A modified oddball paradigm "cross-modal delayed response" and the research on mismatch negativity

A modified oddball paradigm was developed to facilitate the focus of attention and to minimize target effects on deviant-related components of auditory and visual event-related potentials (ERPs) elicited with long interstimulus intervals. Subjects were required to focus on either the visual or auditory stimulus in each stimulus block. Deviant-related components were obtained by subtracting ERPs of the standard stimulus from that of the deviant stimulus for each modality with each stimulus condition. Results showed that auditory mismatch negativity (MMN) and a visual early deviant related negativity (DRN1) were elicited both when stimuli were attended and unattended. In contrast, N2b and P3 were produced only under the attended condition. In comparison of attended MMN and unattended MMN at three time windows (100-150 ms, 150-200 ms, and 200-250 ms) of MMN zone, different scalp distributions were shown, depending on the time windows. This result suggests that the attended auditory MMN is a mixed wave, consisting of genuine MMN, N2b, and possible P165. The effect of attention on MMN may stem from the contamination of these overlapping components. With the present paradigm, at least three sensory memory traces have to be maintained simultaneously in multiple sensory modalities to support automatic processing.     

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.     

Human brain potential correlates of repetition priming in face and name recognition

We investigated repetition priming in the recognition of famous people by recording event-related brain potentials (ERPs) and reaction times (RTs). Participants performed speeded two-choice responses depending on whether or not a stimulus showed a famous person. In Experiment 1, a facilitation was found in RTs to famous (but not to unfamiliar) faces when primed by the same face shown in an earlier priming phase of the experiment. In ERPs, an influence of repetition priming was observed neither for the N170 nor for a temporal N250 component which in previous studies had been shown to be sensitive to immediate face repetitions. ERPs to primed unfamiliar faces were more negative over right occipitotemporal areas than those to unprimed faces, but this effect was specific for repetitions of the same image, consistent with recent findings. In contrast, ERPs to primed familiar faces were more positive than those to unprimed faces at parietal sites from 500-600 ms after face onset, and these priming effects were comparable regardless of whether the same or a different image of the celebrity had served as prime. In Experiment 2, similar results were found for name recognition-a facilitation in RTs to primed familiar but not unfamiliar names, and a parietal positivity to primed names around 500-600 ms. ERP repetition effects showed comparable topographies for faces and names, consistent with the idea of a common underlying source. With reference to current models of face recognition, we suggest that these ERP repetition effects for familiar stimuli reflect a change in post-perceptual representations for people, rather than a neural correlate of recognition at a perceptual level.     

P300 generation by novel somatosensory stimuli.

Event-related potentials (ERPs) to task-relevant target and task-irrelevant novel stimuli were recorded in a somatosensory discrimination task. Subjects pressed a button to mechanical taps of the fifth finger (targets, P = 0.12), randomly interposed in sequences of taps to the second finger (standards, P = 0.76). Two types of infrequent novel stimuli were delivered; one was a mechanical tap to the third or fourth finger (tactile novels, P = 0.06), another was an electric shock at the wrist (shock novels, P = 0.06). Correctly detected targets generated a parietal maximal P300 (P3b, latency 335 msec). Shock novels generated a central maximal P300 with a shorter peak latency (298 msec) than the P3b. Tactile novels generated a P300 with a scalp distribution comparable to the shock novels. Unlike the P3b, P300 amplitude to both the shock and tactile novel stimuli habituated by 20-30% across the first several stimulus presentations. These results indicate that, similar to the auditory and visual modality, task-irrelevant novel somatosensory stimuli generate a novelty P300 ERP. Differences in scalp distribution, latency and habituation characteristics suggest that the novelty P300 may have contributions from intracranial generators independent from target P300 sources.     

