Effects of stimulus repetition, duration, and rise time on startle blink and automatically elicited P300

Probe P3 and blinks: two measures of affective startle modulation

Two concurrent measures of the evoked startle response, the elicited blink reflex and the event-related potential, were measured while individuals viewed pictures that varied in pleasure and arousal. Replicating previous findings, the blink response was modulated by picture pleasantness, with larger reflexes elicited in the context of viewing unpleasant versus pleasant pictures. However, the probe P3 was primarily modulated by picture arousal, with smaller P3 responses elicited when viewing affective (pleasant or unpleasant) than when viewing neutral pictures. Both modulatory effects were sustained for probes presented in a subsequent picture imagery period. These data suggest that two measurable responses to the same startle probe are differentially modified by emotional context, with blink magnitude varying with pleasure and probe P3 varying with stimulus arousal.

P300, stimulus intensity, and modality

Auditory and visual stimulus intensity levels were manipulated systematically in separate conditions to assess the influence of these variables on the P300 event-related brain potential (ERP). Increases in stimulus intensity produced increases in P300 amplitude and decreases in peak latency for both modalities, although the latency effects were stronger for visual stimulation. Similar, somewhat weaker stimulus intensity effects also were observed for the N100, P200, and N200 components. The findings suggest that stimulus intensity contributes to both P300 amplitude and latency measures in important ways and are discussed in relation to the use of ERPs in applied contexts.

P300, stimulus intensity, modality, and probability

Auditory and visual stimulus intensity were manipulated factorially with target probability to assess the influence of these variables on the P300 component of the event-related brain potential (ERP). Increases in stimulus intensity produced reliable increases in P300 amplitude and decreases in peak latency for both modalities that were additive with target stimulus probability effects. Similar, somewhat weaker stimulus intensity effects also were observed for the N100, P200, and N200 components. The findings suggest that stimulus intensity contributes to both P300 amplitude and latency measures in important ways and are discussed in relation to the use of ERPs in applied contexts.

Meta-analysis of P300 normative aging studies

The theoretical and empirical backgrounds for the utility of the P300 event-related potential (ERP) as a measure of cognitive aging are summarized. P300 latency data from 32 different normative aging studies are then reviewed and assessed with meta-analytic procedures. Evaluation of moderator variables indicates that sample characteristics, stimulus factors, and task conditions contribute significantly to the "normal" change in peak latency that occurs with aging. These findings are critiqued in the context of previous reports, and implications are outlined for future applications of ERPs to normative aging. It is concluded that P300 latency can provide useful information about cognitive aging but that specific variables must be considered to obtain more precise results.

The P300 in pain evoked potentials

Pain evoked potentials (EPs) have been used in the last two decades as means of obtaining objective measures of pain, in clinical and experimental setups. The possibility that the pain EP wave contains elements of the endogenous P300 potential rather than being a neurophysiological correlate of pain has been raised by a number of authors, but the issue has not been resolved. In this study, two experiments were performed to study the effect of nonmodality-specific factors on the laser EP: (1) a stimulus attend as opposed to a stimulus-ignore condition and (2) counterbalanced oddball and task P300 stimulus presentations. The latter was to permit full examination of the separate and combined influences of each condition on the EP. Stimuli were given to the radial hand of 10 healthy volunteers using a CO2 laser. The positive component of the laser EP was affected by both manipulations relating to (1) attention (P = 0.0146) and (2) the frequency condition (P = 0.003) in the P300 paradigm. The task condition in the second paradigm did not affect the positive wave on its own, although its effect was visible in interaction with frequency (P = 0.033). In conclusion, although the presence of a somatic component in the laser EP cannot be rules out, we suggest that the laser EP contains a definite non-modality-specific P300 component, and is not a pure neurophysiological correlate of pain intensity.

