The P3: A view from the brain

Evidence for an Integrative Role of P3b in Linking Reaction to Perception

Abstract. Hypotheses about the P3 component of the event-related EEG potential have usually assumed that P3b reflects some processing independent from organizing the response. In contrast, the notion that P3b is related to a decision process implies some mediating function between stimulus and response. If P3b does indeed reflect the link between perceptual processing and response preparation (1) amplitudes should be as large in response-locked averages as in stimulus-locked averages, (2) this should be true independent of response speed, for separate subaverages of slow and fast responses, and (3) latencies should vary across response speed both in stimulus-locked and in response-locked averages. These hypotheses were tested in data evoked by visual and auditory stimuli in choice-response tasks. All three predictions were confirmed. In contrast to this balanced relation to perception and responding, fronto-central P3 with auditory stimuli was stimulus-related and, for comparison, the peak amplitudes of both the response-force and of the lateralized readiness potential were response-related. We conclude that P3b reflects a process that mediates between perceptual analysis and response initiation, possibly monitoring whether the decision to classify some stimulus is appropriately transformed into action.

Posterior brain ERP patterns related to the go/no-go task in children

Event-related potentials (ERPs) and performance correlates of inhibition of responses to no-go stimuli were investigated in 6-12-year-old children and young adults. The percent of correct responses to go stimuli was high and similar in both groups; the percent of false alarm errors to no-go was significantly higher in children. Effective inhibition of responses to no-go stimuli was elucidated by a negative component of ERPs, the frontal-central N2, with peak latency 230-430 ms after stimulus onset. In adults, N2 was larger to no-go than to go stimuli, regardless of stimulus frequency. This effect was more prominent in tasks with high (25% no-gos and 75% gos), than with low (75% no-gos and 25% gos) inhibitory demand. In children, the parietal N2 was generally larger to rare than to frequent stimuli, and it was more specifically related to inhibition. The analysis of the relationship of no-go N2 to the inhibitory content of stimuli, probability of stimuli, and the contextual task difficulty suggests that child/adult differences in behavioral responses and ERPs may be related to both the immaturity of the fronto-parietal cortical-cortical network and to different task strategies.

Limbic P300s in temporal lobe epilepsy with and without Ammon's horn sclerosis

Limbic P300 potentials can be recorded within the mesial temporal lobes of patients with temporal lobe epilepsy (TLE). To delineate possible mechanisms of their generation and pathological alteration, we analysed limbic P300s in 55 TLE patients with and 29 without Ammon's horn sclerosis (AHS) and correlated their amplitudes with neuronal cell counts in 30 histopathological specimens. Limbic P300 amplitudes were reduced on the side of the epileptogenic focus only in patients with AHS. Moreover, in AHS patients, limbic P300 latencies were prolonged bilaterally; and in patients with left-sided AHS, amplitudes were reduced bilaterally. Both findings suggest bilateral functional deficits in TLE with unilateral AHS. Limbic P300 areas correlated significantly with neuronal densities of dentate gyrus granule cells but not hippocampal pyramidal cells in the CA1-4 (cornu ammonis) subfields. This finding points to a potential mechanism for the bilateral effects of unilateral AHS as both dentate gyri exhibit strong reciprocal contralateral connectivity.

Enlarged frontal P300 to stimulus change in panic disorder

This study investigated event-related potential (ERP) indices of information processing in sufferers of panic disorder (PD). ERPs were recorded from 14 PD patients and 15 controls during an auditory target detection task. The task required subjects to discriminate infrequent target tones (p = .14; 2000 Hz) from frequent (p = .72; 1000 Hz) and infrequent (p = .14; 500 Hz) distractor tones. A frontal P300 (P3a) identified in the PD group was characteristic of activity that would be expected to novel, task-irrelevant stimuli and is consistent with junctional pathology involving the prefrontal-limbic pathways. This study provides psychophysiological evidence of an abnormality in PD of the brain's processing of physical changes in the stimulus field that occurs even under conditions of low stimulus load. It may assist in helping to understand the breakdown in information processing that occurs in PD under high load conditions such as crowds and supermarkets.