Auditory event-related potentials in the squirrel monkey: Parallels to human late wave responses

Event-related potentials (ERPs) were recorded from the brain surface in squirrel monkeys during the presentation of two auditory stimulus paradigms which have previously been utilized to elicit scalp-recorded ERPs in humans. In the first paradigm, inter-stimulus interval (ISI) was systematically varied during the presentation of a series of tone pips. The tones produced a negative (70 ms)-positive (130 ms) sequence of components similar in morphology to the human scalp-recorded N1-P2 'vertex' potential. The amplitude of the N70 and P130 components recorded from midline electrodes decreased with decreasing ISI, as previously shown for the human vertex potential. However, this amplitude change with ISI was not observed in ERPs recorded from lateral frontal and temporal electrodes. These results agree with previous studies of monkeys and humans which suggest at least two different sources contribute to N1-P2 components recorded in response to tones. The effects of stimulus probability and novelty on ERP morphology and amplitude were studied in the second paradigm. ERPs elicited by frequent (P = 0.92) and infrequent (P = 0.08) tone pips presented in an unpredictable order were compared. N70 - P130 components were produced by both stimuli, and the infrequent stimuli also elicited a broad, long latency (300 ms) positive complex that decreased in amplitude with repeated presentations. In humans the same infrequent auditory stimuli produce a frontally distributed late positive component that has been interpreted as indicating the activation of orientation mechanisms or of a 'mismatch detector'. These data suggest that in these paradigms squirrel monkeys exhibit ERPs which are similar in several respects to ERPs recorded to identical stimuli in humans.     

Updating sensory versus task representations during task-switching: Insights from cognitive brain potentials in humans

Task-cueing studies suggest that the updating of sensory and task representations both contribute to behavioral task-switch costs [Forstmann, B. U., Brass, M., & Koch, I. (2007). Methodological and empirical issues when dissociating cue-related from task-related processes in the explicit task-cuing procedure. Psychological Research, 71(4), 393-400]. Here we used transition cues to orthogonally manipulate Cue- and Task updating (switches vs. repetitions), in order to identify distinct behavioral indicators and event-related potentials (ERPs) associated with the exogenous and endogenous control of task preparation and execution. Both Cue- and Task updating, as well as their interaction, yielded significant behavioral costs, and evoked distinct cue- and target-locked ERPs. Task-switches enhanced cue-locked early P3 amplitudes (180-220 ms) over mid-central scalp regions, whereas cue switches reduced a fronto-central negativity (N2; 255-295 ms). In contrast, both cue- and task-switches enhanced cue-locked late P3 amplitudes (300-340 ms; novelty P3) over centro-parietal regions, supporting the hypothesis of a common neural substrate for processing stimulus and task novelty [Barceló, F., Escera, C., Corral, M. J., & Perianez, J. A. (2006). Task switching and novelty processing activate a common neural network for cognitive control. Journal of Cognitive Neuroscience, 18(10), 1734-1748]. In the target period, both cue- and task-switches reduced target P3 activity (310-730 ms) with short cue-target intervals only, suggesting that behavioral switch costs reflect the accrual of various time-dependent control operations during task preparation and execution. We conclude that the cognitive control of task-switching seems to emerge from a dynamic interplay between exogenous and endogenous sources of information.     

Auditory selective attention in middle-aged and elderly subjects: an event-related brain potential study.

Reaction times (RTs) and event-related brain potentials (ERPs) were recorded in middle-aged (MA) and elderly (ELD) subjects performing an auditory selective attention task. Subjects attended to tone bursts of a specified pitch and ear of delivery and responded to occasional longer duration target tones (75 vs. 25 msec). Infrequent novel stimuli (computer synthesized sounds and digitized environmental noises) were also included in the stimulus sequence. No significant age-related differences were found in the speed or accuracy of target detection. However, in both groups, RTs were delayed (by more than 300 msec) to targets that followed novel sounds. The prolongation was greater following novel sounds in the attended ear, particularly in the ELD group. The effects of selective attention on ERPs to standard tones were isolated as negative difference waves (Nds) by substracting ERPs to non-attended stimuli from ERPs to the same signals when attended. Nds had similar amplitudes, latencies of onset (60 msec), and distributions in ELD and MA groups. In both groups, Nd waves were more prominent following right ear stimulation, reflecting possible hemispheric asymmetries of generators in posterior temporal regions. The mismatch negativity (MMN) was isolated by subtracting ERPs to standard tones from ERPs to deviant stimuli. MMN amplitudes were reduced in the ELD group. There was also a significant change in MMN distribution with age: the MMN was larger over the right hemisphere for MA subjects but larger over the left for ELD subjects. Elderly subjects showed a trend toward smaller P3 amplitudes and delayed P3 latencies, but group differences did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)     

N1 and P2 components of auditory event-related potentials in children with and without reading disabilities.

