Specific changes in auditory cognitive evoked potentials in those who participated in the liquidation of the chernobyl accident: I. Analysis of the early N1 component

The amplitude and temporal parameters of the N1 component of the auditory cognitive evoked potential (EP) were analyzed in ten people who participated in the elimination of the consequences of the Chernobyl accident (the liquidators) and ten healthy subjects aged 47 ± 6.0 and 50.5 ± 4.0 years, respectively. In the liquidators of the Chernobyl accident, the amplitudes of the N1 component of the auditory EP were decreased in all cortical areas. This decrease was the greatest in the central and frontal areas. The changes in response to stimuli of different significances in the liquidators were inverted as compared to the healthy subjects of the same age. The differences between the control group and the liquidators were the most pronounced in the temporal characteristics of the N1 component. The latent periods (LPs) for all stimuli presented under all experimental conditions were significantly shorter in the group of liquidators, and this effect was even stronger for the significant stimulus in the case of stimulus counting. In the liquidators, the maximum changes in the LPs of the N1 component were observed in the frontal area of the left hemisphere, and they were associated with an inversion of the LP asymmetry. Changes in this parameter were smaller in the central areas and were similar in the parietal areas in both groups studied. Changes in the amplitude and temporal characteristics of the N1 component of the auditory cognitive EP observed in the liquidators of the Chernobyl accident indicate the impairments of their involuntary attention and its capacity due to weakening of inhibition processes as compared to healthy subjects. This effect is similar to that found in elderly subjects. Our data support the hypothesis on the accelerated aging of the brain in the liquidators of the Chernobyl accident due to the effect of low doses of irradiation. The data also suggest that irradiation results in pathological aging.     

Brain bioelectrical activity at a high anxiety level in humans

Brain bioelectrical activity was studied in 38 and 34 subjects with high and low levels of anxiety, respectively, by means of toposelective mapping of EEG spectral power and recording of P300 endogenous event-related auditory evoked potentials (EPs). Analysis of EEG spectra demonstrated, in the subjects with a high level of trait anxiety, a higher power of β₁ oscillations in the central-parietal areas of both hemispheres and the occipital area of the right hemisphere, as well as a higher power of θ and α oscillations in the frontal areas of both hemispheres and the central-parietal area of the left hemisphere. The occipital-frontal gradient of the spectral power of these rhythmic EEG components was altered in subjects with a high level of trait anxiety. Comparison of P300 cognitive auditory EPs in the subjects with high anxiety and in the control group showed that, in the former, the P300 EP amplitude and the habituation distortion (dishabituation) of the P300 EP amplitude were significantly higher in both hemispheres. This indicates that, at a high level of anxiety, the active directed attention was disturbed, which is confirmed by the results of neuropsychological examination, demonstrating reduced selectivity, concentration, and stability of attention in the Münsterberg test and Schulte’s test. The results of electrophysiological examination suggest that the malfunction of regulatory brain modulating systems is an important neurophysiological mechanism of attention pathology and disturbed adaptation in subjects with a high level of trait anxiety.     

P300 component changes of the auditory event-related potential in the patients with typical and atypical panic attacks

84 patients with panic disorders and 36 healthy control subjects with use of clinico-neurologic technique, psychometric, neuropsychological and the neurophysiological method of auditory event-related potentials P300 were examined. Patients with panic disorders were characterized by the raised level of anxiety, depression and cognitive function disturbances in the form of decrease of short-term memory and attention insufficiency in comparison with the healthy control subjects. Patients with atypical panic disorders differed from the patients with typical panic disorders by lower level of anxiety, a greater degree of depression and more expressed cognitive function disturbances. In comparison with the healthy control subjects with atypical panic disorders the decrease of P300 peak amplitude was observed, with typical--its augmentation. It is supposed, that P300 peak change is bound to dysfunction of temporal-limbic-reticular brain structures.     

