Stress-induced alterations of left-right electrodermal activity coupling indexed by pointwise transinformation.

In this study, we tested the hypothesis that experimental stress induces a specific change of left-right electrodermal activity (EDA) coupling pattern, as indexed by pointwise transinformation (PTI). Further, we hypothesized that this change is associated with scores on psychometric measures of the chronic stress-related psychopathology. Ninety-nine university students underwent bilateral measurement of EDA during rest and stress-inducing Stroop test and completed a battery of self-report measures of chronic stress-related psychopathology. A significant decrease in the mean PTI value was the prevalent response to the stress conditions. No association between chronic stress and PTI was found. Raw scores of psychometric measures of stress-related psychopathology had no effect on either the resting levels of PTI or the amount of stress-induced PTI change. In summary, acute stress alters the level of coupling pattern of cortico-autonomic influences on the left and right sympathetic pathways to the palmar sweat glands. Different results obtained using the PTI, EDA laterality coefficient, and skin conductance level also show that the PTI algorithm represents a new analytical approach to EDA asymmetry description.

Late divergence of target and nontarget ERPs in a visual oddball task.

Different mental operations were expected in the late phase of intracerebral ERPs obtained in the visual oddball task with mental counting. Therefore we searched for late divergences of target and nontarget ERPs followed by components exceeding the temporal window of the P300 wave. Electrical activity from 152 brain regions of 14 epileptic patients was recorded by means of depth electrodes. Average target and nontarget records from 1800 ms long EEG periods free of epileptic activity were compared. Late divergence preceded by almost identical course of the target and nontarget ERPs was found in 16 brain regions of 6 patients. The mean latency of the divergence point was 570+/-93 ms after the stimulus onset. The target post-divergence section of the ERP differed from the nontarget one by opposite polarity, different latency of the components, or even different number of the components. Generators of post-divergence ERP components were found in the parahippocampal gyrus, superior, middle and inferior temporal gyri, amygdala, and fronto-orbital cortex. Finding of late divergence indicates that functional differences exist even not sooner than during the final phase of the task.

Very early EEG responses to a meaningful auditory stimulus in the frontal lobes: an intracerebral study in humans.

Frontal auditory evoked potentials (FAEPs) obtained as a response to the warning auditory stimulus of a contingent negative variation task from depth electrodes were investigated. The second, imperative stimulus was visual. Thirteen epileptic patients participated in the study. Records from 20 electrodes of 10 patients exhibited signs of local generation. They were localized in the motor cortices (7 cases), in the superior, medial, and inferior frontal gyri (7 cases), in the cingulate gyrus (5 cases), and in the nucleus caudatus (1 case). A typical FAEP from these generators consisted of three components: (i) first negative wave peaking at 99+/-13 ms; (ii) positive wave peaking at 181 +/- 21 ms; (iii) second negative wave peaking at 324 +/- 63 ms. In 11 generators no evoked activity to visual stimulus was observed; in the remaining 9 generators both auditory and visual stimuli evoked a response. FAEPs with very early onsets (onset latency below 20 ms) were found in three sites in the precentral gyrus.

The level of frontal-temporal beta-2 band EEG synchronization distinguishes anterior cingulate cortex from other frontal regions.

Recent findings indicate that complex cognitive functions are organized at a global level in the brain and rely on large-scale information processing requiring functional integration of multiple disparate neural assemblies. The critical question of the integration of distributed brain activities is whether the essential integrative role can be attributed to a specific structure in the brain or whether this ability is inherent to the cognitive network as a whole. The results of the present study show that mean values of the running correlation function in frontal-temporal EEG pairs with one electrode in the anterior cingulate cortex (ACC) are significantly higher than the same values in other frontal-temporal pairs. These findings indicate a particular role of the ACC in large-scale communication, which could reflect its unique integrative functions in cognitive processing.

Cognitive network interactions and beta 2 coherence in processing non-target stimuli in visual oddball task.

