Spectral-correlative characteristics of the EEG reactions preceding conditioned reflex motor reactions in dogs

The work is a logical continuation of previous studies (analysis of the background electrical activity in the band 1-100 Hz in interstimulus intervals in the process of lever pressing alimentary conditioning in dogs) and it is dedicated to correlation-spectral analysis of prestimulus periods and EEG-reactions to conditioned stimuli, previous to conditioned lever pressing. Visually the EEG reactions present discharges of high-frequency (40-100 Hz) synchronized activity preceding for 40-300 ms the beginning of the changes in EMG of the "working" limb. It is shown that EEG reactions are characterized (in comparison with the background activity) by a higher energetic level and a greater expression of the high coherence (I greater than 0.75) and also by greater phase shifts, in counterbalance to the domination of little phase shifts in the background activity. It is assumed that the patterns of EEG reactions may participate in trigger mechanisms either eliciting conditioned motor reactions (to positive conditioned stimuli) or preventing them (to inhibitory conditioned stimuli).     

A computer analysis of EEG intersignal reactions during the the acquisition of conditioned motor-food reflexes in dogs]

Background electric activity was studied of different neocortex areas in interstimulus intervals at the stage of generalization during elaboration of motor alimentary conditioned reflexes in dogs. For this stage the appearance is typical of short-term (0.1-0.3 s) packs of high frequencies (above 40 osc./s) significantly exceeding the adjacent initial background by frequency and amplitude (along side with motor interstimulus reactions). The index of specific variation, elaborated by us, allowed to single out this EEG pattern in the initial realizations of the background activity during their input in the computer. With the purpose of further evaluation of the above phenomenon parameters non-standard approaches of computer analyses were used, directed to decomposition of the EEG curve into the system of oscillations and receipt of corresponding amplitudes frequencies distributions (maps). It was shown, the described high frequencies packs were localized on these maps in definite sufficiently compact places.     

Electrical reactions in the cat brain during differentiation of photic stimuli]

Study of EEG responses to photic conditioned stimuli in cats has shown that the extent of brain activation depends not on the physical strength of the stimulus, but on its biological significance. The longest activation is recorded to a positive signal, even if it is the weakest flash of light. The intensity of EEG responses to negative stimuli is determined by the nearness of their physical parameters to those of the positive signal. Repeated presentation of a non-reinforced flash leads to a gradual extinction of EEG reactions. Brain activation in response to a reinforced positive signal persists unchanged even after a large number of its repetitions. The revealed properties of brain electrical reactions to stimuli of different significance accord with those previously recorded in response to acoustic stimuli. In both cases the data are in agreement with hypothesis of a central system of signal analysis, which performs the estimation of stimuli according to their biological quality.     

Neuronal correlates of the activation of the brain-reinforcing system in dogs

In analysis of neuronal activity of g. proreus of dogs brain in response to positive and differentiation conditioned cutaneous stimuli, in 44% of 78 studied neurons "late responses" appeared in the form of impulse activity intensification elicited by a positive conditioned stimulus after the end of eating and by a differentiation one--during conditioned signal action; it persisted in different neurones for 30--60 s. By means of various functional tests it has been shown that these reactions are a neurophysiological correlate of animals emotional state gradient.     

Structure of the field of cerebral biopotentials and the latent period of the human motor response

An investigation was made into the statistical interconnection between the latency of human conditioned motor reaction to a flash and the spatial distribution of EEG correlation coefficients of eight cerebral areas in 10-second epoch preceding the stimuli. The greatest similarity of latency variations was observed with changes in the correlation relationships between EEG of the occipital, frontal and central areas of the hemisphere, contralateral to the reacting hand. Analysis of the structure of the brain biopotential field has shown that the probability of a more rapid reaction is greater if in the pre-stimulatory period there is a spatially coherent alpha-rhythm with nearly contraphasic correlations of oscillations in the frontal and occipital brain areas.     

