Somatosensory event-related potentials following different stimulus conditions.

We studied somatosensory event-related potentials (ERPs) in response to rare target, frequent nontarget and rare nontarget stimuli in 12 healthy subjects. Compared with the corresponding peaks following frequent stimuli, the responses elicited by rare target stimuli showed higher amplitudes for N70, P100 and N140 components and those evoked by rare nontarget stimuli showed higher amplitudes for N70 and N140 components. The P300 component following rare nontarget stimuli was shorter in latency and lower in amplitude than that elicited by target stimuli. ERP waveforms evoked by rare nontarget stimuli also showed obvious N240 and P300 components, which differed from those following frequent nontarget stimuli. These findings suggest that there are differences in signal processing in response to target, frequent nontarget and rare nontarget stimuli. The P300 component was distributed symmetrically and there was no significant hemispheric predominance with regard to any ERP component in response to either right or left side stimulation.     

Relationships between attention effects and intensity effects on the cognitive N140 and P300 components of somatosensory ERPs.

OBJECTIVES: This study attempts to elucidate the relative contributions of exogenous and endogenous components to the N140 and P300 potentials elicited by somatosensory stimulation. METHODS: Somatosensory event-related potentials (ERPs) were evoked using an odd-ball paradigm with the frequent (80%) stimuli delivered to the left index finger and the infrequent (20%) stimuli delivered to the right index finger. Both types of stimuli had the same intensity within each experiment. The experiment was repeated using 6 different stimulus intensities ranging from the sensory threshold to 3 times the threshold. Each experiment was done under two conditions. In one, the subjects were asked to count and respond to the infrequent stimuli. In the other, the subjects were instructed to ignore the stimuli whether frequent or infrequent. In addition, the compound sensory potential of the right median nerve was separately recorded from electrodes at the wrist using the same range of stimulus intensities applied to the right index finger. RESULTS: Amplitudes of the N140 and P300 elicited by both attended and unattended infrequent stimuli increased in a parallel fashion as a function of stimulus intensity, so that the amplitude difference between attended and unattended responses was independent of the stimulus intensity. The amplitude of the compound sensory nerve potential at the wrist exhibited a similar slope to those of the N140 and P300. CONCLUSIONS: Thus, it is concluded that the scalp N140 and P300 consist of two components: an endogenous component, which is independent of the stimulus intensity, and an exogenous component, which increases as a function of stimulus intensity. The relative contribution of these components to the N140 and P300 amplitudes is also discussed.     

Effects of a go/nogo task on event-related potentials following somatosensory stimulation.

OBJECTIVE: We investigated the effects of a go/nogo task on event-related potentials (ERPs) evoked by somatosensory stimuli. METHODS: ERPs following electrical stimulation of the second (go stimulus) or fifth (nogo stimulus) left-handed digit were recorded from 9 subjects. The recordings were conducted in 3 conditions: Control, Count and Movement. The subjects were instructed to count the go stimuli silently in Count, and respond to the go stimuli by grasping right hands in Movement. Go and nogo stimuli were presented at an even probability. RESULTS: N140 was recorded in all conditions and P300 in Count and Movement. The mean amplitudes of the nogo stimuli in the interval 140-200 msec and nogo-N140 amplitude were significantly more negative than those of the go stimuli in Count or Movement. Nogo-P300 was larger in amplitude than go-P300 in Movement but not Count. The effect of P300 was applied to Fz and Cz, but not at Pz. CONCLUSIONS: In the present study, effects of a somatosensory go/nogo task on ERPs were investigated, and our findings were very similar to those of previous studies using visual and auditory go/nogo tasks. Therefore, we suggest that cortical activities relating to go/nogo tasks are not dependent on sensory modalities. SIGNIFICANCE: The present study showed for the first time the go/nogo effects on somatosensory-evoked ERPs. These effects were similar to those in visual and auditory ERP studies.     

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.     

Abnormalities in Event-Related Potentials, N100, P200, P300 and Slow Wave in Schizophrenia

Abstract: Event-related potentials were recorded in 54 schizophrenics and 88 age-matched controls during a two-tone discrimination (odd ball) task. All the subjects were free from medication. In the schizophrenics, the mean amplitudes of the N100, P300 and Slow Wave latency ranges were decreased, and the amplitude of the P200 latency range was greater than that for the controls. These reductions and the increase were found both for the ERPs elicited by rare target stimuli and for those elicited by frequent nontarget stimuli. The peak latency of N200 to rare stimuli was more prolonged in the schizophrenics than in the controls. This finding confirms the prolongation of N200 latency that Brecher et al. (1987) found for a different visual stimuli task. Neither the N100 nor P300 latency differed between the two groups.     

