Jan Chládek

The executive functions in frontal and temporal lobes: a flanker task intracerebral recording study.

The occurrence of the local generators of P3-like potentials elicited by a noise-compatibility flanker test was used to study the processing of executive functions, particularly in the frontal and temporal cortices. The test performed with arrows comprised a simpler congruent and a more difficult incongruent task. The two tasks activated the attention and several particular executive functions, i.e., working memory, time perception, initiation, and motor control of executed task. The incongruent task increased demand on executive functions, and besides the functions common for both tasks, an inhibition of automatic responses, the reversal of incorrect response tendency, the internal ordering of the correct response, and the initiation of the target-induced correct response were involved. In seven epilepsy surgery candidates (four men and three women), ranging in age from 26 to 38 years, multicontact depth electrodes were implanted in 590 cortical sites. In the two tasks, the P3-like potential sources were displayed in the mesial temporal structures, the lateral temporal neocortex, the anterior and posterior cingulate, the orbitofrontal cortex, and dorsolateral prefrontal cortex. The P3-like potentials occurred more frequently with the incongruent than with congruent stimuli in all these areas. This more frequent occurrence of P3 sources elicited by the incongruent task appeared significant in temporal lateral neocortex and orbitofrontal cortex. The executive functions are processed in a widespread frontotemporal neurocognitive network. This study confirms the involvement of the temporal neocortex in the executive functions.

Neural correlates of affective picture processing — A depth ERP study

Using functional neuroimaging techniques (PET and fMRI), various cortical, limbic, and paralimbic structures have been identified in the last decade as neural substrates of human emotion. In this study we used a novel approach (intracerebral recordings of event-related potentials) to add to our knowledge of specific brain regions involved in affective picture processing. Ten intractable epileptic patients undergoing pre-surgical depth electrode recording viewed pleasant, neutral, and unpleasant pictures and intracerebral event-related potentials (ERPs) were recorded. A total of 752 cortical and subcortical sites were investigated. Significant differences in ERPs to unpleasant as compared to neutral or pleasant pictures were frequently and consistently observed in recordings from various brain areas--the mesial temporal cortex (the amygdala, the hippocampus, the temporal pole), the lateral temporal cortex, the mesial prefrontal cortex (ACC and the medial frontal gyrus), and the lateral prefrontal cortex. Interestingly, the mean latencies of responses to emotional stimuli were somewhat shorter in the frontal lobe structures (with evidently earlier activation within lateral prefrontal areas when compared to mesial prefrontal cortex) and longer in the temporal lobe regions. These differences, however, were not significant. Additional clearly positive findings were observed in some rarely investigated regions--in the posterior parietal cortex, the precuneus, and the insula. An approximately equivalent number of positive findings was revealed in the left and right hemisphere structures. These results are in agreement with a multisystem model of human emotion, distributed far beyond the typical limbic system and substantially comprising lateral aspects of both frontal lobes as well.

On the Time Course of Synchronization Patterns of Neuronal Discharges in the Human Brain during Cognitive Tasks

Using intracerebral EEG recordings in a large cohort of human subjects, we investigate the time course of neural cross-talk during a simple cognitive task. Our results show that human brain dynamics undergo a characteristic sequence of synchronization patterns across different frequency bands following a visual oddball stimulus. In particular, an initial global reorganization in the delta and theta bands (2–8 Hz) is followed by gamma (20–95 Hz) and then beta band (12–20 Hz) synchrony.