Linear Superposition of Retinal Action Potentials to Predict Electrical Flicker Responses from the Eye of the Wolf Spider, Lycosa baltimoriana (Keyserling)

Retinal action potentials were elicited from light-adapted posterior median ocelli of the wolf spider Lycosa baltimoriana (Keyserling) by rectangular shaped photic stimuli representing 8 per cent increments or decrements of the background illumination. Responses to trains of recurrent incremental or decremental flashes were successfully predicted by graphical linear superposition of a single flash response, which was repeatedly drawn and added to itself at intervals equal to the period of the intermittent stimulus. Incremental stimuli inverted to form decremental stimuli elicited responses which were also inverted. Responses to single incremental flashes were successfully predicted by linear superposition of the response to one incremental step stimulus, which was inverted and added to itself at an interval equal to the duration of the flash.     

Parental generalized EEG alpha activity predisposes to spike wave discharges in offspring

Familial and twin studies have shown that the individual variability of the normal human electroencephalogram (EEG) is largely genetically determined. In epileptology, these genetic parameters of the EEG background activity are almost totally neglected. The aim of the present study has been to investigate whether a special genetic type of background activity might be related to the pathogenesis of epilepsy. EEG recordings of parents of 257 epileptic children were evaluated retrospectively. Some 156 healthy adults served as controls. Special attention was paid to alpha activity extending to the frontal region, both in bipolar and in referential recordings (Alpha I). Alpha I was found significantly more often in parents of children with primary generalized epilepsy (18%) compared with parents of children with focal epilepsy (8%) or controls (9%). In a second step, parental EEGs of children with different EEG patterns associated with epilepsy were studied. Alpha I was found significantly more often in parents of children with focal sharp waves and generalized spikes and waves (26%) than in parents of probands with focal sharp waves without additional generalized spikes and waves (8%) or in controls (9%). Parents of probands with theta rhythms and spikes and waves had alpha I significantly more often (18%) than parents of probands with theta rhythms without additional spikes and waves (8%) or controls (9%). The findings reveal a clear correlation between the type of EEG background activity in parents and the EEG characteristics in their children, thus pointing to common mechanisms.     

Ontogenetic patterns of frequency-power spectra elicited by flickering light in children: a comparative study of evoked and background EEGs.

Frequency-power spectra of the EEG evoked by repeptitive photic stimulation and of the background EEG were studied during childhood in 43 awake subjects aged between 2 months and 14 years. EEG activity was recorded from the middle parieto-occipital region with the aid of a 1-channel analyzer Lysograf-Alvar, analysing 16 frequencies in the range from 2 to 28 c/sec. The responsiveness of the central nervous system to flickering light improved in the course of childhood in parallel with the significant decline of delta activity and with the prominent increase of alpha intensity in the resting EEG. The 4th month of life appeared to be a marked turning point in the development of evoked and background EEGs. From that age, the bioelectric power at the flash rate corresponding to photic "driving" began to increase together with the highest and optimal driving frequencies. The flash rate, at which evoked potentials changed into the "driven" rhythm, also shifted towards higher frequencies. Subsequently, the amount of energy in the resting EEG increased significantly within the theta, alpha and beta bands and, on the contrary, a prominent decline was observed in the delta range. Marked ontogenetic changes at this age closely coincided with the rapid development of exogenous fibres in the occipital cortex, including the thalamo-cortical conncetions, and fibres of the neuropil in cortical layer I, which might play an important role in the genesis of background and "driven" in the occipital region.     

Effects of age and sex on pattern electroretinograms and visual evoked potentials

Pattern-electroretinograms (P-ERGs) and visual evoked potentials (VEPs) were simulataneously recorded in 112 normal individuals aged 20–75. Two sized checks subtending 15′ and 31′ were used as stimuli. A weighted regression analysis was used to determine which of the variables, sex or age, was significant. The latency of the a and b wave of the P-ERGs showed a progressive increase with age but no difference between sexes. The effect was statistically significant for both 15′ and 31′ checks. There was no statistically significant aging effects for VEPs elicited by 31′ checks. Aging, however, affected N70, P100, and the interpeak interval between b wave to N70 and b wave to P100 for responses to 15′ checks. Shorter VEP latencies were noted in females for both 15′ and 31′ checks.The simultaneous recording of P-ERGs and VEPs has demonstrated that aging is a major variable at the retinal level. The effects on the a and b waves are mostly due to optic changes with aging and only partially to aging changes in the neuronal retinal circuitry. The effect of aging on VEPs is different for different size stimuli. The cause is a random neuronal cell loss in the visual pathways from the optic nerve to the visual cortex as the individual ages.The difference in VEP data between sexes may be related to anatomical size and hormonal influences.     

