Photic and pentylenetetrazol-induced seizure susceptibility in Macaca mulatta.

Ninety-five out of 100 male Macaca mulatta of varying ages from a restricted habitat in N. India showed no abnormal seizure susceptibility or EEG response to photic stimulation and no electro-clinical features of epilepsy after pentylenetetrazol, 40 mg/kg sc.c. Autopsy studies on the remaining five monkeys with increased seizure proneness revealed depressed skull fractures with cortical trauma in four and a neoplasm in one. Presumably, these factors were responsible for the lowered seizure susceptibility to photic stimulation and pentylenetetrazol activation.     

Characteristics of EEG reactivity changes during the performance of dual tasks in healthy subjects (voluntary postural control and calculation)

Comprehensive EEG and stabilography investigation with separate and simultaneous performance of motor (voluntary postural control) and cognitive (calculation) tasks has been performed in 20 healthy subjects (22 ± 0.7 years). Specific spatial and frequency reactive changes have been found during motor task performance. These included an increase in coherence in the EEG α band for distant derivation pairs in the right hemisphere, as well as in symmetric parietal-occipital areas in both hemispheres. Cognitive task performance was accompanied by an increase in coherence for the slow bands (δ and θ) with a higher activation in the left hemisphere and frontal cortex areas. In performing the dual task, one could observe activation of spatial and frequency changes including both motor and cognitive tasks. In the dual tasks where both components were performed worse as compared to the control, reactive reorganization of EEG coherence was less pronounced than during the performance of separate tasks. A decrease in the coherence of the α₁ band in the frontal areas appeared as a zone of “conflict of interest” or interference. In dual tasks with better performance of each component as compared to the control, EEG coherence increased in each specific area, as well as in the areas of “conflict of interests.”     

Regional cerebral blood flow thresholds during cerebral ischemia.

The development of methods of determining regional cerebral blood flow (rCBF) has made possible the determination of thresholds for the appearance of cerebral ischemia. These thresholds vary depending on the method used for assessing cerebral ischemia. The following thresholds have been determined in man and nonhuman primates: 20 cc/100 g per min, electroencephalogram (EEG) and evoked cortical potential abnormalities appear, paralysis seen in waking monkeys; 15 cc/100 g per min. EEG and evoked cortical potential are lost; 12 cc/100 g per min, flows at this level in excess of 120 min produce infarction in waking animals; and 6 cc/100 g per min, massive loss of intracellular [K+]. The residual rCBF and the duration of ischemia determine the appearance of infarction in waking Macaca irus monkeys.     

Changes in electrical thresholds for evoking movements from the cat cerebral cortex following lesions of the sensori-motor area

We evaluated motor maps in the cerebral cortex and motor performance in cats before and after lesions of the forelimb representation in the primary motor area. After the lesion there was a reduction in the use of the affected forelimb and loss of accuracy in prehension tasks using the forelimb; some recovery occurred during the mapping study. Electrode tracts and lesion sites were located in cytoarchitectonically identified cortical areas 4γ, 4δ, 6aα, 6aγ, 3a. The lesions were mainly in area 4γ. In the lesioned hemisphere there were many points around the lesion site (in areas 4γ and 3a) from which movements could not be evoked. In some areas distant from the lesion site (e.g. area 6aγ) the mean thresholds for evoking forelimb movements were significantly elevated. Mean thresholds for evoking hindlimb and facial movements were not different from before. In the contralateral hemisphere mean thresholds for evoking forelimb, but not hindlimb or facial movements, were significantly elevated in several sensorimotor areas (area 4γ, 6aγ and 3a). Mean thresholds for evoking forelimb movements appeared to progressively increase during the time of study. Minimal currents required to evoke forelimb movements from the cerebral cortex increase (possibly progressively) following a lesion of the forelimb representation in the primary motor area, affecting many interconnected motor areas in the hemispheres ipsilateral and contralateral to the lesioned site. This increase in thresholds may play a role in the changes in cortical control of the affected and contralateral limbs following brain lesions and explain the increased sense of effort required to produce movements.     

