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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
PubMed2006

Sensory gating of auditory evoked and induced gamma band activity in intracranial recordings.

Oscillatory activity in the gamma band range (30-50 Hz) and its functional relation to auditory evoked potentials (AEPs) is yet poorly understood. In the current study, we capitalized on the advantage of intracranial recordings and studied gamma band activity (GBA) in an auditory sensory gating experiment. Recordings were obtained from the lateral surface of the temporal lobe in 34 epileptic patients undergoing presurgical evaluation. Two kinds of activity were differentiated: evoked (phase locked) and induced (not phase locked) GBA. In 18 patients, an intracranial P50 was observed. At electrodes with maximal P50, evoked GBA occurred with a similar peak latency as the P50. However, the intensities of P50 and evoked GBA were only modestly correlated, suggesting that the intracranial P50 does not represent a subset of evoked GBA. The peak frequency of the intracranial evoked GBA was on average relatively low (approximately 25 Hz) and is, therefore, probably not equivalent to extracranially recorded GBA which has normally a peak frequency of approximately 40 Hz. Induced GBA was detected in 10 subjects, nearly exclusively in the region of the superior temporal lobe. The induced GBA was increased after stimulation for several hundred milliseconds and encompassed frequencies up to 200 Hz. Single-trial analysis revealed that induced GBA occurred in relatively short bursts (mostly <<100 ms), indicating that the duration of the induced GBA in the averages originates from summation effects. Both types of gamma band activity showed a clear attenuation with stimulus repetition.

Acoustic Stimulation↗
PubMed2005

Sensory gating in the human hippocampal and rhinal regions.

OBJECTIVE: The objective of this work was to ascertain if sensory gating can be demonstrated within the human medial temporal lobe. METHODS: Eight patients with intractable epilepsy with depth electrodes implanted in the medial temporal lobe for pre-surgery evaluation underwent evoked response recording to auditory paired-stimuli (S1-S2). Each of the eight subjects had a diagnosis of left medial temporal lobe epilepsy (MTLE). RESULTS: Data from the non-focal right hippocampi revealed a large negative response on S1 (starting at about 190 ms and lasting for approximately 300 ms from stimulus onset). Rhinal region recordings revealed a positive response (starting at about 240 ms with a rapid incline, followed by a long-lasting decline). A significant attenuation of both responses to S2 stimuli was observed. CONCLUSIONS: Data are suggestive of an involvement of the human medial temporal lobe in the processing of simple auditory information which occurs in a time frame later than the neocortical auditory evoked components. The exact role of these anatomical structures in the sensory gating process remains to be defined. SIGNIFICANCE: This study provides the first evidence of an activation of the rhinal cortex after simple auditory stimulation and provides new evidence that the activation of the medial temporal lobe structures occurs at a later stage than that of the neocortex.

Acoustic Stimulation↗
PubMed2001

Auditory verbal hallucinations and dysfunction of the neural substrates of speech.

OBJECTIVE: to evaluate the neural substrate of auditory verbal hallucinations (AVH), the correlation between AVH and subvocal speech (hereafter SVS), and the relationship between speech and AVH. METHOD: we reviewed the papers found by an electronic literature search on hallucinations and speech. The review was extended to the papers cited in these publications and to classical works. RESULTS: there is no conclusive evidence of structural abnormality of the speech perception area in hallucinating schizophrenic patients. However there is evidence of electrophysiological abnormalities of the auditory and speech perception cortices. Functional imaging data are inconsistent, yet point to the left superior temporal gyrus as one of the neural substrates for AVH. There is also evidence that SVS could accompany the experience of AVH. CONCLUSION: there is evidence that dysfunction of brain areas responsible for speech generation is a fundamental mechanism for generating AVH in schizophrenia. It results in a secondary activation of Wernicke's area (speech perception) and Broca's area (speech expression). The first leading to the experience of hallucinations, and the second, eventually, gives rise to a variable degree of vocal muscle activity detectable by EMG, and/or faint vocalizations detectable by sensitive microphones placed at proximity of the larynx. Direct stimulation or disease of Wernicke's area produces AVH without SVS.

