Brain activation difference evoked by different binocular disparities of stereograms: An fMRI study

The binocular disparity of two retina images is a main cue of stereoscopic vision. However, the global dependency between brain response and binocular disparity still remains unclear. Here, we used functional Magnetic Resonance Imaging (fMRI) to identify stereopsis-related brain regions with a modified Random Dot Stereogram (RDS) and plotted the activation variation curves under different disparity size. In order to eliminate the confounding shape difference between the stereogram and the plane, commonly seen in RDS, we modified the RDS to a checkerboard version. We found that V3A, V7 and MT+/V5 in dorsal visual stream were activated in stereoscopic experiment, while little activation was found in ventral visual regions. According to the activation trends, 13 subjects were divided into three groups: 5 subjects with turning points (a shift from increased to decreased activation), 5 subjects without turning points and 3 subjects with activation unrelated to disparity. We inferred that the dorsal visual stream primarily processes spatial depth information, rather than shape information.     

Visual fatigue evaluation of field sequential stereoscopic 3D display using near point distance

The purpose of this paper was to evaluate quantitatively visual fatigue encountered in viewing stereoscopic 3D television. By examining the difference in the visual function involved in watching 2D and stereoscopic 3D displays, we could extract only the effect on visual perception in stereoscopic 3D television. Since the visual fatigue with the 3D display may be caused by the discrepancy between convergence and accommodation, the near point distances were measured by an Accommodo Polyrecorder, where Landolt's ring was pursued with binocularity. Five subjects, all employees of NEC Corporation, participated in the experiment. All subjects had normal or corrected-to-normal vision. Two of the subjects watched a 3D video movie. After a week, they watched another video movie in 2D. The rest of them watched the movies in reverse order. One video movie viewing requires about 120 minutes. The near point distances were measured before and after watching for 30, 60, 90 and 120 minutes. The 3D television system used here is a 3D video disc system with field sequence using glasses with liquid crystal shutters. In the case of 2D, each subject wore the glasses whose shutters were kept open. In the experiment, instruction to watch the video movies in a relaxed posture was given. There was a significant effect in regard to 3D/2D treatments on the change rates of the near point distance measured after watching every 30 minutes to one before watching. In addition, the change rates in 3D watching after 60, 90 and 120 minutes were significantly increased, compared with the corresponding rates in 2D.(ABSTRACT TRUNCATED AT 250 WORDS)     

Anterior regions of monkey parietal cortex process visual 3D shape

The intraparietal cortex is involved in the control of visually guided actions, like reach-to-grasp movements, which require extracting the 3D shape and position of objects from 2D retinal images. Using fMRI in behaving monkeys, we investigated the role of the intraparietal cortex in processing stereoscopic information for recovering the depth structure and the position in depth of objects. We found that while several areas (CIP, LIP, and AIP on the lateral bank; PIP and MIP on the medial bank) are activated by stereoscopic stimuli, AIP and an adjoining portion of LIP are sensitive only to depth structure. Furthermore, only these two regions are sensitive to both the depth structure and the 2D shape of small objects. These results indicate that extracting 3D spatial information from stereo involves several intraparietal areas, among which AIP and anterior LIP are more specifically engaged in extracting the 3D shape of objects.     

Cortical regions activated after rapid eye movements during REM sleep

The present study investigated the cortical regions activated during rapid eye movement (REM) sleep by identifying the sources of electric currents of brain potentials related to rapid eye movements using low-resolution brain electromagnetic tomography (LORETA). The brain potentials measured were the lambda response (P1 and P2) during wakefulness and the lambda-like response (P1r and P2r) during REM sleep. Fifteen healthy university students participated in this study. During wakefulness, the sources of the electric current of the lambda response (P1 and P2) were estimated to be in the primary and secondary visual cortices (BA 17, 18). During REM sleep, the P1r has a source in a higher order visual area (precuneus; BA 7, 31) and P2r comes from the primary and secondary visual cortices (BA 17, 18). In addition, the density of electric current in the premotor and fronto-central regions including anterior cingulate gyrus was higher after rapid eye movements, which was a discriminative feature of REM sleep. The results of this study suggest that these activities that occur after rapid eye movements might underlie the generation of vivid visual images of dreaming.