Changes in electrical thresholds for evoking movements from the cat cerebral cortex following lesions of the sensori-motor area

We evaluated motor maps in the cerebral cortex and motor performance in cats before and after lesions of the forelimb representation in the primary motor area. After the lesion there was a reduction in the use of the affected forelimb and loss of accuracy in prehension tasks using the forelimb; some recovery occurred during the mapping study. Electrode tracts and lesion sites were located in cytoarchitectonically identified cortical areas 4gamma, 4delta, 6aalpha, 6agamma, 3a. The lesions were mainly in area 4gamma. In the lesioned hemisphere there were many points around the lesion site (in areas 4gamma and 3a) from which movements could not be evoked. In some areas distant from the lesion site (e.g. area 6agamma) the mean thresholds for evoking forelimb movements were significantly elevated. Mean thresholds for evoking hindlimb and facial movements were not different from before. In the contralateral hemisphere mean thresholds for evoking forelimb, but not hindlimb or facial movements, were significantly elevated in several sensorimotor areas (area 4gamma, 6agamma and 3a). Mean thresholds for evoking forelimb movements appeared to progressively increase during the time of study. Minimal currents required to evoke forelimb movements from the cerebral cortex increase (possibly progressively) following a lesion of the forelimb representation in the primary motor area, affecting many interconnected motor areas in the hemispheres ipsilateral and contralateral to the lesioned site. This increase in thresholds may play a role in the changes in cortical control of the affected and contralateral limbs following brain lesions and explain the increased sense of effort required to produce movements.     

Changes in the functional parameters of the brain structures under the influence of enkephalin-like tetrapeptidamide

In complex neurophysiological and cytobiochemical study single injections of tetrapeptide amide (TPA) caused a short-term analgetic effect which manifested itself in the absence of motor reactions and EEG changes of cortical and subcortical brain structures after painful stimulation of extremities. This effect was accompanied by changes of some indices of transmitter (monoamine oxidase) and protein metabolism in the cerebral hemispheres at cellular and subcellular levels. In 30-40 min after a TPA injection, EEG suppression and absence of EPs to light flashes were observed in cortical and subcortical structures. Simultaneously motor disorders developed. The observed EEG changes had an undulatory character: on the second day EEGs were restored and on the third day--suppressed once again. This period of TPA action was accompanied by varied changes of the investigated types of metabolism. The question of the necessity of systemic approach to the study of TPA action is discussed, as such an approach allows to reveal complex neurophysiological and fine biochemical relations in the reactions of brain structures and in animal behaviour.     

The asymmetry of cerebral hemispheric activity in dogs in a state of quiet wakefulness under the action of sensory stimuli and food deprivation]

The EEG was recorded in four dogs from symmetrical cortical areas of the left and right brain hemispheres. Activation foci were determined by the maximal values of the mean frequency of EEG oscillations and coherence function. In the background experiments, the hemispheric activation asymmetry was observed in all dogs. The individual differences were in the frequency ranges, which were asymmetrically localized. In three dogs the coherence level was significantly more frequently higher in the right hemisphere than in the left one, in one dog the opposite relations were observed. These differences in activation foci localization were correlated with different tactics of choice between two feeders under conditions of free behavior. Under the action of external stimuli, changes in hemispheric activation were observed, predominantly, in the corresponding projection areas, and at the shifts of food excitability they were localized in symmetrical frontal areas. The results suggest that the left hemisphere becomes more activated during the first presentations of indifferent stimuli, i.e., during the development of the reaction to novelty, and under conditions of food deprivation, which rises the level of brain activation.     

