Episodic multiregional cortical coherence at multiple frequencies during visual task performance

The way in which the brain integrates fragmentary neural events at multiple locations to produce unified perceptual experience and behaviour is called the binding problem. Binding has been proposed to involve correlated activity at different cortical sites during perceptuomotor behaviour, particularly by synchronization of narrow-band oscillations in the gamma-frequency range (30-80 Hz). In the rabbit olfactory system, inhalation induces increased gamma-correlation between sites in olfactory bulb and cortex. In the cat visual system, coherent visual stimuli increase gamma-correlation between sites in both the same and different visual cortical areas. In monkeys, some groups have found that gamma-oscillations transiently synchronize within striate cortex, superior temporal sulcus and somatosensorimotor cortex. Others have reported that visual stimuli produce increased broad-band power, but not gamma-oscillations, in several visual cortical areas. But the absence of narrow-band oscillations in itself does not disprove interregional synchronization, which may be a broad-band phenomenon. We now describe episodes of increased broad-band coherence among local field potentials from sensory, motor and higher-order cortical sites of macaque monkeys performing a visual discrimination task. Widely distributed sites become coherent without involving other intervening sites. Spatially selective multiregional cortical binding, in the form of broad-band synchronization, may thus play a role in primate perceptuomotor behaviour.     

Induction of COX-2 expression by mechanical tension force in human periodontal ligament cells

Spectral EEG powers were compared in 4 frequency ranges (8-13, 15-25, 25-35, and 35-45 Hz) in a group of 20 subjects during the performance of tasks requiring mental rotation of two- and three-dimensional objects. Only those EEG segments corresponding to tasks with identical solution times were analyzed. The spectral powers of oscillations in the alpha range were higher in control conditions than during task performance. Power in the frequency range 15-45 Hz was greater during task performance than in control conditions; this supports the concept that alpha rhythm desynchronization accompanies the synchronization of higher-frequency EEG rhythms. Frequency power during task performance with two-dimensional objects was greater than that during tasks with three-dimensional objects. Since the angle of rotation between two-dimensional objects was greater than that between three-dimensional objects, this factor, rather than the depth of the perceived space, increased the level of cortical activation. In all experimental situations, power at frequencies of 15-45 Hz was significantly greater in the occipital regions than any other regions, reflecting the visual modality of the stimulus. Particular changes were noted in the gamma range (35-45 Hz), where power in the first second of task performance was significantly higher than in the second second; this may provide evidence that this range is more closely associated with perception and recognition processes than with mental transformation of the image.     

The effect of pictorial illusion on prehension and perception

The present study examined the effect of a size-contrast illusion (Ebbinghaus or Titchener Circles Illusion) on visual perception and the visual control of grasping movements. Seventeen right-handed participants picked up and, on other trials, estimated the size of "poker-chip" disks, which functioned as the target circles in a three-dimensional version of the illusion. In the estimation condition, subjects indicated how big they thought the target was by separating their thumb and forefinger to match the target's size. After initial viewing, no visual feedback from the hand or the target was available. Scaling of grip aperture was found to be strongly correlated with the physical size of the disks, while manual estimations of disk size were biased in the direction of the illusion. Evidently, grip aperture is calibrated to the true size of an object, even when perception of object size is distorted by a pictorial illusion, a result that is consistent with recent suggestions that visually guided prehension and visual perception are mediated by separate visual pathways.     

Synchronization of visual responses between the cortex, lateral geniculate nucleus, and retina in the anesthetized cat

