Neurophysiological assessment of sensory gating in psychiatric inpatients: comparison between schizophrenia and other diagnoses

Comparison of four components of sensory gating in schizophrenia and normal subjects: a preliminary report

Dysfunction of sensory gating has been implicated in the pathophysiology of schizophrenia. The goal of this study was to provide evidence that sensory gating dysfunction in schizophrenia patients is a compounded problem with difficulty in filtering out irrelevant input and filtering in relevant input at both an early-preattentive stage and a later, early-attentive stage of information processing. Four components of sensory gating were examined in 12 medicated, stable schizophrenia patients and 12 age- and sex-matched normal control subjects. Evoked potential paradigms designed to examine the effects of stimulus repetition and stimulus change were utilized. Attenuation of the amplitude of the P50 and the N100 evoked potentials with stimulus repetition was significantly decreased in schizophrenia patients as compared to normal control subjects. The presentation of deviant stimuli caused the degree of attenuation to decrease in normal subjects. This effect was much decreased (and at times reversed) in schizophrenia subjects. These data suggest that schizophrenia patients have difficulty inhibiting incoming, irrelevant stimuli and responding to incoming, significant input as measured by preattentive EPs (P50). The data also suggest that similar abnormalities can be demonstrated at a slightly later phase of information processing (i.e. early-attentive phase) using the N100 EP.

Neurobiological abnormalities in the relatives of schizophrenics

The inheritance of a complex illness such as schizophrenia likely involves the segregation of genetic factors, in combination with non-genetic or environmental abnormalities. This paper reviews several family studies of biological and clinical aspects of schizophrenia, that have attempted to observe such segregation in relationship to family history of schizophrenia to identify which factors appear to be related to the transmission of genetic risk.

Amphetamine disrupts P50 suppression in normal subjects

BACKGROUND

P50 suppression is viewed as an operational measure of sensory "gating" that is reduced in patients with schizophrenia and their family members. Previous reports have demonstrated that neural gating is regulated by monoaminergic tone in rodent models of P50 suppression.

METHODS

In this study, 11 healthy subjects participated in P50 event-related potential recordings at baseline and after either oral administration of dextroamphetamine (.3 mg/kg) or placebo, to determine if the administration of a monoaminergic agonist produces P50 suppression deficits similar to those observed in patients with schizophrenia.

RESULTS

As hypothesized, amphetamine disrupted the suppression of the P50 event-related potential. There was a statistically significant decrement in P50 suppression during the amphetamine challenge condition (t10 = 3.15, p < .01, mean difference = -44.1%, d = -2.5) relative to the baseline P50 condition. A comparison of P50 suppression in the placebo and amphetamine conditions (both after a baseline recording session) revealed a significant amphetamine-induced disruption of P50 suppression (t6 = 3.71, p < .01, mean difference = -54.4%, d = -3.14).

CONCLUSIONS

The biochemical alterations associated with an amphetamine-induced disruption of P50 suppression in this study may be related to the pathophysiology of P50 suppression deficits in schizophrenia. The findings are consistent with several careful examinations of suppression deficits in rodent models that have identified the monoaminergic regulation of P50 suppression. These data indicate that amphetamine induces a disruption of P50 suppression in normal subjects.

Elementary phenotypes in the neurobiological and genetic study of schizophrenia

This review describes the strategy of using elementary phenotypes for neurobiological and genetic linkage studies of schizophrenia. The review concentrates on practical aspects of selecting the phenotype and then understanding the confounds in its measurement and interpretation. Examples from the authors' studies of deficits in P50 inhibition and smooth pursuit eye movement dysfunction are presented. These two phenotypes share considerable similarity in their neurobiology, including a similar response to nicotine. They also appear to co-segregate with the genetic risk for schizophrenia as autosomal co-dominant phenotypes. Although most schizophrenic patients inherit these abnormalities unilinealy, i.e., from one parent, apparent bilineal inheritance produces a more severe illness, observed clinically as childhood-onset schizophrenia. The initial study showing linkage of the P50 deficit to the chromosome 15q14 locus of the alpha 7-nicotinic acetylcholine receptor is an example of the potential usefulness of these phenotypes for combined genetic and neurobiological study of schizophrenia.