Spatiotemporal dynamics of event-related potentials (ERP) evoked by non-target stimuli in a visual oddball experiment and the presence of coherent oscillations in beta 2 frequency band of decomposed EEG records from peristimulus period were investigated by means of intracranial electrodes in humans. Twenty-one patients with medically intractable epilepsy participated in the study. The EEG signal was recorded using platinum electrodes implanted in several cortical and subcortical sites. Averaged 2 s EEG records were analyzed. Task-specific EEG changes were found in each patient, ERPs were derived from 92 electrodes used (96 % of possible cases). In the majority of analysed cases, ERPs were composed of several distinct components, and their duration was mostly longer than 1 s. The mean onset of the first ERP component was 158+/-132 ms after the stimulus (median 112 ms, minimum value 42 ms, maximum value 755 ms), and large variability of these onset times was found in all the investigated structures. Possible coherence between neural activities of remote brain sites was investigated by calculating running correlations between pairs of decomposed EEG records (alpha, beta 1, beta 2 frequency bands were used, total number of correlated pairs was 662 in each frequency band). The record pairs exhibiting highly correlated time segments represented 23 % of all the investigated pairs in alpha band, 7 % in beta 1 band, and 59 % in beta 2 band. In investigated 2 s record windows, such segments were distributed evenly, i.e. they were also found before the stimulus onset. In conclusion, the results have implicated the idea that a lot of recorded ERPs was more or less by-products of chance in spreading a signal within the neuronal network, and that their functional relevance was somewhat linked with the phenomenon of activity synchronization.

Beta 2-band synchronization during a visual oddball task.

The study investigated whether specific changes in phase synchrony in the beta 2 frequency band of EEG (25-35 Hz) occurred during a recognition task. The level of synchrony was examined between one hundred and eighty loci in the frontal and temporal lobes of eight epileptic patients with intracerebral electrodes; the EEG records were obtained during a visual oddball task. In each pair of records, the correlation curves were created from the sequence of correlation coefficients calculated. These curves consisted of irregular oscillations between the maximal and minimal r-values. Transient highly synchronized activity was observed during the whole time course of the experiment in all record pairs investigated and a significant relationship was found between the number of such episodes and the mean correlation coefficient (Spearman R 0.84; N 3240; p<0.001). On averaged curves, which were calculated using stimulus onsets as the trigger of averaging, a significant increase of the mean correlation coefficient in the post-stimulus epoch was found (p<0.01 after both target and non-target stimuli; t-test for dependent samples). As the cognitive demand significantly increases after stimulus presentation, the results are considered to be the first evidence from intracranial recording of increased synchronization in the beta 2 frequency band related to the cognitive activity.

[Effects of mental stress on the health status of the accused during a criminal trial]. / Vliv psychického stresu na zdravotni stav obvineného v prubehu trestního rízení.

A court-sworn medical expert is sometimes authorized to pass a medical judgement, whether an older, from serious diseases suffering accused is able to take part in the criminal trial proceedings. The court-sworn medical expert is required to consider the accused's fitness, his mental and physical ability to appear in court, to understand the trial, to answer the questions of the judge, to defend himself, to put questions and objections against the witness's testimony, etc. Such medical expert's opinion is usually a task for a psychiatrist. Judgement of the ability of the accused to take part in the main court trial is of another character, especially when the accused is suffering from a serious disease, e.g. cardiovascular, pulmonary, gastrointestinal, haematological, tumorous or other. In this case the medical judgement is usually required from a doctor of internal medicine. Nevertheless, this is not an easy task for him. As far as these problems are concerned, the expert gathers only little experience of his own during his juridical practice. Similar cases have been extremely sporadically published in medical or juridical literature and if, then in common sense only. It is evident that the expert must face any possible aggravation of the accused's difficulties. At the same time the expert ought to take care lest the court trial should be inadequately extended and even should prevent the accused's avoidance in the main court trial. This paper tries to determine the basic rules for the court-sworn experts in the branch of internal medicine and would like to facilitate them to judge under which circumstances a seriously ill accused may appear in trial proceedings without exposing him to a serious damage of his health or even endangerment of his life.

Neural chaos and schizophrenia.

Recent data indicate that random-like processes are related to the defects in the organization of semantic memory in schizophrenia which is more disorganized and less definable than those of controls with more semantic links and more bizarre and atypical associations. These aspects of schizophrenic cognition are similar to characteristics of chaotic nonlinear dynamical systems. In this context, the hypothesis tested in this study is that dynamic changes of electrodermal activity (EDA) as a measure of brain and autonomic activity may serve as a characteristic which can be used as an indicator of possible neural chaotic process in schizophrenia. In the present study, bilateral EDA in rest conditions were measured in 40 schizophrenic patients and 40 healthy subjects. Results of nonlinear and statistical analysis indicate left-side significant differences of positive largest Lyapunov exponents in schizophrenia patients compared to the control group. This might be interpreted that the neural activity during rest in schizophrenic patients is significantly more chaotic than in the control group. The relationship was confirmed by surrogate data testing. These data suggest that increased neural chaos in patients with schizophrenia may influence brain processes that can cause random-like disorganization of mental processes.

Limbic irritability and chaotic neural response during conflicting stroop task in the patients with unipolar depression.

