Spatial and Frequency Differences of Neuromagnetic Activities in Processing Concrete and Abstract Words

This study investigated the neuromagnetic spatial and frequency differences between recognizing concrete and abstract words using a 275 channel whole head magnetoencephalography (MEG) system. The stimuli consisted of 100 concrete words and 100 abstract words which were presented visually and auditorily simultaneously. The data of 12 right-handed healthy subjects in six different frequency bands were analyzed with synthetic aperture magnetometry (SAM) which can identify the frequency-dependent volumetric distribution of the evoked magnetic field. Concrete and abstract words evoked a very similar neuromagnetic activation pattern in the primary visual and auditory cortices. However, concrete words evoked stronger synchronization in the right hemisphere and abstract words evoked stronger synchronization in the left hemisphere in 1–8 Hz. In addition, concrete words evoked more desynchronization in the left posterior temporal and parietal cortex; while abstract words evoked a clear synchronization in the left posterior temporal cortex and desynchronization in the left inferior frontal cortex in 70–120 Hz. Furthermore, concrete words evoked clear desynchronization in the left inferior frontal cortex while abstract words evoked strong synchronization in the left posterior temporal cortex in 200–300 Hz. These findings suggested that concrete words and abstract words are processed differently in the brain not only in anatomical substrates, but also in the frequency band of neural activation.     

Stronger occipital cortical activation to lower than upper visual field stimuli Neuromagnetic recordings

 We recorded whole-scalp magnetoencephalographic (MEG) responses to black-and-white checkerboards to study whether the human cortical responses are quantitatively similar to stimulation of the lower and upper visual field at small, 0–6°, eccentricities. All stimuli evoked strongoccipital responses peaking at 50–100 ms (mean 75 ms). The activation was modeled with a single equivalent current dipole in the contralateral occipital cortex, close to the calcarine fissure, agreeing with an activation of the V1/V2 cortex. The dipole was, on average, twice as strong to lower than to upper field stimuli. Responses to hemifield stimuli that extended to both lower and upper fields resembled the responses to lower field stimuli in source current direction and strength. These results agree with psychophysical data, which indicate lower visual field advantage in complex visual processing. Parieto-occipital responses in the putative V6 complex were similar to lower and upper field stimuli. Received: 16 March 1998 / Accepted: 9 September 1998     

Synchronization of EEG Theta and Alpha Rhythms in an Unconscious Set to the Perception of an Emotional Facial Expression

Coherence functions in cortical electrical potentials in the theta (4–7 Hz) and alpha ranges (8–13 Hz) recorded during the formation and testing stages of a visual set to facial images bearing an emotional expression (an angry face) were studied in healthy adult subjects (n = 35). Differences in the spatial synchronization between theta and alpha potentials were seen, especially in rigid forms of the set, in which cases of erroneous perception of facial expressions were seen with contrast and assimilative illusions. This group of subjects (n = 23) showed increases in theta potentials between the dorsolateral areas of the frontal cortex (the orbitofrontal cortex) and the temporal area in the right hemisphere. A mechanism is proposed for the development of visual illusions. Analysis of the coherence functions of cortical potentials in the theta and alpha ranges generates a “window” which can be used to study the operation of the two functional systems integrating brain activity, i.e., the corticohippocampal and frontothalamic, in the perception of a facial expression. The frontothalamic system is associated with more diffuse types of cortical activation, especially in its anterior areas. The theta rhythm system evidently facilitates integration of the frontal cortex with the temporal area in the right hemisphere and the connections of the latter with the parietal and central zones in both hemispheres.     

Interhemisphere differences during tasks involving attention and selection of lateralized stimuli

The state of cortical activation in the parietal and temporal areas of the right and left hemispheres was evaluated using evoked potentials (EP) during tasks consisting of selection of visual stimuli lateralized in the right and left visual fields and needing three different types of attention: to stimulus shape, to stimulus position, and simultaneously to stimulus shape and position. EP were recorded in 15 young healthy experimental subjects using six cortical leads: P3, P4, T3, T4, T5, and T6; the following endogenous EP components (in standard terminology) were analyzed: contingent negative variation (CNV), N1, P3, and the N1-P3 complex. Asymmetry in evoked potentials was assessed in terms of differences to contra-and ipsilateral stimuli in the right and left hemispheres. EP asymmetry was detected in the right hemisphere in all types of selection of lateralized stimuli. The magnitude of asymmetry in the right hemisphere depended on the level (or intensity) of attention: the degree of asymmetry increased with increases in the need for attention to analyze the stimuli. There was a significant relationship between the magnitude of asymmetry and the latent periods of the subjects’ responses. The functional significance of these data demonstrating asymmetry may be that it provides better spatial differentiation of visual signals in the right hemisphere, along with dominance of the right hemisphere in attention tasks. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 92, No. 6, pp. 709–722, June, 2006.     