     

Cerebral Asymmetry of fMRI-BOLD Responses to Visual Stimulation

Hemispheric asymmetry of a wide range of functions is a hallmark of the human brain. The visual system has traditionally been thought of as symmetrically distributed in the brain, but a growing body of evidence has challenged this view. Some highly specific visual tasks have been shown to depend on hemispheric specialization. However, the possible lateralization of cerebral responses to a simple checkerboard visual stimulation has not been a focus of previous studies. To investigate this, we performed two sessions of blood-oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) in 54 healthy subjects during stimulation with a black and white checkerboard visual stimulus. While carefully excluding possible non-physiological causes of left-to-right bias, we compared the activation of the left and the right cerebral hemispheres and related this to grey matter volume, handedness, age, gender, ocular dominance, interocular difference in visual acuity, as well as line-bisection performance. We found a general lateralization of cerebral activation towards the right hemisphere of early visual cortical areas and areas of higher-level visual processing, involved in visuospatial attention, especially in top-down (i.e., goal-oriented) attentional processing. This right hemisphere lateralization was partly, but not completely, explained by an increased grey matter volume in the right hemisphere of the early visual areas. Difference in activation of the superior parietal lobule was correlated with subject age, suggesting a shift towards the left hemisphere with increasing age. Our findings suggest a right-hemispheric dominance of these areas, which could lend support to the generally observed leftward visual attentional bias and to the left hemifield advantage for some visual perception tasks.     

Asymmetrical activation in the human brain during processing of fearful faces

Traditional split-field studies and patient research indicate a privileged role for the right hemisphere in emotional processing [1-7], but there has been little direct fMRI evidence for this, despite many studies on emotional-face processing [8-10](see Supplemental Background). With fMRI, we addressed differential hemispheric processing of fearful versus neutral faces by presenting subjects with faces bilaterally [11-13]and orthogonally manipulating whether each hemifield showed a fearful or neutral expression prior to presentation of a checkerboard target. Target discrimination in the left visual field was more accurate after a fearful face was presented there. Event-related fMRI showed right-lateralized brain activations for fearful minus neutral left-hemifield faces in right visual areas, as well as more activity in the right than in the left amygdala. These activations occurred regardless of the type of right-hemifield face shown concurrently, concordant with the behavioral effect. No analogous behavioral or fMRI effects were observed for fearful faces in the right visual field (left hemisphere). The amygdala showed enhanced functional coupling with right-middle and anterior-fusiform areas in the context of a left-hemifield fearful face. These data provide behavioral and fMRI evidence for right-lateralized emotional processing during bilateral stimulation involving enhanced coupling of the amygdala and right-hemispheric extrastriate cortex.     

Stereopsis activates V3A and caudal intraparietal areas in macaques and humans

Stereopsis, the perception of depth from small differences between the images in the two eyes, provides a rich model for investigating the cortical construction of surfaces and space. Although disparity-tuned cells have been found in a large number of areas in macaque visual cortex, stereoscopic processing in these areas has never been systematically compared using the same stimuli and analysis methods. In order to examine the global architecture of stereoscopic processing in primate visual cortex, we studied fMRI activity in alert, fixating human and macaque subjects. In macaques, we found strongest activation to near/far compared to zero disparity in areas V3, V3A, and CIPS. In humans, we found strongest activation to the same stimuli in areas V3A, V7, the V4d topolog (V4d-topo), and a caudal parietal disparity region (CPDR). Thus, in both primate species a small cluster of areas at the parieto-occipital junction appears to be specialized for stereopsis.     