Synchronization of spatially distributed responses in the cortex is often associated with periodic activity. Recently, synchronous oscillatory patterning was described for visual responses in retinal ganglion cells that is reliably transmitted by the lateral geniculate nucleus (LGN), raising the question of whether oscillatory inputs contribute to synchronous oscillatory responses in the cortex. We have made simultaneous multi-unit recordings from visual areas 17 and 18 as well as the LGN and the retina to examine the interactions between subcortical and cortical synchronization mechanisms. Strong correlations of oscillatory responses were observed between retina, LGN, and cortex, indicating that cortical neurons can become synchronized by oscillatory activity relayed through the LGN. This feedforward synchronization occurred with oscillation frequencies in the range of 60-120 Hz and was most pronounced for responses to stationary flashed stimuli and more frequent for cells in area 18 than in area 17. In response to moving stimuli, by contrast, subcortical and cortical oscillations dissociated, proving the existence of independent subcortical and cortical mechanisms. Subcortical oscillations maintained their high frequencies but became transient. Cortical oscillations were now dominated by a cortical synchronizing mechanism operating in the 30-60 Hz frequency range. When the cortical mechanism dominated, LGN responses could become phase-locked to the cortical oscillations via corticothalamic feedback. In summary, synchronization of cortical responses can result from two independent but interacting mechanisms. First, a transient feedforward synchronization to high-frequency retinal oscillations, and second, an intracortical mechanism, which operates in a lower frequency range and induces more sustained synchronization.     

Progressive cortical synchronization of ponto-geniculo-occipital potentials during rapid eye movement sleep

Phasic events, termed ponto-geniculo-occipital potentials, appear in the brainstem, thalamus and cerebral cortex during rapid eye movement sleep. In the cat, the species of choice for ponto-geniculo-occipital studies, these field potentials are usually recorded from the lateral geniculate thalamic nucleus and visual cortex. However, the fact that brainstem cholinergic neurons play a crucial role in the transfer of ponto-geniculo-occipital potentials to the thalamus, coupled with the evidence that mesopontine tegmental neurons project to virtually all thalamic nuclei, together explain why ponto-geniculo-occipital potentials are recorded over widespread territories, beyond the visual thalamocortical system. Here we demonstrate, by means of multi-site unit and field potential recordings from sensory, motor and association cortical areas in behaving cats, that: (i) ponto-geniculo-occipital potentials appear synchronously over the neocortex; and (ii) that their cortical synchronization develops progressively from the period preceding rapid eye movement sleep by 30-90 s (pre-rapid eye movement), to reach the highest degree of intracortical coherence during later epochs of rapid eye movement sleep. We propose that the widespread coherence of cortical ponto-geniculo-occipital potentials underlies the synchronization of fast oscillations (30-40 Hz) during rapid eye movement sleep over many, functionally distinct cortical territories implicated in dreaming, as brainstem-induced ponto-geniculo-occipital-like potentials are consistently followed by such fast oscillations.     

A motor signal and "visual" size perception

Recent models of the visual system in primates suggest that the mechanisms underlying visual perception and visuomotor control are implemented in separate functional streams in the cerebral cortex. However, a little-studied perceptual illusion demonstrates that a motor-related signal representing arm position can contribute to the visual perception of size. The illusion consists of an illusory size change in an afterimage of the hand when the hand is moved towards or away from the subject. The motor signal necessary for the illusion could be specified by feedforward and/or feedback sources (i.e. efference copy and/or proprioception/kinesthesis). We investigated the nature of this signal by measuring the illusion's magnitude when subjects moved their own arm (active condition, feedforward and feedback information available), and when arm movement was under the control of the experimenter (passive condition, feedback information available). Active and passive movements produced equivalent illusory size changes in the afterimages. However, the illusion was not obtained when an after-image of subject's hand was obtained prior to movement of the other hand from a very similar location in space. This evidence shows that proprioceptive/kinesthetic feedback was sufficient to drive the illusion and suggests that a specific three-dimensional registration of proprioceptive input and the initial afterimage is necessary for the illusion to occur.     

The effect of white and filtered noise on contrast detection thresholds

The influence of high-frequency microstimulation (HFMS) of one of the hemispheres on the parameters of spontaneous gamma-oscillations in the neural network containing callosal cells of the motor cortex of both hemispheres. There were three modes in the background oscillation periods distribution, which corresponded to the frequencies 40-60, 70-100, and 100-200 Hz. These oscillation frequencies were also revealed after the HFMS in neural interactions of the cells, which were active before the HFMS; the frequency 40-60 Hz, which dominated before the HFMS, became even more pronounced. The same three groups of oscillation frequencies were found in the activity of cells which became active after the HFMS. The expression of oscillations, the number of oscillatory interactions, as well as the number of neuronal pairs with additional synchronization decreased after the HFMS, which suggests a decrease in synchronization. Taking into account the results of simulation experiments that the frequency of gamma-oscillations is determined by the strength of inhibitory and excitatory input, we suggest that the long-term posttetanic modifications in the efficacy of synaptic inputs of the neurons of both hemispheres underlie the observed posttetanic changes.     