Reduced P300 responses in criminal psychopaths during a visual oddball task.

BACKGROUND: Clinicians have long recognized that psychopaths show deficits in cognitive function, but there have been few experimental studies exploring these deficits. We present here the first in a series of event-related potential (ERP) experiments designed to elucidate and characterize the neural correlates of cognitive processes of psychopaths. METHODS: We recorded ERPs from a topographic array from 11 psychopathic and 10 nonpsychopathic prison inmates, assessed with the Hare Psychopathy Checklist-Revised, during performance of a visual oddball task. ERPs to target (25% of trials) and nontarget (75% of trials) visual stimuli were analyzed. RESULTS: Consistent with previous research, there were no group differences in the latency or amplitude of the ERPs for the nontarget stimuli. For nonpsychopaths, the P300 amplitude was larger when elicited by the target stimuli than when elicited by the nontarget stimuli. In contrast, psychopaths failed to show reliable P300 amplitude differences between the target and nontarget conditions. Psychopaths had a smaller amplitude P300 to target stimuli than did nonpsychopaths. In addition, the amplitude of the P300 was less lateralized in psychopaths than in nonpsychopaths. Psychopaths also had a larger centrofrontal negative wave (N550) during the target condition than did nonpsychopaths. CONCLUSIONS: The results of this study indicate that there are substantial differences between psychopaths and others in the processing of even simple cognitive tasks and provide support for information processing models of psychopathy.     

Task difficulty, probability, and inter-stimulus interval as determinants of P300 from auditory stimuli

The P300 event-related potential was elicited with auditory stimuli in 4 experiments which manipulated combinations of stimulus target probability (10% vs. 30%), task difficulty (easy vs. hard), and inter-stimulus interval (5 sec vs. 2 sec). P300 amplitude was smaller and peak latency longer for the more difficult relative to the easier tasks across experiments. Increases in stimulus target probability generally diminished P300 amplitude and shortened peak latency more for the easy relative to difficult task conditions. Increasing the number of non-target stimulus tones decreased P300 amplitude reliably, but increased latency only slightly. Task difficulty did not interact with variations in inter-stimulus interval which produced generally weak effects for both amplitude and latency. These findings suggest that P300 amplitude and latency obtained from auditory discrimination paradigms reflect processing difficulty independently of stimulus target probability unless differences in task requirements affect stimulus encoding.     

The habituation of event-related potentials to speech sounds and tones

We examined the short- and long-term habituation of auditory event-related potentials (ERPs) elicited by tones, complex tones and digitized speech sounds (vowels and consonant-vowel-consonant syllables). Twelve different stimuli equated in loudness and duration (300 msec) were studied. To examine short-term habituation stimuli were presented in trains of 6 with interstimulus intervals of 0.5 or 1.0 sec. The first 4 stimuli in a train were identical standards. On 50% of the trains the standard in the 5th position was replaced by a deviant probe stimulus, and on 20% of the trains the standard in the 6th position was replaced by a target, a truncated standard that required a speeded button press response. Short-term habituation (STH) was complete by the third stimulus in the train and resulted in amplitude decrements of 50-75% for the N1 component. STH was partially stimulus specific in that amplitudes were larger following deviant stimuli in the 5th position than following standards. STH of the N1 was more marked for speech sounds than for loudness-matched tones or complex tones at short ISI. In addition, standard and deviant stimuli that differed in phonetic structure showed more cross-habituation than did tones or complex tones that differed in frequency. This pattern of results suggests that STH is a function of the acoustic resemblance of successive stimuli. The long-term habituation (LTH) of the ERP was studied by comparing amplitudes across balanced 5.25 m stimulus blocks over the course of the experiment. Two types of LTH were observed. The N1 showed stimulus-specific LTH in that N1 amplitudes declined during the presentation of a stimulus, but returned to control levels when a different stimulus was presented in the subsequent condition. In contrast, the P3 elicited by the deviant stimuli showed non-specific LTH, being reduced across successive blocks containing different stimuli. P3s elicited by target stimuli remained stable in amplitude.     