P300 assessment of early Alzheimer's disease

The P300 (P3) event-related brain potential (ERP) was elicited in 16 demented patients presumed to be in the early stages of Alzheimer's disease and 16 normal control subjects well matched for age, sex, education and occupational level. All subjects performed a simple auditory discrimination task in which a target tone was presented randomly on 20% of the trials. P3 amplitude was smaller and peak latency longer for the Alzheimer patients compared to control subjects. A second ERP task also was administered in which the target tone occurred 50% of the time. Analysis of the target/standard tone presentation sequences indicated that the Alzheimer patient group demonstrated less amplitude difference between the target and standard sequences and longer overall latencies compared to the control group. The results that the P3 ERP component from auditory stimuli can provide useful information about Alzheimer's disease during its early stages.     

Hemispheric asymetry of the evoked electrical activity of the cerebral cortex to letter and non-verbal stimuli]

Average evoked potentials (AEP) were recorded in practically healthy subjects to "meaningless" figures and letters, presented to different halves of the visual field. Analysis of the amplitudes of AEP late components to verbal and non-verbal stimuli reveals hemispheric asymmetry. A higher amplitude of the late positive evoked response (P300) to a "direct" stimulation both by verbal and non-verbal stimuli (in the contralateral field of vision) is recorded in the left hemisphere than in the right one. Similar stimulation of the right hemisphere does not reveal sucha difference. In the left hemisphere the P300 wave is of a clearly greater amplitude to a "direct" stimulation (contralateral visual field) than to an "indirect" one (ipsilateral visual field), regardless of the nature of the stimulus. No such difference is observed in the right hemisphere. The magnitude of the late negative wave (component N200) to non-verbal stimuli is greater in the right hemisphere both in response to "direct" and "indirect" stimulations. No intrahemispheric difference has been found in the amplitude of late evoked responses of the cerebral cortex to verbal and non-verbal stimuli.     

Cognitive auditory evoked potentials in children with special language impairment

Perception and discrimination of auditory and speech stimuli in children aged 7-9 years with either receptive (n=6) or expressive (n=5) type of special language impairment and 7 healthy age-matched controls was investigated using evoked potential technique. The measurements were performed with a 32-channel Neuroscan electroencephalographic system. Two types of stimuli were applied, pure tones (1 kHz and 2 kHz) and double syllabi consisting of one consonant and one vocal characteristic of Croatian language. The stimuli were presented in an oddball paradigm, requiring a conscious reaction for the subjects. Latencies and amplitudes of P1, N1, P2, N2, P3, N4, and SW waves were analized, as well as the reaction time and number of responses. There were found no statistically significant difference between children with special language impairment and the control group in average response time and number of responses to tone burst or double syllable. Analysis of variance of all used variables showed a statistically significant difference in P3 and Sw wave latencies after double syllable stimulation, P3 and N4 waves latencies after target stimulation, P2 and Sw wave amplitude; and in N1 wave amplitude after pure tone stimulation. Our study showed that children with speech and language disorder take longer time to perceive and discriminate between either tonal or speech auditory stimuli than children with typical speech and language development.     

EEG of the interstimulus intervals during habituation of auditory evoked potentials in depressive moods

Averaging of EEG of interstimulus intervals in the process of study of habituation of auditory evoked potentials (EPs) in healthy subjects and patients with endogenous depression, revealed a rhythmic wave process (RWP) especially expressed in patients. RWP appeared and became stronger in successive averaging of 10 realizations completing each of four series of 30 clicks; often (especially in depressive patients) it was manifest in averaging of all 120 realizations with an amplitude comparable with that of main EPs components and even greater. A significant correlation was found of RWP parameters with characteristics of melancholic mood in both subgroups. It is suggested that RWP appears as a result of regular changes of EEG background during multiple stimuli repetition in connection with increased "slow" habituation and in a special manifestation of perceptive defence during depression including mechanisms of active isolation from external world.     