P50 suppression and prepulse inhibition of the startle reflex in humans: a correlational study

BACKGROUND

Sensory gating is an important feature of the normally functioning brain. When not operating correctly, it can contribute to different kinds of psychiatric illnesses by flooding the higher brain functions with useless information. Over the years, two paradigms have evolved to quantify the amount of sensory gating: the prepulse inhibition (PPI) of the startle reflex and the suppression of the P50 evoked potential. To enable comparison across studies it is important to find out to what extent these paradigms reflect the same processes. In the present study, this relationship was explored.

METHODS

Thirty-one healthy male volunteers with no personal or family history of mental illness were tested on their ability to suppress the P50 wave and to inhibit the startle reflex.

RESULTS

A significant positive correlation was found between PPI and P50 suppression mainly early in testing, when habituation of the startle reflex is taking place. Furthermore, a significant negative correlation was found between P50 suppression in the second half of testing and the habituation of the startle reflex.

CONCLUSIONS

PPI and P50 suppression are correlated at an early stage of testing, when the process of habituation of the startle reflex is active. The role of the habituation in the correlation between these two measures needs to be further explored.

The "incredible shrinking" P50 event-related potential

The P50 component of the auditory evoked response has been utilized in studies of sensory gating in schizophrenia for over 15 years. As P50 gating studies have had a greater impact in neuroscience research, investigators have refined several key variables (e.g., filtering) to enhance signal-to-noise ratios. A comprehensive review of P50 reports suggests P50 amplitude has been steadily decreasing over the years. Certain methodological "advances" are suggested as key reasons for this apparent reduction in P50 amplitude. Gating studies continue to yield interesting findings in neuropsychiatric research, especially when ratio vs. absolute difference scores are used.

Is P50 suppression a measure of sensory gating in schizophrenia?

BACKGROUND

Abnormal P50 response has been hypothesized to reflect the sensory gating deficit in schizophrenia. Despite the extensive literature concerning the sensory filtering or gating deficit in schizophrenia, no evidence has been provided to test the relationship of the P50 phenomenon with patients' experiences of perceptual anomalies.

METHODS

Sixteen drug-free DSM-IV diagnosed schizophrenic patients who reported moderate to severe perceptual anomalies in the auditory or visual modality were examined as compared to 16 schizophrenic patients who did not report perceptual anomalies, and 16 normal subjects. Both control groups were age- and gender-matched with the study group.

RESULTS

Patients reporting perceptual anomalies exhibited P50 patterns that did not differ from normal subjects. In contrast, patients who did not report perceptual anomalies showed the abnormal P50 ratios previously found to be associated with schizophrenia.

CONCLUSIONS

These paradoxical findings do not support the hypothetical relationship between the P50 and behavioral measures of sensory gating, suggesting that additional studies are needed to further explore the clinical correlates of the P50.

Kainic acid lesions in adult rats as a model of schizophrenia: changes in auditory information processing

Previous studies have suggested that intracerebroventricular kainic acid injections alter brain anatomy and neurochemistry in a manner similar to what is observed in schizophrenic patients. Disturbances in sensory information processing are one of the major symptoms of schizophrenia. Thus, the present experiments were designed to evaluate the hypothesis that hippocampal damage, induced by administration of kainic acid, would alter the processing of auditory stimuli in a paired-click paradigm. Adult male Sprague-Dawley rats were implanted for surface recording of auditory evoked potentials. At the time of electrode implantation, the rats also received bilateral injections of either kainic acid or the vehicle solution. In vehicle-treated rats, the midlatency N40 component of the auditory evoked potential was diminished in amplitude by approximately 60% in response to the second of a pair of clicks delivered 0.5 s apart. By contrast, no reduction of the N40 wave evoked by the second click was observed in kainate-treated rats. Further, administration of haloperidol, a prototypical neuroleptic agent, did not improve this auditory processing dysfunction in kainate-treated animals. Loss of auditory filtering in the paired-click paradigm and a lack of response to haloperidol in this test are typically observed in schizophrenic humans. Thus, the present results demonstrate that kainate-lesioned rats possess a functional schizophrenia-like abnormality, further reinforcing the utility of this model system for studying the basic neurobiology of schizophrenia-induced sensory processing deficits.

