Dynamics of brain rhythmic and evoked potentials

A package of methods and an experimental set-up for the analysis of dynamics of electrical signals from the brain. The methods described and discussed in this study allow detailed and multipurpose analysis of brain potentials both in the time and frequency domains. Special emphasis is given to a new computer-method introduced in this study: A posteriori selective averaging. The selective averaging method is compared with Wiener Filter Estimation of Evoked Potentials.     

Dynamics of brain rhythmic and evoked potentials

In this study, the simultaneously recorded and selectively averaged evoked potentials in some of the structures of the auditory pathway (acoustical cortex, medial geniculate nucleus, inferior colliculus), in the reticular formation and the hippocampus of the cat during sleep as well as the simultaneous amplitude frequency characteristics of these structures are given. The power spectral density functions computed from the simultaneously recorded spontaneous activities of these structures are also presented. Using these results, the following analyses are accomplished:(1) determination of the dynamics of potentials simultaneously obtained from various structures, in order to evaluate the common features of their system characteristics; (2) determination of the relationship (or interactions) between rhythmic activity and evoked potentials of the brain.     

Brain-stem auditory evoked potentials and brain death

BAEP records were obtained from 30 brain-dead patients. Three BAEP patterns were observed: (1) no identifiable waves (73.34%), (2) an isolated bilateral wave I (16.66%) and (3) an isolated unilateral wave I (10%). When wave I was present, it was always significantly delayed. Significant augmentation of wave I amplitude was present bilaterally in one case and unilaterally in another. On the other hand, in serial records from 3 cases wave I latency tended to increase progressively until this component disappeared. During the same period. wave I amplitude fluctuations were observed. A significant negative correlation was found for wave I latency with heart rate and body temperature in 1 case. Two facts might explain the progressive delay and disappearance of wave I in brain-dead patients: a progressive hypoxic-ischaemic dysfunction of the cochlea and the eight nnerve plus hypothermia, often present in brain-dead patients. Then the incidence of wave I preservation reported by different authors in single BAEP records from brain-dead patients might depend on the moment at which the evoked potential study was done in relation to the onset of the clinical state. It is suggested that, although BAEPs provide an objective electrophysiological assessment of brain-stem function, essential for BD diagnosis, this technique could be of no value for this purpose when used in isolation.     

Important relation between EEG and brain evoked potentials

In this study, we analyze the important relation between the spontaneous and evoked activities of the substructures of the cat brain, such as the reticular formation, hippocampus, inferior colliculus, medial geniculate nucleus and acoustical cortex, with an ensemble of systems theory methods consisting of the following steps: (1) single auditory and/or visual evoked potentials (EPs) and the spontaneous activities (EEG) just preceding the stimuli are recorded from the brain center under study; (2) selectively averaged evoked potentials (SAEPs) are obtained from the recorded EPs; (3) amplitude frequency characteristics are computed from the AAEPs by means of Fourier transform; (4) the single EEG-EP sweeps are theoretically pass-band filtered with adequate band limits determined according to the selectivities revealed by the amplitude characteristics; (5) the EEG and EP components obtained in this way are compared with regard to the amplification in the population response upon the application of the stimulus. The results of this analysis support quantitatively our prediction of various types of resonance phenomena in a number of nuclei in the cat brain and in a large scale of frequencies from 1 Hz to 1000 Hz and show that the amplification factor related to resonance phenomena has probabilistic nature. Therefore, the analogy which we have recently drawn between the behaviors of a neural population and a random-phase probabilistic harmonic oscillator is extended by assigning also the amplitude and the frequency of the oscillations as random variables. A working hypothesis for the dynamics of neuronal populations is elaborated accordingly.Presented in Part at the Third European Meeting on Cybernetics and Systems Research 1976 in Vienna, April 20–23, 1976Supported by Grant No. TAG-345 of the Scientific and Technical Research Council of Turkey     

Thalamocortical relationships during spontaneous and evoked rhythmic activity of the brain]

A study was made in lightly nembutalized and unanaesthetized immunobilized cats of the interrelations between rhythmic afterdischarge evoked in the auditory cortex by a click, and a spontaneous spindle burst under different states of intact animals. The experiments showed: 1) Rhythmic afterdischarge represents a stimulus induced spindle burst, 2) local spindle burst (spontaneous or evoked by peripheral and central stimulations) in the auditory cortex does not change considerably either by stimulation or by lesion of thalamic nonspecific, as well as other specific structures; 3) An afterdischarge in the medial geniculate body (evoked by a click) remains unchanged after cooling or extirpation of the whole auditory cortex. All this suggests a generation of both spontaneous and evoked local rhythmic activity of the auditory thalamo-cortical system, independent of other such systems.     

Global brain dynamics of transient visual evoked potentials

The independent component analysis was applied to multichannel transient visual evoked potentials elicited by a high contrast pattern-reversal and motion-onset (motion velocity of 7 and 23 deg/s). Three overlapping independent components with different topographical distribution over the scalp were described. The first component displayed similar timing in response to all three stimuli (40-200 ms) but was a different in shape and scalp projection. This activation component is considered to reflect the stimulus properties. The second component (100-227 ms), related to negativity at about 160 ms, can be referred to visual processing of motion. The last component, attributed to positivity at 230 ms dominates in the fronto-central area and might represent a cognitive process.     