Pain-related and cognitive components of somatosensory evoked potentials following CO2 laser stimulation in man

We recorded cortical potentials evoked by painful CO₂ laser stimulation (pain SEP), employing an oddball paradigm in an effort to demonstrate event-related potentials (ERP) associated with pain. In 12 healthy subjects, frequent (standard) pain stimuli (probability 0.8) were delivered to one side of the dorsum of the left hand while rare (target) pain stimuli (probability 0.2) were delivered to the other side of the same hand. Subjects were instructed to perform either a mental count or button press in response to the target stimuli. Two early components (N2 and P2) of the pain SEP demonstrated a Cz maximal distribution, and showed no difference in latency, amplitude or scalp topography between the oddball conditions or between response tasks. In addition, another positive component (P3) following the P2 was recorded maximally at Pz only in response to the target stimuli with a peak latency of 593 msec for the count task and 560 msec for the button press task. Its scalp topography was the same as that for electric and auditory P3. The longer latency of pain P3 can be explained not only by its slower impulse conduction but also by the effects of task difficulty in the oddball paradigm employing the pain stimulus compared with electric and auditory stimulus paradigms. It is concluded that the P3 for the pain modality is mainly related to a cognitive process and corresponds to the P3 of electric and auditory evoked responses, whereas both N2 and P2 are mainly pain-related components.     

A subcortical correlate of P300 in man

Event-related potentials in visual and auditory target detection tasks were recorded simultaneously from the scalp, somatosensory thalamus and periaqueductal gray in a chronic pain patient with electrodes implanted subcortically for therapeutic purposes. Short latency tactile responses confirmed the location of the thalamic electrodes.Rare auditory stimuli which were detected by the subject were accompanied by a prominent P300 component at the scalp, and by negative activity at the subcortical sites with the same latency as the scalp positivity. This activity was not seen in responses to frequent non-target stimuli and was not dependent on an overt motor response.Similarly, rare visual stimuli generated a scalp P300 and negative activity subcortically; both scalp and subcortical waves had a longer latency than in the auditory experiment. The reaction time was similarly longer to visual targets.These data are inconsistent with a hippocampal generator for P300, but are consistent with a generator in the thalamus or more dorsally located structures.     

P300 wave: a comparative study of impulsive aggressive criminals

Event-Related potentials are a simple non-invasive neurophysiological method enabling to comprehend certain aspects of the cognitive processing of information in humans. The best-known component of Event-Related Potentials is the so-called P3 wave. Alterations in the parameters of P300 wave have been discovered in certain personality disorders and in persons with impulsively aggressive behaviour. The purpose of this study is to investigate the changes of these parameters, especially an amplitude and latency in the place of Pz electrode. We examined 15 persons with the impulsive aggressive behaviour and compared them to a population comparable of normal age, gender and approximate degree of education. We used P300 auditory and a neuropsychological Eysenck IVE battery. The results showed that significantly lower amplitudes had been found in the aggressive impulsive subjects as compared to the control group. No statistically significant differences have been discovered in the latency. These results seem to confirm previous studies.     

Decreased response to novel stimuli after prefrontal lesions in man

Experiments were conducted to study the contribution of prefrontal cortex to the generation and modulation of two varieties of P300 activity. Control subjects generated typical parietal maximal P300 responses to detected target stimuli. Unexpected, novel auditory stimuli presented to controls generated an earlier latency, fronto-centrally distributed P300 response. A similar earlier latency, fronto-central P300 is generated to unexpected, novel visual stimuli. The occurrence of this phenomenon in both the auditory and visual modalities suggests that it may reflect neural activity of a common CNS system involved in the orienting response.Subjects with unilateral prefrontal damage generated P300 complexes to target stimuli that did not differ from the control responses. Prefrontal damage, however, resulted in a specific defect in the P300 response to the unexpected novel stimulus. Prefrontal patients showed neither N200 enhancement nor the fronto-central P300 response to the novel stimulus that was found in control subjects. These findings indicate that prefrontal regions are critical for the organism's response to unexpected novel stimuli. Abnormalities in prefrontal control of sensory-limbic integration may be a critical element in the decreased P300 to novel stimuli found in these unilateral prefrontal lesioned patients. It is suggested that major features of the human frontal lobe syndrome may be explained by a physiological inability to control attention and orientation systems after prefrontal damage.     