According to recent findings activation of anterior cingulate cortex (ACC) is related to detecting cognitive conflict. This conflict related activation elicits autonomic responses which can be assessed by psychophysiological measures such as heart rate variability calculated as beat to beat R-R intervals (RRI). Recent findings in neuroscience also suggest that cognitive conflict is related to specific nonlinear chaotic changes of the signal generated by neural systems. The present study used Stroop word-color test as an experimental approach to psychophysiological study of cognitive conflict in connection with RRI measurement, psychometric measurement of limbic irritability (LSCL-33), depression (BDI-II) and calculation of largest Lyapunov exponents in nonlinear data analysis of RRI time series. Significant correlation 0.61 between largest Lyapunov exponents and LSCL-33 found in this study indicate that a defect of neural inhibition during conflicting Stroop task is closely related to limbic irritability. Because limbic irritability is probably closely related to epileptiform abnormalities in the temporolimbic structures, this result might represent useful instrument for indication of anticonvulsant treatment in depressive patients who are resistant to antidepressant medication.

Chaotic EEG patterns during recall of stressful memory related to panic attack.

Chaotic transitions likely emerge in a wide variety of cognitive phenomena and may be linked to specific changes during the development of mental disorders. They represent relatively short periods in the behavior of a system, which are extremely sensitive to very small changes. This increased sensitivity has been suggested to occur also during retrieval of stressful emotional experiences because of their fragmentary, temporally and spatially disorganized character. To test this hypothesis we recorded EEG during retrieval of fearful memories related to panic attack in 7 patients and retrieval of anxiety-related memories in 11 healthy controls. Nonlinear data analysis of EEG records showed a statistically significant increase in degree of chaotic dynamics after retrieval of stressful memories in majority of patients as well as in control subjects. This change correlated with subjective intensity of anxiety induced during the memory retrieval. The data suggest a role of nonlinear changes of neural dynamics in the processing of stressful anxiety-related memories, which may play an important role in the pathophysiology of panic disorder.

Identical event-related potentials to target and frequent stimuli of visual oddball task recorded by intracerebral electrodes.

OBJECTIVE: The shape of visually elicited event-related potentials (ERP) of epileptic patients during their presurgical evaluation with intracerebral electrodes was investigated in the study. METHODS: Twenty intractable epileptic patients with depth electrodes at several intracranial locations in the frontal, temporal, parietal lobes, and in the amygdalo-hippocampal complex participated in the study. To evoke the ERP, a standard visual oddball task was used with target stimuli, and frequent non-habituated and habituated stimuli. The averaged responses of the 3 groups were superimposed and visually analyzed whether the shape appeared identical or non-identical. RESULTS: The EEG response to target and frequent stimuli was recorded in 660 intra-cerebral sites. In 88 sites (14 different patients) localized in the amygdala, parahippocampal gyrus, superior, middle, and inferior temporal gyri, fusiform and lingual gyri, sensorimotor cortex, prefrontal cortex, hippocampus, and cingulated gyrus, the identical ERPs to target and both groups of frequent stimuli were observed. In 442 sites located in the above listed structures, and in the basal ganglia and parietal cortex, the shape of the ERP differed from 0.3 to 0.47 s on after the stimulus. The remaining 130 sites did not yield the task-specific potential change. CONCLUSIONS: The existence of identical ERPs to target and frequent stimuli in the oddball task suggests that a part of mental operations underlying the brain engagement in this task is not dependent on the way of responding.

Steep early negative slopes can be demonstrated in pre-movement bereitschaftspotential.

OBJECTIVES: The study presents data suggesting that the classic bereitschaftspotential hides in its early component (BP1) steep increases of negativity which precede the movement at varying intervals in repeated trials. METHODS: In 12 volunteers, surface EEG from Fz, Cz, C3, C4, and Pz electrodes and EMG from the flexor digitorum communis were recorded during self-paced wrist flexions. Two hundred trials were collected from each subject. The single trials were grouped for averaging in two different ways. In the first one, single trials for each subject were used to create individual averages. In the second, all single trials were divided into groups according to the point in time of small steep negative shift from the baseline detected on sweeps before the movement and time group averages were created. The identification of small shifts was based on the comparison of calculated mean amplitudes in the first and the second half of the 1 s time window moved along the time axis. RESULTS: The small negative shifts were identified in 97.2% of analyzed records. In each subject, their position on the time axis varied considerably. Individual averages exhibited the characteristics of classical readiness potential, i.e. slow early component, steep late component, laterality over motor cortices. On the other hand, all time group averages (26) displayed an early steep negative shift followed by plateau which, about 0.5 s before the movement, gave rise to the second, late steep negative shift. The slope values calculated in the definite segments of averaged curves were used as a measure of the amplitude of these shifts over various brain areas. MANOVA showed a significant effect of the electrode position both in the case of early slopes (F(4,115)=9.7; P<0.000) and in the case of late slopes (F(4,115)=22.5; P<0.000). In both cases, the largest value was demonstrated under Cz electrode. In contrast to the late slopes, the values of early slopes did not exhibit laterality and suggested greater importance of pre-frontal regions in their formation. CONCLUSION: We have suggested that the formation of steep early negative shifts from the baseline in time group averages was due to synchronization of a mental process which, under classical averaging procedure, was dispersed uniformly throughout the pre-movement period.