The theta rhythm of the infant EEG and the development of the mechanisms of voluntary control of attention in the 2nd half of the first year of life

The neurophysiological basis of attention control was studied in infants at the second half-year of life, i.e. in the period when the capability for voluntary control over behavior fundamentally improves. EEG was recorded in 60 infants aed 8-11 months in three experimental conditions: 1) attention to an object in the visual field (externally controlled attention, or the baseline state), 2) anticipation of a person in the peek-a-boo game (internally controlled attention), 3) attention to the reappeared person in the peek-a-boo game (control condition). The spectral analysis of the EEG data revealed a sharp increase in the EEG theta (3.6-6.0 Hz) during internally controlled attention as compared to the baseline and control conditions. The theta1 (3.6-4.8 Hz) increase was maximal in the frontal derivations. The reactivity of the frontal theta1 during internally controlled attention discriminated infants with different abilities to maintain this type of attention. The reactivity of the theta2 (5.2-6.0 Hz) was maximal in the right temporal derivation (T6) and did not depend on stability of the anticipatory attention. The findings point to different functional significance of the theta1 and theta2 rhythms in infants. It is suggested that synchronization of the frontal theta1 rhythm in infants reflects the activity of the anterior attention system which realizes the executive attention control. The ability to maintain anticipatory attention increased with age, whereas the frontal theta1 synchronization decreased and totally disappeared at the age of 11 months. At the age of 8 months there was a positive correlation between the frontal theta1 synchronization and behavioral index of stability of the internally controlled attention. On the contrary, this correlation was negative at the age of 9 and 10 months. It is suggested that the age-dependent dynamics of the relationship between the frontal theta1 reactivity and attention reflects a leap in maturation of the anterior attention system resulting in its more economic and efficient functioning.     

Relations entre la notion et la perception de la vitesse relative chez l'enfant.

Administered 2 tasks bearing on the perception and concept of relative velocity to 7-, 9-, 11-, and 13-yr-old children (24 at each age level). The perceptual task presented an illusion created by the movement of a target on a moving background, while the conceptual task was a modified version of Piaget's technique. In each task the 2 movements involved were either in the same (MS) or in the opposite direction. It was found that the illusion appeared earlier than the corresponding concept under the MS condition. The possibility of a retroactive effect of the concept on the percept is suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The motion analogue of the Café Wall illusion

Detecting visual motion is computationally equivalent to detecting spatiotemporally oriented contours. The question addressed in this study is whether the illusory oriented contour in the space-space domain induces corresponding illusory motion perception. Two experiments were conducted. In experiment 1, the Café Wall pattern, which elicits a strong illusion of orientation (Café Wall illusion), was found to induce an illusion of motion when this pattern was converted to the space-time domain. The strength of the motion illusion depends on the mortar luminance and width, as for the Café Wall illusion. In experiment 2, the adaptation to this illusion of motion was found to induce a motion aftereffect in a static test, which indicates that a first-order-motion system contributes to the induction of the motion illusion. In fact, the motion-energy model was able to predict the strength of this motion aftereffect.     

The target in the celestial (moon) illusion.

The visual conditions sufficient to produce the celestial (moon) illusion do not produce it for all presumably suitable celestial targets. For most observers, the illusion is complete for the moon: Apparent visual angle and apparent physical size are inverse functions of elevation, but apparent distance is a direct function. These features of the illusion are attenuated for star clusters and absent for star pairs. Although, in accordance with modern theories of the illusion, the visual terrain may be necessary for the celestial illusion, it is not sufficient; the visual target itself apparently must display particular features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

立体深度运动引发的立体视觉疲劳的脑电评估

3D技术的发展受到其引发的不舒适感的限制,长时间观看立体显示影像将会引起立体视觉疲劳,一种客观评价立体视觉疲劳的有效指标亟待提出.本文利用EEG (electroencephalography)三个频带θ(4~8 Hz)、α(8~13 Hz)、β(13~22Hz)的相对能量及其能量比值E_{(α+θ)/β、Eα/β}、E_{(α+θ)/(α+β)}在八个不同脑区及整个脑区的54个指标作为备选,借助配对t检验、灰色关联度分析(GRA)、支持向量机(SVM),最后得出指示由立体深度运动引发的视觉疲劳的最佳脑电指标为:顶区E_α/β.并比较了三个频带相对能量在不同疲劳状态的变化:疲劳状态下,α频带明显上升(p < 0.01),β频带明显下降(p < 0.01),θ频带保持稳定.     