Study of sleep in a walrus

Several behavioral and physiological adaptations have been developed in evolution of Pinnipeds allowing them to sleep both on land and in water. To date sleep has been examined in detail in eared and true seals (the families of Otariidae and Phocidae). The aim of this study was to examine sleep in another semiaquatic mammal — the walrus, which is the only extant representative of the family Odobenidae. Slow wave and paradoxical sleep (SWS and PS) in the examined walrus (2 year old female, weight 130 kg) averaged 19.4 ± 2.0 and 6.9 ± 1.1% of 24-h when on land, and 20.5 ± 0.8% of 24-h and 1.1 ± 0.6% when in water, respectively. The average duration of PS episode was 6.4 ± 0.6 min (maximum 23 min) when on land and 1.8 ± 0.1 min (maximum 3.3 min) when in water. In water, sleep occurred predominantly while the walrus submerged and lay on the bottom of the pool (89% of total sleep time). The walrus usually woke up while emerging to the surface for breathing. Most often EEG slow waves developed synchronously in both cortical hemispheres (90% of SWS time when on land and 97% when in water). Short episodes of interhemispheric EEG asymmetry usually coincided with brief opening of one eye. The pattern of sleep in the walrus was similar to the pattern of sleep in the Otariidae seals while on land (predominantly bilateral SWS, accompanied by regular breathing) and to the pattern of sleep in the Phocidae while in water (sleep during apneas both in depth and at the surface, interrupted by brief arousal when emerging for breathing).     

Characteristics of the spatial organization of oscillations of brain bioelectric potentials in adolescents

Adolescence is characterized by an intense formation of interregional interaction of cortical areas. In this period, the activity of deep brain structures is significantly reorganizing and cortical-subcortical interaction is augmenting. Our objective was to assess the pattern of changes in the spatial structure of brain bioelectric potentials with age and characteristics of these structures in adolescents. For this purpose, studies of EEG were conducted in 230 subjects of both sexes aged 4 to 35 years. We quantified the interconsistent changes in correlations of oscillations of bioelectric potentials in 20-lead EEG, using the integrated index VOL. Age-related changes in the consistency of EEG correlations were analyzed both in the background state and during verbal activity (comprehension of texts in Russian and in English). Cognitive tasks were performed by subjects older than 8 years. It was discovered that spatial synchronization of EEG processes both in the background state and during cognitive tasks increased with age, but, after 20 years, the rate of changes decreases significantly. In adolescence (12–17 years), sex differences appear in the correlation of EEG processes between the left and right hemispheres in subjects performing verbal tasks. We observed saltatory changes in VOL indices in 12- to 14-year-old boys, whereas in girls of the same age, reorganization of systemic brain activity goes more gradually 1.5–2 years in advance.     

Reorganization of interhemispheric interactions during verbal-mental activity aimed at synthesis of words and sentences

Correlation and coherence analyses of multichannel electroencephalogram (EEG) recordings from 18 subjects (mean age 25 years) were used for investigating the reorganization of systemic interactions between bioelectric potentials of the cortical areas of both hemispheres (20 EEG derivations) during verbal-mental activity connected with generating verbal units from simpler components. When generating either words from aurally presented phonemes or sentences from a set of words, the subjects exhibited specific changes in the spatial structure of the statistical relationships in the EEG, with a significant increase in the interhemispheric interactions. During performance of both tasks, the changes in the interhemispheric interactions were most pronounced in the temporal, temporo-parieto-occipital (TPO), inferofrontal, and occipital areas of both hemispheres. Phonemic synthesis was associated with a more marked increase in the contralateral interactions in the left hemisphere, and generating sentences from words, in the right hemisphere. The coherence analysis of the EEG showed the greatest changes in the Δ, ?, and β frequency bands, with rather slight changes in the α frequency band. For all frequency bands, changes in the EEG coherences were the greatest in Wernicke’s and the TPO areas of the right and left hemispheres during the performance of both tasks, especially during the phonemic synthesis. These findings suggest that neurophysiological processes underlying mental generation of words and sentences require coordinated activity of the left and right hemispheres, which is accompanied by an increase in the interhemispheric interactions in the EEG, especially in the temporal, inferofrontal, and TPO areas.     

