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Biomedical subjects

N N Boutros

Publications and source records attributed to N N Boutros.

At least 19 recordsLinked to original sources
PubMed1999

Midlatency evoked potentials attenuation and augmentation reflect different aspects of sensory gating.

A broad definition of sensory gating refers to the ability of the brain to modulate its sensitivity to incoming sensory stimuli. This definition allows the concept of gating to include both the capacities to minimize or stop responding to incoming irrelevant stimuli (gating out) and to respond when a novel stimulus is presented or a change occurs in ongoing stimuli (gating in). In order to further characterize the function of sensory gating, we examined the attenuation (decreased responding) and augmentation (increased responding) of the P50 EP amplitudes in 22 normal volunteers. Three EP paradigms, each including a number of conditions, designed to examine both EP habituation (inhibition) and dishabituation (excitation) were administered to each subject. In conditions designed to examine habituation (identical pairs of clicks or trains of repetitive identical clicks), the P50 behaved, as expected, with decrease of the amplitude with repetition. In conditions designed to examine dishabituation the amplitude of the P50, EP did not decrease as much (and frequently increased) with stimulus change. The results suggest that the P50 EP is sensitive to the effects of stimulus repetition and stimulus change and can be used to study the different aspects of sensory gating.

Acoustic Stimulation↗
PubMed1998

Test-retest reliability of the rat N40 auditory evoked response: preliminary data.

The N40 auditory evoked potential (EP) in rats has been used to develop an animal model for the study of sensory gating mechanisms. In an examination of the test-retest reliability of sensory gating indices, derived from the rat N40 EP, six rats were tested four times daily for 5 consecutive days. A paired-click paradigm (S1-S2) was used, and both the S2/S1 amplitude ratio and the S1-S2 amplitude difference measures of sensory gating capacity were calculated. Based on the means of four daily trials, reliability coefficients were as follows; r = 0.69 for S1, and r = 0.66 for S2 amplitudes. A reliability coefficient of 0.59 was found for the S1-S2 difference measure, and one of 0.47 for the S2/S1 ratio measure. These results suggest that the N40 can be used to study sensory gating, but caution has to be exercised in interpreting the data particularly in a repeated measures design.

Animals↗
PubMed1998

Chronological association between increases in drug abuse and psychosis in Connecticut state hospitals.

Disagreement remains as to whether drug use can result in an autonomous psychotic disorder. If drug use can create new psychosis cases, an increase in the number of psychosis patients ought to be observable following periods of increased drug use by the general population. First admissions data for the categories of drug abuse and schizophrenia/paranoid disorders from all Connecticut state hospitals from 1965 to 1983 were examined to determine the prevalence of psychotic disorders before, during, and after a period of increased drug use by the general population. Affective disorders first admissions were examined for comparison. A rapid increase in new schizophrenia admissions coincided with a peak period for drug-related admissions. The data suggest that increased drug use of the late 1960s may have contributed to the increase noted 3 to 5 years later in first admissions of patients diagnosed with psychotic disorders.

Adolescent↗
PubMed1997

A parametric study of the N40 auditory evoked response in rats.

BACKGROUND: The N40 auditory evoked potential (EP) in rats is used to study "sensory gating." Our first goal was to compare the effects of systematically varying the characteristics of the pairs of clicks (S1-S2), on the degree of attenuation of the responses to S2 stimuli. A second goal was to examine the effects of changing S2 stimuli on the degree of attenuation of the responses to the deviant stimulus. METHODS: The N40 EP was recorded from 10 rats in eight identical-pair conditions and from 11 rats in two paradigms: nonidentical pairs and short trains of identical stimuli followed by a deviant stimulus. RESULTS: In eight identical-pair conditions changing stimulus duration, intensity, or frequency had no effect on the degree of attenuation of S2 responses. Changing S2 stimulus or presenting a deviant stimulus following a train of identical stimuli had a significant effect on the degree of attenuation of the response to the deviant stimulus. CONCLUSIONS: We conclude that the rat N40 EP is sensitive to stimulus change and can contribute to the study of both habituation and dishabituation mechanisms of "sensory gating."

Acoustic Stimulation↗
PubMed1997

A fuzzy clustering approach to study the auditory P50 component in schizophrenia.

We have recently provided evidence that selective evoked response averaging based on a fuzzy clustering approach is a useful way to increase the signal-to-noise ratio, particularly when recording low-amplitude components, such as the auditory P50. We have also reported that, when stimuli are delivered in pairs (S1 followed by S2) with a short interstimulus interval, the first stimulus (S1) results in synchronization of the EEG producing a large-amplitude evoked response, whereas the second stimulus (S2) causes phase opposition resulting in a lower amplitude average evoked response. In the current study we reanalyzed data previously obtained from 13 normal volunteers and 17 chronic schizophrenia patients. Our results show that the partial EPs corresponding to the S1 stimulus are highly synchronized in normal subjects but not in schizophrenia patients. However, such a synchronization is not present after delivery of the S2 stimulus, neither in normal controls nor in patients. These findings are in agreement with previous reports of decreased amplitude of the S1 response without a significant further decrease in the amplitude of the S2 response in schizophrenia patients.

Adult↗
PubMed1997

Effects of repeated cocaine administration on sensory inhibition in rats: preliminary data.