Apparent relative motion from a checkerboard surround

To better understand the Ouchi illusion in which a stationary picture generates illusory relative motion, the spatial properties of the constituent elements of the rectangular checkerboard background were examined. Results of experiment 1 revealed that the largest illusion was obtained with elements of approximately 20-30 min in width and 4-6 min in height, an orientation of the constituents that was orthogonal to that of the test grating, and a phase shift of the alternate stripes that was close to 180 degrees. In experiment 2 it was found that the illusion increased in magnitude with increasing achromatic contrast but was minimal with a pattern of high chromatic contrast near isoluminance. In experiment 3, two test patches were presented simultaneously in the checkerboard background and were varied independently in their orientation to explore whether or not their motions were perceived as coherent (common fate). Patches having identical orientations, and nearly orthogonal to the surround, were synchronized more strongly than those having reflected orientations. Hysteresis related to the gain control of spatially overlapping visual units differing in their polarity (ON/OFF) was discussed as a possible cause of this phenomenon.     

Spike-wave complexes and fast components of cortically generated seizures. III. Synchronizing mechanisms

The intracortical and thalamocortical synchronization of spontaneously occurring or bicuculline-induced seizures, consisting of spike-wave (SW) or polyspike-wave (PSW) complexes at 2-3 Hz and fast runs at 10-15 Hz, was investigated in cats under ketamine-xylazine anesthesia. We used single and dual simultaneous intracellular recordings from cortical areas 5 and 7, and extracellular recordings of unit firing and field potentials from neocortical areas 5, 7, 17, 18, as well as related thalamic nuclei. The evolution of time delays between paroxysmal depolarizing events in single neurons or neuronal pools recorded from adjacent and distant sites was analyzed by using 1) sequential cross-correlations between field potentials, 2) averaged activities triggered by the spiky component of cortical SW/PSW complexes, and 3) time histograms between neuronal discharges. In all instances, the paroxysmal activities recorded from the dorsal thalamus lagged the onset of seizures in neocortex. The time lags between simultaneously impaled cortical neurons were significantly smaller during SW complexes than during the prior epochs of slow oscillation. During seizures, as during the slow oscillation, the intracortical synchrony was reduced with increased distance between different cortical sites. Dual intracellular recordings showed that, during the same seizure, time lags were not constant and, instead, reflected alternating precession of the recorded foci. After transection between areas 5 and 7, the intracortical synchrony was lost, but corticothalamocortical volleys could partially restore seizure synchrony. These data show that the neocortex leads the thalamus during SW/PSW seizures, that time lags between cortical foci are not static, and that thalamus may assist synchronization of SW/PSW seizures after disconnection of intracortical synaptic linkages.     

EEG asymmetry and heart rate during experience of hypnotic analgesia in high and low hypnotizables