Effect of unconscious interoceptive afferentation on the spatial organization of electrical activity in the human cerebral cortex

Toposcopic studies consisting of EEG recording from 24 cortical points was carried out to characterize the spatial organization of the electrical activity of the human cerebral cortex during the action of unconscious interoceptive stimuli arising from biologically active points associated with different internal organs — the heart, lungs, liver, and intestine. When acupuncture had positive effects, reductions in global synchronization of cortical potentials were noted, which were combined with foci of weakening of the linear and nonlinear correlations in the anterior parts of the right hemisphere, as well as in the posterior and temporal parts of the left hemisphere, with increases in coherence in one of the high-frequency subranges of the EEG (21.5-23.0 Hz). Negative effects and absence of effect correlated with significantly less pronounced weakening of global synchronization of potentials, and increases in their coherence in one of the subranges of alpha activity. Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences, Moscow. Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti, Vol. 45, No. 5, pp. 867–875, September–October, 1995.     

Cortical processing of tactile stimuli applied in quick succession across the fingertips: temporal evolution of dipole sources revealed by magnetoencephalography

We used magnetoencephalography (MEG) in 10 healthy human subjects to study cortical responses to tactile stimuli applied to the fingertips of digits 2–5 of the right hand. Each stimulus lasted 50 ms and was produced by air-driven elastic membranes. Four-hundred stimuli were delivered on each finger in three temporal patterns (conditions). In the “Discrete” condition, stimuli were applied to each finger repetitively with an interstimulus interval (ISI) of 1–2 s. In the “Continuous” condition, stimuli were applied to the fingers sequentially as four-stimulus trains with zero ISI and 1–2 s intervening between trains. Finally, in the “Gap” condition, stimuli were applied as in the Continuous condition but with an ISI of 50 ms. A sensation of tactile motion across fingers (digit 2 → digit 5) was reported by all subjects in the Continuous and Gap conditions. Cortical responses were extracted as single equivalent current dipoles over a period of 1 s following stimulus onset. In all three conditions, initial responses in left primary somatosensory cortex (SI) were observed ~20 to 50 ms after stimulus onset and were followed by additional left SI responses and bilateral responses in the secondary somatosensory cortex (SII). In addition, in the Continuous and Gap conditions, there was an activation of the precentral gyrus, the temporal aspects of which depended on the temporal relation of the administered stimuli, as follows. An ISI of 0 ms led to activation of the precentral gyrus shortly after the second stimulation, whereas an ISI of 50 ms led to activation of the precentral gyrus after the third stimulation. The current findings support results from previous studies on temporal activity patterns in SI and SII, verify the participation of the precentral gyrus during tactile motion perception and, in addition, reveal aspects of integration of sequential sensory stimulations over nonadjacent areas as well as temporal activity patterns in the postcentral and precentral gyri.     

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

The coherence functions of cortical electrical potentials were studied in 35 healthy adults in the alpha (8–13 Hz) and beta (14–25 Hz) ranges, recorded at the stages of formation and testing of a visual set to images of faces bearing different emotional expressions. At the set actualization stage, the frontal area showed significant increases in intra-and interhemisphere coherence of potentials in the alpha range and coherence of potentials between the frontal and temporal areas of the cortex in the right hemisphere. These analytical results support the suggestion that the formation and actualization of a set to emotional facial expression are predominantly associated with activity in the frontal areas of the cortex. This conclusion is based on the view that the extent of spatial synchronization of electrical potentials is a measure of the functional relationships between corresponding cortical areas and their cooperativity, and thus reflects the state of their activity. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 57, No. 1, pp. 33–42, January–February, 2007.     