Rats reared in social isolation show schizophrenia-like changes in auditory gating

Central sensory filtering processes can be demonstrated using a paired stimulus paradigm. Normal humans show a diminished vertex-recorded midlatency auditory-evoked potential to the second of paired clicks (0.5 s apart), a phenomenon termed auditory gating. Schizophrenics routinely fail to suppress the response to the second stimulus; thus, they do not gate. Previous animal studies of auditory gating have used psychotomimetic drug administration to induce a schizophrenia-like loss. However, a nonpharmacologic model of deficient gating would be advantageous. Isolation rearing of weanling rats produces impaired prepulse startle inhibition similar to that observed in schizophrenics. The present studied examined the effects of rearing status upon auditory gating. Male Sprague-Dawley rats raised in social isolation (ISO) were compared to socially raised rats (SOC). Across 10 baseline recording sessions, SOC rats showed substantial gating, while ISO rats failed to gate. Abnormal auditory gating is transiently normalized by nicotine, but not haloperidol, in schizophrenics. ISO rats given nicotine bitartrate showed gating in the normal range for 60 min. By contrast, haloperidol failed to normalize gating in ISO rats. Thus, isolation rearing of weanling rats appears to produce a stable schizophrenia-like gating deficiency that shows the same pattern of response to pharmacological interventions.

Influence of reference electrodes, stimulation characteristics and task paradigms on auditory P50

To clarify the nature of auditory P50, middle latency auditory evoked potentials were recorded by using different conditions of reference electrodes (linked earlobes, LE; balanced non-cephalic, BN), stimulation characteristics (tone burst, human voice) and tasks (counting, simple reaction) in 10 right-handed males (aged 21-36 years). EEG was recorded from Fz, Cz, Pz, C3, C4, T3 and T4 according to the 10-20 system. Two groups of electrode sites were made for the statistical analysis: a midline group, Fz, Cz and Pz, and a lateral group, T3, C3, Cz, C4 and T4. The results were that the P50 amplitudes with BN electrodes were significantly higher than those with LE in both groups (midline, P < 0.01; lateral, P < 0.01); the P50 amplitudes by voice stimulation were significantly higher than those by tone stimulation in the lateral group (P < 0.05), and the P50 latencies under a simple reaction paradigm were significantly shorter than those under a counting task in both groups (midline, P < 0.05; lateral, P < 0.05). These results suggest that various factors including motor response affect the P50 amplitudes and latencies.

Effects of P50 temporal variability on sensory gating in schizophrenia

The conditioning-testing (S1-S2) P50 auditory evoked potential (EP) has been well-documented and accepted as an important tool for measuring sensory gating in schizophrenia research. However, the physiological mechanism of the phenomenon is not known. In this study a single-trial analysis was used to determine the influence of the latency variability of the responses in the formation of the averaged P50. Ten schizophrenic patients and 10 normal controls were tested in the dual-click EP paradigm. Using ensemble averaging analysis, we replicated the previous finding of a lower S1 P50 amplitude and higher S2/S1 ratio in schizophrenics compared with normal controls. The single-trial analysis revealed that patients had significantly higher trial-to-trial latency variability in S1 responses than normal subjects, while the S2 showed the same variability as in controls. Measured by the single-trial procedure, the arithmetic mean amplitudes of P50 responses to S1 and S2 were similar between normal and schizophrenic subjects. The same measure also eliminated the difference in averaged P50 amplitude between S1 and S2 for both groups. Temporal variability appears to be an important factor in the assessment of averaged EPs and thus contribute to the change of P50 amplitude observed in schizophrenia.

Sensory gating in a computer model of the CA3 neural network of the hippocampus

We have developed a unique computer model of the CA3 region of the hippocampus that simulates the P50 auditory evoked potential response to repeated stimuli in order to study the neuronal circuits involved in a sensory processing deficit associated with schizophrenia. Our computer model of the CA3 hippocampal network includes recurrent activation from within the CA3 region as well as input from the entorhinal cortex and the medial septal nucleus. We used the model to help us determine if the cortical and septal inputs to the CA3 hippocampus alone are responsible for the gating of auditory evoked activity, or if the strong recurrent activity within the CA3 region contributes to this phenomenon. The model suggests that the medial septal input is critical for normal gating; however, to a large extent the activity of the medial septal input can be replaced by simulated stimulation of the hippocampal neurons by a nicotinic agonist. The model is thus consistent with experimental data that show that nicotine restores gating of the N40 evoked potential in fimbria-fornix lesioned rats and of the P50 evoked potential in schizophrenic patients.

