P300 and slow wave from oddball and single-stimulus visual tasks: inter-stimulus interval effects.

The effects of inter-stimulus intervals on P300 from an oddball task (target and standard stimuli) and a single-stimulus task (targets only) employing simple visual stimuli were assessed in order to determine how a relatively long ISI affects event-related brain potentials (ERPs). Young adult subjects (n=16) responded by pressing a button to a visual target stimulus of each task condition. ISI was either 2.5 or 30 s and paradigm type was either the oddball or single-stimulus task. ERPs were recorded from the midline electrodes, with amplitude, mean area, and latency of the P300 and other components assessed. The results showed that P300 morphology was dramatically affected by task and ISI such that under the 2.5 s condition, the oddball paradigm produced typical ERP components, whereas the single-stimulus condition demonstrated minimal P300 amplitude. When ISI was 30 s, both the oddball and single-stimulus tasks produced robust P300 components but also evinced strong slow wave (SW) potentials, which contributed to the ERP measurement outcomes. It is concluded that P300 from visual stimuli can be elicited with both oddball and single-stimulus tasks when ISI is relatively long. ERPs from both paradigms produced appreciable SW activity, which needs to be considered when long ISI procedures are employed.     

P300 topography and modality effects from a single-stimulus paradigm

The P300 event-related brain potential (ERP) was elicited with auditory and visual stimuli in two different tasks. The oddball paradigm presented both target and standard stimuli; the single-stimulus paradigm presented a target but no standard stimulus, with the intertarget interval the same as that for the oddball condition. Target probability was .20 for the oddball task, with target stimuli occurring at the same temporal frequency in the single-stimulus paradigm. Scalp topography was assessed with 15 electrode locations. P300 amplitude was larger and latency was longer for the oddball than for single-stimulus procedure. P300 from auditory stimuli was smaller and shorter in latency than that from the visual stimuli, and both modalities showed similar but not identical scalp topographies. The findings suggest that the single-stimulus paradigm may be useful in experimental and applied contexts that require very simple ERP task conditions.     

Event-related brain potentials to attended and ignored olfactory and trigeminal stimuli.

Event-related brain potentials (ERPs) were recorded from 26 young adults, with equal numbers of male and female subjects, using attended and ignored, olfactory and trigeminal stimuli. The amplitudes and latencies of the N1, P2, and P3 components were recorded using a single-stimulus paradigm, with an inter-stimulus interval of 60 s, employing amyl acetate as the olfactory stimulus and ammonia as the trigeminal stimulus. Subjects estimated stimulus intensity in the attend condition or continued with a visual tracking task in the ignore condition. Results indicate that olfactory information is processed 30-70 ms faster than trigeminal information for the N1 and P2 potential and 100 ms faster for the P3 ERP component. N1/P2 interpeak amplitude was greater for the trigeminal than the olfactory stimuli, and greater in the attended than ignored condition. P3 amplitude was greater in the attend than ignore condition for olfactory information processing and equivalent for trigeminal information processing. These findings suggest that neuronal resource allocation is greatest for attended stimuli and that a painful stimulus demands neuronal resources even when ignored.     

Reliability analysis of event-related brain potentials to olfactory stimuli

Olfactory event-related potentials (OERP) have been used to investigate olfactory processing in health and disease. However, the reliability of the OERP has yet to be established statistically. The present study examined test-retest reliability of the OERP over a 4-week interval. EEG was recorded from Fz, Cz, and Pz, using a single-stimulus paradigm with amyl acetate. Reliabilities for ERP component latencies and interpeak amplitudes were assessed as intraclass and Pearson product-moment correlation coefficients. Reliabilities were higher for latency than for amplitude. Highest correlation coefficients were observed for P2 latency, specifically at Cz and Pz P3 amplitude and latency exhibited high reliability at Cz and Pz. Fz demonstrated weakest correlation coefficients. The data suggest that OERP reliability is comparable to that of auditory and visual ERPs, supporting the use of OERPs in both basic research and clinical assessment.     

P300 habituation from auditory single-stimulus and oddball paradigms.

