it works differently from the sensory filter of individuals with schizophrenia.

Phenomenological dimensions of sensory gating

Contemporary sensory gating definitions are generally tied to the perceptual and attentional phenomenology described by McGhie and Chapman, including abnormalities in the quality of sensory input, heightened awareness of background noises, and poor selective attention reported by individuals with schizophrenia. Despite these explicit phenomenological origins, little is known about the experiential phenomena underlying contemporary operationalizations of the sensory gating construct, such as whether the construct is restricted to experiences associated with the modulation of sensory percepts includes selective attention and distractibility or even whether the construct is accessible via self-report. Because clarification of these issues has important implications for the development and testing of psychological theories and the study of psychopathology, a series of studies was conducted to (a) empirically identify the major dimensions of sensory gating-like perceptual and attentional phenomenology in healthy young adults and (b) develop a psychometrically sound self-report rating scale to capture these dimensions, the Sensory Gating Inventory (SGI). Factor analyses of Likert items measuring a broad range of sensory gating-like subjective experiences revealed 1 primary factor that encompassed anomalies of perceptual modulation (eg, perceptions of heightened stimulus sensitivity and sensory inundation) and 3 other factors measuring disturbances in the processes of focal and radial attention as well as exacerbation of sensory gating-like anomalies by fatigue and stress. Psychometrically, the SGI demonstrated strong reliability and validity. An empirically based conceptual demarcation of the sensory gating construct is offered, and directions for future research are described.

The role of nicotine on respiratory sensory gating measured by respiratory-related evoked potentials

Respiratory perception can be altered by changes in emotional or psychological states. This may be due to affective (i.e., anxiety) modulation of respiratory sensory gating. Nicotine withdrawal induces elevated anxiety and decreased somatosensory gating. Respiratory sensory gating is evidenced by decreased amplitude of the respiratory-related evoked potentials (RREP) N1 peak for the second occlusion (S2) when two 150-ms occlusions are presented with a 500-ms interval during an inspiration. The N1 peak amplitude ratio of the S2 and first occlusion (S1) (S2/S1) is <0.5 and due to central neural sensory gating. We hypothesized that withdrawal from nicotine is anxiogenic and reduces respiratory gating in smokers. The RREP was recorded in smokers with 12-h withdrawal from nicotine and nonsmokers using a paired occlusion protocol. In smokers, the RREP was measured after nicotine withdrawal, then with either nicotine or placebo gum, followed by the second RREP trial. Nonsmokers received only placebo gum. After nicotine withdrawal, the smokers had a higher state anxiety compared with nonsmokers. There was a significant interaction between groups (nonsmokers vs. smokers with nicotine vs. smokers with placebo) and test (pre- vs. posttreatment) in RREP N1 peak amplitude S2/S1. The S2/S1 in the smokers were larger than in nonsmokers before treatment. After gum treatment, the smoker-with-placebo group had a significantly larger S2/S1 than the other two groups. The S2/S1 was significantly decreased after the administration of nicotine gum in smokers due to significantly decreased S2 amplitudes. The RREP Nf and P1 peaks were unaffected. These results demonstrated that respiratory sensory gating was decreased in smokers after nicotine withdrawal. Nicotine increased respiratory sensory gating in smokers with a S2/S1 similar to that of the nonsmokers. Nicotine did not change respiratory sensory information arrival, but secondary information processing in respiratory sensation.

Visual paired-pulse stimulation reveals enhanced visual cortex excitability in migraineurs