Replication of a P50 auditory gating deficit in Australian patients with schizophrenia

Schizophrenic patients reportedly have a deficit in the control of sensitivity to auditory stimuli as shown by the P50 auditory evoked potential wave in a conditioning-testing paradigm that measures suppression of response to a repeated stimulus. Although this finding has been replicated by several US laboratories, one European group has not found differences between schizophrenic patients and normal control subjects. In the present study, investigators in the Schizophrenia Research Center at the Prince of Wales Hospital in Sydney, Australia, selected 22 normal control subjects, 11 acutely ill schizophrenic inpatients, and 11 clinically stable schizophrenic outpatients. Both schizophrenic groups were treated with similar doses of classical neuroleptic medications. Evoked potentials were recorded by an investigator from the US laboratory that initially reported the difference; five averages, each the response to 32 stimulus pairs, were recorded from each subject. The normal control subjects demonstrated significantly more suppression of the P50 response to the repeated stimuli than the schizophrenic groups, as previously reported. There were no significant changes in the suppression measure over the five trials. The suppression of the P50 wave by schizophrenic outpatients was somewhat greater than that by schizophrenic inpatients, but both schizophrenic groups had decreased suppression, compared with the normal subjects. The mean P50 suppression for five averages was successfully used in a logistic regression to classify subjects as normal or schizophrenic. This method was more accurate than attempts to classify subjects with only one average. The mean amplitude of the initial conditioning response did not differ between groups. Schizophrenic patients had slightly shorter mean latencies. There was no direct relationship of P50 suppression to measures of clinical psychopathology.

P50 changes with visual interference in normal subjects: a sensory distraction model for schizophrenia

Twenty-five normal subjects were tested in a Conditioning-Testing (S1-S2) auditory P50 study. Each subject was tested twice under two experimental conditions: distraction condition (with light interference) and control condition (without interference). Results showed that S1 P50 amplitude was significantly decreased with visual interference compared with that in the control condition, while the S2 response remained unchanged. Consequently, the S2/S1 gating ratio was also increased remarkably in the distraction condition. The auditory EP changes with the visual distraction in normals closely resembled the abnormal findings in schizophrenic subjects. These data may provide an alternative model to elucidate the psychophysiological mechanism that possibly rules the changes of attention in schizophrenia.

Cocaine abusers have reduced auditory P50 amplitude and suppression compared to both normal controls and alcoholics

The auditory P50 evoked response to click stimuli was recorded from 10 2-week abstinent African-American chronic cocaine abusers and 10 African-American non-substance-abusing controls. Stimuli consisted of pairs of clicks with a 500-msec interval between clicks in a pair, and a 7-8 sec interval between pairs of clicks. After averaging responses to 100 pairs of clicks and digital bandpass filtering between 10 and 50 Hz, P50 amplitude to the first and the second click was measured. The conditioning/testing (C/T) ratio, an index of P50 suppression, was computed as the ratio of P50 amplitude to the second compared to the first click. Chronic cocaine abusers had markedly diminished P50 amplitudes and increased C/T ratios (indicating decreased P50 suppression) in comparison to the controls. These P50 abnormalities were not seen in additional Caucasian gay/bisexual comparison groups of active alcoholics (n = 15) and non-substance-abusing controls (n = 10). Thus, decrements in P50 amplitude and P50 suppression appear to be specific to cocaine abuse, and to differentiate cocaine abuse from alcohol abuse. A response analogous to P50 can be measured in animals, facilitating the development of animal models of this cocaine effect.

Gender differences in gating of the auditory evoked potential in normal subjects

Central nervous system (CNS) inhibitory mechanisms hypothesized to "gate" repetitive sensory inputs have been implicated in the pathology of schizophrenia. The present study investigated gender differences in inhibitory gating of evoked brain responses to repeated stimuli in normal subjects (30 women and 30 men) using an auditory conditioning-testing paradigm. Pairs of click stimuli (S1 and S2) were presented with a 0.5 s intrapair and a 10 s interpair interval. The amplitudes and latencies of the P50, N100, P180 components of the auditory evoked response to the conditioning (S1) and test response (S2) were measured, and the gating ratios were computed (T/C ratio = S2/S1 * 100). The amplitudes to S1 were not significantly different between men and women at P50, N100, or P180. However, women had significantly higher amplitudes to S2 at P50 (p = 0.03) and N100 (p = 0.04). The T/C ratios for women were higher (i.e., less suppression of response to S2) for P50 (p = 0.08) and N100 (p = 0.04) compared to men. The results suggested that differences in auditory gating between men and women were not due to biological differences in the P50 and N100 generators but possibly to differential influence of inhibitory mechanisms acting on the generator substrates of these evoked responses.