Habituation of P300 and reflex motor (startle blink) responses to repetitive startling stimuli in children

Positive EEG deflections with the latency and scalp distribution of the P300 accompany startle in response to loud auditory stimuli in a non-task context. The purpose of this investigation is to determine if habituation would have effects on the P300 similar to those on the startle blink. Thirty-four normal 7 to 11-year-old boys from a startle habituation study had EEG recordings of sufficient quality to provide data for the current study. Startle was measured both as orbicularis oculi EMG and vertical EOG and P300 was recorded at Pz in response to 40,104 dB bursts of white noise presented at 23-s intervals. Both the startle response and the P300 habituated toward asymptotic levels after the first 28 trials, suggesting that both startle and the subsequent cognitive evaluation of the startling stimulus, reflected in the P300 response, are modulated by a common neurophysiological mechanism extrinsic to the direct startle pathway. A modest significant correlation between the P300 and the vertical EOG peak latencies for the initial trials suggests that the cognitive evaluation of the startling stimulus may also include evaluation of the reflex response to that stimulus. Analyses of the within-subject associations between startle and P300 initial amplitudes and rates of habituation showed that these parameters varied independently within the individual subject, suggesting that the P300 is not a component of the startle response. Rather, it reflects an evaluation of the startling stimulus, decreasing in amplitude as the surprising value of the startling stimulus decreases with habituation.

Auditory event-related potentials in fetal alcohol syndrome and Down's syndrome children

Abnormal or borderline electroencephalograms are commonly observed in cases of gross mental retardation. However, fewer studies have focused on the use of event-related responses to aid in the differential diagnosis of developmental cognitive disorders. Fetal alcohol syndrome (FAS) and Down syndrome represent the most common known causes of mental retardation in the Western world. Although Down syndrome is easily diagnosed with a chromosome assay, FAS can be more difficult to diagnose since the diagnostic features are more subjectively based. The present study is the first to characterize auditory event-related potentials (ERPs) in children with FAS and contrast them to subjects with Down syndrome and controls. A passive auditory "oddball-plus-noise" paradigm was utilized to elicit ERPs. Parietal P300 latencies in response to the noise-burst stimuli for the FAS children were significantly longer, as were the P300s from all cortical sites in Down syndrome subjects in response to the both the infrequent tone and noise-burst stimuli when compared with the controls. Frontal P300s in Down syndrome children were significantly larger in amplitude compared to the controls and FAS children in response to the infrequent tone. A discriminant function analysis also revealed that these children could be correctly classified as being either Down syndrome, FAS, or normal controls using measures of latency and amplitude of the P300. These data suggest that an evaluation of ERP characteristics may provide a better understanding of the differences between FAS and Down syndrome children, and prove to be an aid in the early identification of children with FAS. These results demonstrate neurophysiological differences between FAS and Down syndrome, and suggest that P300 amplitude and latency data collected from a passive ERP task may be helpful in the discrimination of developmental cognitive disorders.

P300 from auditory stimuli: intensity and frequency effects

Auditory stimulus intensity (45, 60, 75 dB SPL) and standard/target frequency (250/500) and 1000/2000 Hz) were manipulated factorially to assess their effects on the P3(00) event-related brain potential (ERP). For the target stimuli, intensity increases produced reliable increases in P3 amplitude and decreases in peak latency. P3 latency at the lowest intensity level was marginally longer for the low frequency condition. For the standard stimuli, intensity increases produced reliable P3 amplitude increases, low frequency stimuli yielded smaller components than high frequency stimuli, and several interactions with the electrode factor were obtained. P3 latency decreased as intensity increased, and low frequency tones produced longer latencies than high frequency tones. The N1, P2, and N2 components from both stimulus types generally were affected in the same manner: intensity increases producing larger amplitudes and shorter latencies, with some effects of tone frequency also observed. The findings suggest that auditory stimulus parameters contribute to both P3 amplitude and latency measures in important ways and are discussed in relation to the use of ERPs in applied contexts.

Cognitive and biological determinants of P300: an integrative review

The P300 event-related brain potential (ERP) is thought to reflect neuroelectric activity related to cognitive processes such as attention allocation and activation of immediate memory. However, recent studies have provided evidence that the P300 also is influenced by biological processes such as fluctuations in the arousal state of subjects. The effects of natural (circadian, ultradian, seasonal, menstrual) and environmentally induced (exercise, fatigue, drugs) state variables on the P300 are reviewed. The findings suggest that these factors contribute to P300 measures and are discussed in terms of their theoretical and applied implications.