Mapping human brain networks with cortico-cortical evoked potentials

The cerebral cortex forms a sheet of neurons organized into a network of interconnected modules that is highly expanded in humans and presumably enables our most refined sensory and cognitive abilities. The links of this network form a fundamental aspect of its organization, and a great deal of research is focusing on understanding how information flows within and between different regions. However, an often-overlooked element of this connectivity regards a causal, hierarchical structure of regions, whereby certain nodes of the cortical network may exert greater influence over the others. While this is difficult to ascertain non-invasively, patients undergoing invasive electrode monitoring for epilepsy provide a unique window into this aspect of cortical organization. In this review, we highlight the potential for cortico-cortical evoked potential (CCEP) mapping to directly measure neuronal propagation across large-scale brain networks with spatio-temporal resolution that is superior to traditional neuroimaging methods. We first introduce effective connectivity and discuss the mechanisms underlying CCEP generation. Next, we highlight how CCEP mapping has begun to provide insight into the neural basis of non-invasive imaging signals. Finally, we present a novel approach to perturbing and measuring brain network function during cognitive processing. The direct measurement of CCEPs in response to electrical stimulation represents a potentially powerful clinical and basic science tool for probing the large-scale networks of the human cerebral cortex.     

Dipole tracing of visual evoked potentials in human brain

3D tracing of equivalent current dipoles (ECDs) of averaged human visual evoked potentials (VEP) by their distribution across a 34-electrode array was obtained under short presentation of pattern-onset stimuli (sets of 45 horizontal, vertical bars or crosses). Using a 2-dipole spherical three-layer model, we dynamically (step of 1 ms) localized dipoles in four healthy subjects. Dipole locations were matched to anatomical brain regions visualized in structural MRI. Best-fitting source parameters were superimposed on MR images of each subject to identify the anatomical structures giving rise to the surface patterns. It was found that during 50-300 ms following the onset of the stimuli, the ECDs in all subjects were localized in the occipital cortex and demonstrated reliable systematic shift in localization. Two local (1-2 cm3) zones of the preferable dipole attendance were found at 5-6 cm behind zero line: the first one was localized near the midline of the brain, whereas the other zone was situated in the right hemisphere at a distance of 6-7 cm from the first zone. Their localization and strength of activation were reliably different for crosses and lines and changed during VEP generation. Zones of relatively rare dipole attendance were found also. The data are discussed in relation to localization of initial and endpoint of ECDs trajectories, as well as with sensitivity of the visual cortex to line crossing and branching.     

慢性缺氧性脑病诱发电位、行为与caspase-3凋亡蛋白表达的变化

目的:探讨大鼠慢性间断性缺氧后,脑诱发电位与慢性缺氧性脑损伤的关系,探讨脑诱发电位对缺氧性脑病的评估价值.方法:在建立慢性间断性缺氧大鼠模型的基础上,雄性SD大鼠随机分成缺氧组(H组)和对照组(N组),H组随机分为缺氧2周组(H2组)和缺氧4周组(H4组)2个亚组;应用Morris水迷宫检测各组大鼠的学习记忆能力;测定各组大鼠的脑干听觉诱发电位(BAEP)和短潜伏期体感诱发电位(SLSEP).免疫组织化学法检测caspase-3凋亡蛋白表达的变化.结果:缺氧组BAEP和SEP各波的峰潜伏期和峰间峰潜伏期比对照组明显延长,差异有显著性意义,缺氧组BAEP和SEP的变化与学习记忆能力和caspase-3凋亡蛋白表达有相关性.结论:BAEP和SEP的改变与慢性缺氧性脑损伤及损伤的程度明显相关,是反映缺氧性脑损伤比较敏感的指标.     

Modifications of event-related evoked potentials in physiological and pathological aging of the brain

We compared the parameters of acoustic event-related evoked potentials (ERP; tone stimulation) in healthy young and healthy aged persons with those in patients suffering from Alzheimer’s disease (groups 1–3, respectively). It was found that the mean peak latencies (PL) of the components P1-N2 in group 1 were longer than those in group 2, and the absolute values of the amplitudes of these components were more negative. In Alzheimer patients (group 3), the PL of the components P1–P2 were much longer than those in group 2, and their peak-to-peak amplitudes dropped. The latencies of a simple sensorimotor reaction in groups 1–3 progressively increased (about three times). The ERP observed in two modes (“blackground” and “attention,” the latter with the performance of the sensorimotor reaction) were subjected to spectral analysis. Possible reasons for and mechanisms of those modifications of evoked potentials, which relate to physiological and pathological aging of the brain, are discussed.     

Human brain evoked potentials and discrimination of short acoustic stimuli with various frequency

We found that the mismatch negativity (MMM) was absent in evoked potentials in passive condition for frequency deviant acoustical stimuli when stimulus duration was only 11-30 ms. But it was shown that it is possible for participants to fairly well discriminate these stimuli and the component N2b in RP was generated without preceding MMN. Processing negativity also was absent in potentials by the minimal stimulus duration (11 ms). Auditory discrimination nevertheless was still possible, but reaction time and number of committed errors increased significantly.     

The auditory evoked potentials of the brain stem in the guinea pig

The examination of the standard waves' amplitude and latency of the brain stem auditory evoked response (BAEP) was performed in 20 guinea pigs (males and females, weighing 250 to 300 g). According with the relative loudness of stimuli (90, 70, 50, 30, 10 dB SPL), the latency of BAEP waves was larger (t1 = 0.2 msec), but the conductance time between P1 to P5 was constant (3.1 to 3.6 msec). The highest wave of BAEP was P2 with an amplitude: 90 dB SPL, U = 6.5 +/- 1.2 microV; 70 dB SPL, U = 4.3 +/- 1.0 microV; 50 dB SPL, U = 3.5 +/- 0.6 microV; 30 dB SPL, U = 2.0 +/- 0.4 microV.