Effect of frontal and temporal seizure foci on P50 auditory evoked potentials

Event-related potentials have been occasionally investigated in epilepsy. We recorded P50 auditory evoked potentials in 25 patients with complex partial seizures of frontal and temporal lobe origin. P50 was significantly reduced in amplitude and prolonged in latency in temporal lobe seizure patients as compared to controls. Patients with complex partial seizures originating in the frontal lobes did not differ from controls in P50 amplitude. P50 attenuation differences may be related to interictal behavioral or cognitive changes, but could also reflect medication effects. Event-related potentials may be helpful in differentiating frontal and temporal seizure foci.

The P50 evoked potential component and mismatch detection in normal volunteers: implications for the study of sensory gating

Sensory gating is a complex, multistage, multifaceted physiological function believed to be protecting higher cortical centers from being flooded with incoming irrelevant sensory stimuli. Failure of such mechanisms is hypothesized as one of the mechanisms underlying the development of psychotic states. Attenuation of the amplitude of the P50 evoked potential component with stimulus repetition is widely used to study sensory gating. In the current study, we investigated the responsiveness of the P50 component to changes in the physical characteristics of ongoing trains of auditory stimuli. Forty normal volunteers were studied in a modified oddball paradigm. At all cerebral locations studied, P50 amplitudes were higher in response to infrequent stimuli. We postulate that the increase in P50 amplitude reflects the system's recognition of novel stimuli or "gating in" of sensory input. The ratio of the amplitude of the responses to the infrequent stimuli to those of the frequent stimuli was significantly higher for the posterior temporal regions. This finding provides further evidence that the temporal lobes may be significantly involved in sensory gating processes. Although this study only included normal subjects, the data generated contribute to the understanding of sensory gating mechanisms that may be relevant to psychotic states.

Nicotinic cholinergic normalization of amphetamine-induced loss of auditory gating in freely moving rats

The impairment in normal sensory processing which is usually observed in schizophrenics has been demonstrated using a paired-stimulus paradigm. Normal individuals show a diminished midlatency evoked potential response to the second of a pair of clicks given at a 0.5-s interval. This phenomenon is termed auditory "gating". Schizophrenics routinely fail to suppress their response to the second click in this paradigm; thus, they do not gate. Heavy tobacco use is common among schizophrenics and it has recently been shown that nicotine causes a transient normalization of auditory gating in these individuals. Our laboratory has been utilizing animal models to investigate the sensory deficit observed in schizophrenia. In the present study, rats were administered amphetamine to produce a schizophrenia-like loss of auditory gating. They were then given nicotine, which resulted in a dose-dependent normalization of the amphetamine-induced loss of gating. This effect was blocked by concurrent central administration of d-tubocurarine. Neither nicotine nor d-tubocurarine had any effect on auditory gating when administered alone. These data are in agreement with the human studies showing normalization of auditory gating with nicotine administration and suggest a possible role for the nicotinic cholinergic receptor in the modulation of auditory gating in the rat model.

Preattentive information processing in schizophrenia

Preattentive and attentive information processing was investigated in 24 schizophrenic patients and 24 control subjects using a texture discrimination task based on Julesz's texton theory. Texton theory essentially defines a certain limited number of texture elements that can be detected readily and simultaneously without attentional effort irrespective of the size and information content of the rest of the visual field. During the first task, subjects had to detect texton elements (one 'L' among 35 '+'), which were presented on slides for 40 ms and were followed by a mask after different stimulus onset asynchronies (SOA: 200-800 ms). At all SOAs tested schizophrenics reported significantly fewer correct responses compared to the control group. In the second task, subjects had to search for texton (one 'L' among 35 '+') and non-texton elements (one 'L' among 35 'T') in the stimulus displays, whereby response times were measured. Schizophrenics showed significantly slower response times only to texton elements, whereas response times to non-texton elements did not significantly differ from controls. Additionally, schizophrenics made significantly more errors detecting non-texton elements than controls. The results suggest a deficit in processing of visual information in schizophrenic patients, which is confined to preattentive processes and may consist of a slowing of those processes. Schizophrenics may also have difficulty in sustaining their attention during search tasks.

