Bifurcated P300 peaks: P3a and P3b revisited?

The P300 (P3) component of the event-related brain potential (ERP) was elicited with an auditory discrimination paradigm in a large group (n = 100) of undergraduates. Subjects who displayed bifurcated P3 peaks across trial blocks (n = 35) were classified into three groups based on the consistency of the replication of the two P3 subpeaks. Amplitude and latency measures for the first (P3a) and second (P3b) peaks from each subject demonstrated no statistically reliable differences between groups. Both subcomponents increased in amplitude from the frontal to parietal electrode sites, although the earlier peak was smaller at the frontal electrode site for the second compared to first trial block. The largest P3 peak for each trial block (P3MAX) from each subject was measured and produced amplitude and latency values that closely matched normative data from the same paradigm. The findings suggested that the P3a and P3b subcomponents from auditory stimuli may be distributed in the population in an asymmetric fashion, and that the P3MAX measurement technique provides a reasonable means of assessing amplitude and latency values from individuals with bifurcated peaks.     

P3a and P3b from typical auditory and visual stimuli.

OBJECTIVE: Target/standard discrimination difficulty was manipulated systematically to assess how this variable affects target and nontarget P300 scalp distributions for both auditory and visual stimuli. DESIGN AND METHODS: A 3-stimulus paradigm (target, standard, nontarget) was employed in which subjects (n = 16) responded only to an infrequently occurring target stimulus. The perceptual discrimination difficulty between the target and more frequently occurring standard stimuli was varied as Easy or Difficult in different conditions, while holding the nontarget stimulus properties constant. RESULTS: When target/standard discrimination was Easy, P300 amplitude was larger for the target than the nontarget across all electrode sites, and both demonstrated parietal maximums. In contrast, when target/standard discrimination was Difficult, target amplitude (P3b) was larger parietally and occurred later than nontarget components, whereas nontarget amplitude (P3a) was larger and earlier than the target P300 over the frontal electrode sites. Similar outcomes across task conditions were obtained for both auditory and visual stimuli. CONCLUSIONS: The findings suggest that target/standard discrimination difficulty, rather than stimulus novelty, determines P3a generation for both auditory and visual stimulus modalities.     

The cortical generators of P3a and P3b: a LORETA study

The P3 is probably the most well known component of the brain event-related potentials (ERPs). Using a three-tone oddball paradigm two different components can be identified: the P3b elicited by rare target stimuli and the P3a elicited by the presentation of rare non-target stimuli. Although the two components may partially overlap in time and space, they have a different scalp topography suggesting different neural generators. The present study is aimed at defining the scalp topography of the two P3 components by means of reference-independent methods and identifying their electrical cortical generators by using the low-resolution electromagnetic tomography (LORETA). ERPs were recorded during a three-tone oddball task in 32 healthy, right-handed university students. The scalp topography of the P3 components was assessed by means of the brain electrical microstates technique and their cortical sources were evaluated by LORETA. P3a and P3b showed different scalp topography and cortical sources. The P3a electrical field had a more anterior distribution as compared to the P3b and its generators were localized in cingulate, frontal and right parietal areas. P3b sources included bilateral frontal, parietal, limbic, cingulate and temporo-occipital regions. Differences in scalp topography and cortical sources suggest that the two components reflect different neural processes. Our findings on cortical generators are in line with the hypothesis that P3a reflects the automatic allocation of attention, while P3b is related to the effortful processing of task-relevant events.     

Towards an integrative theory of cognition

A framework is outlined for connecting brain imaging activity with the underlying biophysical properties of neural networks, and their mechanisms of action and organizing principles. The main thrust of the framework is a dynamic theory of semantics based on functional integration of biophysical neural networks. It asserts that higher-brain function arises from both synaptic and extrasynaptic integration in the neuropil where information on environmental changes are represented dynamically through a discourse of semantics. Consequently, integrative neural modeling is shown to be an important methodology for analyzing the response activities of functional imaging studies in elucidating the relationship between brain and structure, function and behavior.     

Auditory and visual P300 topography from a 3 stimulus paradigm.

