Auditory evoked potentials in schizophrenic patients before and during neuroleptic treatment. Relationship to psychopathological state

Is auditory processing measured by the N100 an endophenotype for psychosis? A family study and a meta-analysis

BACKGROUND

The N100, an early auditory event-related potential, has been found to be altered in patients with psychosis. However, it is unclear if the N100 is a psychosis endophenotype that is also altered in the relatives of patients.

METHODS

We conducted a family study using the auditory oddball paradigm to compare the N100 amplitude and latency across 243 patients with psychosis, 86 unaffected relatives, and 194 controls. We then conducted a systematic review and a random-effects meta-analysis pooling our results and 14 previously published family studies. We compared data from a total of 999 patients, 1192 relatives, and 1253 controls in order to investigate the evidence and degree of N100 differences.

RESULTS

In our family study, patients showed reduced N100 amplitudes and prolonged N100 latencies compared to controls, but no significant differences were found between unaffected relatives and controls. The meta-analysis revealed a significant reduction of the N100 amplitude and delay of the N100 latency in both patients with psychosis (standardized mean difference [s.m.d.] = -0.48 for N100 amplitude and s.m.d. = 0.43 for N100 latency) and their relatives (s.m.d. = - 0.19 for N100 amplitude and s.m.d. = 0.33 for N100 latency). However, only the N100 latency changes in relatives remained significant when excluding studies with affected relatives.

CONCLUSIONS

N100 changes, especially prolonged N100 latencies, are present in both patients with psychosis and their relatives, making the N100 a promising endophenotype for psychosis. Such changes in the N100 may reflect changes in early auditory processing underlying the etiology of psychosis.

Glutamatergic and GABAergic Receptor Modulation Present Unique Electrophysiological Fingerprints in a Concentration-Dependent and Region-Specific Manner

Brain function depends on complex circuit interactions between excitatory and inhibitory neurons embedded in local and long-range networks. Systemic GABAA-receptor (GABAAR) or NMDA-receptor (NMDAR) modulation alters the excitatory-inhibitory balance (EIB), measurable with electroencephalography (EEG). However, EEG signatures are complex in localization and spectral composition. We developed and applied analytical tools to investigate the effects of two EIB modulators, MK801 (NMDAR antagonist) and diazepam (GABAAR modulator), on periodic and aperiodic EEG features in freely-moving male Sprague Dawley rats. We investigated how, across three brain regions, EEG features are correlated with EIB modulation. We found that the periodic component was composed of seven frequency bands that presented region-dependent and compound-dependent changes. The aperiodic component was also different between compounds and brain regions. Importantly, the parametrization into periodic and aperiodic components unveiled correlations between quantitative EEG and plasma concentrations of pharmacological compounds. MK-801 exposures were positively correlated with the slope of the aperiodic component. Concerning the periodic component, MK-801 exposures correlated negatively with the peak frequency of low-γ oscillations but positively with those of high-γ and high-frequency oscillations (HFOs). As for the power, θ and low-γ oscillations correlated negatively with MK-801, whereas mid-γ correlated positively. Diazepam correlated negatively with the knee of the aperiodic component, positively to β and negatively to low-γ oscillatory power, and positively to the modal frequency of θ, low-γ, mid-γ, and high-γ. In conclusion, correlations between exposures and pharmacodynamic effects can be better-understood thanks to the parametrization of EEG into periodic and aperiodic components. Such parametrization could be key in functional biomarker discovery.

Neurophysiology in psychosis: The quest for disease biomarkers

Psychotic disorders affect 3% of the population at some stage in life, are a leading cause of disability, and impose a great economic burden on society. Major breakthroughs in the genetics of psychosis have not yet been matched by an understanding of its neurobiology. Biomarkers of perception and cognition obtained through non-invasive neurophysiological tools, especially EEG, offer a unique opportunity to gain mechanistic insights. Techniques for measuring neurophysiological markers are inexpensive and ubiquitous, thus having the potential as an accessible tool for patient stratification towards early treatments leading to better outcomes. In this paper, we review the literature on neurophysiological markers for psychosis and their relevant disease mechanisms, mainly covering event-related potentials including P50/N100 sensory gating, mismatch negativity, and the N100 and P300 waveforms. While several neurophysiological deficits are well established in patients with psychosis, more research is needed to study neurophysiological markers in their unaffected relatives and individuals at clinical high risk. We need to harness EEG to investigate markers of disease risk as key steps to elucidate the aetiology of psychosis and facilitate earlier detection and treatment.