We have recently reported that acute administration of cocaine to rats alters their sensory inhibitory capacity as tested in a paired click paradigm (S1/S2). Whether such acutely induced changes are persistent, is not known. In order to shed some light on the degree of spontaneous reversibility of cocaine-induced decreased sensory inhibition, rats were tested immediately after cocaine administration and 9 days after cessation of cocaine exposure. Six rats received cocaine HCl 20 mg/kg intraperitoneally and six rats received normal saline for 5 consecutive days. The amplitudes of the S1 responses were significantly decreased in the cocaine animals during the injection days only, but not 9 days later. Two measures of sensory inhibition were employed, S2/S1 x 100 amplitude ratio and S1-S2 amplitude difference. The ratio measure indicated a significant decrease in inhibitory capacity in the cocaine group during the injection days, and remained significantly decreased 9 days after cessation of cocaine administration. The data suggest that repeated cocaine administration can induce persistent deficit in the ability of the rat's brain to inhibit incoming irrelevant sensory stimuli.

Animals↗
PubMed1997

A fuzzy clustering approach to EP estimation.

The problem of extracting a useful signal (a response) buried in relatively high amplitude noise has been investigated, under the conditions of low signal-to-noise ratio. In particular, we present a method for detecting the "true" response of the brain resulting from repeated auditory stimulation, based on selective averaging of single-trial evoked potentials. Selective averaging is accomplished in two steps. First, an unsupervised fuzzy-clustering algorithm is employed to identify groups of trials with similar characteristics, using a performance index as an optimization criterion. Then, typical responses are obtained by ensemble averaging of all trials in the same group. Similarity among the resulting estimates is quantified through a synchronization measure, which accounts for the percentage of time that the estimates are in phase. The performance of the classifier is evaluated with synthetic signals of known characteristics, and its usefulness is demonstrated with real electrophysiological data obtained from normal volunteers.

Algorithms↗
PubMed1997

Auditory event-related potentials and statistical probability mapping in obsessive-compulsive disorder.

The current exploratory investigation was undertaken to replicate and extend previous findings of auditory event related potentials (ERPs) observed in obsessive-compulsive disorder (OCD). Similar to previous ERP studies, this study revealed a decreased slow wave (SW) (post P300) latency, a trend towards decreased P300 latency and a greater N200 amplitude in OCD subjects than in controls. In addition, the chronicity of OCD symptoms was correlated with the 140-170 millisecond integrated amplitude and the severity of OCD symptoms correlated with the 386-438 millisecond integrated amplitude. Current findings lend additional support to evidence suggesting OCD represents, in part, hyperarousal of the cortex.

Adult↗
PubMed1996

Chronic substance-induced psychotic disorders: state of the literature.

Whether or not drug use can cause a chronic psychotic disorder that is clinically similar to schizophrenia and related disorders is an important question. In this review, the authors attempt to determine whether there is enough evidence in the literature to support the notion that illicit drug use can cause chronic psychotic disorders. They conclude the literature strongly suggests that a number of drugs of abuse in different classes (psychostimulants, hallucinogens, marijuana, and possibly industrial inhalants) can cause or increase the susceptibility for a state of chronic psychosis. It is also likely that the abuse of combinations of these drugs is capable of inducing similar syndromes.

Central Nervous System Stimulants↗
PubMed1996

Diffuse electroencephalogram slowing in psychiatric patients: a preliminary report.

Diffuse slowing constitutes 40% of all electroencephalogram (EEG) abnormalities in psychiatric patients. Correlations have been demonstrated between the degree of slowing of the EEG and impairment of functions such as awareness, attention, memory, and comprehension. We conducted the current study in order to determine whether diffuse EEG slowing in hospitalized psychiatric patients correlated with hospitalization indices. Twenty-five patients with diffusely slow EEGs were selected for the study, and 25 patients with normal EEGs were matched to these subjects. Medical records were reviewed for each patient's diagnosis, length of stay, number of medications, and the dosages. Length of stay was significantly longer in the slow EEG group. The number of psychotropic medications used and the dosages of antipsychotic medications were also significantly higher in the slow EEG group. We concluded that the longer length of stay and the increased number of medications and dosages in the slow EEG group may be a reflection of increased illness severity.

Adolescent↗
PubMed1995

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.

Adolescent↗
PubMed1995

Clinical electroencephalograms in patients with catatonic disorders.

Catatonia is a neuropsychiatric syndrome of motor signs most frequently found in affective disorders and schizophrenia. Catatonic disorder due to a general medical condition has been added to the DSM-IV nosology. Laboratory studies, such as electroencephalography (EEG) may assist in the differential diagnosis of catatonic disorders. Twenty-six patients hospitalized on a general psychiatric unit or medical psychiatric unit received electroencephalograms (EEGs) as part of their routine care. Clinical EEG abnormalities were reported in 17 of these patients. The presence of abnormalities was associated with age greater than 40, diagnosis of neuroleptic malignant syndrome and the presence of general medical conditions associated with the development of catatonia. Although no specific EEG patterns were associated with catatonic disorder due to general medical conditions, these findings suggest that the EEG is an important tool in the evaluation of patients presenting with catatonia.

Adolescent↗
PubMed1994

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.

Acoustic Stimulation↗
PubMed1994

Reliability of P50 auditory event-related potential indices of sensory gating.

We examined the reliability of three traditional P50 auditory event-related potential indices under paired-click conditions: (a) the conditioning response (C), (b) the testing response (T), and (c) the testing to conditioning suppression ratio (T/C). Three alternative indices, (a) the (C - T) difference, (b) the (C - T)/(C + T) adjusted difference, and (c) the (T - T') residualized difference, where T' is the regression of T on C, were also studied. The N100 wave was used as a generalizability check. Although C and T amplitudes were reliably measured by traditional means, the T/C suppression ratio was not. For psychometric reasons that are described, the reliability of the suppression ratio is undermined principally by the correlation between C and T. The C - T difference score is a promising alternative to the unreliable T/C suppression ratio. Theoretical consequences of changed metrics are discussed.

Acoustic Stimulation↗