The origin of activity in the biceps brachii muscle during voluntary contractions of the contralateral elbow flexor muscles

During strong voluntary contractions, activity is not restricted to the target muscles. Other muscles, including contralateral muscles, often contract. We used transcranial magnetic stimulation (TMS) to analyse the origin of these unintended contralateral contractions (termed “associated” contractions). Subjects (n = 9) performed maximal voluntary contractions (MVCs) with their right elbow-flexor muscles followed by submaximal contractions with their left elbow flexors. Electromyographic activity (EMG) during the submaximal contractions was matched to the associated EMG in the left biceps brachii during the right MVC. During contractions, TMS was delivered to the motor cortex of the right or left hemisphere and excitatory motor evoked potentials (MEPs) and inhibitory (silent period) responses recorded from left biceps. Changes at a spinal level were investigated using cervicomedullary stimulation to activate corticospinal paths (n = 5). Stimulation of the right hemisphere produced silent periods of comparable duration in associated and voluntary contractions (218 vs 217 ms, respectively), whereas left hemisphere stimulation caused a depression of EMG but no EMG silence in either contraction. Despite matched EMG, MEPs elicited by right hemisphere stimulation were ∼1.5–2.5 times larger during associated compared to voluntary contractions (P < 0.005). Similar inhibition of the associated and matched voluntary activity during the silent period suggests that associated activity comes from the contralateral hemisphere and that motor areas in this (right) hemisphere are activated concomitantly with the motor areas in the left hemisphere. Comparison of the MEPs and subcortically evoked potentials implies that cortical excitability was greater in associated contractions than in the matched voluntary efforts.     

Somatosensory evoked magnetic fields following passive movement compared with tactile stimulation of the index finger

Cortical processing of passive finger movement was assessed magnetoencephalographically in 12 healthy volunteers and compared with somatosensory evoked magnetic fields (SEF) following tactile stimulation. A new device comprising a clamp-like digit holder facilitated bilateral guidance of the briskly elevated index finger. Both passive movement and tactile stimulation induced activation of the contralateral primary somatosensory (SI) cortex, indicated by six SEF deflections with inter-individually rather consistent peak latencies of 20–230 ms following proprioceptive and 20–300 ms following tactile stimulation. SEF responses to the two stimulus modalities clearly differed with regard to peak latencies, amplitudes and orientations of equivalent current dipoles (ECDs). The strength and orientation of proprioception-related ECDs suggested sequential activation of SI generators, with possible involvement of areas 3a and/or 2 at around 20 ms, area 4 at approximate peak latencies of 65 and 100 ms and area 3b between 150 to 230 ms. Passive movement elicited additional activation of cortical regions outside SI, including the bilateral perisylvian regions and the contralateral cingulate gyrus at latencies of 40–470 and 150–500 ms respectively. The study provides new results with respect to the spatiotemporal analysis of proprioception-related cortical processing and may contribute to a better understanding of the modality-specific organization of the human somatosensory cortex. Electronic Publication     

Evoked Synchronization/Desynchronization of Cortical Electrical Activity in Response to Facial Stimuli during Formation of a Set to an Emotionally Negative Expression

Evoked EEG theta and alpha rhythm synchronization/desynchronization responses to facial stimuli were studied in healthy subjects (n = 35) in an experiment involving formation of a set to an emotionally negative facial expression. The magnitude of the evoked theta activity synchronization response in the group of subjects with the plastic type of set was greater and the latent period was shorter than in the group with the rigid type of set. These differences were particularly clear in the temporal and parietal-occipital areas. A sufficiently high level of the phasic theta potentials synchronization response, reflecting the level of activity of the corticohippocampal feedback system during the perception of facial stimuli, was required for rapid substitution of the set to facial expressions. In subjects with plastic sets, the evoked low-frequency alpha potentials response was apparent as synchronization, while that in subjects of the “rigid” group consisted of desynchronization. These results were interpreted in terms of the concept of Klimesch (2007) that the evoked alpha potentials synchronization response is a measure of inhibition in cognitive activity. The alpha potentials synchronization response reflects the process of inhibitory control, which plays an important coordinating role in organizing the plastic properties of the set in relation to its inhibition when it ceases to correspond to new stimuli. The involvement of the tonic and phasic forms of cortical activation, mediated by the corticohippocampal and frontothalamic brain systems, in the functional organization of the cognitive set to an emotionally negative facial expression is discussed.     