Localization of human brain areas activated for chaotic and ordered pattern perception

The aim of our work was to localize cortical areas involved in the processing of incomplete figures using functional MRI (fMRI) for 8 healthy volunteers (18-30 year old) with the did of anatomical and fMRI fast imaging technique: echo planar imaging (EPI), whole brain scan (36 slices) matrix 64 x 64, 3.7 second. We used 1.5 T MR-scanner and BOLD-method (Blood Oxygenation Level Dependent), based on distinctions of magnetic properties of hemoglobin. Fast imaging technique on modern MR-scanners with > or = 1.5 T provides precise statistical maps of oxygenation increase with high spatial resolution. For test stimuli we used matrix of Gabor grating. We used two types of 10 x 10 matrices with chaotic and ordered orientation of Gabor gratings. The size, brightness and contrast of the stimuli were identical. The chaotic and ordered patterns activated different brain areas. We establish that ordered patterns activated only primary visual cortex - V1 and V2, (BA17-18), wheareas chaotic patterns activated in addition primary visual cortex, the V3,V4,V5 (BA19) of the occipital cortex and the area 7 of parietal area (BA7) classification. Decision making for that task is localized in prefrontal and frontal cortex, including (BA 6, 9, 10).     

Functional magnetic resonance study of deliberate deception

The goal of the study was analysis of the cerebral mechanisms of deliberate deception. The eventrelated functional magnetic resonance (ER fMRI) imaging technique was used to assess the changes in the functional brain activity by means of recording the blood oxygen level-dependent (BOLD) signal. Twelve right-handed healthy volunteers aged 19–44 years participated in the study. The BOLD images were obtained during three experimental trials: deliberate deception, manipulative honest and control truthful trials (catch trials). The deliberate deception and manipulative honest actions were characterized by a BOLD signal increase in the anterior cingulate (Brodmann’s area (BA) 32), frontal (BAs 9/10, 6), and parietal (BA 40) cortices as compared with a truthful response. Comparison of the ER fMRI data with the results of earlier studies where event-related potentials (ERPs) were recorded under similar conditions indicates the involvement of the brain mechanism of error detection in deliberate deception.     

Activation of brain structures by fMRI data when viewing the video clips and recall of shown actions

In 10 healthy volunteers, brain tomograms were recorded using an fMRI scanner with a 3T-field magnet. Emotionally neutral and emotionally involving videos were used for stimulation. Registration consisted of seven series: two series of viewing a fixation point and two kinds of video clips, one series of viewing of a succession of two types of video clips, two series of watching videos with subsequent recall, and two series of viewing the fixation point followed by recall of content online. Viewing content online caused the greatest degree of metabolism increase localized in the visual cortex. This activation was more pronounced during the presentation of an emotionally involving video clip. In addition to the occipital lobe, it actively involved the temporal, parietal and, to a lesser extent, the frontal cortex. Activation of the motor cortex was detected only in some subjects. The "interference" effect in which the increase in metabolism was minimal was observed during a consequent demonstration of video-clips. Immediate recall of video-clips after viewing caused the greatest activation of the posterior frontal and motor cortex. Delayed recall activated mostly the anterior frontal cortex. There was a decrease of metabolism in the visual cortex during the recall. The greatest reduction in the visual cortex was observed during immediate recall. Immediate and delayed recall activated the structures associated with the maintenance of consciousness, memory and a system of mirror neurons.     

Effects of cortical damage on binocular depth perception

Stereoscopic depth perception requires considerable neural computation, including the initial correspondence of the two retinal images, comparison across the local regions of the visual field and integration with other cues to depth. The most common cause for loss of stereoscopic vision is amblyopia, in which one eye has failed to form an adequate input to the visual cortex, usually due to strabismus (deviating eye) or anisometropia. However, the significant cortical processing required to produce the percept of depth means that, even when the retinal input is intact from both eyes, brain damage or dysfunction can interfere with stereoscopic vision. In this review, I examine the evidence for impairment of binocular vision and depth perception that can result from insults to the brain, including both discrete damage, temporal lobectomy and more systemic diseases such as posterior cortical atrophy.This article is part of the themed issue ‘Vision in our three-dimensional world’.     