This study evaluates the effects of hypnotic analgesia and hypnosis on bilateral EEG activity recorded from frontal, central and posterior areas during three painful electrical stimulation conditions: waking, hypnosis/no-analgesia, hypnosis/analgesia. Eight high-hypnotizable and eight low-hypnotizable (right handed) subjects participated in the experiment. The following measures were obtained: pain and distress tolerance ratings; EEG spectral amplitudes for the frequency bands: delta (0.5-3.75 Hz), theta 1 (4-5.75 Hz), theta 2 (6-7.75 Hz), alpha 1 (8-9.75 Hz), alpha 2 (10-12.75 Hz), beta 1 (13-15.75 Hz), beta 2 (16-31.75 Hz), total band (0.5-31.75 Hz), '40-Hz' (36-44 Hz); cardiac interbeat interval (ms); mid-frequency and high-frequency peaks from power spectral analysis of heart period variability. During hypnosis/analgesia, high hypnotizable subjects displayed significant reductions in pain and distress scores compared to hypnosis/no-analgesia and waking conditions. In each experimental condition these subjects displayed significant lower total and beta 1 amplitudes compared to low hypnotizables. High hypnotizables, on central and posterior recording sites, during both hypnosis/analgesia and hypnosis/no-analgesia conditions also showed total and delta EEG amplitude reductions in both hemispheres and a theta 1 amplitude reduction in the left hemisphere. However, for total, delta and beta 1 bands in the hypnosis/analgesia condition the amplitude reduction was more pronounced in the right hemisphere as shown by hemispheric asymmetry in favor of the left hemisphere. Low hypnotizables, on posterior recording sites, displayed a delta amplitude reduction during hypnosis/no-analgesia and hypnosis/analgesia conditions. These subjects also showed, for all recording sites, a reduction in theta 1 amplitude during hypnosis/no-analgesia compared to the waking condition. Lows, however, failed in evidencing amplitude differences between hypnosis/no-analgesia and hypnosis/analgesia conditions. During hypnotic analgesia the hemispheric asymmetry found in high hypnotizables was parallel to a significant reduction in the spectral mid-frequency peak of heart period variability which indicated a decrease in the level of sympathetic activity. In contrast, during hypnosis/no-analgesia the EEG amplitude reduction was not paralleled by a decrease in sympathetic activity.     

Poverty, cultural disadvantage and brain development: a study of pre-school children in Mexico

Forty-two children, who had been studied previously at the age of 18-30 months, were studied again at 4 years of age. Twenty-two belonged to low socioeconomic strata and were classified as high-risk children (HRC) the other 20 were classified as low-risk children (LRC), and belonged to middle and middle-high socioeconomic strata. Ten minutes of EEG using reference derivations (with linked earlobes) were recorded from each subject. Twenty EEG segments of 3.2 s each were selected by visual inspection for Fourier analysis. Absolute power (AP) was computed for the total EEG energy (1.5-19 Hz) as well as each reference derivation in 4 frequency bands: delta (1.5-3.5 Hz), theta (4-7.5 Hz), alpha (7.5-12.5 Hz) and beta (12.5-19 Hz). HRC had significantly more delta AP than LRC in frontal and central leads, and higher values of theta AP in frontal leads. Alpha AP was higher in LRC in occipital areas and in F8 and T4. This study suggests a maturational lag in HRC.     

Gamma-range activity evoked by coherent visual stimuli in humans

We tested the hypothesis of a role of gamma-range synchronized oscillatory activity in visual feature binding by recording evoked potentials from 12 subjects to three stimuli: two coherent ones (a Kanizsa triangle and a real triangle) and a non-coherent one (a Kanizsa triangle in which the inducing disks had been rotated so that no triangle could be perceived). The evoked potentials were analysed by convoluting the signal for each subject and each stimulation type by Gabor wavelets centred from 28 up to 46 Hz, providing a continuous measure of frequency-specific power over time. A first peak of activity was found around 38 Hz and 100 ms with a maximum at electrode Cz in each experimental condition. A second peak of activity occurred around 30 Hz and 230 ms, with a maximum at O1 in response to the real triangle and a maximum at Cz in the case of the illusory triangle. At 100 ms we did not find any variations of the gamma-band component of the evoked potential with stimulation type, but the power of the 30 Hz component of the evoked potential between 210 and 290 ms differed from noise only in the case of a coherent triangle, no matter whether real or illusory. We thus found a 30 Hz component whose power correlates with stimulus coherency, which supports the hypothesis of a functional role of high-frequency synchronization in feature binding.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sensitivity to dynamic auditory and visual stimuli predicts nonword reading ability in both dyslexic and normal readers