Migraine is a common ictal disorder with an interindividual heterogeneous characteristic, whose underlying mechanisms remain elusive. On the one hand migraine is associated with abnormal cortical hyperexcitability. On the other hand, studies reported lower amplitudes of visual-evoked potentials (VEPs) and concluded that low preactivation levels imply decreased excitability. Here we measured visual cortex excitability and paired-pulse suppression in subjects suffering from migraine without aura and in a group of aged- and gender-matched healthy subjects to address the relation between activation levels and excitability. To that aim, we analysed amplitudes of VEPs and paired-pulse suppression evoked by a paired-pulse stimulation paradigm using stimulus onset asynchronies (SOAs) between 80 and 133 ms. We found that in migraineurs in the interictal state the amplitudes of the first VEP were reduced as compared with healthy subjects by approximately 20%. In the case of paired-pulse suppression comparable to healthy controls, the second response amplitude should be reduced as well, which was not the case. Instead, the ratio between the first and second VEP was higher than in healthy controls and did not depend on SOA in the range tested, which demonstrates reduced paired-pulse suppression and therefore implicates increased cortical excitability. Our data show that in migraineurs VEPs were reduced presumably due to reduced activation levels. However, paired-pulse suppression using short SOAs in the range of 100 ms or less was even higher than in normal subjects. Thus, our data show that signatures of both hyper- and hypoexcitability can be found depending on stimulation condition.

The Abnormal Recovery Cycle of Somatosensory Evoked Potential Components in Children with Migraine can be Reversed by Topiramate

The aim of this study was to compare the recovery cycle of somatosensory evoked potentials (SEPs) in children with migraine without aura before and after treatment with topiramate. Eleven migraine children were studied before and after a 3-month treatment with topiramate at the average dose of 1.3 mg/kg/day. We calculated the SEP latency and amplitude modifications after paired electrical stimuli at 5, 20 and 40 ms interstimulus intervals, comparing them with a single stimulus condition assumed as baseline. In nine patients, who had a significant reduction in headache frequency after treatment, the recovery cycles of the P24 ( P = 0.03) and N30 ( P < 0.005) potentials were longer after than before topiramate treatment. In two migraineurs who did not show any improvement, the recovery cycles of the cortical SEP components were even shorter after treatment. Our results suggest that topiramate efficacy in paediatric migraine prophylaxis is probably related to restored cortical excitability.

Correlation Between Abnormal Brain Excitability and Emotional Symptomatology in Paediatric Migraine

We investigated a possible correlation between brain excitability in children with migraine and tension-type headache (TTH) and their behavioural symptomatology, assessed by using the Child Behaviour Checklist (CBCL). The mismatch negativity (MMN) and P300 response were recorded in three successive blocks to test the amplitude reduction of each response from the first to the third block (habituation). MMN and P300 habituation was significantly lower in migraineurs and TTH children than in control subjects (two-way ANOVA: P < 0.05). In migraineurs, but not in TTH patients, significant positive correlations between the P300 habituation deficit and the CBCL scores were found ( P < 0.05), meaning that the migraineurs with the most reduced habituation showed also the worst behavioural symptomatology. To the best of our knowledge, this is the first study showing a correlation between neurophysiological abnormality and emotional symptomatology in migraine, suggesting a role of the latter in producing the migrainous phenotype.

Maturation of sensory gating performance in children with and without sensory processing disorders

Recent interest in sensory gating in children with and without neuropsychological disorders has resulted in a number of studies and the results regarding the developmental trajectory of sensory gating are inconsistent. We investigated the maturational course of sensory gating in samples of typically developing children and children with sensory processing deficits (SPD) and compared their performance to adults. Besides gating ratios, we also examined the brain responses to conditioning and test click stimuli in the sensory gating paradigm separately to clarify if the changes in click amplitudes could explain the maturational change in the T/C ratio in children. Eighteen adults with no known disorders, 25 typical children, and 28 children with SPD participated in this study. The children ranged in ages between 5 and 12 years. The three groups differed in their P50 and N100 ERP components. Both child groups displayed significantly less gating than the adults. Children with SPD demonstrated significantly less gating and more within-group variability compared to typical children. There were significant relationships between age and T/C ratios and between age and peak-to-peak amplitude of the conditioning click in typical children but not in children with SPD. Typical children demonstrated significantly smaller brain response amplitudes to the clicks as compared to adults. These findings suggest that there is a maturational course of sensory gating in typical children and if there is a maturational trajectory in children with SPD it appears to be different than typical children. In addition, children with SPD were found to be lacking in their ability to filter out repeated auditory input and failed to selectively regulate their sensitivity to sensory stimuli.

