Pz Electrode Research Articles

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

A paradigm for measuring the olfactory event-related potential in the clinic

Recent research on the olfactory event-related potential (OERP) using inter-stimulus intervals (ISIs) of 90 s and shorter has revealed a marked decrease in component amplitude after the first trial, with a leveling off for the remaining trials. Studies manipulating the ISI in olfactory and other modalities demonstrate an association between higher amplitudes and longer ISIs, suggesting that habituation occurs at short time intervals between each stimulus presentation. The present study attempted to reduce the effects of habituation by using a 10-min ISI and fewer trials. OERPs were recorded monopolarly at the Fz, Cz and Pz electrode sites in ten subjects (five males, five females), for three trials using a 10-min ISI. Results demonstrated no significant reduction in component amplitudes across trials and no significant difference in latencies over trials, indicating no habituation effect at this ISI. These results indicate that with a 10-min ISI and three trial recordings, a complete reduction in habituation can be achieved. These findings may prove to be clinically useful to physicians who can implement this technique to assess olfactory functioning in cognitively impaired individuals or to assess malingering.

Substance abuse-related P300 differences in response to an implicit memory task

The current study examined electrophysiological measures of cognitive efficiency in alcoholics and controls using a negative priming paradigm derived from DeSchepper and Treisman (J. Exp. Psychol. Learn. Mem. Cog. 22 (1996) 27). In this task, sets of novel shapes were presented: Two overlapping green and red shapes on the left and a single white shape on the right. Participants were instructed to ignore the red shape, but to determine whether the green shape was the same as or different from the white shape. On primed trials, previously red (to be ignored; i.e., irrelevant) shapes became green (relevant) shapes in a second component of the task. Participants who were capable of ignoring irrelevant stimuli were expected to experience more difficulty in the primed condition. Therefore, we predicted that, if alcohol-related impairment in cognitive efficiency is due to inability to respond “appropriately” (i.e., ignore irrelevant stimuli), alcoholics would experience less negative priming than normal controls. Both amplitude and latency of the P300 component of the event-related potential were measured in response to each trial condition. Using a 2×2 (group×condition) ANOVA with repeated conditions, a significant pattern of group×condition interactions was observed at right frontal, F4 ( p=.05) and central parietal, Pz ( p=.03) electrode sites on measures of P300 amplitude. A significant group×condition latency interaction was observed at the central parietal electrode, Pz ( p=.006). Overall, controls exhibited increased P300 amplitude and latency in response to negatively primed trials. As predicted, alcoholics did not demonstrate this pattern, a finding consistent with alcohol-related cognitive inefficiency.

Lexical Access in College Students with Learning Disabilities

The purpose of this study was to compare the semantic processing abilities of college students with learning disabilities (LD) to those of their peers without learning disabilities (NLD) who were matched for age, gender, and intelligence. Participants were compared on results from the Test of Adolescent/Adult Word Finding (TAWF) and from event-related potential (N400) sampling to the processing of semantically incongruous sentences. The LD and NLD groups did not significantly differ in accuracy on the TAWF; however, students with LD demonstrated a significantly greater number of delayed responses. The LD group's N400 responses were significantly delayed at the Pz electrode site. Effect size indicators also revealed somewhat reduced amplitudes at Fz and Cz locations. The significant delays of the students with LD on standardized testing and on N400 suggest an inefficiency in the semantic processing of these individuals, in both automatic and attention-based aspects of lexical access.