Changes in auditory evoked brain potentials during ultra-low frequency whole-body vibration of man or of his visual surround

Auditory evoked brain potentials (AEP) were recorded from nine healthy male subjects during three types of condition: A - subject and visual field stationary; B - subject vibrated (z-axis, 0.6 Hz, 1.85 ms-2 rms), visual field stationary; C - subject stationary, visual field vibrated (as for B). The visual surround was confined to a checkerboard pattern in front of the subject. Auditory stimuli (1000 Hz, 86 dB, interstimulus interval 7 s) were delivered via headphones to evoke AEP. Vibration-synchronous activity in the EEG was eliminated by a subtraction technique. In comparison with condition A, conditions B and C caused an attenuation of P2 and N1P2 components of AEP together with an increased latency of N1. Effects of conditions B and C did not differ. Direct vestibular stimulation and mechanisms specific for whole-body vibration were rejected as modes of action. The AEP-changes and the subjective evaluation of experimental conditions, arousal and performance, as well as symptoms of kinetosis (motion sickness) suggest a sensory mismatch, leading to a "latent kinetosis" with de-arousal, as the dominating mechanism by which the processing of information was affected. This suggestion was supported by an additional pilot study. Under real working conditions a similar effect can be expected during relative motion between the driver and his visual surround, i.e. even with perfect vibro-isolation of the driver's seat.     

Figure and ground in the visual cortex: v2 combines stereoscopic cues with gestalt rules

Figure-ground organization is a process by which the visual system identifies some image regions as foreground and others as background, inferring 3D layout from 2D displays. A recent study reported that edge responses of neurons in area V2 are selective for side-of-figure, suggesting that figure-ground organization is encoded in the contour signals (border ownership coding). Here, we show that area V2 combines two strategies of computation, one that exploits binocular stereoscopic information for the definition of local depth order, and another that exploits the global configuration of contours (Gestalt factors). These are combined in single neurons so that the "near" side of the preferred 3D edge generally coincides with the preferred side-of-figure in 2D displays. Thus, area V2 represents the borders of 2D figures as edges of surfaces, as if the figures were objects in 3D space. Even in 3D displays, Gestalt factors influence the responses and can enhance or null the stereoscopic depth information.     

Cerebral Inefficient Activation in Schizophrenia Patients and Their Unaffected Parents during the N-Back Working Memory Task: A Family fMRI Study

Background

It has been suggested that working memory deficits is a core feature of symptomatology of schizophrenia, which can be detected in patients and their unaffected relatives. The impairment of working memory has been found related to the abnormal activity of human brain regions in many functional magnetic resonance imaging (fMRI) studies. This study investigated how brain region activation was altered in schizophrenia and how it was inherited independently from performance deficits.

Method

The authors used fMRI method during N-back task to assess working memory related cortical activation in four groups (N = 20 in each group, matching task performance, age, gender and education): schizophrenic patients, their unaffected biological parents, young healthy controls for the patients and older healthy controls for their parents.

Results

Compared to healthy controls, patients showed an exaggerated response in the right dorsolateral prefrontal cortex (brodmann area [BA] 46) and bilateral ventrolateral prefrontal cortex, and had reduced activation in bilateral dorsolateral prefrontal cortex (BA 9). In the conjunction analysis, the effect of genetic risk (parents versus older control) shared significantly overlapped activation with effect of disease (patients versus young control) in the right middle frontal gyrus (BA 46) and left inferior parietal gyrus (BA 40).

Conclusions

Physiological inefficiency of dorsal prefrontal cortex and compensation involvement of ventral prefrontal cortex in working memory function may one physiological characteristics of schizophrenia. And relatively inefficient activation in dorsolateral prefrontal cortex probably can be a promising intermediate phenotype for schizophrenia.     

Sequential neural processes in abacus mental addition: an EEG and FMRI case study

Abacus experts are able to mentally calculate multi-digit numbers rapidly. Some behavioral and neuroimaging studies have suggested a visuospatial and visuomotor strategy during abacus mental calculation. However, no study up to now has attempted to dissociate temporally the visuospatial neural process from the visuomotor neural process during abacus mental calculation. In the present study, an abacus expert performed the mental addition tasks (8-digit and 4-digit addends presented in visual or auditory modes) swiftly and accurately. The 100% correct rates in this expert's task performance were significantly higher than those of ordinary subjects performing 1-digit and 2-digit addition tasks. ERPs, EEG source localizations, and fMRI results taken together suggested visuospatial and visuomotor processes were sequentially arranged during the abacus mental addition with visual addends and could be dissociated from each other temporally. The visuospatial transformation of the numbers, in which the superior parietal lobule was most likely involved, might occur first (around 380 ms) after the onset of the stimuli. The visuomotor processing, in which the superior/middle frontal gyri were most likely involved, might occur later (around 440 ms). Meanwhile, fMRI results suggested that neural networks involved in the abacus mental addition with auditory stimuli were similar to those in the visual abacus mental addition. The most prominently activated brain areas in both conditions included the bilateral superior parietal lobules (BA 7) and bilateral middle frontal gyri (BA 6). These results suggest a supra-modal brain network in abacus mental addition, which may develop from normal mental calculation networks.     

