P50 variations in Behcet`s patients without neurologic findings.

OBJECTIVE: In the present study, subclinical lesion involvement was investigated using the P50 component in Behcet`s patients without neurological manifestation. METHODS: We performed this clinical research in Erciyes University, Faculty of Medicine between December 2000 and November 2001. The studies were carried out on 18 Behcet`s patients without neurologic findings and 18 volunteers for control. Standard Ag/AgCl electrodes in plastic cups were used for monopolar EEG derivations. They were attached with electrode paste and tape at the Cz (vertex) according to the 10-20 system. The auditory stimuli were delivered in pairs. The P50 waves, which may be taken from approximately 50 msec from the stimuli, were collected by computer system. Amplitudes and latencies of the P50 components were measured in the same system. RESULTS: This study showed that the suppression of P50 responses performed by the test stimuli, was significantly more decreased in Behcet`s patients than the control subjects. CONCLUSION: The decrease of the suppression of the auditory P50 response to repeated stimuli reflects a deficit in the central nervous system`s ability, such as attention, cognition, and sensory input in Behcet`s patients and can be used as a neurophysiological marker in subclinical lesions in these patients.

Effect of PUVA therapy on electrodermal activity parameters in vitiligo patients.

UNLABELLED: Recent electrophysiological studies on autonomic dysfunction in vitiligo patients show an autonomic dysfunction as measured by absent sympathetic skin response (SSR). Nothing is known about the reversibility of these autonomic parameters with treatment. The present study examined how Electrodermal Activity (EDA) parameters were affected from vitiligo illness before PUVA therapy and whether any electrophysiological gains acquired from PUVA therapy would influence the progression of the condition itself. We studied in 14 healthy subjectS and 14 patients with generalized vitiligo before and after treatment. EDA was recorded with a skin conductance unit connected to a personal computer. Before treatment, skin conductance level (SCL) and habituation number (HN) was higher in vitiligo group than control groups. After treatment, SCL and HN were decreased nearly to normal value. Before and after treatment, prevalence of non-responsivity was higher in vitiligo group than controls. CONCLUSION: The sympathetic nervous system might have a particular role in the pathogenesis of vitiligo. Thus, patients with vitiligo may have changes to EDA parameters that are reversible to great extent with PUVA therapy. EDA is a useful method of studying the autonomic dysfunction in humans.

Effects of olanzapine on auditory P300 in schizophrenia.

Reduced auditory P300 amplitude generally has been considered to be a trait marker of schizophrenia, independent of antipsychotic treatment and clinical symptoms. However, several seemingly well-conducted studies have found P300 amplitude to be a state marker correlated with clinical symptoms. Recent research on atypical antipsychotics indicate that these medications may alter P300 amplitude as well as having beneficial clinical effects. The objective of the present study was to further elucidate the effects of schizophrenia, symptom severity, and medication status on the P300. The baseline auditory P300 was assessed in unmedicated schizophrenic patients who then were treated with olanzapine for 6 weeks and reassessed. Healthy control subjects were assessed at baseline and again at 6 weeks. Compared to healthy controls, the unmedicated patients' P300s were attenuated and delayed prior to treatment. Subsequent antipsychotic treatment increased the patients' P300 amplitudes without affecting latency. Frontal P300 amplitude was normalized, but parietal P300 amplitude remained below that of healthy controls. Although olanzapine was effective in reducing the patients' symptoms, there were no correlations between symptoms and P300 amplitude or latency either before or after treatment. The results of the present study lend support to the view that P300 amplitude behaves as a trait marker. No evidence is found of a P300 clinical state marker.

Effect of hyperglycemia on electrodermal activity in diabetic rats.

This study investigated the relationship between hyperglycemia and electrodermal activity (EDA) parameters in streptozotocin (STZ) induced diabetic rats. The article evaluates the course of development of neurophysiological alterations in the peripheral nervous system in diabetic rats through EDA. Rats were made diabetic using a moderate dose of STZ (DI) and high dose (DII). The placebo group (P) was injected with physiological saline. EDA was recorded 1 h before the injection (beginning, 0, day), 1st day (one day after the injection) and 10th day. Skin conductance level (SCL) was lower in DII than P on the 1st and the 10th days. The SCL and SC fluctuation rate (SCFr) of DI were significantly lower on the 10th day compared to their first record. SC response rate (SCRr) was lower on the 10th day compared to the 1st day, in the DI. In the DI, SCL, SC fluctuation rate (SCFr) and SC response rate (SCRr) were lower on the 10th day compared to the 1st day. The DII was statistically higher in electrodermal non-responsiveness compared to other groups on the 1st day. The results obtained show that hyperglycemia affects the peripheral nervous system, and EDA parameters are affected by blood glucose level. It is suggested that EDA is a simple and non-invasive electrophysiological method in early diagnosis of diabetic neuropathy.