Spectral analysis of the human EEG in acutely developing foci of irritation at the diencephalic and brain stem levels

The dynamic study of EEG spectra and coherence in 52 patients in early period after tumor ablation at the diencephalic (27 patients) and brainstem (25 patients) levels with favourable (24 patients) and lethal (28 patients) outcomes revealed a dependence of their changes on the reversibility or irreversibility of pathological irritation of these brain levels. At regressively developing foci and retained compensatory mechanisms characteristic changes of EEG relations were seen in the central cortical areas, i. e. in cortical projection zone of the nonspecific thalamic pathways. The changes observed consisted of EEG synchronization in the band of 7 cps and sharp coherence increase while changes of EEG correlations in other cortical areas were unsimilar. Gradual EEG normalization with alpha-rhythm restoration passed through the stage of sigma-rhythm and slow sleeplike waves which indicated the safety of brainstem-subcortical hypnogenic systems. In patients with destructive foci at the diencephalic and brainstem levels, i. e. under conditions of brain functioning similar to "cerveau isolé" and "encephale isolé",--a general coherence decrease and EEG synchronization in the band of 5 cps, or generalized slow, monomorphic oscillations were observed.     

Functional coupling of cortical areas during problem-solving task: Analysis of θ rhythm coherence

The coherence of the components of the EEG θ rhythm was analyzed in subjects performing a visual object classification task under the conditions of uncertainty after a feedback. The functional coupling between cortical areas in the course of strategy formation was demonstrated to be stronger than at the stage when the strategy had already been formed. The θ-related functional connectivity were characterized by a specific topographic pattern: they converged to the foci located in the polar frontal cortex and reflect the interaction of these frontal areas with the anterior associative and temporal cortices of the left hemisphere, as well the parietal and occipital areas of both hemispheres. The frequency and topographic characteristics of the functional cortical links suggest that they reflect the functioning of a distributed neural network through which the limbic structures and the controlling frontal cortical structures interact in the process of cognitive strategy formation.     

EEG characteristics determining the quality of subsequent recognition of visual images

Recognition of noisy pictures of Arabic numerals was accompanied by an increase in EEG coherence in the frontal cortical regions, especially in the left hemisphere, and between the frontal and occipital areas in both left and right hemispheres. Coherence values decreased in the temporo-centro-occipital areas of both hemispheres. A correlation was found between the coherence pattern in the prestimulus period and the quality of subsequent activity. Correct recognition was preceded by left-side asymmetry of the EEG coherence. Before erroneous recognition, EEG coherence levels were higher than before a correct response, and the increase in coherence was widely generalized over the cortex (especially in the Δ, ?, and α₁ frequency bands). The frequency of expression of an increased integral EEG coherence was higher before erroneous recognition than before a correct response. These changes in coherence were symmetrical.     

Time-Dependent Statistical and Correlation Properties of Neural Signals during Handwriting

To elucidate the cortical control of handwriting, we examined time-dependent statistical and correlational properties of simultaneously recorded 64-channel electroencephalograms (EEGs) and electromyograms (EMGs) of intrinsic hand muscles. We introduced a statistical method, which offered advantages compared to conventional coherence methods. In contrast to coherence methods, which operate in the frequency domain, our method enabled us to study the functional association between different neural regions in the time domain. In our experiments, subjects performed about 400 stereotypical trials during which they wrote a single character. These trials provided time-dependent EMG and EEG data capturing different handwriting epochs. The set of trials was treated as a statistical ensemble, and time-dependent correlation functions between neural signals were computed by averaging over that ensemble. We found that trial-to-trial variability of both the EMGs and EEGs was well described by a log-normal distribution with time-dependent parameters, which was clearly distinguished from the normal (Gaussian) distribution. We found strong and long-lasting EMG/EMG correlations, whereas EEG/EEG correlations, which were also quite strong, were short-lived with a characteristic correlation durations on the order of 100 ms or less. Our computations of correlation functions were restricted to the spectral range (13–30 Hz) of EEG signals where we found the strongest effects related to handwriting. Although, all subjects involved in our experiments were right-hand writers, we observed a clear symmetry between left and right motor areas: inter-channel correlations were strong if both channels were located over the left or right hemispheres, and 2–3 times weaker if the EEG channels were located over different hemispheres. Although we observed synchronized changes in the mean energies of EEG and EMG signals, we found that EEG/EMG correlations were much weaker than EEG/EEG and EMG/EMG correlations. The absence of strong correlations between EMG and EEG signals indicates that (i) a large fraction of the EEG signal includes electrical activity unrelated to low-level motor variability; (ii) neural processing of cortically-derived signals by spinal circuitry may reduce the correlation between EEG and EMG signals.     