Neural correlates of individual performance differences in resolving perceptual conflict

Attentional mechanisms are a crucial prerequisite to organize behavior. Most situations may be characterized by a 'competition' between salient, but irrelevant stimuli and less salient, relevant stimuli. In such situations top-down and bottom-up mechanisms interact with each other. In the present fMRI study, we examined how interindividual differences in resolving situations of perceptual conflict are reflected in brain networks mediating attentional selection. Doing so, we employed a change detection task in which subjects had to detect luminance changes in the presence and absence of competing distractors. The results show that good performers presented increased activation in the orbitofrontal cortex (BA 11), anterior cingulate (BA 25), inferior parietal lobule (BA 40) and visual areas V2 and V3 but decreased activation in BA 39. This suggests that areas mediating top-down attentional control are stronger activated in this group. Increased activity in visual areas reflects distinct neuronal enhancement relating to selective attentional mechanisms in order to solve the perceptual conflict. Opposed to good performers, brain areas activated by poor performers comprised the left inferior parietal lobule (BA 39) and fronto-parietal and visual regions were continuously deactivated, suggesting that poor performers perceive stronger conflict than good performers. Moreover, the suppression of neural activation in visual areas might indicate a strategy of poor performers to inhibit the processing of the irrelevant non-target feature. These results indicate that high sensitivity in perceptual areas and increased attentional control led to less conflict in stimulus processing and consequently to higher performance in competitive attentional selection.     

The human brain from above: an increase in complexity from environmental stimuli to abstractions

Contrary to common belief, the brain appears to increase the complexity from the perceived object to the idea of it. Topological models predict indeed that: (a) increases in anatomical/functional dimensions and symmetries occur in the transition from the environment to the higher activities of the brain, and (b) informational entropy in the primary sensory areas is lower than in the higher associative ones. To demonstrate this novel hypothesis, we introduce a straightforward approach to measuring island information levels in fMRI neuroimages, via Rényi entropy derived from tessellated fMRI images. This approach facilitates objective detection of entropy and corresponding information levels in zones of fMRI images generally not taken into account. We found that the Rényi entropy is higher in associative cortices than in the visual primary ones. This suggests that the brain lies in dimensions higher than the environment and that it does not concentrate, but rather dilutes messages coming from external inputs.     

Illusions of Visual Motion Elicited by Electrical Stimulation of Human MT Complex

Human cortical area MT⁺ (hMT⁺) is known to respond to visual motion stimuli, but its causal role in the conscious experience of motion remains largely unexplored. Studies in non-human primates demonstrate that altering activity in area MT can influence motion perception judgments, but animal studies are inherently limited in assessing subjective conscious experience. In the current study, we use functional magnetic resonance imaging (fMRI), intracranial electrocorticography (ECoG), and electrical brain stimulation (EBS) in three patients implanted with intracranial electrodes to address the role of area hMT⁺ in conscious visual motion perception. We show that in conscious human subjects, reproducible illusory motion can be elicited by electrical stimulation of hMT⁺. These visual motion percepts only occurred when the site of stimulation overlapped directly with the region of the brain that had increased fMRI and electrophysiological activity during moving compared to static visual stimuli in the same individual subjects. Electrical stimulation in neighboring regions failed to produce illusory motion. Our study provides evidence for the sufficient causal link between the hMT⁺ network and the human conscious experience of visual motion. It also suggests a clear spatial relationship between fMRI signal and ECoG activity in the human brain.