OBJECTIVE: The effects of within stimulus presentation rate and rise time on basic auditory processing were investigated in children with reading disabilities and typically reading children. METHODS: Children with reading disabilities (RD; N=19) and control children (N=20) were studied using event-related potentials (ERPs). Paired stimuli were used with two different within-pair-intervals (WPI; 10 and 255 ms) and two different rise times (10 and 130 ms). Each stimulus was presented with equal probability and long between-pair inter-stimulus intervals (1-5s). The study focused on N1 and P2 components. RESULTS: The P2 responses to the first tone in the pair showed differences between children with RD and control children. Also, children with RD had larger N1 response than control children to stimuli with short WPI and long rise time. CONCLUSIONS: These results provide evidence for basic auditory processing abnormalities in children with RD. This processing difference could be related to extraction of stimulus features from sounds or to attentional mechanisms. SIGNIFICANCE: Our results show support for behavioral findings that children with RD and control children process rise times differently. More than half of children with RD showed atypical auditory processing.     

Event-related potentials in a guessing task: the gleam in the eye effect.

Event-related potentials (ERPs) were recorded from a single subject performing a forced-choice guessing task. On each trial, ERPs were elicited by four, sequential, graphic images; 2 1/2 seconds after the last stimulus was delivered, the subject guessed which of the four images was experimentally (randomly) designated as the target. P200 had greater amplitude over the posterior scalp for stimuli which were guessed by the subject to be targets than for not-guessed stimuli. The amplitude of the P100, N100, and P300 components was unrelated to the subject's guess. A positive displacement evident in the waveforms from about 150-500 ms post-stimulus onset suggested that Slow Wave may have been partially responsible for the observed differences. These results suggest that ERPs may contain predictive information about a subject's subsequent responses in forced-choice guessing tasks. We termed this the "gleam in the eye" effect.     

Neural substrates of visual perceptual learning of simple and complex stimuli.

OBJECTIVE: The two experiments described here used event-related potentials (ERPs) to investigate whether perceptual learning of different complexities of stimuli involves different levels of visual cortical processing in human adults. METHODS: Reaction times and ERPs were recorded during 3 consecutive training sessions in which subjects discriminated between simple stimuli made of line segments or complex stimuli made of compound shapes. RESULTS: Reaction times in both experiments were shortened across training sessions. For simple stimuli, training resulted in a decreased N1 (125-155ms) and an increased P2 (180-240ms) over the occipital area. For complex stimuli, however, training resulted in a decreased N1 (125-155ms) and N2 (290-340ms) and an increased P3 (350-550ms) over the central/parietal areas. CONCLUSIONS: These findings suggest that perceptual learning modifies the response at different levels of visual cortical processing related to the complexity of the stimulus. SIGNIFICANCE: The neuronal mechanisms involved in perceptual learning may depend on the nature (e.g. the complexity) of the stimuli used in the discrimination task.     

Event-related potentials in a self-paced novelty oddball task

The event-related potentials (ERPs) to the stimuli triggered by a participant's self-paced key press were compared with the ERPs to the same stimuli presented at an external pace. Fourteen participants responded to 2000 Hz target tones interspersed among 1000 Hz standard tones and various unique novel sounds. The amplitudes of the P3s elicited by target and novel stimuli were larger in the self-triggered condition than in the machine-triggered condition in which the stimuli were presented automatically with the same intervals as in the self-triggered condition. The effect was prominent at fronto-central scalp sites. When the timing of stimulus is unequivocal, a neural activity related to stimulus evaluation may increase and manifest itself as a large late positive ERP component.     