The habituation of auditory P300 event-related brain potential (ERP) from single-stimulus paradigm was evaluated and compared to that from oddball paradigm. Three task conditions were: oddball with a button press (oddball/press) response, single-stimulus with a button-press (single-stimulus/press) response and a silent count (single-stimulus/count) response. The oddball/press condition demonstrated larger P300 amplitude and longer latency overall than either single-stimulus condition, but P300 amplitude decreased and peak latency increased similarly over successive trial blocks for all three tasks. Thus, the oddball and single-stimulus ERP tasks produce analogous changes under repeated measurements and indicate that the single-stimulus task can serve as an alternative method for eliciting the P300 in applied and clinical settings.     

Evaluation of auditory, visual and olfactory event-related potentials for comparing interspersed- and single-stimulus paradigms

Background

An interspersed-stimulus paradigm (ISP) for event-related potential (ERP) recordings in which different sensory modality stimuli are presented within the same test session was developed to minimize recording time and facilitate modality comparison. The present study compared the ISP with a single-stimulus paradigm (SSP), using auditory, visual, and olfactory stimuli.

Method

Normal participants (n = 16) were assessed on two independent test occasions to obtain data on inter-paradigm and test-retest reliability. Peak amplitude/latency and area measures were obtained for the N1, P2 and P3 peaks for each paradigm.

Results

Except for larger auditory and visual P3 peaks and smaller visual P2 peaks in the ISP, no significant differences in amplitudes or latencies were found between the two paradigms. Correlation coefficients between paradigms were generally fairly high (amplitude mean r = 0.76; latency r = 0.42). Test-retest reliability within paradigms for amplitudes (ISP r = 0.70; SSP r = 0.68) and latencies (ISP r = 0.44; SSP r = 0.42) was similar across paradigms.

Conclusion

The findings suggest that the ISP, compared to the SSP, produces, in general, highly comparable auditory, visual, and olfactory peak amplitudes and latencies, and comparable reliability estimates, even though the ISP takes much less time to record (25 vs. 50 min). The larger auditory and visual P3 peaks and smaller visual P2 peaks in the ISP may be attributable to a less predictable stimulus environment. Thus, this method enables systematic comparisons of ERP peaks across sensory modalities while reducing testing time. Practical implications are discussed.     

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.     

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.     

"Initial-" and "change-orienting reactions": an analysis based on visual single-trial event-related potentials

The present study was concerned with brain potentials elicited by, respectively, the first of a series of stimuli ("initial-orienting reaction", I-OR), and infrequent deviants ("change-orienting reaction", C-OR). Single-trial event-related potentials (ERPs) to visual stimuli were estimated from recordings at Oz, Pz, Cz and Fz. The design included both a habituation series as well as a series of occasional deviant trials against a background of standards. This was done with both task-relevant and neutral stimuli, and in two interstimulus interval (ISI) conditions: 2.45 s and 8.45 s. In the latter ISI condition, skin conductance responses (SCRs) were recorded as well. Decrease (Habituation) in the habituation series was found for a non-specific N1, a posteriorly distributed P3, and the SCR, but not for P2-N2. Deviant stimuli produced an enhancement of the central P2-N2, the P3, the N1 (on the first few deviant trials only, in both ISI conditions), and the SCR (with task-relevant stimuli only). Elongation of ISI delayed both short-term and long-term decrease of P3, but had no effect on enhancement of P2-N2 due to stimulus deviance. It was concluded that, with respect to ERP parameters, the I-OR is marked by the N1, whereas the C-OR coincides with the P2-N2.     

P300 Development from Auditory Stimuli

Event-related potentials (ERPs) were elicited with an auditory discrimination paradigm in 20 adult subjects. The amplitude and latency of the N1, P2, N2, and P3 (P300) components were measured from each two-trial average and successively after each two-trial block were added to the ERP average. The dual trial-to-trial analysis generally demonstrated consistent component amplitudes and latencies across trials. The successive average analysis found that component amplitudes decreased significantly while their latencies remained relatively constant as additional trials were incorporated into the average. The results suggest that ERP component latencies are stable, while amplitudes decrease with increased numbers of trials. The implications for the application of P3 in the assessment of individual differences are discussed.     