The topography of 4 subtraction ERP-waveforms derived from a 3-tone auditory oddball task in healthy young adults

Five components were studied in 4 subtraction waveforms derived from ERPs obtained in passive and active conditions of a 3-tone oddball task (common = 70%, C, 0.8 KHz; deviant = 15%, D, 2 KHz; 1.4 KHz = 15%, t, also used as a target (T)). These waveforms reflect different stimulus-mismatch processes and thus their topography could be revealing of different brain regions mediating them. The following mismatches were studied: stimulus-mismatch (deviant--common, D/C, rarity and pitch confounded), pitch-mismatch (T--deviant, T/D, rarity not target features controlled), attention-mismatch (T-t), T/t, controlled for pitch and rarity to show the influence of target features). These are compared with Goodin's procedure [G-wv, (T--common (active))--(t--common (passive))]. There were main site effects in normalized data in all cases (not P2 and N2 latency). There were separate frontal and posterior contributions to P1, with the former emphasized where target comparisons were involved. Frontal N1 peaks, largest in D/C, spread posterior and to the right where target matching was involved. P2 posterior maxima were also less localized where target features were involved in the comparison. N2 topography was similar between waveforms but spread slightly more to each side in the T/t comparison. Onset was earlier in the D/C comparison. Parietal P3 peaks in waves based on target-ERPs showed a left temporal shift (vs D/C), though in T/D P3 was in fact maximal on the right. Thus an attentional effect is evident as early as 60 ms. Target features modify the anteroposterior distribution of positivity and negativity for the early components and in the lateralization of P3-like positivity. A comparison of waveforms by latency of potential shift (running t-test) vs peak identification (MANOVA) is illustrated and discussed. D/C and T/t (rather than T/D or G-wv) waveforms are recommended for distinguishing comparator mechanisms for stimulus- and task-relevant features.

The topography of event-related potentials in passive and active conditions of a 3-tone auditory oddball test

Normalized event-related potential (ERP) data were analysed for topographical differences of ERP amplitude or latency in two conditions of a 3-tone oddball paradigm. The aim was to compare perception-related features relating to tone-type (passive non-task condition) with focussed attention-related features (active discrimination of target from non-target) in 5 ERP components from 23 young healthy subjects. The tones used were a common standard (70%, 0.8 KHz), a deviant standard (15%, 2 KHz) and a 1.4 KHz tone (15%, t) also used as the target (T). A site x tone interaction was obtained for P1 amplitude (augmenting with pitch anterior to posterior). The opposite tendency was seen for P2 to the right of midline maxima. No interaction was obtained for N1 amplitude. Condition became relevant for the N2-P3 complex. Frontal N2 amplitude increased after rare tones in the active condition. Posterior P3 peak size distinguished between tone (more widespread response to the common tone) and condition (more right-sided in the passive condition). The common tone elicited more widespread shift to the right than the rare tones. Latency was affected by condition from the P2 onwards and confirmed many of the amplitude interactions. This report extends and qualifies well-known main effects of tone and condition through main site effects to lateral sites. It supports claims of multiple sources of ERP components, except for N1 and P2. The contributions of these sources are influenced by tone-features (from P1) and the presence or absence of focussed attention (from the N2-P3 complex).

Mapping P300 waves onto inhibition: Go/No-Go discrimination

Subjects viewed letters presented at 2 sec intervals and prepared a fast button press whenever an "O" appeared. If the next letter was an "X" the button press was executed (Go signal), but if the letter was a non-X character (T, H, Z) suppression of the response was required (No-Go cue). No-Go signals elicited a P300-like wave that was larger at central and frontal scalp sites contralateral to the prepared movement, compared to P300s elicited by Go cues which were symmetric about the sagittal midline and dominant at parietal sites. Subtraction of preparatory CNVs from the No-Go P300 did not remove differences in scalp topography, or reduce the amplitude of the No-Go P300 to that seen following control letters that required perceptual identification but did not call for suppression of prepared motor responses. Principal components analysis identified a middle positive wave following X-alone control stimuli whose topography resembled the No-Go P300. These findings suggest that the source of augmented No-Go P300s is a generator involved with sensorimotor inhibition. We discuss the mechanism of P300 waves and evidence linking these waves with inhibition in other task arrangements.

Abnormal stimulus processing in posttraumatic stress disorder

This study investigated event-related potential (ERP) indices of information processing in sufferers of posttraumatic stress disorder (PTSD). ERPs were obtained from 18 PTSD patients and 20 controls while they performed a target discrimination task requiring the detection of infrequent target tones from a background sequence of frequent and infrequent distractor tones. A delayed N2 and an attenuated P3 that failed to differentiate target from distractor tones indicated that patients had abnormal difficulty distinguishing task stimuli of differing relevance. It is proposed that this difficulty is reflected behaviorally in the slowed reaction time by patients to target stimuli and may underlie the disturbed concentration and memory impairments found in PTSD. It may also be related to dysfunction in central noradrenaline function, which has been shown to be both crucial in selective attention and abnormal in PTSD.