Effect of interstimulus interval on visual P300 in Parkinson's disease

OBJECTIVE: Visual event related potentials (ERPs) were studied during an oddball paradigm, to testify whether cognitive slowing in Parkinson's disease exists and to investigate whether cognitive information processing can be influenced by different interstimulus intervals (ISIs) of an oddball task in patients with Parkinson's disease and normal subjects. METHODS: ERPs and reaction time were measured in 38 non-demented patients with Parkinson's disease and 24 healthy elderly subjects. A visual oddball paradigm was employed to evoke ERPs, at three different interstimulus (ISI) intervals: ISI(S), 1600 ms; ISI(M), 3100 ms; and ISI(L), 5100 ms. The effect of ISIs on ERPs and reaction time was investigated. RESULTS: Compared with the normal subjects, P300 latency at Cz and Pz was significantly delayed after rare target stimuli in patients with Parkinson's disease only at ISI(L). Reaction time was prolonged in patients at all the three ISIs, compared with the normal controls. There was also significantly delayed N200 and reduced P300 amplitude at Cz and/or Pz to rare non-target stimuli in patients at the three ISIs, compared with the normal controls. During rare target visual stimulation, P300 latency and reaction time in the patients with Parkinson's disease and reaction time in the normal subjects were gradually prolonged as the ISI increased. CONCLUSION: Prolonged N200 latency to rare non-target stimuli might indicate that automatic cognitive processing was slowed in Parkinson's disease. Cognitive processing reflected by P300 latency to rare target stimuli was influenced by longer ISI in patients with Parkinson's disease.     

Event-related brain potentials in response to novel sounds in dementia.

OBJECTIVE: Non-target, deviant stimuli generate an earlier latency, front-central novelty P3, whereas correctly detected task-relevant stimuli generate a parietal maximal target P3. We examined whether the P3 component to novel stimuli is affected by dementing processes, and is therefore useful for distinguishing Alzheimer's type dementia (AD) from vascular dementia (VD). METHODS: We recorded ERPs to task-relevant stimuli (target P3) and novel task-irrelevant stimuli (novelty P3) in an auditory oddball task in AD (n = 16), VD (n = 16), and age-matched controls (n = 18). The amplitude, latency, and scalp topography of target and novelty P3 were compared among 3 groups using ANOVA. The relationship between P3 measures and intelligence scores were evaluated by correlation analysis. RESULTS: The amplitude, latency and scalp topography of the target P3 were comparably affected by both AD and VD. However, the amplitude of the novelty P3 was markedly reduced in VD, but not in AD, and the scalp topographics were different in the 3 groups. The amplitude was maximal at frontal sites in controls, at central sites in AD, and at parietal sites in VD. The target P3 latency was prolonged in both AD and VD, whereas the novelty P3 latency was only prolonged in VD. AD was discriminated satisfactorily from VD by using the novelty amplitude at Cz and the ratio of the amplitudes at Fz and Pz as independent variables. CONCLUSIONS: These results suggest that the response to novel stimuli is differentially affected by dementia with degenerative and vascular etiology.     

Luminance and spatial attention effects on early visual processing

Event-related potentials (ERPs) were recorded from healthy subjects in response to unilaterally flashed high and low luminance bar stimuli presented randomly to left and right field locations. Their task was to covertly and selectively attend to either the left or right stimulus locations (separate blocks) in order to detect infrequent shorter target bars of either luminance. Independent of attention, higher stimulus luminance resulted in higher ERP amplitudes for the posterior N95 (80–110 ms), occipital P1 (110–140 ms), and parietal N1 (130–180 ms). Brighter stimuli also resulted in shorter peak latency for the occipital N1 component (135–220 ms); this effect was not observed for the N1 components over parietal, central or frontal regions. Significant attention-related amplitude modulations were obtained for the occipital P1, occipital, parietal and central N1, the occipital and parietal P2, and the parietal N2 components; these components were larger to stimuli at the attended location. In contrast to the relatively short latencies of both spatial attention and luminance effects, the first interaction between luminance and spatial attention effects was observed for the P3 component to the target stimuli (350–750 ms). This suggests that interactions of spatial attention and stimulus luminance previously reported for reaction time measures may not reflect the earliest stages of sensory/perceptual processing. Differences in the way in which luminance and attention affected the occipital P1, occipital N1 and parietal N1 components suggest dissociations among these ERPs in the mechanisms of visual and attentional processing they reflect. Nonetheless, scalp current density mappings of the attention effects throughout the latency ranges of the P1 and N1 components show the most prominent attention-related activity to be in lateral occipital scalp areas. Such a pattern is consistent with the spatially selective filtering of information into the ventral stream of visual processing which is reponsible for complex feature analysis and object identification.     