Effects of cocaine on sensory inhibition in rats: preliminary data

The purpose of this study was to determine the effect of cocaine on inhibitory sensory processing mechanisms in the brain. To accomplish this aim, recording electrodes were surgically placed into the vertex region of 12 rats. After recovery from surgery, rats were injected once daily for 5 days with either cocaine (20 mg/kg, IP) or saline. Immediately and 23 hr after each injection, the rats were tested for sensory gating mechanisms. They were presented with a series of two clicking sounds, a conditioning and testing click, delivered 0.5 sec apart, and the amplitude of the N40 responses to each of these clicks was recorded. The ratios of the amplitude of the N40 response to the testing click over that of the conditioning click (T/C ratio) were calculated for each animal for each testing period. The T/C ratios of the control (Saline-injected) animals were less than one, indicating that the conditioning stimulus was able to activate inhibitory neural pathways, producing a decrease in the response to the testing stimulus. The T/C ratios of the cocaine-treated animals were significantly greater than those of controls when the tests were conducted either immediately after injection or 23 hr later. These observations suggest that cocaine can impair mechanisms involved in the gating of responses to auditory stimuli. The higher T/C ratio found at 23 hr after cocaine injection suggests that an impairment in the gating mechanism may be produced by an arousal response that is associated with the environment in which the animals had been injected with cocaine.

Within-session changes in sensory gating assessed by P50 evoked potentials in normal subjects

1. The authors studied within-session changes in P50 suppression occurring in a group of 28 normal subjects. 2. A conditioning-testing paradigm was used with 120 pairs of 110 Db peak intensity clicks. Clicks were of 0.04 msec duration, 500 msec separation and delivered through headphones at 10 second intervals. 3. Mean P50 suppression ranged from 60.5% during the first 30 click pairs to -19.1% during the last 30 pairs, with an overall mean suppression of 25.4%. 4. The authors concluded that P50 suppression is a dynamic process in normal subjects, and that further work is necessary to elucidate the factors affecting P50 suppression.

Concurrent assessment of acoustic startle and auditory P50 evoked potential measures of sensory inhibition

The acoustic startle response (ASR) and midlatency auditory evoked potentials (AEP) have been utilized in the measurement of sensory inhibition. Using these different paradigms, abnormalities suggesting a lack of normal inhibition have been noted in a number of psychiatric syndromes. To date, the most commonly used sensory inhibition paradigms have not been studied in the same individuals, making generalizations across studies tenuous. In this report, reduction of ASR over multiple trials (habituation), prepulse inhibition (PPI) of ASR (decrease in ASR caused by low intensity prepulses) and P50 suppression (P50 AEP amplitude reduction in a paired-click paradigm) were measured in the same individuals. Relationships between these measures of acoustic startle and AEP inhibition were then assessed. Twenty subjects with no personal history of psychiatric disorder were tested and exhibited significant habituation and PPI of ASR as well as P50 suppression. Habituation of ASR was significantly and positively correlated with P50 suppression early, but not late, in AEP testing. Only a modest trend for a positive association between PPI and P50 suppression was noted. Habituation and PPI of startle were both highly correlated (positively) with P50 AEP amplitude. Habituation of startle remained significantly predictive of P50 suppression after controlling for P50 amplitude, whereas the modest association between PPI and P50 suppression was removed when P50 amplitude was factored out. Results indicate that habituation of acoustic startle, but not PPI, is highly associated with P50 suppression in control subjects. An unexpected finding was a robust positive correlation between P50 amplitude and both measures of startle inhibition. These findings and methodologic issues are discussed in terms of possible neural substrates involved in different measures of sensory inhibition.