Organization of the spatial-temporal relationships of cerebral electrical processes in children during exposure to verbel commands]

An EEG cross-correlation analysis has shown that in children aged four to five years higher sensory analysis of verbal commands and their meaning was reflected in the nature of synchronous interactions between oscillatory processes and their spatial-temporal patterns. At the moment of perception of the command "listen" highly synchronous synphasic relations were recorded between biopotentials in the associative infero-parietal cortex and projection temporal centres of the left hemisphere. Oscillations of the parietal areas preceded the rhythms of the occipital, motor and frontal lobes in the left hemisphere; slow oscillations with a 3 osc/sec frequency predominated, and the intensity of the periodic processes increased. The command "look" evoked a high degree of synchronous synphasic relations of biopotentials in the parietal-occipital cortical parts of both hemispheres; oscillations with 6 osc/sec frequency predominated; their intensity rose; synphasic relations of oscillations in parietal and motor and temporal centres grew more manifest, while the rhythmic activity in the parietal zones preceded the potentials in the frontal lobes of both hemispheres.     

Behavioral and electroencephalographic correlates of 40-Hz EEG biofeedback training in humans

Two groups of eight adults successfully trained with biofeedback for increases in 40-Hz EEG responses in left or right hemispheres also demonstrated significant 40-Hz EEG increases during baseline periods, and increases in the contralateral hemisphere during training periods. No changes in heart rate, 40-Hz EMG, or 21- to 31-Hz beta, alpha, or theta EEG occurred over training days. Three subjects returning for additional training demonstrated suppression of 40-Hz EEG. A group of four subjects experiencing daily bidirectional training produced substantial within-session control of 40-Hz EEG but no changes over days. Data from posttraining tests without feedback for successful subjects in both groups indicated significant control of 40-Hz EEG responses in the initial parts of these sessions, and some correlated changes in other EEG responses. Measures of successful subjects' experiences during training and control tests indicated awareness of changes in subjective concomitants of EEG responses. This study suggests further strategies for research on behavioral correlates of EEG activity.     

Cortical Bilateral Adaptations in Rats Submitted to Focal Cerebral Ischemia: Emphasis on Glial Metabolism

This study was performed to evaluate the bilateral effects of focal permanent ischemia (FPI) on glial metabolism in the cerebral cortex. Two and 9 days after FPI induction, we analyze [¹⁸F]FDG metabolism by micro-PET, astrocyte morphology and reactivity by immunohistochemistry, cytokines and trophic factors by ELISA, glutamate transporters by RT-PCR, monocarboxylate transporters (MCTs) by western blot, and substrate uptake and oxidation by ex vivo slices model. The FPI was induced surgically by thermocoagulation of the blood in the pial vessels of the motor and sensorimotor cortices in adult (90 days old) male Wistar rats. Neurochemical analyses were performed separately on both ipsilateral and contralateral cortical hemispheres. In both cortical hemispheres, we observed an increase in tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), and glutamate transporter 1 (GLT-1) mRNA levels; lactate oxidation; and glutamate uptake and a decrease in brain-derived neurotrophic factor (BDNF) after 2 days of FPI. Nine days after FPI, we observed an increase in TNF-α levels and a decrease in BDNF, GLT-1, and glutamate aspartate transporter (GLAST) mRNA levels in both hemispheres. Additionally, most of the unilateral alterations were found only in the ipsilateral hemisphere and persisted until 9 days post-FPI. They include diminished in vivo glucose uptake and GLAST expression, followed by increased glial fibrillary acidic protein (GFAP) gray values, astrocyte reactivity, and glutamate oxidation. Astrocytes presented signs of long-lasting reactivity, showing a radial morphology. In the intact hemisphere, there was a decrease in MCT2 levels, which did not persist. Our study shows the bilateralism of glial modifications following FPI, highlighting the role of energy metabolism adaptations on brain recovery post-ischemia.     

