Relation of visual evoked potentials to the integral characteristics of cognitive activity in 8- to 9-year-old children

Amplitude and temporal parameters of evoked potentials (EPs) in response to a checkerboard pattern, picture of a house, the Russian word "dom", meaning house, combination of letters "DMO" and a number of other stimuli, correlated with indices of the verbal, nonverbal, and general intelligence as well as with those of the cognitive style "field dependence-independence". Maximum number of statistically significant correlations was found in the course of comparison of integrative cognitive characteristics and parameters of EPs to stimuli with increased semantic complexity. No interhemispheric differences were found in the character of interrelations between cognitive characteristics and parameters of EPs to verbal and spatially structured stimuli.     

Visual evoked potentials and event related potentials in congenitally deaf subjects

The purpose was to test parameters of visual evoked potentials (VEPs) and of event-related potentials (ERPs) in deaf subjects to verify visual and cognitive CNS functions in a handicapped group of the population. Three types of visual stimuli (with dominating parvocellular or magnocellular system activation or with cognitive tasks) were used in the study. Six deaf persons (4 women, 2 men, mean age 17 years) and 6 persons with normal hearing (sex- and age-matched) were included in this pilot study. In all types of stimulation, latencies and amplitudes of main VEPs and ERPs components were evaluated. No significant latency differences were found. However, significantly reduced amplitudes were found in the occipital area for responses to motion and cognitive stimuli which might be interpreted as a part of functional reorganization of the extrastriate and cognitive cortical areas of deaf subjects.     

Analysis of visual evoked potentials through Wiener filtering applied to a small number of sweeps

We introduce a method for processing visual evoked potentials, on the basis of a Wiener filter algorithm applied to a small number of consecutive responses. The transfer function of the filter is obtained by taking into account both the average of 99 sweeps (as an estimate of the true signal) and the EEG signal just before the stimulus onset (as an estimate of the noise superimposed on each individual response). The process acts as a sweep-by-sweep filter (in the sense of the mean square error) which considers the possible non-stationarities of the EEG signal during a complete clinical procedure. The average of a small number of consecutive filtered sweeps reveals variations in the morphology of the evoked responses which produce a change in the principal latencies. Applications are foreseen in neurophysiological studies of visual evoked potential responses, and in the clinic, where it is important to evaluate adaptive mechanisms, dynamic changes in single groups of visual evoked potentials and cognitive responses.     

Development of a function to recognize angry facial expressions in 5- to 11-year-old children

In 5- to 6-, 7- to 8-, and 10- to 11-year-old children, age-related features of the effects of former experience on the recognition of emotional facial expressions were found using a cognitive set model. In five- to six-year-old children, an inert set to an angry facial expression was formed and expressed during testing as a large number of erroneous recognition of facial expressions of the perseverative type (assimilative) illusions. Set plasticity was increased in seven- to eight-year-old children and the number of assimilative illusions decreased. In 10- to 11-year-old children, the cognitive set was similar to adults in terms of its plasticity and a ratio of assimilative and contrast illusions. Changes in the spatial synchronization of electrical potentials in the ??- and ??-frequency bands were observed in all age groups, mainly during set formation. In all age groups, we observed a correlation between the bioelectrical data and the effects of former experience on the recognition of facial expression. Based on the data on the coherence of the potentials of the ??- and ??-ranges we propose age-related changes in the involvement of the cortico-hippocampal and fronto-thalamic functional systems of integration of brain activity in organizing the sets to emotionally negative facial expressions.     

Dynamics of the gamma-responses in an 8-second interval between facial and trigger stimuli as dependent the success of task performance

A cognitive set to facial expression was used as a model with the loading on working memory being increased by increasing the interval between the facial and triggering stimuli to 8 seconds. The aim was to determine whether the intensity of brain potentials evoked in a range of 41–60 Hz (the range 15–60 Hz was used) by facial stimuli is associated with the “success” of task performance (mistake rate). An index of average amplitudes of EEG oscillations was used to measure the response to facial stimuli, and γ responses proved to be associated with the number of mistakes in performing the task. The results make it possible to consider the γ responses to facial stimuli as an EEG correlate of the internal states that correspond to adequate actions of the subject in the test with a 8-s interval between the facial and trigger stimuli.     