EEG of the interstimulus intervals during habituation of auditory evoked potentials in depressive moods

Averaging of EEG of interstimulus intervals in the process of study of habituation of auditory evoked potentials (EPs) in healthy subjects and patients with endogenous depression, revealed a rhythmic wave process (RWP) especially expressed in patients. RWP appeared and became stronger in successive averaging of 10 realizations completing each of four series of 30 clicks; often (especially in depressive patients) it was manifest in averaging of all 120 realizations with an amplitude comparable with that of main EPs components and even greater. A significant correlation was found of RWP parameters with characteristics of melancholic mood in both subgroups. It is suggested that RWP appears as a result of regular changes of EEG background during multiple stimuli repetition in connection with increased "slow" habituation and in a special manifestation of perceptive defence during depression including mechanisms of active isolation from external world.     

Effect of thyrotropin-releasing hormone (TRH) on EEG topography

EEG topography by a microcomputer system (ATAC-3700 Nihon-Kohden) was performed in the rabbit in order to investigate the mechanism of TRH action on the brain wave. Power spectral analysis was carried out using a fast Fourier transform algorithm. The square root of the power spectra was defined as the equivalent potential over each frequency band by Ueno & Matsuoka's method. Potential fields of EEG frequency band were printed out on the topographic maps. The potentials of the electrocortical delta and theta waves were high, while the potentials of the alpha, beta 1 and beta 2 waves were low. Stimulation of the nucleus ventralis anterior (VA) by 3 Hz and 8 Hz resulted in a decrease in these potentials, especially, those of the alpha, beta 1 and beta 2 waves. The potentials of the alpha and fast waves were increased following unilateral destruction of VA. In the rabbit, in which TRH 0.5 mg/kg had been administered beforehand, there was no decrease in the potential of each wave induced by stimulation of VA with frequencies of 3 Hz and 8 Hz. The findings suggest involvement of the diffuse thalamocortical projection system in the activation of EEG by TRH.     

Turner's syndrome: a qualitative and quantitative analysis of EEG background activity

Summary A qualitative and quantitative analysis was performed on the EEG background activity in 62 Danish girls and women with Turner's syndrome (30 with karyotype 45,X and 32 with other karyotypes) whose ages ranged from 6 to 47 years (87% were aged 15 years or more) and age-matched controls. The pooled data and a case-control study showed characteristic features in Turner subjects, including: (1) more rapid frequency, larger amplitude and lower amount of alpha waves, (2) higher amount of theta waves, (3) larger amplitude and higher amount of delta waves and (4) larger amplitude and higher amount of beta waves than in controls. These findings in Turner subjects were more pronounced in the left hemisphere, and more typical, except for the amplitude in alpha waves, in Turner subjects with 45,X than in those with other karyotypes. The effects of advancing age on the EEG background activity observed in controls — including more rapid frequency, decreased amplitude and amount of alpha waves, increased amount of theta and delta waves, and increased amount of beta waves, particularly after 35 years of age — were found in some Turner subjects. Hemispheric differences with higher activity (i.e. more rapid frequency, larger amplitude and higher amount of alpha waves, particularly at Fp₁ and F₃, and, inversely, lower amount of theta or delta waves) at P₃, T₃, T₅ and O₂ than at the opposite side were found in many Turner subjects. However, these findings were not specific for Turner subiects, since the same hemispheric differences were also observed much more markedly in controls. These topographic distributions with hemispheric differences did not provide evidence for hypofunction in the temporo-parieto-occipital tertiary area of the right hemisphere in Turner subjects, though this had been expected on the basis of neuropsychological examinations. Our findings, including transiently appearing brain hypofunction at the parietal, temporal and occipital areas, most often in the right hemisphere, indicate a relationship between the chromosomal constitution 45,X and EEG background activity. They suggest the presence of functional brain disturbance in the thalamus and in the ascending reticular activating system, which tends to disturb the thalamo-cortical circuit. Further studies, including topographic and sequential power spectrum analysis of EEG background activity, 24-h continuous EEG recording, blood flow studies (positron computerized tomography) and neuropathological examination, may be needed.Tables I-VI are available on request     