The posterior medial cortex is involved in visual but not in verbal memory encoding processing: an intracerebral recording study

The objective is to study the involvement of the posterior medial cortex (PMC) in encoding and retrieval by visual and auditory memory processing. Intracerebral recordings were studied in two epilepsy-surgery candidates with depth electrodes implanted in the retrosplenial cingulate, precuneus, cuneus, lingual gyrus and hippocampus. We recorded the event-related potentials (ERP) evoked by visual and auditory memory encoding–retrieval tasks. In the hippocampus, ERP were elicited in the encoding and retrieval phases in the two modalities. In the PMC, ERP were recorded in both the encoding and the retrieval visual tasks; in the auditory modality, they were recorded in the retrieval task, but not in the encoding task. In conclusion, the PMC is modality dependent in memory processing. ERP is elicited by memory retrieval, but it is not elicited by auditory encoding memory processing in the PMC. The PMC appears to be involved not only in higher-order top-down cognitive activities but also in more basic, rather than bottom-up activities.

The Role of Anterior Nuclei of the Thalamus: A Subcortical Gate in Memory Processing: An Intracerebral Recording Study.

Objective To study the involvement of the anterior nuclei of the thalamus (ANT) as compared to the involvement of the hippocampus in the processes of encoding and recognition during visual and verbal memory tasks. Methods We studied intracerebral recordings in patients with pharmacoresistent epilepsy who underwent deep brain stimulation (DBS) of the ANT with depth electrodes implanted bilaterally in the ANT and compared the results with epilepsy surgery candidates with depth electrodes implanted bilaterally in the hippocampus. We recorded the event-related potentials (ERPs) elicited by the visual and verbal memory encoding and recognition tasks. Results P300-like potentials were recorded in the hippocampus by visual and verbal memory encoding and recognition tasks and in the ANT by the visual encoding and visual and verbal recognition tasks. No significant ERPs were recorded during the verbal encoding task in the ANT. In the visual and verbal recognition tasks, the P300-like potentials in the ANT preceded the P300-like potentials in the hippocampus. Conclusions The ANT is a structure in the memory pathway that processes memory information before the hippocampus. We suggest that the ANT has a specific role in memory processes, especially memory recognition, and that memory disturbance should be considered in patients with ANT-DBS and in patients with ANT lesions. ANT is well positioned to serve as a subcortical gate for memory processing in cortical structures.

Complex motor-cognitive factors processed in the anterior nucleus of the thalamus: an intracerebral recording study.

Abstract Cognitive adverse effects were reported after the deep brain stimulation (DBS) of the anterior nucleus of the thalamus (AN) in epilepsy. As the AN may have an influence on widespread neocortical networks, we hypothesized that the AN, in addition to its participation in memory processing, may also participate in cognitive activities linked with the frontal neocortical structures. The aim of this study was to investigate whether the AN might participate in complex motor–cognitive activities. Three pharmacoresistant epilepsy patients implanted with AN–DBS electrodes performed two tasks involving the writing of single letters: (1) copying letters from a monitor; and (2) writing of any letter other than that appearing on the monitor. The cognitive load of the second task was increased. The task-related oscillatory changes and evoked potentials were assessed. Local event-related alpha and beta desynchronization were more expressed during the second task while the lower gamma synchronization decreased. The local field event-related potentials were elicited by the two tasks without any specific differences. The AN participates in cognitive networks processing complex motor–cognitive tasks. Attention should be paid to executive functions in subjects undergoing AN–DBS.

Hippocampal negative event‐related potential recorded in humans during a simple sensorimotor task occurs independently of motor execution

A hippocampal‐prominent event‐related potential (ERP) with a peak latency at around 450 ms is consistently observed as a correlate of hippocampal activity during various cognitive tasks. Some intracranial EEG studies demonstrated that the amplitude of this hippocampal potential was greater in response to stimuli requiring an overt motor response, in comparison with stimuli for which no motor response is required. These findings could indicate that hippocampal‐evoked activity is related to movement execution as well as stimulus evaluation and associated memory processes. The aim of the present study was to investigate the temporal relationship between the hippocampal negative potential latency and motor responses. We analyzed ERPs recorded with 22 depth electrodes implanted into the hippocampi of 11 epileptic patients. Subjects were instructed to press a button after the presentation of a tone. All investigated hippocampi generated a prominent negative ERP peaking at ∼420 ms. In 16 from 22 cases, we found that the ERP latency did not correlate with the reaction time; in different subjects, this potential could either precede or follow the motor response. Our results indicate that the hippocampal negative ERP occurs independently of motor execution. We suggest that hippocampal‐evoked activity, recorded in a simple sensorimotor task, is related to the evaluation of stimulus meaning within the context of situation.