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.

Stereotyped topography of different elevated contingent negative variation components in children with migraine without aura points towards a subcortical dysfunction

Increased negativity during contingent negative variation (CNV) is thought to reflect abnormal neural activation in adult migraineurs' attention related processing. Findings in childhood and adolescence have yielded less clear results. This study characterizes the age-dependent development of CNV topography in migraine during childhood in order to elucidate the origin and cerebral generators of described CNV elevations. A large sample of children with primary headache (migraine with/without aura, tension type headache) and healthy controls aged 6-18 years was examined in a CNV paradigm using 64-channel high resolution DC-EEG. Patients were tested for diagnose-related topographic group differences of initial CNV (iCNV), late CNV (lCNV) and postimperative negative variation (PINV). All three CNV components of 6-11-year-old migraineurs without aura showed elevated negativity over the supplementary motor area (SMA) and around the vertex. Migraine children lacked age-dependent development of late CNV around Cz as previously reported. However, they showed a normal development of late CNV over pre-/primary motor cortex (MI). There was no marked elevation of iCNV amplitude over frontal areas (orienting reaction) nor specific amplitude elevations over "motor" or "sensory" areas during sustained attention (late CNV). Additional "pre-mature" activation e.g., in the locus coeruleus (leading to diffuse cortical activation summing up to a maximum over the vertex) or the basal ganglia (interacting with SMA) explained the rather stereotyped CNV elevation around the vertex better than a specific implication of the cortical systems responsible for orienting, motor preparation or sensory attention.

Reduced P50 auditory sensory gating response in professional musicians

Evoked potential studies have demonstrated that musicians have the ability to distinguish musical sounds preattentively and automatically at the temporal, spectral, and spatial levels in more detail. It is however not known whether there is a difference in the early processes of auditory data processing of musicians. The most emphasized and studied early process, especially for neuropsychiatric purposes, is sensory gating. The suppression percentage of the midlatency auditory evoked potential P50, and rarely the N100, wave is used for sensory gating studies. Our aim in this study was to investigate whether there was a difference in the auditory P50 and N100 suppression of control subjects who were professional musicians with no psychiatric problems. 34 professional musicians and 19 non-musicians (the control group) were included in this study. P50 and N100 measurements were taken, the suppression percentage of P50 and N100 was calculated and the results compared. Musicians showed significantly less P50 suppression when compared to non-musicians. There was no significant difference for N100 suppression. What the decreased P50 suppression in musicians when compared to non-musician subjects means, when we also take into account that N100 suppression is not decreased, and how it may contribute to the music perception and production processes of these persons is discussed.

Reduced brain habituation to somatosensory stimulation in patients with fibromyalgia

OBJECTIVE

To examine brain activity elicited by repetitive nonpainful stimulation in patients with fibromyalgia (FM) and to determine possible psychophysiologic abnormalities in their ability to inhibit irrelevant sensory information.

METHODS

Fifteen female patients with a diagnosis of FM (ages 30-64 years) and 15 healthy women (ages 39-61 years) participated in 2 sessions, during which electrical activity elicited in the brain by presentation of either tactile or auditory paired stimuli was recorded using an electroencephalogram. Each trial consisted of 2 identical stimuli (S1 and S2) delivered with a randomized interstimulus interval of 550 msec (+/-50 msec), which was separated by a fixed intertrain interval of 12 seconds. Event-related potentials (ERPs) elicited by 40 trials were averaged separately for each sensory modality.

RESULTS

ERP amplitudes elicited by the somatosensory and auditory S2 stimuli were significantly reduced compared with those elicited by S1 stimuli in the healthy controls. Nevertheless, significant amplitude reductions from S1 stimuli to S2 stimuli were observed in FM patients for the auditory, but not the somatosensory, modality.