Pathophysiology underlying diminished attention to novel events in patients with early AD

BACKGROUND: Patients with mild to moderate AD often are apathetic and fail to attend to novel aspects of their environment. OBJECTIVE: To investigate the mechanisms underlying these changes by studying the novelty P3 response that measures shifts of attention toward novel events. METHODS: While event-related potentials were recorded, mildly impaired AD patients and matched normal controls (NC) viewed line drawings that included a repetitive background stimulus, an infrequent target stimulus, and infrequent novel stimuli. Subjects controlled how long they viewed each stimulus by pressing a button. This served as a measure of their allocation of attention. They also responded to targets by depressing a foot pedal. Patients did not differ from NC in age, education, estimated IQ, or mood but were judged by informants to be more apathetic. RESULTS: P3 amplitude to novel stimuli was significantly smaller for AD patients than NC. However, P3 amplitude to target stimuli did not differ between groups. For NC, P3 response to novel stimuli was much larger than to background stimuli. In contrast, for patients with AD, there was no difference in P3 response to novel vs background stimuli. Although NC spent more time looking at novel than background stimuli, patients with AD distributed their viewing time evenly. Remarkably, for patients with AD, the amplitude of the novelty P3 response powerfully predicted how long they would spend looking at novel stimuli (R2 = 0.52) and inversely correlated with apathy severity. CONCLUSIONS: The decreased attention to novel events exhibited by patients with AD cannot be explained by a nonspecific reduction in their attentional abilities. The novelty P3 response is markedly diminished in mild AD, at a time when the target P3 response is preserved. The disruption of the novelty P3 response predicts diminished attention to novel stimuli and is associated with the apathy exhibited by patients with AD.     

Anatomical substrates of auditory selective attention: behavioral and electrophysiological effects of posterior association cortex lesions

Even-related brain potentials (ERPs) and reaction times (RTs) were recorded in an auditory selective attention task in control subjects and two groups of patients with lesions centered in (1) the temporal/parietal junction (T/P, n = 9); and (2) the inferior parietal lobe (IPL, n = 7). High pitched tones were presented to one ear and low pitched tones to the other in random sequences that included infrequent longer-duration tones and occasional novel sounds. Subjects attended to a specified ear and pressed a button to the longer-duration tones in that ear. IPL and T/P lesions slowed reaction times (RTs) and increased error rates, but improved one aspect of performance — patients showed less distraction than controls when targets followed novel sounds. T/P lesions reduced the amplitude of early sensory ERPs, initially over the damaged hemisphere (N1a, 70–110 ms) and then bilaterally (N1b, 110–130 ms, and N1c 130–160 ms). The reduction was accentuated for tones presented contralateral to the lesion, suggesting that N1 generators receive excitatory input primarily from the contralateral ear. IPL lesions reduced N1 amplitudes to both low frequency tones and novel sounds. Nd components associated with attentional selection were diminished over both hemispheres in the T/P group and over the lesioned hemisphere in the IPL group independent of ear of stimulation. Target and novel N2s tended to be diminished by IPL lesions but were unaffected by T/P lesions. The mismatch negativity was unaffected by either T/P or IPL lesions. The results support different roles of T/P and IPL cortex in auditory selective attention.     

Auditory distraction with different presentation rates: an event-related potential and behavioral study.

OBJECTIVE: The present study addresses the question of whether behavioral and electrophysiological effects obtained with the auditory distraction paradigm proposed by Schr?ger et al. [Clin Neurophysiol 2000;111:1450] depend on the timing of stimulus occurrence. METHODS: Subjects had to discriminate the duration of tones. Occasionally, task-irrelevant frequency changes were used as distractors. In 3 experiments the stimulus onset asynchrony (SOA) was manipulated: In Experiment 1, SOAs of 1500, 2000 and 3000 ms were used in separate blocks; in Experiment 2, 5 different SOA of lengths between 1300 and 2500 ms were used within the blocks; in Experiment 3, a constant SOA of 1400 ms was compared with a SOA of random lengths between 1300 and 1500 ms. Performance data was analyzed for distraction effects. Event-related potentials (ERPs) were examined for deviance-related components, i.e. the mismatch negativity (MMN), the P3a and the re-orienting negativity (RON). RESULTS: Behavioral distraction effects were obtained in all experimental conditions. The electrophysiological data show MMN, P3a and RON for the deviating tones in all experimental conditions as well. CONCLUSIONS: The behavioral and electrophysiological deviance-related effects were not sensitive to the SOA manipulations. Therefore, the timing of the presentation can be adjusted to the proficiency level of the population to be tested without loosing the distraction effects.     