P300 and symptom improvement in schizophrenia

A reduced amplitude of the auditory evoked P300 was interpreted as a trait marker of schizophrenia but reports about correlations between schizophrenic psychopathology and P300 amplitude indicate also a state character. To shed light upon these trait and state aspects a longitudinal study was performed to investigate the influence of symptom improvement and atypical neuroleptics on the amplitudes of the P300 and their subcomponents. P300 was recorded in 17 schizophrenic patients before and after 4 weeks under either clozapine or olanzapine in a double-blind controlled design. For comparison, 17 age- and sex-matched healthy subjects were investigated. Parietal and frontal P300 subcomponents were investigated separately using dipole source analysis. Schizophrenic patients had smaller parietal (temporo-basal dipole) but not frontal subcomponent amplitudes (temporo-superior dipole) than controls. For the whole sample subcomponent amplitudes did not change over 4 weeks despite clinical improvement but patients with a pronounced improvement of the PANSS positive score showed a slight enhancement of both subcomponents. This was not significant when the P300 amplitude was measured at a single electrode (Pz). No significant difference between clozapine and olanzapine concerning effects on P300 amplitudes were observed. The results indicate that P300 subcomponents are modulated by changes of positive but not by changes of negative symptoms or different neuroleptics. This result was obvious for P300 subcomponents but not for Pz electrode measurement, which may be due to a higher reliability of the dipole source activity. The results can be integrated into a hypothetical model containing two pathophysiological subgroups of schizophrenia.

Steep early negative slopes can be demonstrated in pre-movement bereitschaftspotential

Objectives: The study presents data suggesting that the classic bereitschaftspotential hides in its early component (BP1) steep increases of negativity which precede the movement at varying intervals in repeated trials. Methods: In 12 volunteers, surface EEG from Fz, Cz, C3, C4, and Pz electrodes and EMG from the flexor digitorum communis were recorded during self-paced wrist flexions. Two hundred trials were collected from each subject. The single trials were grouped for averaging in two different ways. In the first one, single trials for each subject were used to create individual averages. In the second, all single trials were divided into groups according to the point in time of small steep negative shift from the baseline detected on sweeps before the movement and time group averages were created. The identification of small shifts was based on the comparison of calculated mean amplitudes in the first and the second half of the 1 s time window moved along the time axis. Results: The small negative shifts were identified in 97.2% of analyzed records. In each subject, their position on the time axis varied considerably. Individual averages exhibited the characteristics of classical readiness potential, i.e. slow early component, steep late component, laterality over motor cortices. On the other hand, all time group averages (26) displayed an early steep negative shift followed by plateau which, about 0.5 s before the movement, gave rise to the second, late steep negative shift. The slope values calculated in the definite segments of averaged curves were used as a measure of the amplitude of these shifts over various brain areas. MANOVA showed a significant effect of the electrode position both in the case of early slopes ( F(4,115)=9.7; P<0.000) and in the case of late slopes ( F(4,115)=22.5; P<0.000). In both cases, the largest value was demonstrated under Cz electrode. In contrast to the late slopes, the values of early slopes did not exhibit laterality and suggested greater importance of pre-frontal regions in their formation. Conclusion: We have suggested that the formation of steep early negative shifts from the baseline in time group averages was due to synchronization of a mental process which, under classical averaging procedure, was dispersed uniformly throughout the pre-movement period.

Tactile-visual links in exogenous spatial attention under different postures: convergent evidence from psychophysics and ERPs.

Tactile-visual links in spatial attention were examined by presenting spatially nonpredictive tactile cues to the left or right hand, shortly prior to visual targets in the left or right hemifield. To examine the spatial coordinates of any crossmodal links, different postures were examined. The hands were either uncrossed, or crossed so that the left hand lay in the right visual field and vice versa. Visual judgments were better on the side where the stimulated hand lay, though this effect was somewhat smaller with longer intervals between cue and target, and with crossed hands. Event-related brain potentials (ERPs) showed a similar pattern. Larger amplitude occipital N1 components were obtained for visual events on the same side as the preceding tactile cue, at ipsilateral electrode sites. Negativities in the Nd2 interval at midline and lateral central sites, and in the Nd1 interval at electrode Pz, were also enhanced for the cued side. As in the psychophysical results, ERP cueing effects during the crossed posture were determined by the side of space in which the stimulated hand lay, not by the anatomical side of the initial hemispheric projection for the tactile cue. These results demonstrate that crossmodal links in spatial attention can influence sensory brain responses as early as the N1, and that these links operate in a spatial frame-of-reference that can remap between the modalities across changes in posture.