The effect of immobilization stress on sensory gating in mice.

Central sensory filtering processes can be demonstrated using a paired stimulus paradigm. Normal humans show a diminished, vertex-recorded mid-latency (50 ms) of auditory evoked potential to the second of paired clicks (0.5 s apart), a phenomenon termed as auditory gating. A loss of 50 ms in auditory gating is strongly related to psychosis. The N40 auditory evoked potential (EP) in rats has been used to develop an animal model for the study of sensory gating mechanisms. Previous animal studies of auditory gating have used psychotomimetic drug administration to induce sensory gating. However, a nonpharmacologic model of deficient gating would be advantageous. In the present study we investigated the effect of immobilization stress on sensory gating in twelve adult male mice. Evoked responses to the paired auditory click stimuli from vertex location of scalp were recorded using a silver needle electrode, a bioelectric amplifier, and an analog-digital converter. The mice were exposed to immobilization stress (IS) for 3 h. Data showed that the N40 potential was depressed in response to the second of the paired stimuli before application immobilization stress. At the end of the 3-h immobilization, the depression of the second N40 response was not observed. It was concluded that sensory gating is present in the mice and acutely disrupted by stressful stimuli, as shown in human subjects and rats.

Effects of cigarette smoking on cognitive processing.

Several previous studies have reported that cigarette smoking enhances performance of cognitive processing. These enhancements are generally attributed to the pharmacological effects of nicotine, while there is some debate whether the effects of smoking/nicotine are a result of recovery from abstinence. Evoked potentials (EPs) and event related potentials (ERPs) of the brain have been applied as an index of information processing in a wide variety of normal and cognitive impaired subjects. This study was carried out on 20 healthy students (23 +/- 2.3 years old) from the medical faculty of City University. Study population comprised ten chronic cigarette smokers consuming an average of 14 +/- 4.2 cigarettes per day, with a history of smoking for more than one year. Ten non -smokers served as control. Standard oddball paradigm was presented, and EEG activity was recorded at the Fz, Cz, Pz electrode sites. Twenty responses to target stimuli were averaged at each location. N1, P2, N2, and P300 components were evaluated in these recordings. Amplitudes were measured relative to prestimulus baseline, and peak latencies were defined as the time point of maximum amplitude. It was found that there were no significant differences between either N1, P2, N2, P300 amplitudes or peak latency values of cigarette smokers and non smokers. As a result, chronic cigarette smoking generally does not improve cognitive processing.

Sex-related differences in time estimation and the role of expectancy.

In this study, using auditory sequences, the authors designed an examination with three phases of stimulus-driven attention that is based on the possibility that involuntarily time shifts of attention are caused by nonunique stimulus properties. The purpose was to investigate whether attending and temporal expectancies are influenced by stimulus's properties and by sex. In each phase, an auditory stimulus train was presented, and the participant was asked to tap rhythmically in order to anticipate every fifth stimulus (or, in the third phase, the lack of it). The time between button pressing and stimulus onset was measured using a computer. Time estimation was accepted as a false response if the subject responded before 150 ms or 150 ms later from onset stimulus time. Error numbers were greater in Phase 3 and there was no significant difference between the male and female subjects for any of the phases when error numbers were compared. On the other hand, males pressed the button more accurately than females. Time estimation performance was affected by sex and expectancy-related motor responses are very important for time estimation.

Evaluation of auditory evoked potentials from the inferior colliculus in rat.

This study aimed to investigate the usefulness of auditory evoked potentials (AEPs) in rats. To this end, N1, P2 latencies, and the N1-P2 amplitude of responses to different acoustic stimuli from rats, which were implanted with permanent electrodes in the inferior colliculus (IC), were evaluated and used to demonstrate the frequency characteristics of IC region. Permanent electrodes were implanted in IC regions of 7 male albino rats by the stereotaxic method. The animals were exposed to five tones series of stimuli (1000 Hz, 2000 Hz, 4000 Hz, 6000 Hz, and 8000 Hz tones with 1500 ms interstimulus intervals) of 70 dB with a duration of 1000 ms. AEPs) were recorded and analyzed with the Brain-Data Acquisition system. There were no statistically significant differences in N1, P2 latencies, and the N1-P2 amplitude of AEPs from IC regions of rats as a result of changes in the frequency of stimulus. It was determined that the dominant frequency activity of the IC to acoustic stimulus was theta-alpha band, with theta as the peak frequency.