Human electrophysiological and cognitive effects of exposure to ELF magnetic and ELF modulated RF and microwave fields: a review of recent studies

The investigation of weak (<500 microT), extremely low frequency (ELF, 0-300 Hz) magnetic field (MF) exposure upon human cognition and electrophysiology has yielded incomplete and contradictory evidence that MFs interact with human biology. This may be due to the small number of studies undertaken examining ELF MF effects upon the human electroencephalogram (EEG), and the associated analysis of evoked related potentials (ERPs). Relatively few studies have examined how MF exposure may affect cognitive and perceptual processing in human subjects. The introduction of this review considers some of the recent studies of ELF MF exposure upon the EEG, ERPs and cognitive and perceptual tasks. We also consider some of the confounding factors within current human MF studies and suggest some new strategies for further experimentation.     

Analysis of Visual Cognitive Impairments in Schizophrenia at the Early Stages of the Disease and Their Correction by Interactive Virtual Environment

The paper describes the results of studies aimed at evaluating the effect of interactive virtual environments on the visual system, including the magno-and parvo-systems. Analysis was conducted in patients diagnosed with paranoid schizophrenia diagnosed from one to five years ago. Comparative analysis of visual evoked potentials during the perception of images that differed in their semantic (animate/inanimate) and physical characteristics (filtration images at high/low spatial frequencies) was used for the assessment of the impact of virtual environments. The images of objects were filtered via digital filtration for selective effect on the magno-and parvo-channels of the visual system. To evaluate the function of visual perception, the measurement of contrast sensitivity using Gabor elements was used. At the early stages of schizophrenia, the patients exhibited a decrease in the amplitudes of the components of cognitive visual evoked potentials to stimuli filtered at high spatial frequencies and reduced contrast sensitivity at high spatial frequencies. The effect of virtual environments on the visual system resulted in a significant increase in the amplitude of the cognitive components of visual evoked potentials in the paradigm of presentation of images filtered at the high spatial frequencies, which allows the conclusion about a stimulating effect of the virtual environment on the parvo-system functioning. The activation of the magno-system occurred to a lesser extent. The present study represents the findings obtained by the studies of cognitive impairments in schizophrenia and the methods of their correction conducted at the Laboratory of Physiology of Vision of the Pavlov Institute of Physiology of the Russian Academy of Sciences and at the Laboratory of Neurobiology of Action Programming of the Bechtereva Institute of the Human Brain of the Russian Academy of Sciences.     

Effect of context on the plasticity of cognitive activity

The hypotheses that the plasticity or flexibility of cognitive activity substantially depends on the ability to replace the previous cognitive sets by new sets that are more appropriate to new conditions is substantiated. Working memory overload results in a decrease in set-shifting and, as a consequence, increased erroneous stimuli recognition. The plasticity of set-shifting is changed depending on the context of cognitive activity. On the basis of the data from the analysis of the coherence function and induced synchronization/desynchronization responses of potentials in the θ (4–7 Hz) and low-frequency α (8–10 Hz) bands, the roles of the tonic and phasic forms of activity of the cortico-hippocampal and fronto-thalamic functional systems of cerebral integration in changes of plasticity of cognitive functions are discussed.     

The challenge of non-invasive cognitive physiology of the human brain: how to negotiate the irrelevant background noise without spoiling the recorded data through electronic averaging.

Brain mechanisms involved in selective attention in humans can be studied by measures of regional blood flow and metabolism (by positron emission tomography) which help identify the various locations with enhanced activities over a period of time of seconds. The physiological measures provided by scalp-recorded brain electrical potentials have a better resolution (milliseconds) and can reveal the actual sequences of distinct neural events and their precise timing. We studied selective attention to sensory inputs from fingers because the brain somatic representations are deployed over the brain convexity under the scalp thereby making it possible to assess distinct stages of cortical processing and representation through their characteristic scalp topographies. In the electrical response to a finger input attended by the subject, the well-known P300 manifests a widespread inhibitory mechanism which is released after a target stimulus has been identified. P300 is preceded by distinct cognitive electrogeneses such as P40, P100 and N140 which can be differentiated from the control (obligatory) profile by superimposition or electronic subtraction. The first cortical response N20 is stable across conditions, suggesting that the first afferent thalamocortical volley is not affected by selective attention. At the next stage of modality-specific cortex in which the sensory features are processed and represented, responses were enhanced (cognitive P40) only a very few milliseconds after arrival of the afferent volley at the cortex, thus documenting a remarkable precocity of attention gain control in the somatic modality. The physiology of selective attention also provides useful cues in relation to non-target inputs which the subject must differentiate in order to perform the task. When having to tell fingers apart, the brain strategy for non-target fingers is not to inhibit or filter them out, but rather to submit their input to several processing operations that are actually enhanced when the discrimination from targets becomes more difficult. While resolving a number of such issues, averaged data cannot disclose the flexibility of brain mechanisms nor the detailed features of cognitive electrogeneses because response variations along time have been ironed out by the bulk treatment. We attempted to address the remarkable versatility of humans in dealing with their sensory environment under ecological conditions by studying single non-averaged responses. We identified distinct cognitive P40, P100, N140 and P300 electrogeneses in spite of the noise by numerically assessing their characteristic scalp topography signatures. Single-trial data suggest reconsiderations of current psychophysiological issues. The study of non-averaged responses can clarify issues raised by averaging studies as illustrated by our recent study of cognitive brain potentials for finger stimuli which remain outside the subject's awareness. This has to do with the physiological basis of the 'cognitive unconscious', that is, current mental processes lying on the fringe or outside of phenomenal awareness and voluntary control, but which can influence ongoing behaviour. Averaged data suggest that, in selective auditory attention, the subject may not notice mild concomitant finger inputs. The study of non-averaged responses documents the optional and independent occurrence of the cognitive P40, P100 and N140 (but not P300) electrogeneses while the finger inputs remain outside phenomenal awareness. These results suggest that the subject unconsciously assigns limited cognitive resources to distinct somatic cortical areas thereby submitting finger inputs to an intermittent curtailed surveillance which can remain on the fringe or outside consciousness. The study of cognitive electrogeneses in single non-averaged responses is making possible a neurophysiology of cognition in real time.     