Elderly men and women are less responsive to startling noises: N1, P3 and blink evidence

Previously we observed that the P3 component of the event-related brain potential (ERP) elicited by startling noises, and to a lesser extent P3 to target tones, is reduced in the elderly (Ford & Pfefferbaum, 1991). In the current experiment, we tried to eliminate possible effects of age-related hearing deficits on the responses to noises by filtering them to include only frequencies heard best by the elderly (0-1000 Hz) and by setting noise intensity relative to each subject's threshold (sensation level, SL). Twelve younger (mean 22 years) and 12 older (mean 69 years) men and women listened to three sequences of tones (80%, 500 Hz, 70 dB SPL) and noises (20%). One type of noise occurred in each sequence (wide band noise set to 107 dB SPL, narrow band noise set to 107 dB SPL, or narrow band noise set to approximately 65 dB SL). The order of the three sequences was counterbalanced across age and sex. Younger subjects blinked to the noise 4-5 times more often than older subjects and had N1 and P3 amplitudes that were 2-3 times larger, regardless of the noise type. N1 amplitude to the background frequent tones and non-startle blinks did not differ between groups. Thus, even when noises were narrow band and set relative to each subject's threshold, older subjects were less responsive to startling auditory stimuli than were younger.

P300 from a single auditory stimulus

The P3(00) event-related brain potential (ERP) was elicited with auditory stimuli to compare 2 different discrimination tasks. The oddball paradigm presented both target and standard tones; the single-stimulus paradigm presented a target but no standard tone stimulus. Experiment 1 manipulated target stimulus probability (0.20, 0.50, 0.80) and produced highly similar P3 amplitude and latency results across probability levels for each paradigm. Experiment 2 factorially varied inter-stimulus interval (2 sec, 6 sec) and target stimulus probability (0.20, 0.80). P3 amplitude and latency were highly similar for both the oddball and single-stimulus procedures across all conditions.

Prestimulation-induced modulation of the P300 component of event related potentials accompanying startle in children

Positive EEG deflections with the latency and scalp distribution of the P300 accompany startle in response to loud auditory stimuli in a non-task context. The purpose of this investigation is to determine if inhibitory and facilitatory prestimulation would have effects on the P300 similar to those on the startle blink. Prestimulation conditions were chosen to induce startle amplitude facilitation (4000 msec sustained tone), startle amplitude inhibition (120 msec prestimulation interval), and startle onset latency facilitation (60 msec prestimulation interval). Ninety-three boys (including normals and those with ADHD and/or enuresis) from a startle modulation study had EEG recordings of sufficient quality to provide data for the current study. Repeated measures analyses of variance demonstrated startle amplitude and P300 amplitude facilitation following the 4000 msec tone, startle amplitude and P300 amplitude inhibition following the 120 msec prestimulation interval, and startle onset latency and P300 peak latency facilitation (shorter latencies) following the 60 msec prestimulation interval. Hence, the vertex-recorded P300 elicited by startling stimuli was modulated by non-startling prestimulation in a manner that paralleled that of modulation of the brain-stem generated startle blink. Startle inhibition by prestimulation is mediated by an inhibitory pathway in the mesopontine lateral tegmentum. This brain-stem circuitry has a similar effect on the P300 even though the latter may be generated in more rostral structures. Alternatively, this automatically elicited P300 may represent a limbic or cortical reflection of the sensory processing taking place in the brain-stem. Either interpretation suggests a "bottom-up" as contrasted with a "top-down" mode of sensory processing. This P300 obeys the rules of startle modulation by brain-stem mechanisms rather than indexing cortical evaluation of stimuli for task relevance, stimulus probability, and prior uncertainty.

The relationship between P300 amplitude and regional gray matter volumes depends upon the attentional system engaged

Event-related potentials (ERPs) and brain magnetic resonance images (MRIs) were acquired from 28 normal men, age 21-60 years. ERPs were recorded during 3 paradigms designed to elicit automatic or effortful attention, and a combination of both. MRI-derived measures of brain gray matter, white matter and cerebral spinal fluid (CSF) volumes were computed from frontal, parietal and temporal lobes. P300 amplitude correlated significantly with gray matter volumes but not with white matter or CSF volumes. Furthermore, the relationships between P300 amplitude and gray matter volumes reflected functional rather than direct topographical relationships: P300 recorded at Pz during automatically elicited attention correlated significantly with frontal but not parietal lobe gray matter volumes, P300 recorded during effortful attention correlated significantly with parietal but not frontal lobe gray matter volumes, and P300 recorded when both types of attention were invoked correlated significantly with both frontal and parietal gray matter volumes. Startle blinks, also elicited during automatic attention-engaging paradigms, were significantly correlated with frontal but not parietal lobe gray matter volumes. There was no evidence for a direct spatial relationship between P300 amplitude and the gray matter volumes underlying the recording electrode.