P3a from a passive visual stimulus task

OBJECTIVE: Visual event-related brain potentials (ERPs) were elicited using a 3-stimulus oddball paradigm to assess the P3a with passive stimulus processing. METHODS: Young adults (n=12) were presented with a series of visual stimuli consisting of a solid circle standard stimulus (P=0.76) that was difficult to discriminate from a larger target circle (P=0.12), with a large square distractor stimulus (P=0.12) presented randomly in the series. Subjects were instructed in the passive condition to simply look at the stimuli and in the active condition to press a mouse key only to the target stimulus. ERPs were recorded from 15 scalp electrodes, with the amplitude and latency of the P300 from the distractor and target stimuli assessed. RESULTS: The P3a from the distractor stimulus was similar in amplitude, scalp topography, and peak latency across the passive and active task conditions. The P3b from the target stimulus demonstrated much smaller amplitude, highly altered scalp topography, and longer latency for the passive compared to active task conditions. CONCLUSIONS: The P3a can be obtained with visual stimuli in the 3-stimulus paradigm under passive viewing conditions. Theoretical implications and clinical applications are discussed.     

Mismatch responses related to temporal discrimination of somatosensory stimulation.

OBJECTIVE: To determine the existence of a pre-attentively evoked somatosensory mismatch negativity component and to investigate the use of that component in objective clinical diagnostics. METHODS: First we determined the temporal discrimination threshold (DT) of paired stimuli in each subject, and applied two sequential electrical stimuli to the hand with paired stimulus times of (1) DT-10 ms, (2) DT-30 ms and (3) DT+50 ms. Then, we recorded ERPs using an oddball paradigm, frequent (standard) and rare (deviant). We used two stimuli, DT-30 ms and DT-10 ms, in the first experiment, and DT-30 ms and DT+50 ms, in the second experiment. RESULTS: In each experiment, two specific components, a negative component peaking at approximately 60ms (N60) and a large positive component peaking around 100-200 ms (P150), were identified, mainly following the deviant stimulus, which were considered somatosensory mismatch components. N60 was more remarkably identified in the second experiment and P150 in the first. CONCLUSIONS: N60 might be generated during tasks which subjects can clearly discriminate, but P150, which seems to correspond to auditory mismatch negativity, might be generated in tasks which require fine discrimination. SIGNIFICANCE: We confirmed that our new method could be used for the objective examination of temporal discrimination.     

Impaired novelty P3 potentials in multiple system atrophy--correlation with orthostatic hypotension

Although neuropsychological tests demonstrate frontal lobe dysfunction in multiple system atrophy (MSA), assessment of frontal function using event-related brain potentials (ERPs) has not been sufficiently performed in MSA. The correlation between frontal lobe dysfunction and orthostatic hypotension (OH), which is known to cause frontal hypoperfusion, remains unclear. Our objectives were to assess frontal lobe dysfunction in MSA patients using ERPs and to elucidate the relevance of OH to changes in ERPs. Nine consecutive patients with MSA and nine age- and gender-matched healthy controls were compared by performance in the Wisconsin Card Sorting Test (WCST) and somatosensory ERPs to target and novel stimuli, namely, parietal maximal P3 (target P3) and fronto-central P3 (novelty P3), respectively. The correlation between novelty P3 and OH was evaluated in the MSA group. The MSA group showed a poorer performance in categories achieved (CA), total errors (TE) and perseverative errors by Nelson's (PEN) method in the WCST compared with the control group (CA and PEN: p<0.01; TE: p<0.02). Novelty and target P3s in the MSA group showed significantly prolonged latency (novelty: p<0.05; target: p<0.01) and reduced amplitude (novelty: p<0.02; target: p<0.01) compared with the control group. There was a significant negative correlation between novelty P3 latency and a drop in systolic blood pressure (r=0.76; p<0.02). Abnormalities of novelty P3 in the MSA group might reflect frontal lobe dysfunction, namely failure of attentional set-shifting, that was identified by the WCST. OH may play a role in the development of frontal lobe dysfunction in MSA.