Apolipoprotein E epsilon4 positive individuals demonstrate delayed olfactory event-related potentials.

Apolipoprotein E epsilon4 positive individuals have deficits in the ability to identify and remember odors, as demonstrated by psychophysical measures of olfactory function. The purpose of the present study was to identify olfactory deficits in this population using an objective electrophysiological measure: the olfactory event-related potential (OERP). Olfactory and auditory ERPs were recorded from the Fz, Cz, and Pz electrode sites in 10 epsilon4 positive individuals and 10 age and gender-matched epsilon4 negative individuals in a single-stimulus paradigm. The results indicate: (1) individuals who are positive for the apolipoprotein E epsilon4 allele demonstrated delays (of approximately 100 ms) in the processing of olfactory information compared to those who are epsilon4 negative; (2) OERP latency is more sensitive than psychophysical measures of olfactory function; (3) delays in the cognitive P3 component of the OERP are associated with deficits in the ability to identify an odor; and (4) unlike the moderate ranges found in auditory ERP, OERP latency showed high sensitivity and specificity in classifying epsilon4 positive and negative individuals.

ORIGINAL ARTICLE: Inter‐peak Latency of Auditory Event‐related Potentials (P300) in Cases of Aged Schizophrenia and Alzheimer‐type Dementia

Background: Both patients with schizophrenia and those with dementia show cognitive difficulties, and in many cases of schizophrenia the cognitive disturbance is progressive, as it is in dementia. Event‐related potentials have revealed cognitive impairments in patients with schizophrenia and dementia, but most studies of event‐related potentials in cases of psychiatric illness or dementia have focused on the single peak latency of the event‐related potential components. In the present study, we investigated the cognitive function in elderly patients with schizophrenia and Alzheimer‐type dementia (AID) using auditory event‐related potentials (P300). Methods: P300 was recorded using the tone discrimination task and peak latencies for N1, P2, N2 and P3 at the Pz electrode site were measured. In addition to analyzing peak latencies of P300, we also analyzed inter‐peak latencies (IPL; N1‐P2, P2‐N2, and N2‐P3). Twenty‐two elderly residual‐type schizophrenics and 36 patients with AID were compared with 39 age‐matched healthy volunteers. Results: The mean latencies of P3 and mean IPL of P2‐N2 in elderly schizophrenic patients were longer than those of the controls. In ATD the mean latencies of N2 and P3 and the mean IPL of P2‐N2 were longer than those of the controls. When the mean latencies of ATD patients were compared with those in patients with schizophrenia, P2, N2, and P3 latencies and N1‐P2 and P2‐N2 IPL were longer. Conclusion: These findings suggest that a similar impairment of the cognitive process is found in elderly patients with schizophrenia and those with ATD and that the degree of the impairment of patients with ATD is more severe than that of elderly patients with schizophrenia.

Auditory P300 event related potential and serotonin reuptake inhibitor treatment in obsessive-compulsive disorder patients

Neuropsychological findings in obsessive-compulsive disorder (OCD) have been explained in terms of reduced cognitive shifting ability as a result of low levels of frontal inhibitory activity. This deficit could be reflected in an abnormal P300 component of the event-related potential. The improvement in cognitive processing due to pharmacological treatment would modify the P300 component, bringing it close to that of normal controls. Nineteen patients suffering from OCD and 19 normal controls were recorded. We used a computerized version of the auditory ‘odd-ball paradigm’ to obtain the P300 component at the Pz electrode. Patients were tested twice, drug-free and under treatment with clomipramine in 250–300 mg doses. We observed the P300 component to have lower amplitude and longer latency in drug-free OCD patients when compared with controls. P300 amplitude in OCD increased after treatment, although this was supported only by a statistical trend. There was no modification in P300 latency after treatment. It is possible that inhibitory activity improves with treatment and allows patients to answer with more confidence, which results in an increase in P300 amplitude. This study suggests that cognitive dysfunction in OCD fluctuates with changes in the clinical associated with treatment, probably in relationship to central serotoninergic transmission.