CONCLUSION

Our findings suggest that in FM patients, there is abnormal information processing, which may be characterized by a lack of inhibitory control to repetitive nonpainful somatosensory information during stimulus coding and cognitive evaluation.

Schizophrenia-relevant behavioral testing in rodent models: a uniquely human disorder?

Animal models are extremely useful tools in defining pathogenesis and treatment of human disease. Creating adequate animal models of complex neuropsychiatric disorders such as schizophrenia represents a particularly difficult challenge. In the case of schizophrenia, little is certain regarding the etiology or pathophysiology of the human disease. In addition, many symptoms of the disorder are difficult to measure directly in rodents. These challenges have not daunted neuroscientists who are capitalizing on even subtle overlaps between this uniquely human disorder and rodent behavior. In this perspective, we detail the features of ideal animal models of schizophrenia, the potential utility of such models, and the rodent behaviors used to model certain aspects of schizophrenia. The development of such models will provide critical tools to understand the pathogenesis of schizophrenia and novel insights into therapeutic approaches to this complex disorder.

Auditory Middle Latency Evoked Responses: A Standardizing Study

The presence of auditory middle latency evoked responses allows us to make an evaluation of the peripheral and central auditory system integrity, as well as the nucleus and auditory ways existing until the level of the thalamus-cortical region and primary auditory cortex. Aim: Our objective is to evaluate the presence or not of this numerous peaks, as well as, their latencies and intervals and extend to make a standardizing study. Way of study: Contemporary study of Coorte with transversal cut and the outline was quantitative, descriptive e non experimental. Material and method: Studying several peaks, positives and negatives, caused by the middle latency auditory potentials, in a population of young adults individuals, ranging from 18 to 30 years old, from both genders, with normal hearing. It was used a monoauricular resonant stimulation and a capitation, separately, in both cerebral hemispheres, with surface electrodes. Result: In this research was verified that the analyzed crossings did not present statistically significant results and it was stipulated a pattern from the obtained results. Based on the non-statistical difference found we can affirm that to the Po waves was obtained respectively an average and standard deviation of 12,09 and 1,84; for Na 17,91 and 2,60; for Pa 29,41 and 5,66; for Nb 41,43 and 8,89; to for 51,44 ms e 12,63 and finally to the interval Na-Pa 11,52 and 4,99. Conclusion: 1- The presence of the defluxions Po, Na, and Pa was verified in all the registers, whereas the defluxions Nb and Pb were absent in only 06 registers. 2- By having these registers, we evaluated that the inveiglement of these defluxions can be used as a reliable method to detect the average latency of the auditory potentials, by electrical generated activities, possibly in sites located in the thalamus-cortical area, evoked by sonorous stimulation. From that point, we establish a pattern of responses for young ones with normal hearing, helping us with future studies in patients with alterations in the hearing system.

P50 sensory gating deficit in children with centrotemporal spikes and sharp waves in the EEG

Sensory gating refers to the ability of the brain to inhibit irrelevant sensory input. In several studies, a pathogenic role of the CHRNA7 gene and the CHRNA7-like gene, respectively, is suggested. In linkage analysis concerning familial centrotemporal spikes and sharp waves (CTS) and benign rolandic epilepsy, evidence for linkage was found to a region on chromosome 15q14, close to the alpha-7 subunit gene of the neuronal nicotinic acetylcholine receptor (CHRNA7). According to these findings, P50 evoked potentials to paired click stimuli were studied in 13 children with CTS in the EEG to determine whether they had normal sensory gating. The control group consisted of 13 healthy probands matched for gender and age. Children with CTS showed a significant sensory gating deficit (p=0.001). These results (1) suggest an inhibitory deficit in early pre-attentive auditory sensory processing in children with CTS and (2) confirm the assumption of a cholinergic pathology in CTS.