A topographical ERP study of healthy premature 5 year old children in the auditory and visual modalities

The aim of this research is to study the impact of extreme prematurity on the cognitive development of the child as assessed at age 5 years 9 months. Our samples include 15 healthy prematures born between 25 and 28 weeks of gestational age carefully matched with 15 full-term controls. In the first experiment, two different auditory stimuli were presented to the subjects who listened passively without instruction. The second experiment consisted of a standard visual oddball task in which the subjects were instructed to `catch' two different animals, by pushing a left or right button for a moose (n=120) or a raccoon (n=40), respectively. In the auditory task, 3 ERP peaks were analyzed (frontal N100 and P3a, temporal P2). All premature children demonstrated normal early frontal N100 and temporal P2 responses. The group differences were apparent in the late positivity (P3a) where controls showed a larger amplitude to the rare tones applied evenly to both ears. In contrast, the prematures did not show sensitivity to rare tones but showed a larger P3a upon left ear stimulation, when compared to the right. Also, the ERPs to the visual oddball task showed normal early positivities (P250–300) in the premature group. Once again, deviations from the normal were evident in late waves. The ERPs recorded from prematures showed a more diffuse topography especially between 500 and 600 ms post-stimulus and around the posterior area (P550). The succeeding negativity (SW) was not altered in the premature group. The ERP data suggest that premature children, even without clinically apparent problems, convey specific ERP singularity when engaged in a task that involves complex processing.     

Characteristics of the spatio-temporal organization of the P300 component of AEP during the "active" and "passive" stimulus perception in healthy subjects

The concern of the work was in detection and analysis of P300 component of the acoustic evoked potential in healthy subjects in different experimental situations. During counting the rare sounds, P300 was most pronounced in the frontocentral and parietooccipital areas mainly of the left-hemisphere. The response shape was correlated with characteristics of the basic rhythm of the background EEG. Responses of simple and complex shapes were distinguished. The simplest responses were recorded in subjects with hypersynchronous alpha-rhythm. Analysis of three-dimensional dipole source localization showed that structures of the brainstem, limbic system, and frontal lobes participate in generation of the wave. In all the subjects, the decisive role in response generation was played by the brainstem structures. In persons with hypersynchronous alpha-rhythm, the contribution of the frontal lobes was less pronounced. During "passive" listening of sounds, P300 parameters significantly differed from those observed during counting only in 46% of cases (in persons having no hypersynchronous alpha-rhythm). A simplification of the response shape during "passive" listening was observed in these cases, the area of the maximal response expression was shifted to symmetrical areas of the right-hemisphere, the number of dipole sources reduced due to a decrease in the contribution of the frontal and limbic structures into the response generation.     

Features of Auditory P300 in Relatives of Schizophrenic Patients

The subjects were parents, siblings, and children of schizophrenic patients. Auditory evoked potentials (EPs) (P300) were recorded in the standard oddball paradigm with a probability of the target stimuli presentation of 0.2 and sound (tone) intensity of 60 dB. A comparison of these data with the results of the examination of reference groups (normal subjects free of a family history of mental pathology) showed significantly longer latent periods of N1, N2, and P3 in EPs to target stimuli in siblings and children of schizophrenic patients, as well as significantly decreased amplitudes of N1 and P2 in EPs to nontarget (standard) stimuli and longer latent periods of N2 in EPs to target stimuli in the parents of schizophrenic patients.     

Changes in Evoked Potentials Depending on Attention Level in Performance of Visual Tasks

Evoked potentials (EPs) in the parietal and temporal leads were recorded in 14 young subjects in response to successively administered right- and left-side simple visual symbols, squares and circles, during passive viewing and reactions to randomly presented target stimuli. Depending on task conditions and context, the stimuli were divided into four groups: (1) passively perceived stimuli, (2) irrelevant stimuli administered on the side opposite to the target, (3) irrelevant stimuli on the side of the target, and (4) target stimuli. The EPs were averaged over the groups. With an increase in the demands of attention from the first to the fourth groups of stimuli, a linear increase in activation, estimated by the total amplitude of the N1–P3 component, was observed in the parietal leads. The P3b component was mainly responsible for the growth of the EP amplitude. In the temporal leads, the activation was substantially weaker than in the parietal leads and displayed lower between-group differences. The results support the idea that the parietal cortex in humans is of primary importance in tasks involving visual attention and stimuli selection.     