The auditory P200 is both increased and reduced in schizophrenia? A meta-analytic dissociation of the effect for standard and target stimuli in the oddball task

OBJECTIVE

Conflicting reports of P200 amplitude and latency in schizophrenia have suggested that this component is increased, reduced or does not differ from healthy subjects. A systematic review and meta-analysis were undertaken to accurately describe P200 deficits in auditory oddball tasks in schizophrenia.

METHODS

A systematic search identified 20 studies which were meta-analyzed. Effect size (ES) estimates were obtained: P200 amplitude and latency for target and standard tones at midline electrodes.

RESULTS

The ES obtained for amplitude (Cz) for standard and target stimuli indicate significant effects in opposite directions: standard stimuli elicit smaller P200 in patients (d = -0.36; 95% CI [-0.26, -0.08]); target stimuli elicit larger P200 in patients (d = 0.48; 95% CI [0.16, 0.82]). A similar effect occurs for latency at Cz, which is shorter for standards (d = -0.32; 95% CI [-0.54, -0.10]) and longer for targets (d = 0.42; 95% CI [0.23, 0.62]). Meta-regression analyses revealed that samples with more males show larger ES for amplitude of target stimuli, while the amount of medication was negatively associated with the ES for the latency of standards.

CONCLUSIONS

The results obtained suggest that claims of reduced or augmented P200 in schizophrenia based on the sole examination of standard or target stimuli fail to consider the stimulus effect.

SIGNIFICANCE

Quantification of effects for standard and target stimuli is a required first step to understand the nature of P200 deficits in schizophrenia.

Reduced auditory evoked potential component N100 in schizophrenia--a critical review

The role of a reduced N100 (or N1) component of the auditory event related potential as a potential trait marker of schizophrenia is critically discussed in this review. We suggest that the extent of the N100 amplitude reduction in schizophrenia depends on experimental and subject factors, as well as on clinical variables: N100 is more consistently reduced in studies using interstimulus intervals (ISIs) >1 s than in studies using shorter ISIs. An increase of the N100 amplitude by allocation of attention is often lacking in schizophrenia patients. A reduction of the N100 amplitude is nevertheless also observed when such an allocation is not required, proposing that both endogenous and exogenous constituents of the N100 are affected by schizophrenia. N100 is more consistently reduced in medicated than unmedicated patients, but a reduction of the N100 amplitude as a consequence of antipsychotic medication was shown in only two of seven studies. In line with that, the association between the N100 reduction and degree of psychopathology of patients appears to be weak overall. A reduced N100 amplitude is found in first degree relatives of schizophrenia patients, but the risk of developing schizophrenia is not reflected in the N100 amplitude reduction.

Inhibition of auditory evoked potentials and prepulse inhibition of startle in DBA/2J and DBA/2Hsd inbred mouse substrains

Previous data have shown differences among inbred mouse strains in sensory gating of auditory evoked potentials, prepulse inhibition (PPI) of startle, and startle amplitude. These measures of sensory and sensorimotor gating have both been proposed as models for genetic determinants of sensory processing abnormalities in patients with schizophrenia and their first-degree relatives. Data from our laboratory suggest that auditory evoked potentials of DBA/2J mice differ from those previously described for DBA/2Hsd. Therefore, we compared evoked potentials and PPI in these two closely related substrains based on the hypothesis that any observed endophenotypic differences are more likely to distinguish relevant from incidental genetic heterogeneity than similar approaches using inbred strains that vary across the entire genome. We found that DBA/2Hsd substrain exhibited reduced inhibition of evoked potentials and reduced startle relative to the DBA/2J substrain without alterations in auditory sensitivity, amplitude of evoked potentials or PPI of startle. These results suggest that gating of auditory evoked potentials and PPI of startle measure different aspects of neuronal function. The differences between the substrains might reflect genetic drift. Alternatively, differences could arise from different rearing environments or other non-genetic factors. Future studies will attempt to determine the cause of these differences in sensory and sensorimotor processing between these two closely related inbred mouse strains.

Cerebral signs of altered adaptability in females with acute psychosis

In psychosis, behavior is not guided by sensory cues from surroundings. Novel, meaningful behaviors require intact integrative functions such as short-term memory and motor planning, as well as an optimized level of arousal. In this study, we monitored markers of automatic auditory processing in 15 female never-medicated psychotic patients. Fifty-eight channels of EEG were recorded simultaneously with sympathetic skin responses while arousing auditory stimuli were delivered. Neuropsychological tests concentrating on frontal lobe functions were also performed. Prominent neurophysiological and behavioral signs of increased cortical activation were observed in psychotic patients. This widespread disinhibition may attempt to compensate for the impairment of neuronal processing of sensory input from surroundings in the earliest stages of a psychotic illness.