Brain↗
PubMed2001

Elevated motor threshold in drug-free, cocaine-dependent patients assessed with transcranial magnetic stimulation.

BACKGROUND: Transcranial magnetic stimulation (TMS) provides a noninvasive method of examining cortical inhibitory and excitatory processes and cortical excitability in awake subjects. There is evidence from clinical and electroencephalographic (EEG) data that cortical excitability may be abnormal in some psychiatric populations. Chronic cocaine abuse influences a number of neurotransmitters that are involved in the excitatory/inhibitory balance of the cerebral cortex. This pilot study was conducted to ascertain the possible utility of TMS in examining cortical excitability in a population of chronic cocaine abusers. METHODS: The right and left motor thresholds of ten cocaine-dependent subjects, according to DSM-IV, and ten normal control subjects were examined using single pulse TMS. RESULTS: The resting motor thresholds resulting from stimulation of the right or the left motor cortical regions were significantly elevated in cocaine-dependent subjects compared with matched control subjects. CONCLUSIONS: These pilot data suggest that chronic cocaine use significantly alters cortical excitability in the direction of increased inhibition or decreased excitability. We hypothesize that this observation reflects adaptation to those effects of cocaine intoxication that promote cortical excitability and seizures.

Adult↗
PubMed2001

EEG monitoring in depressed patients undergoing repetitive transcranial magnetic stimulation.

To date, 33 subjects diagnosed with major depressive disorder have undergone transcranial magnetic stimulation (TMS) in the authors' clinic. Five of these patients showed minimal electroencephalogram (EEG) variants at baseline. The authors describe the course of treatment and serial EEGs in 3 of the 5 patients who did not show progressive EEG changes in association with active rTMS. These three cases suggest that minimal EEG anomalies at baseline need not serve as a contraindication to undergoing rTMS. Two patients with progressive EEG changes in association with sham rTMS in one and active rTMS in the other are also discussed.

Adult↗
PubMed2001

Effect of tryptophan depletion on alcohol cue-induced craving in abstinent alcoholic patients.

BACKGROUND: The capacity of alcohol cues to precipitate the desire to drink may be an important determinant of relapse to alcohol use in recovering alcohol-dependent patients. This study evaluated whether attenuation of serotonin synthesis via depletion of its precursor tryptophan reduces the magnitude of cue-induced craving for alcohol in recently abstinent alcoholic individuals. METHODS: Alcohol-dependent patients (n = 16), 1 to 3 months after detoxification, who exhibited a 20% or greater increase in reported craving when presented with an alcoholic beverage, completed two additional alcohol cue-exposure test days, 1 week apart. Each cue exposure was preceded by administration of a concentrated amino acid drink that resulted in a rapid and significant decline in plasma free tryptophan (active depletion, no tryptophan supplementation) or a similar drink containing tryptophan (placebo depletion). Tests were conducted in a randomized, double-blind fashion. RESULTS: There were no significant changes in the magnitude of cue-induced craving with active tryptophan depletion compared with placebo. CONCLUSIONS: These data question the dependence of alcohol cue-induced craving in sober alcoholics on the ongoing synthesis of serotonin.

Adult↗
PubMed2000

A randomized clinical trial of repetitive transcranial magnetic stimulation in the treatment of major depression.