Effects of risperidone on event-related potentials in schizophrenic patients

In order to examine the effects of risperidone on cognitive impairment in schizophrenia, event-related potentials (ERPs) were recorded before and after switching from conventional neuroleptics to risperidone in schizophrenic patients. ERPs were recorded during two auditory discrimination tasks (an oddball task and a distraction task) in 10 medicated schizophrenic patients during conventional neuroleptic and risperidone treatments. The amplitudes and latencies of N 100 and P300 component were measured in ERPs for target stimuli in the oddball task and in ERPs for target and novel stimuli in the distraction task. Although N 100 amplitude and latency and P 300 amplitude did not change significantly after switching the drug compared to that during conventional neuroleptic treatment, P 300 latency for target stimuli shortened significantly during risperidone treatment in both tasks, accompanied by the shortening of the reaction time in the distraction task. The P 300 latency change did not correlate with the change of the severity of psychopathology. These findings suggest that risperidone may speed the information processing in schizophrenic patients, contributing to the improvement of cognitive functions.     

Event-related potentials to intranasal trigeminal stimuli change in relation to stimulus concentration and stimulus duration.

Few data are available on the relation of EEG-derived trigeminal event-related potentials (ERPs) to stimulus duration or stimulus concentration. Thus, the aim of this study was to analyze the relation between ERP components and both stimulus duration and stimulus concentration. Twenty healthy young subjects participated. Trigeminal ERPs were recorded after stimulation with CO(2). Five concentrations (45 to 65% volume per volume CO(2)) and five stimulus durations (100 to 300 msec) were used. Trigeminal ERPs were quantified in terms of amplitudes and latencies of its major peaks N(410) (termed N1) and P(622) (termed P3). The relation between stimulus duration, concentration, and amplitudes or latencies of trigeminal ERP components could be described as a model of power, following the formula p = b + k.I g1.D(g2). A linear relationship was found between stimulus concentration, amplitude N1, and amplitude P3, and between stimulus duration and amplitude P3 respectively. Furthermore, a linear relationship was seen between intensity ratings, and stimulus duration and concentration. These data confirm that the different ERP components encode different stimulus characteristics. Specifically, later components of the trigeminal ERP encode not only stimulus concentration but, other than earlier ERP components, also encode stimulus duration. Thus, they reflect the integration of stimuli over relatively long periods of time.     

Depression and somatosensory evoked potentials: I. Correlations between SEP and monoamine and purine metabolites in CSF

In 32 patients with major depressive disorders diagnosed according to Research Diagnostic Criteria (RDC), somatosensory evoked potentials elicited at four levels of tactile fingertip stimulation were recorded. Four peak-to-baseline amplitudes (P100, N140, P200, and P300) and two peak-to-trough amplitudes (P100-N140 and N140-P200) plus their amplitude/stimulus intensity slopes were selected for analysis. All 12 measures were adjusted to same sex, age, height, and weight. Values were linearly and curvilinearly correlated with adjusted levels of homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5HIAA), 3-methoxy-4-hydroxyphenylglycol (MPHG), hypoxanthine, and xanthine in the cerebrospinal fluid (CSF), monoamine and purine metabolites, respectively. Significant negative linear correlations were found between the P300 amplitude and both HVA and hypoxanthine, and between the P200 slope and both 5HIAA and hypoxanthine. A significant positive correlation existed between the N140-P200 slope and 5HIAA. Curvilinear bivariate regressions demonstrated complex topologies of regression surfaces. Neither attention nor benzodiazepine medication were of significant importance in these relationships.     

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.     

Diminished responsiveness of ERPs in schizophrenic subjects to changes in auditory stimulation parameters: implications for theories of cortical dysfunction

Event-related potentials (ERPs) were recorded from 15 schizophrenic patients and 17 normal controls in an auditory oddball paradigm in order to investigate the effects of stimulus probability and interstimulus interval (ISI) on deficits in mismatch negativity (MMN) generation in schizophrenia. MMN amplitude was reduced for schizophrenics overall, with the degree of deficit increasing as deviant probability decreased. In contrast, schizophrenic subjects were no more affected by alterations in ISI than controls. The experimental design also permitted evaluation of N1 generation as a function of ISI in schizophrenia. Schizophrenic subjects showed decreased N1 amplitude across conditions, with the degree of deficit increasing with increasing ISI. For both MMN and N1, therefore, the degree of deficit increased with increasing component amplitude in normals, implying that the deficit in ERP generation in schizophrenia may reflect a decrease in maximal current flow through underlying neuronal ensembles. The observed pattern of dysfunction is consistent both with observations of impaired precision of processing in schizophrenia, and with predictions of the PCP/NMDA model.     