Modification of sudden onset auditory ERP by involuntary attention to visual stimuli.

To investigate the cross-modal nature of the exogenous attention system, we studied how involuntary attention in the visual modality affects ERPs elicited by sudden onset of events in the auditory modality. Relatively loud auditory white noise bursts were presented to subjects with random and long inter-trial intervals. The noise bursts were either presented alone, or paired with a visual stimulus with a visual to auditory onset asynchrony of 120 ms. In a third condition, the visual stimuli were shown alone. All three conditions, auditory alone, visual alone, and paired visual/auditory, were randomly inter-mixed and presented with equal probabilities. Subjects were instructed to fixate on a point in front of them without task instructions concerning either the auditory or visual stimuli. ERPs were recorded from 28 scalp sites throughout every experimental session. Compared to ERPs in the auditory alone condition, pairing the auditory noise bursts with the visual stimulus reduced the amplitude of the auditory N100 component at Cz by 40% and the auditory P200/P300 component at Cz by 25%. No significant topographical change was observed in the scalp distributions of the N100 and P200/P300. Our results suggest that involuntary attention to visual stimuli suppresses early sensory (N100) as well as late cognitive (P200/P300) processing of sudden auditory events. The activation of the exogenous attention system by sudden auditory onset can be modified by involuntary visual attention in a cross-model, passive prepulse inhibition paradigm.     

P300 amplitude is determined by target-to-target interval

P300 event-related brain potential (ERP) measures are affected by target stimulus probability, the number of nontargets preceding the target in the stimulus sequence structure, and interstimulus interval (ISI). Each of these factors contributes to the target-to-target interval (TTI), which also has been found to affect P300. The present study employed a variant of the oddball paradigm and manipulated the number of preceding nontarget stimuli (0, 1, 2, 3) and ISI (1, 2, 4 s) in order to systematically assess TTI effects on P300 values from auditory and visual stimuli. Number of preceding nontargets generally produced stronger effects than ISI in a manner suggesting that TTI determined P300 measures: Amplitude increased as TTI increased for both auditory and visual stimulus conditions, whereas latency tended to decrease with increased TTI. The finding that TTI is a critical determinant of P300 responsivity is discussed within a resource allocation theoretical framework.     

Poststimulus EEG spectral analysis and P300: attention, task, and probability

Event-related potentials (ERPs) were elicited with auditory stimuli, and spectral analysis was performed on the poststimulus electroencephalographic (EEG) activity to assess how variables that influence the P300 affect spectral parameters of the resultant ERP. In Experiment 1, a no-stimulus condition was compared with a single repeated tone that was either ignored or counted. In Experiment 2, an auditory oddball paradigm was used in which the subject ignored all stimuli, counted only the target, or counted both the target and the standard stimuli in different conditions. In Experiment 3, stimulus probability was manipulated in separate conditions (.20, .50, .80), with the subject required to count the target stimulus. Delta and theta band spectral power increased whenever P300 amplitude increased. However, as the attentional requirements increased across tasks, alpha-1 and alpha-2 power and mean frequency increased. The findings indicate that auditory stimulus processing modulates the EEG more than just by adding ERP components to the epoch.     

Time-course of trigeminal versus olfactory stimulation: Evidence from chemosensory evoked potentials

Habituation of responses to chemosensory signals has been explored in many ways. Strong habituation and adaptation processes can be observed at the various levels of processing. For example, with repeated exposure, amplitudes of chemosensory event-related potentials (ERP) decrease over time. However, long-term habituation has not been investigated so far and investigations of differences in habituation between trigeminal and olfactory ERPs are very rare. The present study investigated habituation over a period of approximately 80 min for two olfactory and one trigeminal stimulus, respectively. Habituation was examined analyzing the N1 and P2 amplitudes and latencies of chemosensory ERPs and intensity ratings. It was shown that amplitudes of both components – and intensity ratings – decreased from the first to the last block. Concerning ERP latencies no effects of habituation were seen. Amplitudes of trigeminal ERPs diminished faster than amplitudes of olfactory ERPs, indicating that the habituation of trigeminal ERPs is stronger than habituation of olfactory ERPs. Amplitudes of trigeminal ERPs were generally higher than amplitudes of olfactory ERPs, as it has been shown in various studies before. The results reflect relatively selective central changes in response to chemosensory stimuli over time.     