Intracerebral recording of readiness potential induced by a complex motor task.

While exploring 11 epileptic patients with intracerebral electrodes, we recorded readiness potential (RP) preceding a complex motor task. Multilead depth electrodes were positioned stereotactically into the cortex. In three patients, it was also possible to record RP from the putamen. The movement triggering the recording was the turning of a page in an architectural book. The movement was performed under two conditions: in the first condition, without looking at the pictures on the page (typical self-pacing); and in the second condition, following the inspection of the pictures. There were no significant differences in the appearance of RP under these two conditions, neither in duration nor in amplitude. That could be explained by the fact that "self-paced" does not mean "spontaneous," but covers the internal non-conscious program related to a given task. RP were present in the contralateral primary sensorimotor cortex and the bilateral supplementary motor area (SMA), and in the anterior caudal cingulate cortex. No difference between the cortical topography of RP preceding a simple motor task and the topography of RP occurring in connection with complex movement was observed.

Synchronizing effect of clock rhythm on the 'when to move' decision in repeated voluntary movements.

In 13 volunteers, surface EEGs from F(z), C(z), C(3), C(4), and P(z) electrodes and EMG from the flexor digitorum communis were recorded during an experimental task in which the performance of wrist flexion was linked with the selection of a clock sound. In the epoch from 4 to 1 s before movement, more than 95% of the records exhibited a small negative shift from the baseline. The position of these shifts on the time axis made it possible to create groups of time trials. The average EEG curves from these groups showed one prominent negative shift from the baseline, which could be related to the position of particular clock sounds. The slope values of these shifts were highest under the F(z) and C(z) electrodes. We suggested that these negative shifts coincided with 'when to move' decisions, which preceded the execution of the movement at varying intervals.

The early component of the premovement readiness potential and its behavioral determinants.

Fifteen healthy subjects were asked to randomly select a tick of a mechanical clock which was operating throughout the experiment and to flex their wrist at the chosen tick. The individual averages of EEG recordings collected during the period of the putative decision to begin the task exhibited steep slopes of negativity followed by plateaus. These slopes preceded the selection of the signal sound at varying intervals, the longest interval was 3 s. The grand average of individual averages depicted a waveform whose shape was identical to the early component of the classical readiness potential. Another interesting finding came from experiments with mental counting of clock sounds, which demonstrated that the generation of the first mentally-counted number is preceded by a distinct negative potential shift.

The impact of a decision process upon scalp recorded premovement potential.

Twelve normal subjects were asked to select one finger after a warning signal and to move it. Using different modes of averaging the EEG responses, it is shown that: (i) the selection of a finger is accompanied by a distinct negative slow potential consisting of a rapid set-up and a following plateau which is the most prominent under the Fz electrode, and (ii) the decision process, when dispersed within a large interval in repeated trials, gives rise to a slow progressive increase of negativity resembling the early component of premovement slow cortical potential from the classical self-paced paradigm.

Readiness potentials related to self-initiated movement and to movement preceded by time estimation: a comparison.

Two procedures for eliciting premovement potentials were compared: (1) the estimation of a 3 s interval elapsed after a warning auditory signal, and (2) classical "self-pacing". Eleven healthy right-handed subjects participated in the experiment, EEG records from scalp electrodes placed at CZ, C3+ and C4+ were analyzed. It has been shown that both procedures induced similar premovement potentials except that in the first procedure the early component of the potential was longer. The time estimation itself induced a negative slow potential consisting of a rapid set-up and a subsequent plateau.

Psychophysiological mechanisms in hypochondriasis.

The paper has analysed hypochondriasis in terms of defence behaviour. The study sample consisted of 39 treated neurotics who felt themselves menaced by a serious disease which was not confirmed by appropriate medical examination and who came to the therapist with anxious states. Specific defence acts induced by hypochondriacal threat, stimuli inducing the states of threat and mechanisms responsible for formation and maintenance of their capability for inducing emotion were found in every patient. The results demonstrated that many manifestations of hypochondriasis considered generally as psychopathological symptoms were in fact meaningful defence responses against a threat which the patient believed existed.