Increased frontal phase-locking of event-related alpha oscillations during task processing

Recent findings substantiate the view that electroencephalographic (EEG) alpha rhythm (7–13 Hz) is functionally involved in cognitive stimulus processing. Our previous results have shown that enhanced alpha responses to auditory task stimuli can be well synchronized with stimulus until 800–1000 ms. The present study analyzed the effect of perceptual uncertainty and difficulty in decision making on event-related alpha oscillations in single auditory event-related brain potentials (ERPs). EEG was recorded from Fz, Cz and Pz electrodes in 10 subjects participating in two experimental sessions, in which auditory stimuli with equal physical parameters were presented under passive and task instructions. Separate measurements of single alpha response amplitude and phase-locking were performed and statistically analyzed for consecutive time windows in the post-stimulus epoch. Major results show that, during the cognitive task, the phase-locking of alpha oscillations at the frontal site is significantly increased in the time window of 500–1000 ms after stimulation. Thus, the involvement of enhanced and synchronized frontal alpha activity in higher brain processes is strongly emphasized.

The Effects of Performance Enhancement Training on Hypertension, Human Attention, Stress, and Brain Wave Patterns

Abstract Background: The purpose of this study was to evaluate the effects of alpha-increase neurofeedback training (Performance Enhancement Training) on blood pressure, stress reduction, attention, and observe changes in brainwave patterns. A forty-nine-year-old male college student diagnosed with essential hypertension controlled by medication had undergone twenty-six sessions of alpha-increase biofeed-back (8-13 Hz) at PZ electrode site for a period of 15 weeks. Method: Pre- and post-blood pressure measurements were taken for every session. At the beginning of week number eight, the participant discontinued his medication as advised by his physician. Pre- and post-visual TOVA CPT test was administered to assess the changes in accuracy, reaction time (RT), and RT variability. Osterkamp and Press Self-Assessment Stress Inventory was administered before and after training to assess the level of stress. QEEG evaluation was conducted prior, as well as upon completion of the study. Results: Mean Arterial Blo...

P300 component of visual event-related potentials distinguishes patients with idiopathic parkinson's disease from patients with essential tremor.

A considerable rate of misdiagnosis has recently been reported in movement disorders. One of the most difficult clinical problems is the differentiation of Parkinson's disease and essential tremor. In this study, we have examined whether event-related potentials (ERPs) could aid in the solution of this differential diagnostic problem. Visual ERPs were obtained by using an "oddball" paradigm in 20 patients with idiopathic Parkinson's disease (IPD), 20 patients with essential tremor (ET), and 20 age-matched control subjects. We found that the P300 amplitudes were selectively reduced in the IPD group at the midline (Fz, Cz, Pz) electrode sites, whereas the ET group exhibited selectively elevated P300 amplitudes at the left parietal and frontal (F3, P3) recording sites. The patients with IPD, but not ET, showed a significant prolongation of the P300 latency at each electrode site. Similarly, only the IPD patients were significantly slower in responding to the target stimulus. The primary visual evoked potential (P100) did not distinguish among the IPD, ET, and control subjects. These results suggest that visual ERPs might provide a useful diagnostic method for differentiating IPD from ET.