Selective attention and multisensory integration: multiple phases of effects on the evoked brain activity

We used event-related potentials (ERPs) to evaluate the role of attention in the integration of visual and auditory features of multisensory objects. This was done by contrasting the ERPs to multisensory stimuli (AV) to the sum of the ERPs to the corresponding auditory-only (A) and visual-only (V) stimuli [i.e., AV vs. (A + V)]. V, A, and VA stimuli were presented in random order to the left and right hemispaces. Subjects attended to a designated side to detect infrequent target stimuli in either modality there. The focus of this report is on the ERPs to the standard (i.e., nontarget) stimuli. We used rapid variable stimulus onset asynchronies (350-650 msec) to mitigate anticipatory activity and included "no-stim" trials to estimate and remove ERP overlap from residual anticipatory processes and from adjacent stimuli in the sequence. Spatial attention effects on the processing of the unisensory stimuli consisted of a modulation of visual P1 and N1 components (at 90-130 msec and 160-200 msec, respectively) and of the auditory N1 and processing negativity (100-200 msec). Attended versus unattended multisensory ERPs elicited a combination of these effects. Multisensory integration effects consisted of an initial frontal positivity around 100 msec that was larger for attended stimuli. This was followed by three phases of centro-medially distributed effects of integration and/or attention beginning at around 160 msec, and peaking at 190 (scalp positivity), 250 (negativity), and 300-500 msec (positivity) after stimulus onset. These integration effects were larger in amplitude for attended than for unattended stimuli, providing neural evidence that attention can modulate multisensory-integration processes at multiple stages.     

Auditory training alters the physiological detection of stimulus-specific cues in humans

ObjectiveAuditory training alters neural activity in humans but it is unknown if these alterations are specific to the trained cue. The objective of this study was to determine if enhanced cortical activity was specific to the trained voice-onset-time (VOT) stimuli ‘mba’ and ‘ba’, or whether it generalized to the control stimulus ‘a’ that did not contain the trained cue.MethodsThirteen adults were trained to identify a 10 ms VOT cue that differentiated the two experimental stimuli. We recorded event-related potentials (ERPs) evoked by three different speech sounds ‘ba’ ‘mba’ and ‘a’ before and after six days of VOT training.ResultsThe P2 wave increased in amplitude after training for both control and experimental stimuli, but the effects differed between stimulus conditions. Whereas the effects of training on P2 amplitude were greatest in the left hemisphere for the trained stimuli, enhanced P2 activity was seen in both hemispheres for the control stimulus. In addition, subjects with enhanced pre-training N1 amplitudes were more responsive to training and showed the most perceptual improvement.ConclusionBoth stimulus-specific and general effects of training can be measured in humans. An individual’s pre-training N1 response might predict their capacity for improvement.SignificanceN1 and P2 responses can be used to examine physiological correlates of human auditory perceptual learning.     

The effect of accomplishment and failure on P300 potentials evoked by neutral stimuli

The effects of emotional states of 'being successful' vs. 'being unsuccessful' were studied by measuring the P300 component of event-related potentials (ERPs). Nine subjects were instructed to reduce their P300 amplitude using feedback. Feedback was random but the relative probability of different signals created the situations of 'being successful' or 'being unsuccessful'. The probability of 'small' feedback was 0.7 in 'successful' and 0.15 in 'unsuccessful' trials. ERPs recorded without the feedback were used as a reference. Potentials, evoked by light stimuli in a standard 'odd-ball' procedure, were recorded from Fz, Cz and Pz scalp sites. The amplitudes of P300 components were reduced in 'unsuccessful' trials whereas in 'successful' trials they did not differ significantly from responses recorded without the feedback. There were no significant differences in peak latencies. These findings indicate that tonic emotional states affect the processing of neutral stimuli and that late components of ERPs can be useful indices in the analysis of these alterations. The results also indicate that the effects of positive and negative emotional states are not always reciprocal. Manipulated feedback is suggested as an useful model in the studies of emotions. Data can also facilitate the interpretation of the real feedback effects.     