Neurophysiological Correlates of Induced Discrete Emotions in Humans: An Individually Oriented Analysis

Studies on 30 right-handed subjects addressed EEG characteristics (62 channels) in conditions of laboratory simulation of induced emotions of happiness, joy, anger, disgust, fear/anxiety, and sadness. Induced emotions were found to produce, along with common features, individual patterns in the distribution of amplitude-frequency EEG characteristics. Induced positive and negative discrete emotions were characterized by interhemisphere activatory asymmetry in the theta-2 (4–6 Hz), alpha-2 (10–12 Hz), and beta-1 (12–18 Hz) ranges. Experience of the emotions of joy, anger, and disgust occurred on the background of asymmetrical increases in activity in the anterior cortex of the left hemisphere in the theta-2 range, suggesting a leading role for the activity of these areas in realizing the cognitive components of emotional reacting. In addition, some high-ergicity negative emotions evoked combined alpha-2 and beta-1 desynchronization (disgust) or beta-1 desynchronization (fear/anxiety) in the right parietal-temporal cortex, suggesting its involvement in the mechanisms of non-specific emotional activation. These data provide evidence that each of these emotions is characterized by its own individual pattern in the distribution of the amplitude-frequency characteristics of the EEG and, on the other hand, that series of ranges and cortical areas show similar but different (in terms of intensity) effects in response to emotional activation for emotions of different flavor. __________ Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 90, No. 12, pp. 1457–1471, December, 2004.     

Neuronal activity of somatosensory cortex in a cross-modal (visuo-haptic) memory task

Studies have shown that in the monkey′s associative cerebral cortex, cells undergo sustained activation of discharge while the animal retains information for a subsequent action. Recent work has revealed the presence of such ″memory cells″ in the anterior parietal cortex (Brodmann′s areas 3a, 3b, 1, and 2) – the early stage of the cortical somatosensory system. Here we inferred that, in a cross-modal visuo-haptic short-term memory task, somatosensory cells would react to visual stimuli associated with tactile features. Single-unit discharge was recorded from the anterior parietal cortex – including areas of hand representation – of monkeys performing a visuo-haptic delayed matching-to-sample task. Units changed firing frequency during the presentation of a visual cue that the animal had to remember for making a correct tactile choice between two objects at the end of a delay (retention period). Some units showed sustained activation during the delay. In some of them that activation differed depending on the cue. These findings suggest that units in somatosensory cortex react to visual stimuli behaviorally associated with tactile information. Further, the results suggest that some of these neurons are involved in short-term active memory and may, therefore, be part of cross-modal memory networks. Received: 24 March 1997 / Accepted: 8 May 1997     

Multiple temporal components of optic flow responses in MST neurons

 Neurons in monkey medial superior temporal cortex (MST) respond to optic flow stimuli with early phasic, tonic, and after-phasic response components. In these experiments we characterized each response component to compare its potential contributions to visual motion processing. The early responses begin 60–100 ms after stimulus onset and last between 100 and 250 ms, the tonic responses begin 100–300 ms after stimulus onset and last for as long as the evoking stimulus persists, and the after-responses begin about 60 ms after the stimulus goes off and last for 100–350 ms. A neuron’s tonic responses were evoked by specific optic flow stimuli: over two-thirds of the 264 neurons showed tonic responses evoked by two to five stimuli, whereas only 15% responded to either all or none of the stimuli. The tonic responses continued with stimulus presentations as long as 15 s, with their directional preferences being maintained throughout stimulation. However, the tonic response to a given stimulus was seen to change in amplitude when it was presented in random sequence with different sets of other stimuli. Thus, the tonic responses might convey substantial information about optic flow patterns, which continue with prolonged stimulation, but can be modified by the visual context created by other visual motion stimuli. Only about one-third of the 264 neurons had early responses that were selective for specific stimuli. In neurons yielding at least one early response, that neuron was most often activated by all the visual motion stimuli. After-rsponses occurred in only half the neurons, but they were more often specifically related to particular optic flow stimuli, regardless of whether those stimuli had evoked tonic excitatory or tonic inhibitory responses. The presence of early and after-responses complicates the interpretation of activity evoked when one stimulus immediately follows another. However, under those conditions, early responses and after-responses might contribute to signaling changes in the ongoing pattern of optic flow. We conclude that several components of MST responses should be recognized and that they potentially play different roles in the cortical analysis of optic flow. Tonic responses show the greatest specificity for particular optic flow stimuli, and possess characteristics which make them suitable neuronal participants in self-movement perception. Received: 1 April 1996 / Accepted: 1 October 1996     