Analysis of event-related potentials (ERP) by damped sinusoids

Several researchers propose that event-related potentials (ERPs) can be explained by a superposition of transient oscillations at certain frequency bands in response to external or internal events. The transient nature of the ERP is more suitable to be modelled as a sum of damped sinusoids. These damped sinusoids can be completely characterized by four sets of parameters, namely the amplitude, the damping coefficient, the phase and the frequency. The Prony method is used to estimate these parameters. In this study, the long-latency auditory-evoked potentials (AEP) and the auditory oddball responses (P300) of 10 healthy subjects are analysed by this method. It is shown that the original waveforms can be reconstructed by summing a small number of damped sinusoids. This allows for a parsimonious representation of the ERPs. Furthermore, the method shows that the oddball target responses contain higher amplitude, slower delta and slower damped theta components than those of the AEPs. With this technique, we show that the differentiation of sensory and cognitive potentials are not inherent in their overall frequency content but in their frequency components at certain bands. Received: 6 October 1997 / Accepted in revised form: 26 February 1998     

The effect of phloretin on single potassium channels in myelinated nerve

The effect of phloretin, a dipolar organic compound, on single potassium channel currents of myelinateed nerve fibres of Xenopus laevis has been investigated, using inside-out patches prepared by the method of Jonas et al. (1989). The I channel, a potential dependent K channel with intermediate deactivation kinetics, was reversibly blocked by 20 µM phloretin applied on the inside; the block was strongest at negative membrane potentials and less pronounced at positive potentials. Phloretin shifted the curve relating open probability to membrane potential towards more positive potentials and reduced its slope and maximum. This confirms previous findings on the effect of phloretin on the voltage dependence of the fast macroscopic K conductance. Single channel conductance and deactivation kinetics were not altered by phloretin. Offprint requests to: Correspondence to: H. Meves     

Exposure to ELF magnetic and ELF-modulated radiofrequency fields: the time course of physiological and cognitive effects observed in recent studies (2001-2005)

In 2002, we published a review of the cognitive and physiological effects of extremely low frequency magnetic fields (ELF MFs) and ELF-modulated radiofrequency fields associated with mobile phones. Since the original preparation of that review, a significant number of studies have been published using techniques such as electroencephalography, event-related potentials and positron emission tomography to investigate electromagnetic field effects upon human physiology and various measures of performance (cognitive, perceptual, behavioral). We review these recent studies, and when effects were observed, we reference the time course of observed effects (immediate or delayed). In our concluding remarks, we discuss a number of variables that are not often considered in human bioelectromagnetics studies, such as personality, individual differences and the specific laterality of ELF MF and mobile phone exposure over the brain. We also consider the sensitivity of various physiological assays and performance measures in the study of biological effects of electromagnetic fields.     

Upper airway afferents are sufficient to evoke the early components of respiratory-related cortical potentials in humans.