Memory-based comparison process not attenuated by haloperidol: a combined MEG and EEG study

Auditory P50 and N100 responses reflect preattentive processing, whereas subsequent mismatch negativity (MMN) response indexes memory-based comparison process. Divergent ERP responses have been found in schizophrenia and in Parkinson's disease (PD), which have abnormalities in cerebral dopamine activity. We used simultaneously magnetoencephalography and electroencephalography to investigate, whether a single dose of haloperidol, a dopamine D2-receptor antagonist, modulates preattentive auditory processing using a randomized, double-blind, placebo-controlled crossover design. Our results showed that haloperidol did not alter MMN to frequency and duration changes, whereas the magnetic MMN to frequency change was significantly accelerated. The amplitude and latency changes of the electric and magnetic P50 and N100 were insignificant. Our results indicate that memory-based sound comparison and preceding cortical processing underlying stimulus detection are not attenuated by haloperidol, whereas haloperidol appears to accelerate preattentive sound comparison.

N100 evoked potential latency variation and startle in schizophrenia

The contribution of evoked potential (EP) latency jitter, a measure of CNS temporal variability, on startle and EP gating defects in schizophrenic subjects has not been characterized. The amplitude of the N100/P200 EP complex (peak to trough) derived using a time-locked averaging procedure, N100 EP latency jitter derived from single trial analysis, acoustic startle response and clinical symptoms were measured in 51 schizophrenic subjects. N100 latency jitter was inversely correlated with N100/P200 EP amplitude in both cross-sectional and longitudinal analysis. Subjects with elevated EP gating ratios (>0.5) had similar latency jitter values for initial (S1) and test (S2) stimuli, while subjects with a low gating ratio (0-0.5) had a lower level of S1 latency jitter. Temporal variability thus plays a significant and complex role in previously reported sensory gating deficits in schizophrenic subjects.

Auditory event-related potentials and clinical scores in unmedicated schizophrenic patients

Event-related potentials (ERPs) have been widely examined in schizophrenic patients. However, although neuroleptic medication could be a potentially confounding variable, studies with unmedicated patients are relatively scarce. The present work was undertaken to determine whether ERP abnormalities persist in stabilized schizophrenic patients after drug withdrawal. In addition, ERP amplitudes and latencies were compared with clinical ratings (the Positive and Negative Syndrome Scale, PANSS) by means of Spearman rank order correlation coefficients. The P300 and N200 responses to rare tones and the P200 and N100 responses to frequent tones were recorded in 20 clinically stabilized drug-free schizophrenic patients and 19 age-matched control subjects during a two-tone discrimination task. Major findings were that the schizophrenic patients had reduced P300, N200 and N100 amplitudes and an increased P300 latency. The P300 amplitude was negatively correlated with age in patients. The P200 latency was negatively correlated with the PANSS positive syndrome score. The ERP abnormalities shown in this study appear to be enduring traits of the disorder as they persist in stabilized patients even after drug withdrawal.

Correlations between standard auditory evoked potentials and symptomatology in a group of 50 schizophrenic patients

Standard auditory evoked potentials (AEP) were recorded in 50 schizophrenic patients and 47 normal controls. All patients were rated on the Brief Psychiatric Rating Scale (BPRS), the Scale for the Assessment of Negative Symptoms (SANS), the Scale for the Assessment of Positive Symptoms (SAPS), and the Positive and Negative Syndrome Scale (PANSS), and were classified in three groups (positive-type [n = 10], negative-type [n = 23]and mixed-type [n = 17]patients) according to the normative criteria suggested by Kay. The mean latencies of AEP components (N1, P2, N2) and mean peak-to-peak amplitudes (N1P2, P2N2) did not correlate with age, duration of illness, length of hospitalisation or neuroleptic dosage. The evoked response did not differ between the three groups of patients (positive, negative and mixed). There was only a trend (P = 0.075) to a longer N1 latency in the negative-type group and a shorter one in the positive-type group than in the mixed-type and the control groups. The latency of N1 component correlated significantly with negative symptoms of schizophrenia (SANS scores). This correlation was related to the severity of a depressive dimension of the disorder reflected by the "depressive factor" of BPRS or "affective flattening" and "avolition" subscales of SANS.