Effects of azaleptine and its new derivative seleptine on spontaneous EEG activity and the activation reaction in rabbits

The neuroleptic azaleptine and its new derivative seleptine with anticonvulsive properties were examined in a chronic experiment on rabbits for their comparative effects on the spontaneous electroencephalogram (EEG) and the activation reaction in the sensorimotor cortex and dorsal hippocampus. Azaleptine induced synchronization of electroencephalographic activity in all frequency ranges of both cortical and hippocampal EEGs, while seleptine induced desynchronization in the cortical EEG and synchronization in the δ, θ and β ranges of the hippocampal EEG. Both compounds prevented the activation or altered its pattern, leading to a decrease in the power of the β range rather than increasing it as is normally observed. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 119, N ^o 3, pp. 252–255, March, 1995 Presented by G. N. Kryzhanovskii, Member of the Russian Academy of Medical Sciences     

Limited plasticity of difference neurons in the visual cortex and hippocampus in rabbits during the oddball (random substitutions) test

The activity of 41 visual cortex neurons and 20 hippocampal field CA1 neurons was studied in rabbits during application of the oddball stimulation paradigm using color stimuli of different intensities. Among these cells, about one third were plastic cells (34% of cortical cells and 37% of hippocampal cells). These neurons showed significant increases in late responses, at times 200–500 and 200–1000 msec for visual cortex neurons and 300–550 msec for hippocampal neurons, to rare deviant stimuli of lesser intensity as compared with responses to the frequent standard stimuli of greater intensity. The initial peak of the response (40–120 msec), the “difference discharge,” remained stable in responses to deviant and standard stimuli throughout the experiment. It is suggested that the strengthening of the late components of neuron responses to rare deviant stimuli (limited plasticity) reflects inclusion of the mechanisms of the orientational reflex. __________ Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 55, No. 3, pp. 360–367, May–June, 2005.     

Direct demonstration of interhemispheric inhibition of the human motor cortex produced by transcranial magnetic stimulation

 Electromyographic (EMG) responses evoked in hand muscles by a magnetic test stimulus over the motor cortex can be suppressed if a conditioning stimulus is applied to the opposite hemisphere 6–30 ms earlier. In order to define the mechanism and the site of action of this inhibitory phenomenon, we recorded descending volleys produced by the test stimulus through high cervical, epidural electrodes implanted for pain relief in three conscious subjects. These could be compared with simultaneously recorded EMG responses in hand muscles. When the test stimulus was given on its own it evoked three waves of activity (I-waves) in the spinal cord, and a small EMG response in the hand. A prior conditioning stimulus to the other hemisphere suppressed the size of both the descending spinal cord volleys and the EMG responses evoked by the test stimulus when the interstimulus interval was greater than 6 ms. In the spinal recordings, the effect was most marked for the last I-wave (I₃), whereas the second I₂-wave was only slightly inhibited, and the first I-wave (I₁) was not inhibited at all. We conclude that transcranial stimulation over the lateral part of the motor cortex of one hemisphere can suppress the excitability of the contralateral motor cortex. Received: 31 August 1998 / Accepted: 26 October 1998     

Dynamics of Changes in Electrical Activity in the Rabbit Cerebral Cortex during Sequential Sessions of “Animal Hypnosis”

The dynamics of changes in individual electrical activity rhythms in the premotor, sensorimotor, and temporal-parietal areas of the cortex in both hemispheres were studied in chronic experiments in rabbits during sequential sessions of “animal hypnosis.” These experiments showed that during the first session of “animal hypnosis,” significant changes in electrical activity occurred only in the premotor area of the cortex of the right hemisphere, where there were increases in spectral power in the delta-1 and delta-2 ranges and decreases in spectral power in other ranges of electrical activity. Subsequent sessions of “animal hypnosis” formed increasing changes in electrical activity, which were particularly marked in cortical areas in the right hemisphere. Significant changes in spectral power in the delta and theta ranges of electrical activity in cortical areas did not arise at the beginning of the hypnotic state, but after 4–6 min. During the third session of “animal hypnosis,” the course of electrical activity in the alpha and beta rhythms in the premotor and sensorimotor areas of the cortex became wave-like in nature.     