Brain activation responses to subliminal or supraliminal rectal stimuli and to auditory stimuli in irritable bowel syndrome

Visceral hypersensitivity in irritable bowel syndrome (IBS) has been associated with altered cerebral activations in response to visceral stimuli. It is unclear whether these processing alterations are specific for visceral sensation. In this study we aimed to determine by functional magnetic resonance imaging (fMRI) whether cerebral processing of supraliminal and subliminal rectal stimuli and of auditory stimuli is altered in IBS. In eight IBS patients and eight healthy controls, fMRI activations were recorded during auditory and rectal stimulation. Intensities of rectal balloon distension were adapted to the individual threshold of first perception (IPT): subliminal (IPT -10 mmHg), liminal (IPT), or supraliminal (IPT +10 mmHg). IBS patients relative to controls responded with lower activations of the prefrontal cortex (PFC) and anterior cingulate cortex (ACC) to both subliminal and supraliminal stimulation and with higher activation of the hippocampus (HC) to supraliminal stimulation. In IBS patients, not in controls, ACC and HC were also activated by auditory stimulation. In IBS patients, decreased ACC and PFC activation with subliminal and supraliminal rectal stimuli and increased HC activation with supraliminal stimuli suggest disturbances of the associative and emotional processing of visceral sensation. Hyperreactivity to auditory stimuli suggests that altered sensory processing in IBS may not be restricted to visceral sensation.

Multilevel somatosensory system disinhibition in children with migraine

Although migraine is characterised by an abnormal cortical excitability level, whether the central nervous system is hyper- or hypo-excitable in migraine still remains an unsolved problem. The aim of our study was to compare the somatosensory evoked potential (SEP) recovery cycle, a marker of the somatosensory system's excitability, in a group of 15 children suffering from migraine without aura (MO) (mean age 11.7+/-1.6 years, five males, 10 females) and 10 control age-matched subjects (CS) (mean age 10.9+/-2.1 years, six males, four females). We calculated the SEP's latency and amplitude modifications after paired electrical stimuli at 5, 20 and 40 ms interstimulus intervals (ISIs), comparing it with a single stimulus condition assumed as the baseline. In MO patients, the amplitudes of the cervical N13 and of the cortical N20, P24 and N30 responses at 20 and 40 ms ISIs showed a higher recovery than in CS (two-way ANOVA, P<0.05). Since, the SEP recovery cycle depends on the inhibitory interneuron function, our findings suggest that a somatosensory system disinhibition takes place in migraine. This is a generalized phenomenon, not limited to the cerebral cortex, but concerning also the cervical grey matter. The SEP recovery cycle reflects the intracellular concentration of Na(+), therefore, the shortened recovery cycle in our MO patients suggests a high level of intracellular Na(+) and a consequent depolarized resting membrane potential, possibly due to an impaired Na(+) -K(+) ATPase function in migraine.

Sensory gating impairment in development of post-concussive symptoms in mild head injury

Post-concussive symptoms reported by mild head injury (MHI) patients have been inadequately understood. Post-concussive symptoms reported by patients with MHI have so far been explained in terms of impairment in neurocognitive functions or deficits in modulation of flow of information. There are no studies that have looked into sensory gating impairment in MHI and its relation to post-concussive symptoms. The purpose of the present paper was to investigate the role of sensory gating impairment in post-concussive symptoms in mild head injury patients. Thirty MHI patients were evaluated for their neuropsychological functions, sensory gating deficits, and post-concussive symptoms. Neuropsychological functions were in the domain of attention, executive functions, and learning and memory. Sensory gating was assessed by Structured Interview for Assessing Perceptual Anomalies and post-concussive symptoms were assessed using the Neurobehavioral Rating Scale. Multiple regression method was used to identify predictors for post-concussive symptoms. Post-concussive symptoms were predicted by sensory gating deficits when sensory gating deficit was one of the predictors along with neuropsychological functions. Post-concussive symptoms were predicted by scores of Digit Vigilance and Digit Symbol Substitution Test, when predictors were restricted to neuropsychological functions. Sensory gating deficits were correlated with performance on Digit Symbol Substitution test. Post-concussive symptoms reported by MHI patients are the result of poor modulation of incoming sensory information.