Reappraisal of Filter Effects on P300 Voltage and Latency

The selection of which high-pass filter cutoff to use in P300 studies continues to be a serious methodological consideration. To determine whether there was an optimal range of bandpass widths-a range in which P300 voltage and latency would not show statistically significant differences-the authors recorded P300 responses to the auditory "oddball" paradigm from Cz and Pz electrodes in a group of eight healthy males. The authors used high-pass filter cutoffs of 0.01, 0.1, 0.3, and 1.0 Hz with low-pass filter cutoffs of 30 and 100 Hz and measured both P300 peak voltages and P300 integrated mean voltages at 12 bandpass settings. There were statistically significant differences in 7 out of 12 bandpass comparisons for P300 peak voltages and in 7 out of 12 bandwidth comparisons for P300 integrated mean voltages. For P300 latencies, there were statistically significant differences in 9 out of 12 bandwidth comparisons. Based on these results, the best recommendation, therefore, is that the high-pass filter be set no higher than 0.3 Hz.

Olfactory event-related potentials and aging: normative data

Unlike the clinical usages of evoked potentials (e.g. brain stem auditory evoked potentials for the assessment of auditory function), normative data for the olfactory event-related potential (OERP) have been unavailable. The principal objective was to establish normative data across the human life span for OERPs with a given set of parameters. Participants were 140 persons from seven age groups (16–19, 20–29, 30–39, 40–49, 50–59, 60–69 and 70–79 years of age), with equal numbers of males and females, screened for nasal health and dementia. The odor stimulus was amyl acetate, presented at nasal temperature in a humidified airstream delivered by an air-dilution olfactometer at a constant flow rate, using a 60-s inter-stimulus interval. OERPs were recorded at Fz, Cz, and Pz electrode sites, amplified and averaged over trials. Amplitudes of the N1/P2 and P3 and latencies of the P2 and P3 were analyzed. Processing speed decreased at a constant rate over decades for the sensory (P2 latency) as well as cognitive (P3 latency) components. Decline in amplitude over decades was also apparent. Normative data will be useful in research on olfactory function and in clinical assessment of olfactory functional status.

Pain measurement with evoked potentials: combination of subjective ratings, randomized intensities, and long interstimulus intervals produces a P300-like confound

Evoked potentials in response to painful stimuli have been studied as objective measures of pain. Bromm has advocated experimental conditions in which, (1) stimulus intensities are randomized, and (2) subjects rate each stimulus. However, a cognitive, i.e. information processing, ‘late positive component’ (LPC), e.g. the P300, may be elicited by these same conditions, whether or not the stimuli are painful. The LPC may overlap, and interfere with the measurement of, responses that are only seen with painful stimuli. We compared the LPC in two experimental protocols using ten subjects and electrical stimuli. In the ‘Rating Protocol’, shocks of different intensity levels were randomly presented and subjects rated the intensity of each stimulus. In the ‘Oddball Standards Protocol’, the same levels were used, but each was presented in a separate block of a single level. Stimuli were presented more rapidly and subjects had to push a button in response to occasional double shocks (oddball targets), but not to single shocks (oddball standards). The oddball targets served to direct subjects’ attention to the stimuli, but only the evoked potential responses to the oddball standards were used for data analysis. To look at the difference between protocols, we computed a difference condition (Rating protocol responses minus Oddball Standards protocol responses) which we called Incremental activity. The Incremental LPC (average amplitudes from 350 to 650 ms) had a more parietal topography (amplitude at electrode Pz greater than at Cz) than the Oddball Standards LPC (Cz>Pz; protocol×electrode interaction P<0.001). This implies that the Rating Protocol LPC included P300-like activity. The parietal Incremental activity began as early as 250–350 ms after the stimulus in the responses to the most painful stimuli and therefore can confound the measurement of pain activity in the evoked potential.