Transient impairment in P50 auditory sensory gating induced by a cold-pressor test

Diminished gating of the auditory evoked response to repeated stimuli is a psychophysiological defect associated with schizophrenia and several other psychiatric illnesses. The P50 wave of the auditory evoked response to the second of paired stimuli is decreased in most normal subjects, whereas many psychotic subjects show significantly less decrement. The aim of this experiment was to test whether the cold-pressor test, which causes transient distress and pain accompanied by increased sympathetic activity, also causes a transient impairment in P50 auditory sensory gating in normal control subjects. Ten normal control subjects with normal gating of the P50 response immersed their hands in an ice water bath for 2 min. This cold-pressor test diminished P50 auditory gating in nine of these subjects, although the degree of impairment was highly variable among subjects. The impairment in gating was transient, with partial resolution by 30 min. The cold-pressor test was subjectively viewed as painful and also caused blood pressure to increase. Thus, a transient stressor can impair P50 auditory gating in some subjects.

Contextual effects on choice reaction time and accuracy in acute and chronic schizophrenics. Impairment in selective attention or in the influence of prior learning?

Two hypotheses were tested concerning the nature of the cognitive dysfunction in schizophrenia: (a) that there is a broadening of selective attention; and (b) that there is an impairment in associational learning. RDC-diagnosed acute and chronic schizophrenics and normal controls carried out a choice reaction time (RT) task in which conflict between the correct response to a target (a letter in the centre of a computer screen) and that cued by simultaneously presented flankers (two letters either side of the target) increased RT. For 80 ('valid') trials, flankers and targets were consistent in the response cued (pressing a button with either left or right hand); on 8 ('invalid') trials they conflicted. On invalid trials there was a slowing of RT, and an increase of errors for left-hand responses. Chronic schizophrenics showed the same reactions to cue validity as normal controls, both groups differing significantly from acute schizophrenics. For the latter, the RT data supported hypothesis (b), but the error rates appeared to support hypothesis (a).

Dopaminergic and noradrenergic modulation of amphetamine-induced changes in auditory gating

Dopaminergic and noradrenergic mediation of central sensory gating were assessed in Sprague-Dawley rats using a condition-test paradigm in which auditory evoked potentials were recorded. In this paradigm, unmedicated rats 'gate', i.e. suppress the response to the second of a pair of clicks delivered at a 0.5 s interval. Amphetamine-treated rats fail to gate; in this respect, they resemble schizophrenic humans. Previous studies had indicated noradrenergic involvement in the mediation of auditory gating in rats. In this study, we used selective antagonists to assess the contribution of alpha- and beta-adrenergic receptors, and dopamine D1- and D2-receptors, to amphetamine-induced alterations in gating. Both the alpha-antagonist, phentolamine, and the beta-antagonist, timolol, normalized gating by potentiating amphetamine-induced decreases in the amplitude of the test response. SCH 23390, a D1-receptor antagonist, also normalized gating, but by elevating the amphetamine-reduced amplitude of the conditioning response. Sulpiride did not significantly alter amphetamine-induced changes in gating. Thus, both noradrenergic alpha- and beta-receptors and dopamine D1-receptors appear to modulate gating. However, their dissimilar means of normalizing gating suggests that noradrenergic and dopaminergic drugs act via different mechanisms and possibly different neuroanatomical loci.

Middle latency auditory evoked potentials (MAEPs) in chronic schizophrenics

Middle latency auditory evoked potentials were recorded in medicated chronic schizophrenics and controls at stimulation rates of 10/s, 2/s, and 1/s. Increasing the stimulation rate did not change Pa amplitude but decreased Pb amplitude. There was no difference between the two groups.

Replication and extension of P50 findings in schizophrenia

In a paired click "conditioning (S1), Testing (S2)" paradigm the amplitudes of responses to (S1) as well as the degree of attenuation of S2 as compared to S1 (S2/S1) were studied in two schizophrenic groups. Thirteen undifferentiated/disorganized (US) and thirteen paranoid (PS) patients were compared to thirteen age and sex matched normal volunteers. The US patients had significantly lower (S1) response amplitudes (P less than 0.001), as well as degree of attenuation of the response to (S2) (P less than 0.001) than the other two groups. No significant differences were found between the PS and N groups. Our data replicates the prior finding of decreased attenuation of the amplitude of the P50 wave in a paired click paradigm in schizophrenia. In addition, we showed that this phenomenon is significant mainly in the disorganized/undifferentiated patients as compared to the paranoid schizophrenics.