Preictal dynamics of EEG complexity in intracranially recorded epileptic seizure: a case report.

AbstractRecent findings suggest that neural complexity reflecting a number of independent processes in the brain may characterize typical changes during epileptic seizures and may enable to describe preictal dynamics. With respect to previously reported findings suggesting specific changes in neural complexity during preictal period, we have used measure of pointwise correlation dimension (PD2) as a sensitive indicator of nonstationary changes in complexity of the electroencephalogram (EEG) signal. Although this measure of complexity in epileptic patients was previously reported by Feucht et al (Applications of correlation dimension and pointwise dimension for non-linear topographical analysis of focal onset seizures. Med Biol Comput. 1999;37:208–217), it was not used to study changes in preictal dynamics. With this aim to study preictal changes of EEG complexity, we have examined signals from 11 multicontact depth (intracerebral) EEG electrodes located in 108 cortical and subcortical brain sites, and from 3 scalp EEG electrodes in a patient with intractable epilepsy, who underwent preoperative evaluation before epilepsy surgery. From those 108 EEG contacts, records related to 44 electrode contacts implanted into lesional structures and white matter were not included into the experimental analysis.The results show that in comparison to interictal period (at about 8–6 minutes before seizure onset), there was a statistically significant decrease in PD2 complexity in the preictal period at about 2 minutes before seizure onset in all 64 intracranial channels localized in various brain sites that were included into the analysis and in 3 scalp EEG channels as well. Presented results suggest that using PD2 in EEG analysis may have significant implications for research of preictal dynamics and prediction of epileptic seizures.

Intracranial EEG Connectivity Analysis and Result Imaging

We are presenting a method for analyzing signals from deep brain structures, measured by intracranial electrodes, to reveal connectivity in the human brain. Time evaluation of the correlation technique is applied for every available contact pair to determine dependencies between EEG channels. This produces a large amount of results that are not easy to interpret. Here we introduce a procedure for complex and comprehensive result imaging which helps us focus on significant parts of the results. Changes of power are examined along with correlation changes. Results are demonstrated for one subject. Five channels were selected from the hippocampus for detailed analysis. How the changes of correlation are connected to changes of power is shown in addition to the coupling between channels.

Dissociative States and Chaotic Patterns of Electrodermal Activity During Associative Experiment

A dynamic concept of schizophrenia linked to the theory of dissociated complexes was experimentally demonstrated by Jung in “The Psychology of the Dementia Praecox”. According to him, during schizophrenia the psyche is split-off into a plurality of autonomous complexes and the whole personality is pathologically disintegrated. This pathological disintegration is frequently observed in schizophrenic associations that display “chaotic randomness”. The “chaotic randomness” does not mean a true randomness because schizophrenic associations are not without underlying order and causality. An important aspect of schizophrenic dissociation is an extreme subjective sensitivity. These two signs of schizophrenic associations are analogical to known characteristics of chaotic nonlinear dynamical systems. The hypothesis tested in the present study is that neural chaos, calculated from electrodermal activity (EDA), during rest and word-association process is more prominent in schizophrenic patients compared to healthy controls. To test the hypothesis we have measured EDA during the experiment performed in 25 schizophrenic patients and 21 healthy control subjects. Results of nonlinear and statistical analysis indicate that the neural chaos characterized by positive largest Lyapunov exponents during rest and the word-association process is significantly higher in the schizophrenic patients. These data suggest that pseudo-randomness of schizophrenic associations and increased sensitivity related to dissociative states might be linked to the chaotic neural dynamics.