Repeated inspiratory occlusions in humans elicit respiratory-related cortical potentials, the respiratory counterpart of somatosensory-evoked potentials. These potentials comprise early components (stimulus detection) and late components (cognitive processing). They are considered as the summation of several afferent activities from various part of the respiratory system. This study assesses the role of the upper airway as a determinant of the early and late components of the potentials, taking advantage of the presence of a tracheotomy in patients totally or partially deafferented. Eight patients who could breathe either through the mouth or through a tracheotomy orifice (whole upper airway bypassed) were studied (4 quadriplegic patients with phrenic pacing, 4 patients with various sources of inspiratory pump dysfunction). Respiratory-related evoked potentials were recorded in CZ-C3 and CZ-C4. They were consistently present after mouth occlusions, with a first positive P1 and a first negative N1 components of normal latencies (P1: 40.4 +/- 6.1 ms in CZ-C3 and 47.6 +/- 7.6 ms in CZ-C4; N1: 84.4 +/- 27.1 ms in CZ-C3 and 90.2 +/- 17.4 ms in CZ-C4) and amplitudes. Tracheal occlusions did not evoke any cortical activity. Therefore, in patients with inspiratory pump dysfunction, the activation of upper airway afferents is sufficient to produce the early components of the respiratory-related evoked cortical potentials. Per contra, in this setting, pulmonary afferents do not suffice to evoke these components.     

Neurophysiological Age Differences During Task-Performance in a Stereoscopic Virtual Environment

In today’s society, there is an increasing number of workplaces in virtual environments (VE). But, there are only a few reports dealing with occupational health issues or age effects. The question arises how VR generally interferes with cognitive processes. This interference might have relevant implications for workability and work-efficiency in virtual environments. Event-related potentials are known to reflect different stages of stimulus reception, evaluation, and response. We have established an electroencephalographic (EEG) monitoring, focussing on event-related potentials (N100; mismatch negativity, i.e., MMN) to obtain access to attention dependent and pre-attentive processing of sensory stimuli applied in VE. The MMN is known to be correlated with the ability of subjects to react to an unexpected event. The aim of the present study was to investigate cognitive responses to distracting auditory stimuli in two different age groups in a virtual environment (VE) and in a real environment (“real reality”), and to compare characteristic neurophysiological response patterns. Data show that stimulus detection as given by the N100 amplitude and latency does not differ in both age groups and task conditions. In contrast, the pre-attentive processing as given by the MMN is altered in the VR such as the non-VR condition in an age-related manner. A relevant finding of the present study was that the age related differences seen in the non-VR condition were not strengthened in VR.     

Detecting number processing and mental calculation in patients with disorders of consciousness using a hybrid brain-computer interface system

Background

For patients with disorders of consciousness such as coma, a vegetative state or a minimally conscious state, one challenge is to detect and assess the residual cognitive functions in their brains. Number processing and mental calculation are important brain functions but are difficult to detect in patients with disorders of consciousness using motor response-based clinical assessment scales such as the Coma Recovery Scale-Revised due to the patients’ motor impairments and inability to provide sufficient motor responses for number- and calculation-based communication.

Methods

In this study, we presented a hybrid brain-computer interface that combines P300 and steady state visual evoked potentials to detect number processing and mental calculation in Han Chinese patients with disorders of consciousness. Eleven patients with disorders of consciousness who were in a vegetative state (n?=?6) or in a minimally conscious state (n?=?3) or who emerged from a minimally conscious state (n?=?2) participated in the brain-computer interface-based experiment. During the experiment, the patients with disorders of consciousness were instructed to perform three tasks, i.e., number recognition, number comparison, and mental calculation, including addition and subtraction. In each experimental trial, an arithmetic problem was first presented. Next, two number buttons, only one of which was the correct answer to the problem, flickered at different frequencies to evoke steady state visual evoked potentials, while the frames of the two buttons flashed in a random order to evoke P300 potentials. The patients needed to focus on the target number button (the correct answer). Finally, the brain-computer interface system detected P300 and steady state visual evoked potentials to determine the button to which the patients attended, further presenting the results as feedback.

Results

Two of the six patients who were in a vegetative state, one of the three patients who were in a minimally conscious state, and the two patients that emerged from a minimally conscious state achieved accuracies significantly greater than the chance level. Furthermore, P300 potentials and steady state visual evoked potentials were observed in the electroencephalography signals from the five patients.

Conclusions

Number processing and arithmetic abilities as well as command following were demonstrated in the five patients. Furthermore, our results suggested that through brain-computer interface systems, many cognitive experiments may be conducted in patients with disorders of consciousness, although they cannot provide sufficient behavioral responses.