OBJECTIVE: The P300 event-related brain potential (ERP) was elicited with auditory and visual stimuli in a separate session of a 3 stimulus oddball paradigm, and the scalp topography was assessed with 15 electrode locations. METHODS: Target (0.10), standard (0.80), and infrequent non-target (0.10) stimuli in the auditory task were 2000, 1000 and 500 Hz tone, and in the visual task, 'X', 'O', and 'H', respectively. The stimuli were presented in a random series, once every 2 s, and participants responded only to the target (N = 12). RESULTS: Target stimuli elicited larger P300 components than non-target did in both stimulus modalities. For both target and non-target stimuli, P300 amplitude was larger and latency longer for the visual compared with the auditory stimulus. Analysis of normalized P300 amplitude data indicated that the target and non-target P300s from both modalities had identical topography. CONCLUSION: The findings suggest that both target and non-target stimuli in 3 stimulus oddball paradigm elicited the same type of P300 (P3b) for both stimulus modalities.     

Assessment of P3a and P3b after moderate to severe brain injury.

The purpose of the study was to examine the P3a and P3b components of the event-related brain potential (ERP) in patients sustaining moderate to severe brain injury. Electrophysiological and behavioral responses were recorded in brain injured (N = 18) and healthy control (N = 21) participants performance of an auditory 3-stimulus distractor paradigm. Auditory stimuli consisted of a series of repetitive standard tones (75 ms), occasionally interrupted by equiprobable target (25 ms) and distractor sounds (white noise). Tone duration discrimination accuracy was similar in patients and controls, but patients had prolonged reaction times to targets. The reaction time delay was paralleled by a prolongation of P3b latency to targets in the patient group relative to controls. The stimulus and task dependent modulation of ERP responses in the brain injury group was similar to that of controls in terms of the spatial distribution of ERPs over the scalp. However, the brain injury group had attenuated P3a and P3b amplitudes to distractor and target stimuli, respectively. The electrophysiological data suggest a deficit in the allocation of attentional resources to the processing of deviant stimuli in the brain injury group.     

P3a and P3b auditory ERPs in HIV patients receiving anti-viral medication.

The effects of human immunodeficiency virus (HIV) infection on central nervous system function were studied with the P3a and P3b event-related brain potentials (ERPs) in patients with HIV compared to unaffected matched controls (n = 14/group). All patients were on anti-viral medication for at least 2 months before testing. Auditory stimuli were employed in an easy 2-stimulus oddball discrimination task to obtain a typical P3b (P300) subcomponent. A 3-stimulus distractor paradigm also was employed in which the target/standard discrimination was very difficult, and an infrequent high-pitched tone non-target was presented to elicit the P3a subcomponent. Subjects responded only to the target stimulus in each task. P3a amplitude was significantly smaller for HIV compared to control subjects. No reliable P3b effects were obtained. The findings suggest that P3a rather than P3b may be a more sensitive measure of cognitive impairment in HIV patients on anti-viral medication.     

P300 after head injury: pseudodelay caused by reduced P3A amplitude.

OBJECTIVE: We compared conventional P300 analysis with source analysis in normal subjects and head-injury patients. Based on earlier findings of improved P300 component identification and reduced P3B latency variability with source analysis in normal subjects, our aim was to investigate whether source analysis could improve the distinction between these groups. METHODS: In total, 21 healthy control subjects and 21 patients with mild to moderate head injury were included in this study. A standard auditory 2-tone oddball paradigm was used. Latencies and amplitudes obtained with conventional P300 analysis were compared with source analysis results. RESULTS: With conventional analysis, head-injury patients had delayed P300 latencies and reduced P300 amplitudes in comparison to controls, while source analysis showed no latency differences for both P3A and P3B components. Instead, source analysis indicated absence of P3A components in 43% of patients. CONCLUSIONS: The P300 delay in head-injury patients, observed with conventional analysis, is a pseudodelay caused by decreased P3A amplitudes. Consequently, the unaffected P3B component with its later latency determines conventional P300 latency in these patients. SIGNIFICANCE: Conventional P300 latency cannot be used to conclude that there was delayed early stimulus processing in head-injury patients.     

P300 variations in parkinsonian patients before and during dopaminergic monotherapy: a suggested dopamine component in P300.

P300 was recorded, using an 'odd ball' paradigm, in 18 parkinsonian patients before and during dopaminergic monotherapy. The data were compared with those of a homogeneous standard group of 20 subjects. The main finding was an increase in the P300 latency of parkinsonian patients before therapy, which recovered during dopaminergic monotherapy. In 11 voluntary healthy subjects the same therapy did not produce a reduction of the P300 latency. The data are discussed in relation to a possible dopaminergic component in P300 origin.     