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.     

Cognitive evoked potentials to anticipated oesophageal stimulus in humans: quantitative assessment of the cognitive aspects of visceral perception

Evoked potential studies provide an objective measure of the neural pathways involved with perception. The effects of cognitive factors, such as anticipation or awareness, on evoked potentials are not known. The aim was to compare the evoked potential response to oesophageal stimulation with the cortical activity associated with anticipation of the same stimulus. In 12 healthy men (23.5 +/- 4 years), oesophageal electrical stimulation (15 mA, 0.2 Hz, 0.2 msec) was applied, and the evoked potentials recorded using scalp electrodes. A computerized model of randomly skipped stimuli (4:1 ratio) was used to separately record the evoked potentials associated with stimulation and those associated with an anticipated stimulus. The electrical stimulus represented the nontarget stimulus and the skipped impulse the target (anticipatory) stimulus. This anticipatory evoked potential was also compared to auditory P300 evoked potentials. Reproducible evoked potentials and auditory P300 responses were elicited in all subjects. Anticipatory evoked potentials (peak latency 282.1 +/- 7.9 msec, amplitude 8.2 +/- 0.7 microV, P < 0.05 vs auditory P300 evoked potential) were obtained with the skipped stimulus. This anticipatory evoked potential was located frontocentrally, while the auditory P300 potential was located in the centro-parietal cortex. The anticipatory evoked potential associated with expectation of an oesophageal stimulus, although of similar latency to that of the auditory P300 evoked response, originates from a different cortical location. The recording of cognitive evoked potentials to an expected oesophageal stimulus depends on attention to, and awareness of, the actual stimulus. Anticipatory evoked potentials to GI stimuli may provide an objective electrophysiological tool for the assessment of the cognitive factors associated with visceral perception.     

Long-latency event-related potentials in squirrel monkeys: further characterization of wave form morphology, topography, and functional properties

Event-related potentials (ERPs) were recorded from the brain surface of untrained monkeys exposed to sequences of auditory stimuli (2 kHz and 6 kHz tones of 40 msec duration). Stimulus probability and interstimulus interval (ISI) were systematically varied in different paradigms. In an oddball paradigm with a 1 sec ISI in which one stimulus constituted 90% of all trials and the other 10%, a 'monkey' late positive component (MLPC), characterized by two peaks (P248 and P369), was recorded prominently over lateral parietal areas in response to the unpredictable and infrequent shifts in pitch. The amplitude of this late positivity was found to be sensitive to stimulus probability and to exhibit trial-to-trial sequential dependencies similar to those described for the human P300. The amplitude of MLPC was also found to be larger following longer ISIs. In addition, a 'monkey' late negative component (MLNC), with characteristics similar to those of the human slow wave (SW), was recorded following the infrequent shifts in pitch and found to temporally overlap with MLPC. MLNC was recorded with maximal amplitude over frontal cortex and was sensitive to stimulus probability but not to trial-to-trial changes in stimulus sequence. Thus MLPC and MLNC which appear to reflect similar yet distinct processes exhibit several analogies to the human P3a and SW, respectively.     

Visual p300 effects beyond symptoms in concussed college athletes

In order to assess whether cerebral anomalies may be observed in the absence of clinical symptoms, the current study compared the effects of concussions on attentional capacities (reaction times, accuracy) and Event-Related Potentials (ERPs) in concussed athletes with (n = 10) or without (n = 10) symptoms as well as in athletes who never had a concussion (n = 10). The P300 response was recorded from 28 electrodes during a modified visual oddball paradigm. Participants were instructed to press a key upon the appearance of the frequent stimuli as well as when a rare nontarget stimulus followed the frequent one. The other key was to be pressed when the subsequent rare stimuli (rare target) appeared until a frequent one reappeared. The symptomatic athletes displayed longer reaction times than the other two groups of athletes. The P300 amplitude to the rare target stimuli was significantly more attenuated in the symptomatic athletes than in the other two groups. Moreover, the P300 amplitude varied inversely with the severity of post-concussion symptoms but was not influenced by time elapsed since injury. Although the clinical significance of the P300 differences shown by the symptomatic athletes is still uncertain, the results do indicate that symptom severity may be a crucial indicator of functional impairments following mild traumatic brain injury.