On the Problem of Cooperation of the Reactions of Hands: II. Cooperation of Hand Reactions to Auditory and Visual Stimuli in Patients with Focal Brain Lesions

The cooperation of responses of hands to auditory and visual stimuli with a warning signal was studied in patients with focal lesions of the visual or auditory nerves or the cerebral cortex, parastem tumors, tumors of the cerebellum or the spinal cord, inflammation processes in the brain tunics, or some chronic neurological disorders. The cooperation of hand reactions to auditory and visual stimuli was compared for healthy subjects and the patients in order to determine the morphological structures involved. The patients with focal lesions, like the healthy subjects, showed a strong positive correlation between the response times of the left and right hands; an individual variation of this correlation in multiple tests was attributed to constitutional characteristics of the subject.     

Changes in evoked potentials during differentiation inhibition

Evoked responses (EPs) of the auditory and the sensorimotor cortical areas were studied in experiments on cats during formation of a positive food-procuring conditioned reflex to a rhythmic sequence of clicks and during formation of the differentiation inhibition in response to the clicks of the same parameters, but with different frequency. In the positive conditioned reflex the EPs amplitude in the sensorimotor cortex increases; they are enriched by late components and in their general configuration they become much similar to EPs in the auditory area. The EPs patterns both in the auditory and in the sensorimotor areas considerably change in response to the differentiation stimulus, but differently in each of the sites.     

P300 from a single-stimulus paradigm: passive versus active tasks and stimulus modality

The P300 component of the event-related brain potential (ERP) was elicited with auditory and visual stimuli in separate experiments. Each study compared an oddball paradigm that presented both target and standard stimuli with a single-stimulus paradigm that presented a target but no standard stimuli. Subjects were instructed in different conditions either to ignore the stimuli, press a response key to the target, or maintain a mental count of the targets. For the passive ignore conditions, P300 amplitude from the single-stimulus paradigm was larger than that from the oddball paradigm. For the active tasks, P300 amplitude from the oddball paradigm was larger than that from the single-stimulus paradigm. For the press and count conditions, P300 amplitude and latency were highly similar for the oddball and single-stimulus procedures. The findings suggest that the single-stimulus paradigm can provide reliable cognitive measures in clinical/applied testing for both passive and active response conditions.     

Hemispheric interaction in man during perception of visual stimuli]

Averaged evoked potentials (AEP) to verbal (letters) and nonverbal (random shapes) stimuli exposed in the left and right visual fields were registered in healthy subjects with normal vision. Analysis of the later AEP latencies pointed to asymmetry in the temporal parameters of the interhemispheric interaction. The late AEP latency is shorter in the right hemisphere than in the left hemisphere. The difference is more pronounced in responses to nonverbal stimuli. The earlier development of the evoked potential in the right hemisphere (or the later one in the left hemisphere) accounts for the interhemispheric difference in the temporal parameters of the late AEP components. Comparison of the latency of the component P300 to verbal and nonverbal stimuli presented in the ipsilateral or the contralateral visual fields reveals a transfer of the results of the cortical processing of visual information in the course of interhemispheric interaction.     

Correlations of the Characteristics of Evoked EEG Potentials with the Neuroticism Level in Healthy Adults

We studied correlations between the estimates of the neuroticism level (one of the most significant factors of the emotional sphere of a personality) and the amplitude/time characteristics of evoked EEG potentials (EPs). Passive and negative emotiogenic, as well as neutral (from the emotional aspect) visual images (stimuli from the set of the International Affective Picture System, IAPS), were presented to 102 tested persons. The neuroticism level was estimated based on Eysenck’s personality questionnaire. We found that subjects with high estimates of the neuroticism level are characterized, in general, by somewhat higher rates and intensities of processing of emotionally negative information, a higher level of activation of the processes of automatic attention, and readiness to react to both significant and insignificant visual signals (with the aim of probably fighting of a threat). These peculiarities were manifested as relatively shorter latencies of the Р1, N1, Р2, N2, and Р3 components and as higher amplitudes of the Р2 component in the EPs induced by emotionally negative stimuli, as compared with the corresponding indices in subjects with a low neuroticism level. The amplitudes of the N2 component in the case of presentation of negative and neutral stimuli showed a trend toward a decrease. The approach used can be applied for obtaining objective indices interpreted as correlates of peculiarities of the emotional responsiveness typical of a personality.