The mechanism of action of a reinforcing stimulus]

Experiments on alert non-immobilized rabbits revealed that electrical cutaneous stimulation of a limb, used as a reinforcing agent in elaboration of a conditioned reflex to photic flashes, weakened slow polyrhythmic oscillations of background EEG and late components of evoked potentials in the visual cortex to photic flashes. Against this background, the connection between slow potentials and spike activity in both the visual and sensorimotor cortical areas considerably diminished. During EEG activation, induced by the reinforcing stimulus, inhibitory pauses and post-inhibitory activation in the firing of the neocortical units weakened and protracted, ordered spike activity appeared. The data obtained are in agreement with the hypothesis that weakening of the recurrent inhibition system is one of the basic mechanisms in the action of the reinforcing stimulus in conditioning.     

Lateral inhibition in neuronal networks and the shape of alpha-rhythm in the EEG

In 15 volunteers, the background EEG was registered from the right occipital area with eyes closed. Rhythmic photo-stimulation conjugated with a certain phase of the alpha-waves (10 phases) elicited responses that were compared by means of measurement of the alpha-wave average amplitude in each protocol. The wave shape was compared by asymmetry at the level of ascending and descending fronts. The shape changes were most obvious during the stimuli in middle of the descending front, the changes shrply differing from other 9 phases of the stimulation.     

Changes in the configuration of conditioned reactions of visual cortex neurons during changes in reinforcement parameters]

In order to study the influences of controlled changes of defensive integration on the activity of visual cortical units their responses to a conditioned light flash and electric cutaneous stimulation with a 600 msec interval between them were recorded in experiments on alert rabbits. It has been shown that in a third of the neurones the types of reaction to light flashes and electric stimuli coincide. The changes in parameters of the reinforcing shock led to a changed response of most cells to the conditioned photic stimulus and electric stimulation. The changes may have affected units which produce any activation phase, including cells with activity characteristic of detectory ("simple" and "complex") visual neurones. The data obtained suggest that the special function of the visual cortex is used in different ways in systemic mechanisms of conditioned and unconditioned defensive acts and that the integrated system of a behavioral act exerts control both on the use of the unit in a certain systemic process and on its receptive field.     

Classical conditioning of ventilatory responses in humans

A classical conditioning experiment, in which an auditory stimulus was paired with a hypoxic stimulus, was carried out on 34 normal subjects assigned to two groups (experimental and control). Each subject took part in one session divided into two phases, acquisition and test. In the acquisition phase, eight hypoxic and eight auditory stimuli were paired in the experimental group and unpaired in the control group. In the test phase, which was identical for the two groups, the hypoxic stimuli were suppressed and three purely auditory stimuli were presented. Significant differences between the two groups in ventilatory response to these auditory stimuli provided evidence for conditioning. In the control group, no significant changes were elicited by the auditory stimuli, whereas a conditioned increase in total cycle duration was observed in the experimental group. The conditioned response closely resembled the first component of the hypoxic response. Analysis of the pattern of the conditioned response, along with postexperimental interviews, strongly suggests that this response was not mediated by volitional factors.     

The effect of unconscious color hue saturation on the emotional state of humans

The effect of color hue saturation on the emotional state (ES) of humans has been investigated. Frontal EEG asymmetry was used to determine the subject’s ES. The emotionogenic stimuli caused converse dynamics of frontal EEG asymmetry. Negative stimuli elicited a decrease in the value of frontal EEG asymmetry, and positive stimuli increased the value of frontal EEG asymmetry in the anterofrontal and posterofrontal leads. These dynamics of frontal EEG asymmetry indicates the formation of an ES corresponding to the presented stimuli. Blue and red color balance modification of stimuli leads to changes in the dynamics of frontal EEG asymmetry during the scanning of emotionally positive and negative stimuli. None of the subjects noticed the color modification of the video stimuli used. This leads us to the conclusion that the change in the frontal asymmetry in response to modified stimuli resulted from an unconscious perception of the modification of the color characteristics of the stimuli. The results show the possibility of the effect of unconscious perception of color characteristics of video stimuli on the ES of humans.     