P 300 slow potential. Clinical interest in 3 mental diseases and neurobiology: a review]

P300 is a late component of evoked potential which meet special relevance to the study of cognitive processes. P300 indexes categorization processes and the context updating of memory. Its latency reflects the stimulus evaluation time, and P300 amplitude is related to some psychological variables such as expectancy, attention and stimulus significance. In this review, clinical correlation between P300 components and mental diseases are reported, especially dementia, schizophrenia and depression. Delayed P300 latency has been found in Alzheimer disease and in other forms of dementia. Reduced P300 amplitude as well as altered topography has been reported in schizophrenia. In depression, reduced P300 amplitude has been related with longer reaction time. Unfortunately, the diagnosis utility of P300 seems limited. The authors also propose an overview of the actual knowledge on neurobiological findings in the generation of the P300 wave. Anatomical data point out the importance of the limbic system, more specifically, of the hippocampus and the locus coeruleus, in generating and modulating P300 wave. Data from the literature on the psychopharmacological modifications induced by cholinergic, catecholaminergic and other agents, are reviewed. Although the dopaminergic and noradrenergic systems are of some importance, these data emphasise the importance of the cholinergic system for the generation and modulation of P300 amplitude and latency. The value and interpretation of these neurobiological and clinical findings are discussed.     

事件相关电位P3a和P3b在认知功能评测中的临床应用

事件相关电位是现代研究人的认知功能主要方法之一，随着研究技术的发展，事件相关电位的主要内源性成分P300在认知方面的研究中越来越多的被其亚型P3a和P3b所替代，本文主要对P3a和P3b的发生起源和临床方面的应用进行综述。     

P300 and blink instructions.

OBJECTIVES: The effects of instructions to refrain from blinking on the P300 event-related brain potential (ERP) from auditory and visual stimuli were assessed. METHODS: An oddball paradigm was employed in which young adult subjects (n = 20) silently counted the infrequent target stimuli and were given either no instructions or told "do not blink" in different conditions, with auditory and visual stimulus tasks employed for all subjects. ERPs were recorded from the midline electrodes, with amplitude and latency of the P300 and other components obtained. RESULTS: P300 amplitude for both modalities and target/standard stimulus conditions was smaller and visual peak latency longer in the "do not blink" condition. Blink instructions did not directly affect the other components. CONCLUSIONS: Instructions to refrain from blinking can decrease P300 amplitude and can increase peak latency.     

Habituation and dishabituation of P300.

OBJECTIVE: We aimed to see the consequences of habituation and posthabituation by means of repeatedly measuring the effects over a longer period. METHOD: The study was performed on 27 healthy volunteers. The event-related potentials were recorded from the Fz, the Cz, and the Pz electrode sites. The rare tone-frequent tone probability ratio was 20%. All subjects were asked to press a button when they heard a rare tone. The test was continued until 20 artifact-free rare tones were averaged, which was accepted as 1 trial block. After 10 trial blocks were obtained in a sequential manner, the test was completed. RESULT: This study has indicated that P300 amplitudes decrease with repeated stimulations, that is, there is a habituation period. As the test continues, the speed of amplitude decrease slows down and after a while it even starts to increase: that is, a dishabituation occurs. CONCLUSIONS: It is very likely that this habituation relates to a period of learning and dishabituation relates to a period of mental fatigue. In these processes, changes of amplitude and latency values reflect changes in amount of neuronal activation.     

P300 asymmetry in schizophrenia: a meta-analysis

P300 event-related brain potential (ERP) amplitude is smaller in patients with schizophrenia compared to unaffected controls, but whether left temporal component amplitude is also smaller is debated. The present study employed meta-analytical methods to quantitatively assess previous P300 schizophrenia asymmetry findings. All P300 articles on schizophrenia using an auditory oddball paradigm published before January 2000 were obtained by comprehensive literature searches and cross-referencing for related articles. A total of 19 original articles reporting complete midline electrode data and 11 articles reporting lateral asymmetry electrode data were reviewed, which included different independent conditions that yielded 50 independent data sets. P300 amplitude differences between patients with schizophrenia and control subjects from the midline electrodes yielded effect sizes that differed among recording sites, such that Fz was significantly smaller than Pz, with Cz effect sizes smaller than Pz but larger than Fz. Comparison of P300 amplitude from the lateral data for the T3 and T4 electrodes found no reliable effect size difference when these electrodes were analyzed separately. However, comparison of P300 amplitude effect sizes from the TCP1 was significantly larger than that from the TCP2 when these electrodes were analyzed separately. P300 amplitude is smaller overall in patients with schizophrenia compared to control subjects and differs in its effect size topography across the midline and temporal electrode sites, with the strongest effect sizes obtained for the Pz midline and TCP1 lateral electrodes.     