Single trial ERP estimation in the frequency domain using orthogonal polynomial trend analysis (OPTA): estimation of individual habituation

A new Event Related Potential (ERP) model is described in which ERPs are estimated as single cortical responses. This model is based on an Orthogonal Polynomial Trend Analysis of Variance (OPTA) in the frequency domain. The orthogonal polynomials are limited to the fifth order in this study. The means and trend-coefficients which are used to estimate the ERPs are tested for significance with the F-statistics. Coefficients not reaching a preset significance criterion are set to zero. Subsequently significant means and trend-coefficients multiplied with the polynomials are inversely transformed to the time domain for each trial. The method is demonstrated with artificial signal-in-noise EEG (electroencephalogram) series in which the signal component (the ERP) decreases in a relatively short time span. The estimated signals approximate closely the input signals and a signal-to-noise improvement on single trial level is reached of about a factor 10. Comparison with the statistical 'Wiener' filtering method shows that the OPTA detects weaker signals. Single trial ERPs estimated with the OPTA from EEGs collected in a habituation paradigm suggest that the averaged evoked potential model may be inadequate in detecting ERP change over a few trials. It is shown that the frontal P3b wave habituated in 7-9 trials, a habituation speed which is comparable to the habituation rate of the visual orienting reaction and the electrodermal orienting reaction.     

Insufficient processing resources in Parkinson's disease: evaluation using multimodal event-related potentials paradigm

The purpose of our study was to demonstrate impaired allocation of processing resources in non-demented patients with early-stage mild Parkinson's disease (PD) using a multimodal event-related potential (ERP) paradigm. The multimodal ERP paradigm was performed in 18 non-demented medicated patients with early-stage PD (Mini-Mental State Examination Score >26) and 16 matched normal controls, the Global Field Power (GFP) was employed for ERP components analysis, and the new modified Wisconsin Card Sorting Test (WCST) was used to evaluate frontal lobe function. Patients with PD did not exhibit novelty P3s, and P3 latency to non-target novel stimuli in visual and auditory modalities was significantly longer in PD patients than in controls. P3 amplitude for the target stimuli (P3b) was higher in PD in both auditory and visual modalities; however, P3b latency was not different between the two groups. Patients with PD showed a significantly lower score of achieved categories and made more perseverative errors in WCST as compared to controls. Our results showed that there were no natural novelty P3s in patients with PD; this finding suggests that non-demented patients with mild PD do not have sufficient mental resources to allocate to the central executive, due to dysfunction of the frontal lobe.     

Heritability of event-related brain potentials in families with a history of alcoholism.

Event-related brain potentials (ERPs) are altered in patients with a variety of psychiatric disorders and may represent quantitative correlates of disease liability that are more amenable to genetic analysis than disease status itself. Estimates of heritability are presented for amplitude and latency of the N1 and P3 components of the ERP measured at 19 scalp locations in response to visual and auditory stimuli for 604 individuals in 100 pedigrees ascertained as part of the Collaborative Study on the Genetics of Alcoholism. Significant heritabilities were found for visual P3 amplitude in response to all stimuli and for visual P3 latency in response to target and novel, but not non-target, stimuli. Heritability of visual N1 latencies was uniformly low, whereas heritability of visual N1 amplitude was significant for all electrodes in response to the non-target stimuli but only for posterior electrodes in the other two stimulus conditions. Heritabilities for auditory target P3 were similar to those of the visual stimuli, with auditory target P3 amplitudes and latencies both demonstrating significant heritability. For auditory P2 in response to non-target stimuli, peak amplitude was heritable, but latency was not. Auditory N1 amplitude and latency were significantly heritable for both target and non-target conditions and did not demonstrate the anterior/posterior patterning obtained for visual N1 amplitude. This study represents the first systematic assessment of heritability of these potential neurophysiological markers in families with a history of alcoholism and suggests that many of these ERP phenotypes have heritabilities strong enough to justify genomic screening for loci jointly influencing ERP abnormalities and liability to alcoholism.     