Effects of Serotonin-Selective and Classical Antidepressants on the Auditory P300 Cognitive Potential

The cognitive potential, P300, is a phenomenon frequently studied in relation to template matching of the brain. To understand the neurochemical mechanisms of its generation, we compared the effects of three antidepressants, fluoxetine, tianeptine and clomipramine after single and repeated application as well as after 1 week of withdrawal on the P300 and N200 waves in an auditory ‘odd-ball’ paradigm in three parallel groups of 10 healthy volunteers. Following single administration, both fluoxetine and clomipramine reduced (–39 ± 14%, p < 0.01) the peak amplitude of P300 at the Pz electrode. For fluoxetine and tianeptine, reduced amplitudes of 19 ± 7% and 24 ± 11%, respectively, were found following 8 days of treatment, 2 h after administration. However, for clomipramine no additional diminution was found on day 8 with respect to day 1. Topographic distributions tended to be significantly modified at the frontal scalp area 1 h after the tianeptine administration on day 8, whereas the postdosing changes induced by fluoxetine were localised in the midline and right centrotemporal scalp regions. Only minor reductions in peak latencies have been observed. It can be concluded that serotonin selective drugs have a slower onset of P300 amplitude decrease than clomipramine, which has additional effects on monoaminergic and on cholinergic systems. These results suggest that serotonin has a regulatory function in the neurotransmission of cerebral structures which are involved in the evaluation of stimulus relevance.

Event-related alpha oscillations in task processing

Objectives: Recent findings substantiate the view that electroencephalographic (EEG) alpha rhythm (7–13 Hz) is functionally involved in information processing. However, the association of alpha rhythms with cognitive brain processes is less well understood because both augmentation and suppression of alpha oscillations have been observed to accompany task performance. The present study evaluates the effect of task processing on event-related alpha oscillations at the level of single-sweep analysis.Methods: EEG was recorded from Fz, Cz and Pz electrodes in 10 subjects participating in two experimental sessions, in which auditory stimuli with equal physical parameters were presented under different instructions (passive and task). Separate measurements of single-sweep amplitude and phase-locking were performed and statistically analyzed for consecutive time windows in the poststimulus epoch.Results: Major results show that, during the cognitive task, the phase-locking of alpha oscillations at the frontal site is significantly increased for the time window of 500–1000 ms after stimulation.Conclusions: The involvement of enhanced and synchronized frontal alpha activity in higher brain processes is strongly emphasized.

Individuals with Down's syndrome demonstrate abnormal olfactory event-related potentials

Objective: Recent research has demonstrated that individuals with Down's syndrome (DS) develop plaques and tangles in the brain similar to people with Alzheimer's disease. As a result, they show increased dementia and decreased olfactory functioning compared to healthy individuals. The olfactory event-related potential (OERP) has been used as an objective quantitative measure of olfactory functioning in normal and clinical populations. The present study investigated the utility of the latency and amplitude of the OERP components in examining olfactory dysfunction in DS individuals.Methods: OERPs were recorded monopolarly at the Fz, Cz and Pz electrode sites, using amyl acetate at a 60 s inter-stimulus interval, from individuals with DS (mean age 26.0 years) and age-matched normal controls. Participants were screened for nasal health and odor thresholds were assessed. Dementia was assessed using the dementia rating scale (DRS).Results: Results indicate that DS subjects have significantly longer latencies in the sensory (N1, P2, and N2) and cognitive (P3) components of the OERP than normal controls. Odor threshold was significantly associated with sensory OERP components. In addition, DS subjects with a higher level of dementia showed significantly longer P3 latencies than those with lower dementia levels.Conclusions: The study suggests that the OERP may be a useful measure of olfactory dysfunction in DS which may precede developing dementia in this population.

Olfactory P3 in young and older adults.

Olfactory event-related potentials (OERPs) were recorded monopolarly at the Fz, Cz, and Pz electrode sites in 16 young adults and 16 older adults to assess aging effects on the olfactory P3. Amyl acetate was used to elicit the OERPs, with an intertrial interval of 45 s. Young adults produced significantly larger P3 amplitudes and shorter P3 peak latencies than older adults. The olfactory P3 response appears to be sensitive to age-related changes in the olfactory system and may reflect cognitive slowing in the central nervous system.