Estimation of habituation and signal-to-noise ratio of cortical evoked potentials to oesophageal electrical and mechanical stimulation

Electrical and mechanical stimulation of the oesophagus has been recently proposed to examine the physiological effects of autonomic stimulation in humans. Cortical evoked potentials (EPs) to oesophageal stimulation provide an assessment of afferent fibres and central processing. However, habituation takes place during averaging of cortical EPs and reduces the signal-to-noise ratio (SNR) as the number of stimuli increases. The SNR of cortical EPs to oesophageal stimulation is computed for 15 normal subjects. Habituation is characterised by the Euclidean distance between the EEG response to single stimuli and the averaged EP, to serve as an objective measure of similarity between the averaged EP and the single-stimulus EEG. With electrical stimulation, the SNR is highest (0.41±0.21) for 1–12 stimuli and then significantly decreases to 0.2±0.08 for 13–24 stimuli (p<0.001). With balloon distension (BD), the SNR is highest (0.22±0.16) for 1–12 stimuli and lowest (0.12±0.14) for 13–24 stimuli, but these SNRs are not significantly different from each other. Both electrical and mechanical stimulation of the oesophagus produce rapidly adapting EPs. The SNR of the EPs is higher with electrical stimulation than with BD. The EPs response to BD has a higher variability and is more noisy. Consequently, these results suggest that the overall cortical EP response to electrical stimulation of the oesophagus is more reproducible than that due to balloon distension.     

Short and medium latency muscle responses evoked by electrical vestibular stimulation are a composite of all stimulus frequencies

Electrical vestibular stimulation produces biphasic responses in muscles maintaining balance. The two components of these muscle responses (termed the short latency and medium latency components) are believed to be independent and elicited by vestibular stimuli of different frequencies. We tested these hypotheses by determining (a) if frequency-specific stimulation protocols could evoke independently the short and medium latency responses and (b) whether these two components are triggered by distinct brain regions with a fixed time delay, interacting around 10 Hz. First, subjects were provided 10–25 Hz, 0–10 Hz, and 0–25 Hz vestibular stimuli to selectively modulate the short latency, medium latency, or both components of the response; and second, they were provided twenty sinusoidal stimuli from 1 to 20 Hz with a 0–20 Hz control trial, designed to determine whether an interaction between the short and medium latency responses occurs at a specific stimulation frequency. Both the 0–10 Hz and 10–25 Hz vestibular stimuli elicited multiphasic waveforms, suggesting the short and medium latency components were not modulated independently by the frequency-specific stimuli. Sinusoidal vestibular stimuli evoked responses at the stimulated frequency but no evidence of a reflex component interaction was observed. Instead, summation of the responses evoked by each of the sinusoidal stimuli resembled the biphasic response to broad bandwidth stimuli. Due to the lack of interaction and linear contribution of all stimulus frequencies to both the short and medium latency responses, the present results support the use of broad bandwidth electrical vestibular signal for physiological or clinical testing.     

Visually triggered K-complexes: a study in New Zealand rabbits

K-complexes are the EEG elements recorded during the state of developing sleep and during slow wave sleep. They are the only EEG components which can be elicited by sensory stimulation during sleep. The peculiarity of New Zealand rabbits to sleep with their eyes open allows the use of visual stimuli to elicit K-complexes. Experiments were performed with three rabbits. For visual stimulation, an elongated screen illuminated by LED flashes was attached to an implant on the animal’s skull. The screen covered 20–120° of the visual field of one eye, and moved with the head during animal motion. One-millisecond flashes (15-s interval) were used during daytime in an illuminated room. Flashes elicited evoked responses, which, during the first stages of sleep, were often accompanied by K-complexes. The induced K-complexes were recorded from electrodes located both above visual and somatosensory areas. Evoked responses to visual stimuli were also recorded from both pairs of electrodes, although they were generated exclusively in the visual cortex. Correlation analysis showed that visual evoked responses and K-complexes induced by this stimulation were generated in visual cortex, and passively spread to the electrodes above the somatosensory area. Investigation of the latencies of induced K-complexes revealed two time windows when these complexes could be seen. Within each window there was no correlation between latency and amplitude of K-complexes. There was also no correlation between amplitudes of the visual evoked responses and K-complexes elicited by these responses. We propose that visual stimulation in light sleep temporarily opens a gate for some independent external signals, which evoke activation of the visual cortex, reflected in K-complexes.