EEG alpha activity and the ERP to target stimuli in an auditory oddball paradigm.

Peak-to-peak amplitudes of the N1P2 and N2P3 components in the target ERPs from a fixed interstimulus interval auditory oddball paradigm were investigated as a function of within-subject pre-stimulus levels of alpha activity. Fourteen subjects were each presented with 600 auditory stimuli in a two-tone auditory oddball paradigm which required a button-press to targets, presented with 50% probability. Pre-stimulus alpha activity at Pz was assessed for each trial by digital filtering from 8 to 13 Hz, and alpha RMS amplitude was used to sort the ERPs at Pz and Cz. A direct relationship was obtained between component amplitudes at both Pz and Cz and pre-stimulus alpha level at Pz. Component latencies were strongly related to post-stimulus alpha peaks and troughs. These data confirm the intimate relationship between central nervous system activation, as evidenced by spontaneous EEG in the pre-stimulus period, and the ERP resulting from stimulus presentation.     

Theta rhythmicities following expected visual and auditory targets.

Evoked (EPs) as well as event-related potentials (ERPs) were recorded from two groups of 10 healthy, voluntary subjects in auditory and visual modalities. For ERP recordings 'the omitted stimulus paradigm' was employed, in which the subjects were expected to mark mentally the onset time (time prediction task) of the omitted stimulus (target). The standard auditory (AEP) and visual (VEP) evoked potentials and auditory and visual ERPs to the preceding stimuli of the omitted ones were analyzed in time and frequency domains. In the time domain the time prediction task induced increases of the amplitudes of waves existing in standard EPs; however, an additional wave or component could not be detected. Analysis of amplitude frequency characteristics (AFCs) revealed, however, selective, significant increases of the theta (3-6 Hz) frequency components of the responses concerned. These theta increases were especially evident in the frontal and parietal recording sites. Our findings suggest an association between the theta frequency components of transient evoked responses, the association areas of the brain and cognitive performance. The neurophysiological basis of scalp recorded ERPs are discussed in relation to the findings of animal studies with EEG and single unit recordings from cortical and subcortical structures.     

Heritability of event-related brain potentials in families with a history of alcoholism

Event-related brain potentials (ERPs) are altered in patients with a variety of psychiatric disorders and may represent quantitative correlates of disease liability that are more amenable to genetic analysis than disease status itself. Estimates of heritability are presented for amplitude and latency of the N1 and P3 components of the ERP measured at 19 scalp locations in response to visual and auditory stimuli for 604 individuals in 100 pedigrees ascertained as part of the Collaborative Study on the Genetics of Alcoholism. Significant heritabilities were found for visual P3 amplitude in response to all stimuli and for visual P3 latency in response to target and novel, but not non-target, stimuli. Heritability of visual N1 latencies was uniformly low, whereas heritability of visual N1 amplitude was significant for all electrodes in response to the non-target stimuli but only for posterior electrodes in the other two stimulus conditions. Heritabilities for auditory target P3 were similar to those of the visual stimuli, with auditory target P3 amplitudes and latencies both demonstrating significant heritability. For auditory P2 in response to non-target stimuli, peak amplitude was heritable, but latency was not. Auditory N1 amplitude and latency were significantly heritable for both target and non-target conditions and did not demonstrate the anterior/posterior patterning obtained for visual N1 amplitude. This study represents the first systematic assessment of heritability of these potential neurophysiological markers in families with a history of alcoholism and suggests that many of these ERP phenotypes have heritabilities strong enough to justify genomic screening for loci jointly influencing ERP abnormalities and liability to alcoholism. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:383–390, 1999. © 1999 Wiley-Liss, Inc.