Comparison of electrical thresholds for evoking movements from sensori-motor areas of the cat cerebral cortex and its relation to motor training

Motor maps and electrical thresholds for evoking movements from motor areas of the cerebral cortex were evaluated in normal cats by using intracortical microstimulation techniques. Stainless steel chambers were implanted over craniotomies in adult cats trained to perform reaching and retrieval movements with their forelimbs. Prehensile motor training was continued and movement performance monitored for about 6-10 weeks during which the cortex was progressively explored with sharp tungsten electrodes inserted into cortical gyri (anterior and posterior sigmoid, and coronal) and the banks of sulci (cruciate, presylvian and coronal). Twice weekly, under light general anaesthesia, 3-4 tracks were made in either hemisphere till about 50 tracks were made in each hemisphere. Mean thresholds for evoking forelimb movements from different cytoarchitectonic areas (4gamma, 4delta, 6agamma and 3a) were compared and no consistent or significant differences were observed between the different areas. In the animals (4/6) which used either forelimb to perform the tasks, there were no consistent differences in the mean thresholds for evoking forelimb movements from the two hemispheres. However, in 2 animals, which used their right forelimbs predominantly or exclusively to perform all the tasks, mean thresholds for evoking forelimb movements was significantly higher in areas 4gamma and 6agamma of the left hemisphere (compared to the right); no consistent differences in the mean thresholds for evoking hindlimb or facial movements were observed between the two hemispheres. These findings suggest that ICMS thresholds for evoking forelimb movements may be similar in different sensorimotor areas of the cat cerebral cortex, and these thresholds could be influenced by motor training.     

Comparison of electrical thresholds for evoking movements from sensori-motor areas of the cat cerebral cortex and its relation to motor training

Motor maps and electrical thresholds for evoking movements from motor areas of the cerebral cortex were evaluated in normal cats by using intracortical microstimulation techniques. Stainless steel chambers were implanted over craniotomies in adult cats trained to perform reaching and retrieval movements with their forelimbs. Prehensile motor training was continued and movement performance monitored for about 6–10 weeks during which the cortex was progressively explored with sharp tungsten electrodes inserted into cortical gyri (anterior and posterior sigmoid, and coronal) and the banks of sulci (cruciate, presylvian and coronal). Twice weekly, under light general anaesthesia, 3–4 tracks were made in either hemisphere till about 50 tracks were made in each hemisphere. Mean thresholds for evoking forelimb movements from different cytoarchitectonic areas (4γ, 4δ, 6aγ and 3a) were compared and no consistent or significant differences were observed between the different areas. In the animals (4/6) which used either forelimb to perform the tasks, there were no consistent differences in the mean thresholds for evoking forelimb movements from the two hemispheres. However, in 2 animals, which used their right forelimbs predominantly or exclusively to perform all the tasks, mean thresholds for evoking forelimb movements was significantly higher in areas 4γ and 6aγ of the left hemisphere (compared to the right); no consistent differences in the mean thresholds for evoking hindlimb or facial movements were observed between the two hemispheres. These findings suggest that ICMS thresholds for evoking forelimb movements may be similar in different sensorimotor areas of the cat cerebral cortex, and these thresholds could be influenced by motor training.