Gating of auditory response in schizophrenics and normal controls. Effects of recording site and stimulation interval on the P50 wave

Auditory evoked potentials were recorded using a paired stimulus, conditioning-testing paradigm from 14 schizophrenic patients and 13 normal subjects with no family history of psychotic disorder. Previous studies of the vertex P50 wave using this paradigm have demonstrated a possible sensory gating deficit in schizophrenics, as shown by their failure to diminish the response to a test stimulus presented 500 ms after a conditioning stimulus. Recordings were made at Cz, Fz, C3, T3, C4, and T4, to compare effects at different recording sites with this paradigm. Schizophrenics had significantly poorer sensory gating than normals, with the most significant difference between the groups at Cz. In addition to the 500 ms interval, subjects were also recorded at a conditioning-testing interval of 100 ms. Most schizophrenics showed normal sensory gating at the 100 ms interval, despite their abnormalities at 500 ms. The results indicate that Cz is optimal recording site for this paradigm, and that gating abnormalities in schizophrenic subjects are limited to specific interstimulus intervals.

Sensory gating in normals and schizophrenics: a failure to find strong P50 suppression in normals

In a series of investigations, suppression of the auditory-evoked P50 potential to the second of two paired clicks presented 500 msec apart has been shown to be absent in schizophrenic patients, whereas normals suppress their second response to less than 20% of the first response. The phenomenon has been discussed as a possible trait marker for schizophrenia. The present study with 19 schizophrenics and 23 healthy control subjects was intended as an extended replication of the phenomenon using different stimulus parameters and a slightly different method of measuring P50 amplitudes. Replication was unsuccessful, revealing only weak suppression scores in normal subjects not significantly superior to schizophrenics. Retest sessions yielded generally stronger P50 suppression suggesting that the stability of the measure over time is questionable. The methodological changes are discussed as possible sources of this failure to replicate. It is concluded that the conditions under which P50-suppression occurs should be better clarified in order to facilitate replication.

Sensory gating deficits in psychiatric inpatients: relation to catecholamine metabolites in different diagnostic groups

Acutely ill psychiatric inpatients were examined for a deficit in sensory gating, measured as failure to suppress the P50 wave of the auditory-evoked response to the second of paired stimuli. Previously, we had found that in mania, this sensory gating deficit is correlated with increased plasma-free levels of the noradrenergic metabolite 3-methoxy, 4-hydroxyphenylglycol (pMHPG), whereas in schizophrenia, there is no correlation with catecholamine metabolism. To assess the generalizability of these findings, we examined inpatients with a broader range of diagnoses, including those with multiple DSM III-R Axis I, II, and III diagnoses. The patients were grouped into three diagnostic spectra for analysis: schizophrenic, manic, and depressive. In the schizophrenic patients, there was no relationship between pMHPG or other catecholamine metabolites and the sensory gating deficit. In manic patients, however, a positive correlation between pMHPG level and the sensory gating deficit was again observed. This relationship did not extend to the depressive patients, who uniquely showed sensory gating deficits that correlated negatively with the severity of their illness. The data suggest that sensory gating deficits are common to these three diagnostic spectra, but the deficits in each group have different relationships to catecholamine metabolism and symptom severity that may reflect differences in the underlying neuronal pathophysiology of these illnesses.

Sensory gating in schizophrenics and normal controls: effects of changing stimulation interval

Auditory evoked potentials were recorded using a paired click, conditioning-testing paradigm in 10 schizophrenics and in 10 normal subjects with no family history of psychotic disorder. The paradigm is used to demonstrate central nervous system gating of responsiveness to auditory stimuli by examining the extent to which the response to the conditioning stimulus diminishes the response to a test stimulus occurring a short time later. Recordings were made at conditioning-testing intervals of 500 msec, 150 msec, and 75 msec to determine subjects' gating of responsiveness to stimuli repeated at various intervals. The schizophrenics had conditioning-testing ratios indicative of poor gating of the auditory P50 wave at the 500-msec and 150-msec intervals, but most patients had good sensory gating at the 75-msec interval. Normal subjects showed good sensory gating at all three intervals. Results suggest that although sensory gating mechanisms responsible for changes in neuronal response at longer intervals are chronically defective in schizophrenics, other gating mechanisms functioning at shorter intervals appear to be intact and function well in most patients. The results may lead to increased specification of the neurobiological basis of sensory abnormalities in schizophrenia.