Positive shifts of event-related potentials: a state of cortical disfacilitation as reflected by the startle reflex probe

Cortical positivity as measured by slow event-related potentials is assumed to represent a decreased excitability of cortical networks and suppression of their behavioral-cognitive output. The blink reflex probe is a commonly used defensive electromyographic response whose amplitude was shown to be modulated by emotional and attentional orientation. It was used here as an indicator of cortico-subcortical excitation. In study 1, 33 healthy subjects took part in a continuous performance test (CPT). Event-related potentials were recorded from 15 standard scalp locations. Acoustic startling noise bursts were delivered during conditions that required either performance of prepared motor responses (Go), inhibition of prepared motor responses (NoGo), or had no motor significance (Irrelevant condition). During the NoGo condition, EEG surface potentials showed a widespread P300-like positivity with a central maximum. Startle responses were inhibited during the NoGo condition as compared to the Irrelevant condition. In study 2 (21 subjects) the same format was used, except that the startle reflex was elicited visually. Startle reflexes again showed smaller magnitude during the NoGo condition, which evoked larger positivity at central sites in comparison to the Irrelevant condition. The relationship between positivity in the EEG and inhibited startle responses is in line with the hypothesis that positive EEG shifts reflect a state of cortical disfacilitation.

P300 in young and elderly subjects: auditory frequency and intensity effects

Auditory event-related potentials (ERPs) were assessed in young and elderly subjects when stimulus intensity (40 vs. 60 dB SL) and standard/target tone frequency (250/500 Hz and 1000/2000 Hz) were manipulated to study the effects of these variables on the P3(00) and N1, P2 and N2 components. Auditory thresholds for each stimulus type were obtained, and the stimulus intensity was adjusted to effect perceptually equal intensities across conditions for each subject. Younger subjects demonstrated larger P3 amplitudes and shorter latencies than elderly subjects. The low frequency stimuli produced larger P3 amplitude and shorter latencies than the high frequency stimuli. Low intensity stimuli yielded somewhat smaller P3 amplitudes and longer peak latencies than high intensity stimulus tones. Although additional stimulus intensity and frequency effects were obtained for the N1, P2 and N2 components, these generally differed relatively little with subject age. The findings suggest that auditory stimulus parameters contribute to P3 measures, which are different for young compared to elderly subjects.

Lead stimulation effects on reflex blink, exogenous brain potentials, and loudness judgments

Prepulse inhibition of the reflex blink by a weak stimulus shortly preceding a blink-eliciting stimulus has been described as a sensorimotor gating phenomenon that may protect processing of the first stimulus. To determine how a stimulus configuration that elicits prepulse inhibition also affects exogenous evoked potentials and perceived loudness of the paired stimuli, the three types of response were recorded simultaneously under four conditions: tone pairs of 75-110 dB and 75-75 dB and single control tones of each intensity. Two studies using different intrapair intervals found that blinks and exogenous potentials peaking after 50 ms were smaller for the second tone of pairs than for equal-intensity single tones. Pairing also reduced the loudness of 110-dB second tones, but the loudness of 75-dB first and second tones was unaffected or increased. These effects are discussed in terms of parallel processing of transient, unmodulated information in specific paths, steady-state modulated information in nonspecific paths, and a context-dependent effect on loudness judgments.

Auditory event-related potentials and electrodermal activity in medicated and unmedicated schizophrenics

Event-related potentials (ERPs) and electrodermal activity were studied in 14 medicated schizophrenics, 17 unmedicated schizophrenics, and 23 age- and education-matched controls. Subjects were run in three auditory stimulus paradigms differing from the usual ERP paradigms in having interstimulus intervals greater than 12 sec to permit measurement of the longer latency skin conductance response (SCR). In every paradigm medicated but not unmedicated schizophrenics had smaller N120 amplitudes and fewer SCRs than controls. In addition, medicated schizophrenics showed reduced P200 amplitude and latency, longer P320 latency, and reduced skin conductance levels in certain paradigms. These effects cannot easily be attributed to different mental states of medicated and unmedicated patients, since their Brief Psychiatric Rating Scale scores were almost the same. It is more probable that antipsychotic and antiparkinsonian drugs reduced electrodermal activity through anticholinergic mechanisms and that the antipsychotic drugs attenuated N120 through other biological mechanisms.