BACKGROUND: Developmental dyslexia is a specific disorder of reading and spelling that affects 3-9% of school-age children and adults. Contrary to the view that it results solely from deficits in processes specific to linguistic analysis, current research has shown that deficits in more basic auditory or visual skills may contribute to the reading difficulties of dyslexic individuals. These might also have a crucial role in the development of normal reading skills. Evidence for visual deficits in dyslexia is usually found only with dynamic and not static stimuli, implicating the magnocellular pathway or dorsal visual stream as the cellular locus responsible. Studies of such a dissociation between the processing of dynamic and static auditory stimuli have not been reported previously. RESULTS: We show that dyslexic individuals are less sensitive both to particular rates of auditory frequency modulation (2 Hz and 40 Hz but not 240 Hz) and to dynamic visual-motion stimuli. There were high correlations, for both dyslexic and normal readers, between their sensitivity to the dynamic auditory and visual stimuli. Nonword reading, a measure of phonological awareness believed crucial to reading development, was also found to be related to these sensory measures. CONCLUSIONS: These results further implicate neuronal mechanisms that are specialised for detecting stimulus timing and change as being dysfunctional in many dyslexic individuals. The dissociation observed in the performance of dyslexic individuals on different auditory tasks suggests a sub-modality division similar to that already described in the visual system. These dynamic tests may provide a non-linguistic means of identifying children at risk of reading failure.     

Size illusion, distance illusion, and terrestrial passage: Comment on Reed.

Comments on C. F. Reed's (see record 1985-29807-001) terrestrial-passage theory, in which it is assumed that the moon's failure to increase in visual subtense while elevating is accounted for strictly by perceptual distancing. This allows a formal account of the moon distance illusion, but at the expense of a compelling explanation of the moon size illusion. In order to explain the distance illusion, Reed also assumes that all objects, regardless of their perceived altitude, are perceived to start from a common point at the horizon. Several alternative applications of Reed's terrestrial-passage foundation to the actual illusions are suggested. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intracellular analysis of relations between the slow (< 1 Hz) neocortical oscillation and other sleep rhythms of the electroencephalogram

The newly described slow cortical rhythm (approximately 0.3 Hz), whose depolarizing-hyperpolarizing components are analyzed in the preceding article, is now investigated from the standpoint of its relations with delta (1-4 Hz) and spindle (7-14 Hz) rhythmicity. Regular-spiking and intrinsically bursting cortical neurons were mostly recorded from association suprasylvian areas 5 and 7; fewer neurons were also recorded from pericruciate motor and posterolateral visual areas. Although most cells were investigated under various anesthetics, a similar slow cortical rhythm was found in animals with brainstem transection at the low- or high-collicular levels. These cerveau isolé (isolated forebrain) preparations display the major sleep rhythms of the EEG in the absence of general anesthetics. In 38% of recorded cortical neurons (n = 105), the slow rhythm was combined with delta oscillation. Both cellular rhythms were phase locked to the slow and delta oscillations in the surface- and depth-recorded EEG. In a group of this cell sample (n = 47), delta activity occurred as stereotyped, clock-like action potentials during the interdepolarization lulls of the slow rhythm. In another neuronal subsample (n = 58), delta events were grouped in sequences superimposed upon the depolarizing envelope of the slow rhythm, with such sequences recurring rhythmically at approximately 0.3-0.4 Hz. The associations between the two cellular and EEG rhythms (1-4 Hz and 0.3-0.4 Hz) were quantified by means of autocorrelograms, cross-correlograms, and spike-triggered averages. In 26% of recorded neurons (n = 72), the slow rhythm was combined with spindle oscillations. Regular-spiking cortical neurons fully reflected the whole frequency range of thalamically generated spindles (7-14 Hz). However, during similar patterns of EEG spindling, intrinsically bursting cells fired grouped action potentials (with intraburst frequencies of 100-200 Hz) at only 2-4 Hz. The dependence of the slow cortical oscillation upon the thalamus was studied by lesions and stimulation. The slow rhythm survived extensive ipsilateral thalamic destruction by means of electrolytic lesions or kainate-induced loss of perikarya in thalamic nuclei that were input sources to the recorded cortical neurons. To further prevent the possibility of a thalamic role in the genesis of the slow rhythm, through the contralateral thalamocortical systems and callosal projections, we also transected the corpus callosum in thalamically lesioned animals, and still recorded the slow rhythm in cortical neurons. These data indicate that the thalamus is not essentially implicated in the genesis of the slow rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)