     

The use of endogenous <Emphasis Type="Italic">P</Emphasis>300 event-related potentials of the brain for assessing cognitive functions in healthy subjects and in clinical practice

Assessment of higher mental functions, objective detection of cognitive impairments, and investigation of pathophysiological mechanisms underlying these impairments in various neuropsychological diseases are of great importance for neuropsychophysiology. The endogenous event-related potential (ERP) approach is one of the instrumental neurophysiological methods that are currently used for assessing these complicated processes because recorded potentials reflect the intrinsic brain activity and changes in these potentials are caused by endogenous factors of the brain activity. The P300 cognitive evoked potential, induced by selective attention to a stimulus, has been the most widely used endogenous ERP. This potential may be helpful for studying mechanisms of mental disturbances, as it reflects neuronal processes connected with nonspecific activating reticulothalamic systems, as well as with limbic and neocortical mechanisms of selective attention and short-term memory.     

Physiology and physiopathology of somatic sensations studied in man by the method of evoked potentials

The physiology of somatic sensation can be investigated noninvasively in man by recording the electric activity of peripheral nerves, spinal cord and brain. Since these responses have a small voltage, it is necessary to use electronic averaging methods for improving the signal-to-noise ratio. These methods are described and discussed, as well as principles of interpretation of somatosensory evoked potentials. It is agreed that the traces thus obtained involve a series of components (extracellular potentials) which reflect distinct neural generators. These generators have been identified and localized at different levels of the subcortical somatosensory pathway and in different cortical areas. Several components reflect generators located under the recording electrodes (nearfield potentials), while other reflect extracellular potentials diffusing at a distance in the volume conductor of the neck and head (farfield potentials). The analysis of these components provides a wealth of new data for the physiology and pathophysiology of the somatic sensory system in man. Besides so-called "obligatory" components that are present irrespective of the attention of the subject, the studies have uncovered "cognitive" components which reflect neural mechanisms involved in the intellectual processus of perception and decision.     

Changes in the spatial organization of the cortical electrical activity during formation and actualization of a cognitive set to facial expression

Coherence function of the EEG in the bands of 8-13 (alpha rhythm) and 14-25 Hz (beta rhythm) was analyzed in 35 healthy adult subjects during formation and testing of a visual cognitive set to pictures of faces with different emotional expressions. The intra- and interhemispheric coherences of the potentials in the frontal area and coherence between the right frontal and temporal derivation were shown to increase at the stage of set actualization. The results of the analysis confirm the suggestion that the frontal cortical areas are predominantly involved in formation and actualization of the set to facial emotional expression. The conclusion is based on the idea that the spatial synchronization of the brain electrical potentials is an index of the functional relations between the corresponding cortical areas and their cooperative involvement in a certain kind of activity (their simultaneous activation).     

Control of the European rabbit in central Spain

The European rabbit is a growing problem for agriculture in parts of its natural range. In this study, our aim was to use historical records over two periods within the last 50 years to analyze trends in the number of requests made for rabbit control in Central Spain. We gathered data on rabbit control applications made in 1967 from Rabbit and Hare Control Authorization Records (CARs) and corresponding information for 2005 from Technical Hunting Plans (THPs). THPs are currently the official mechanism to apply for rabbit control licenses in the country. We show that although only 4.2 % of municipalities requested to control rabbits in 1967, this proportion was 71 % in 2005. Given that there is no evidence of rabbit population increases in the study region, we suggest that other factors may explain the observed rise in control requests. We contend that sport hunting is the main reason for the higher numbers of control requests in 2005. Evidence for this is the fact that hunting has increased since the 1960s as a means of augmenting income for landowners, and that the most requested method for control was the shotgun. Based on these results, we recommend that in order to adequately assess the real negative impacts of rabbits on human interests in Spain there is a need to implement a more robust data-gathering mechanism when control requests are made. We suggest the development of a more detailed control application form, similar to that used in Spain in the 1960s, in which the reason(s) for a rabbit control request can be clearly described.     

Amplitude of miniature potentials of motor neurons in the frog Rana ridibunda

Miniature synaptic potentials have been recorded from motoneurones of the isolated spinal cord of the frog Rana ridibunda. In normal Ringer's solution, their frequency varied from 5 to 50/sec, whereas their amplitude reached 2-5 mV. Only 50-300 microV (rarely 0.5-1.5 mV) potentials persisted when TTX was added to Ringer's solution and/or Ca was replaced by Mn. However, in Ca-free solution, TTX in combination with Mn did not decrease the amplitude of miniature potentials, provided the initial values varied within 50-300 microV. Noise fluctuations did not exceed 40-50 microV, and the ratio of the number of miniature potentials of 50 microV to the number of 50 microV noise potentials was about 10:1. The observed miniature potentials with an amplitude of 50-100 microV coincide with the quantal units calculated by other authors from statistical analysis of the unitary EPSPs evoked by primary afferents or by ventrolateral tract fibers.