BACKGROUND: Multiple groups have reported on the use of repetitive transcranial magnetic stimulation (rTMS) in treatment-resistant major depression. The purpose of this study is to assess the efficacy of rTMS in unmedicated, treatment-resistant patients who meet criteria for major depression. METHODS: Depressed subjects, who had failed to respond to a median of four treatment trials, were assigned in a randomized double-blind manner to receive either active (n = 10; 20 2-sec trains of 20 Hz stimulation with 58-sec intervals; delivered at 80% motor threshold with the figure-of-eight coil positioned over the left dorsolateral prefrontal cortex) or sham (n = 10; similar conditions with the coil elevated and angled 45 degrees tangentially to the scalp) rTMS. These sequences were applied during 10 consecutive weekdays. Continuous electroencephalogram sampling and daily motor threshold determinations were also obtained. RESULTS: The group mean 25-item Hamilton Depression Rating Scale (HDRS) score was 37.2 (+/- 2.0 SEM) points. Adjusted mean decreases in HDRS scores were 14.0 (+/- 3.7) and 0.2 (+/- 4.1) points for the active and control groups, respectively (p <.05). One of 10 subjects receiving active treatment demonstrated a robust response (i.e., HDRS decreased from 47 to 7 points); three other patients demonstrated 40-45% decreases in HDRS scores. No patients receiving sham treatment demonstrated partial or full responses. CONCLUSIONS: A 2-week course of active rTMS resulted in statistically significant but clinically modest reductions of depressive symptoms, as compared to sham rTMS in a population characterized by treatment resistance.

Adolescent↗
PubMed2000

Electroencephalogram and repetitive transcranial magnetic stimulation.

Scalp recordings of the electroencephalogram (EEG) have been used in association with repetitive transcranial magnetic stimulation (rTMS) investigations as a safety measure in monitoring ongoing EEG activity and as a neurophysiologic tool in examining the specific effects induced by the magnetic stimulus on the EEG or evoked potentials (EPs). Medline review on the use of EEG or EPs with rTMS reveals that this area has been largely unexplored. Limited available studies attest to the potential for studies combining EEG/EPs and rTMS to be useful in further elucidating the normal brain physiology. Herein, we report on our experience with continuous EEG sampling combined with rTMS in patients with major depression (n = 14), schizophrenia (n = 7), and obsessive-compulsive disorder (n = 5). Our data support the practice of using continuous EEG monitoring when the stimulation parameters fall outside established safety guidelines.

Brain Mapping↗
PubMed2000

Similarities in the disturbances in cortical information processing in alcoholism and aging: a pilot evoked potential study.

OBJECTIVE: To examine the hypothesis that chronic alcohol use causes accelerated aging of the brain. METHODS: The auditory evoked potentials (EPs) were compared in three groups of 10 subjects each: (a) middle-aged individuals meeting DSM-IV criteria for alcohol dependence, (b) age- and gender-matched group of healthy individuals, and (c) an older (>65 years) group of gender-matched healthy individuals. Multiple levels of cortical information processing were examined using EPs. Early stages of information processing, related to sensory gating and stimulus classification (P50, N100/P200), were studied using a paired-click paradigm. Later stages of information processing associated with memory upgrading and identification of novel stimuli (P300) were studied using an oddball paradigm. RESULTS: The amplitude and latency of the P300 of the alcoholic patients and the older healthy subjects differed significantly from those of the younger healthy group. Both groups showed changes that have been reported in association with aging. A tendency towards decreased sensory gating in later stages of information processing was noted in the aged healthy individuals. CONCLUSIONS: These data suggest that alcohol dependence may accelerate the aging process. The tendency towards a sensory gating deficit during the attentive phase of information processing in older healthy subjects requires further investigation because it may be a marker for an increased proneness to developing psychotic symptoms in that group.

Adult↗
PubMed1999

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.

Adult↗
PubMed1999

Transcranial magnetic stimulation of left temporoparietal cortex in three patients reporting hallucinated "voices".

BACKGROUND: Prior studies suggest that auditory hallucinations of "voices" arise from activation of speech perception areas of the cerebral cortex. Low frequency transcranial magnetic stimulation (TMS) can reduce cortical activation. METHODS: We have studied three schizophrenic patients reporting persistent auditory hallucinations to determine if low frequency TMS could curtail these experiences. One hertz stimulation of left temporoparietal cortex was compared with sham stimulation using a double-blind, cross-over design. RESULTS: All three patients demonstrated greater improvement in hallucination severity following active stimulation compared to sham stimulation. Two of the three patients reported near total cessation of hallucinations for > or = 2 weeks. CONCLUSIONS: TMS may advance our understanding of the mechanism and treatment of auditory hallucinations.

Adult↗
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↗