Influence of segmental and extra-segmental conditioning stimuli on cortical potentials evoked by painful electrical stimulation

This study evaluated the effects of two different types of segmental/extra-segmental conditioning stimuli (tonic muscle pain and non-painful vibration) on the subjective experience (perceived pain intensity) and on the cortical evoked potentials to standardized test stimuli (cutaneous electrical stimuli). Twelve subjects participated in two separate sessions to investigate the effects of tonic muscle pain or cutaneous vibration on experimental test stimuli. The experimental protocol contained a baseline registration (test stimuli only), a registration with the test stimuli in combination with the conditioning stimuli, followed by a registration with the test stimuli only. In addition, the effects of the conditioning stimuli were examined at two anatomically separated locations (segmental and extra-segmental). Compared with the test stimulus alone, the perceived pain intensity and peak-to-peak amplitudes of the evoked potentials were unchanged in the presence of non-painful conditioning stimuli at either location. In contrast, a significant decrease of the perceived pain intensity and peak-to-peak amplitudes was found in the presence of painful conditioning stimuli at the extra-segmental sites. Moreover, the topographic maps of the 32-channel recordings suggested that the distribution of the scalp evoked potentials was almost symmetrical around the vertex Cz in the baseline registration. The evoked potentials were generally decreased during hypertonic saline infusion at the extra-segmental sites, but the distribution of the topographic maps did not appear to change. Vibration has previously been shown to inhibit pain, but in the present study the perceived intensity of phasic painful electrical stimuli was unchanged. The reduced perceived pain intensity and the smaller peak-to-peak amplitude of the evoked potential in the presence of extra-segmental conditioning pain are in accordance with the concept of diffuse noxious inhibitory control.     

Effect of feedback contingencies on the control of occipital alpha

Ten color transparencies were presented 30 times each to ten normal adults in response to changes in their occipital-parietal EEG's. By means of a feedback paradigm, detected alphas caused each slide to flash and stay on as long as alpha persisted, and then to turn off when alpha attenuated, according to four different contingency conditions. For half of the feedback trials, stimulus presentation depended on alpha detection in only one hemisphere and was not influenced by changes in the simultaneously recorded contralateral EEG. For the other feedback trials, stimulus presentation was bilaterally contingent. These contingency configurations were compared with sham feedback, a noncontingent condition during which slide presentation was controlled by a prerecorded tape. For both alpha and no-alpha, the ratio of mean duration over standard error was used as a quantification of the EEG response to visual stimulation. It was assumed that larger ratios indicated increased control of the EEG. Compared with the sham condition, all feedback contingencies produced greater ratios, and hence, improved control of the EEG. The highest ratios were obtained during unilateral feedback from the EEG in which the occurrence of alpha elicited the visual stimulus. The results show that contingency between a visual stimulus and the EEG is an important parameter with regard to experimental control of the EEG.     

Vector representation of associative learning

I. P. Pavlov [12] has shown that conditioned reflexes are selective both with respect to conditioned stimuli and to conditioned reflexes elicited by those conditioned stimuli. At the neuronal level selective aspects of conditioned stimuli are based on detectors selectively tuned to respective stimuli. The selective aspects of conditioned reflexes are due to command neurons representing specific unconditioned reflexes. It can be assumed that conditioned reflexes result from association between selective detectors and specific command neurons. The detectors activated by a conditioned stimulus constitute a combination of excitations--a detector excitation vector. The detector excitation vector acts on a command neuron via a set of plastic synapses--a synaptic weight vector. Plastic synapses are modified in the process of learning making command neuron selectively tuned to a specific conditioned stimulus. The selective tuning of a particular command neuron to a specific excitation vector referred to a conditioned stimulus is a basis of associative learning. The probabilities of conditioned reflexes elicited by conditioned and differential stimuli implicitly contain information concerning excitation vectors that encode respective stimuli. Contribution of the vector code to associative learning was explored combining differential color conditioning with intracellular recording from color-coding neurons. It was shown that colors in carps and monkeys are represented on a hypersphere in the four-dimensional space similar to human color space. The basis of the color space is constituted by red-green, blue-yellow, brightness and darkness neurons.