P300 (latency) event-related potential: an accurate predictor of memory impairment.

To determine if P300 latency changes precede and correlate with memory and mental status, patients (N=1506 aged 20-100 years) who received medical and psychiatric diagnoses (from 1997 to 2002), were assessed for P300 (N=1496), WMS-III (N=694), and MMSE (N=456). Patient and control groups included, a) normal WMS-III on all 4 subscales (N=36), b) normal WMS-III and MMSE (N=189) with subjective memory/mental status complaints, and c) medical patients with normal WMS-III and no memory complaints (N=205), and d) P300 control group without medical, psychiatric or memory problems for ROC. Patients with impaired/borderline memory had a prolonged P300 latency (P<0.02) compared to age matched non-impaired controls; in patients with normal WMS-III/MMSE, with subjective mild memory/mental status impairment, P300 latency was prolonged compared to controls (P=0.0004). The P300 latency increased by 0.72ms per year (P=7.9x10(-65)) and voltage decreased by 0.03dV per year (P=6.7x10(-10)), and both parameters were linearly correlated with the age of the subjects. Male subjects had an average voltage of 6.1dV and female 6.8dV (P=0.00009). Statistically, prolonged latency began at age range 41-50 (P=0.0002); reduced P300 voltage began at age range 51-60 (P=0.003). WMS-III memory decline for all measures began in females at age range 61-70 (P value at least=0.02) and for males at age range 61-80 (P=0.02). Prolonged P300 latency (P<0.0001) and memory impairment (at least <0.02) were greater for females than males. MMSE memory decline, male and female, began at age range 81-90 (P value of at least 0.00007). In our logistic regression model P300 latency was more predictive of WMS-III impairment than MMSE > 24. In patients whose WMS-III score is impaired < or = 69, or borderline < or = 79 (P at least=0.004), a P300 latency more prolonged than the norm (> or = 300 + 30 + Age) identifies these patients, whereas a MMSE > 24 failed. With the ROC curve, we confirmed that P300 latency could accurately identify borderline/impaired memory.     

The visual P3a in schizophrenia and bipolar disorder: effects of target and distractor stimuli on the P300

Amplitude reduction of the P300 event-related potential has long been suggested as a marker for schizophrenia. However, recent research has shown that this reduction in the P300 amplitude is not specific to schizophrenia as it can also be observed in related illnesses such as bipolar disorder. Due to this lack of specificity the P300 elicited using traditional oddball paradigms may be a less valuable endophenotypic marker. The current study employed a cognitively demanding three-stimulus oddball paradigm to elicit the P300 to visual target and distracting stimuli. Patients with schizophrenia showed amplitude reductions of P300 components to targets, distractors and frequent stimuli. The P300 in patients with bipolar disorder was not significantly different from either group. The pattern of results may further the understanding of the nature of the impairment in schizophrenia.     

P300 and response time from a manual Stroop task.

OBJECTIVES: Manual response time (RT) and P300 event-related potential (ERP) measures were recorded in a Stroop color naming task to determine if previous results with vocal responses would be obtained using an arbitrary stimulus-response (S-R) mapping. METHODS: Subjects (n = 32) were instructed to respond to the display color of a word but to ignore its meaning. Display color was congruent, neutral, or incongruent with word meaning. RESULTS: Stroop facilitation and interference effects were observed, as RT was shortest in the congruent condition, intermediate in the neutral condition, and longest in the incongruent condition. In contrast, P300 latency did not vary across color/word congruence conditions, suggesting that the RT difference between congruence conditions originated after stimulus evaluation. CONCLUSIONS: These manual RT/P300 findings support the view that Stroop interference and facilitation originate from response competition between the relevant and irrelevant stimulus attributes. By employing an arbitrary mapping of color words onto buttons, the present results indicate that the disparate effects of Stroop stimuli on RT and P300 latency do not depend on the nature of the S-R translation.     

Attention and entrainment: P3b varies as a function of temporal predictability

Recently, it has been shown that feature discrimination in temporally regular rhythms results in enhanced performance compared with feature discrimination in temporally irregular rhythms. In this study, we investigated the influence of temporal predictability on attentional processing. We show that temporal predictability of a sequence results in a decreased peak latency of the P3b compared with temporally random sequences. The present findings clearly illustrate that temporal predictability results in faster processing of deviant stimuli.