不同相干水平视觉运动刺激皮层反应特征的fMRI研究

目的探讨随机点动态运动图作为刺激源是否能够对参与视觉运动觉处理的大脑皮层区域进行准确的功能定位,并在此基础上进一步观测在不同运动相干水平情况下,相关大脑皮层的血氧水平依赖反应特点。方法12名受试者在功能磁共振扫描过程中接受三种不同相干水平的视觉运动刺激(5%,20%,80%),刺激呈现采用组块设计模式。数据经预处理和统计分析得到激活图,并进一步进行兴趣区分析。结果随机点动态运动图作为刺激源能够有效的激活视觉运动觉处理相关视觉皮层区域;以hMT 作兴趣区分析得到三种不同相干水平运动刺激下该区域的激活体积。结论随机点动态运动图刺激能对参与视觉运动觉处理的大脑皮层区域进行准确的功能定位;hMT 的激活体积随着相干水平的提高而减小。     

单眼散光弱视儿童对比敏感度的研究

目的：分析探讨单眼散光弱视患儿对比敏感度（CS）视功能的受损特点。方法：对正常儿童组36例、单眼散光弱视组34例、单眼非散光弱视组33例,共103例,用静态F.A.C.T图表和计算机Gabor斑CS检查程序分别检查患儿对侧眼、弱视眼及90°和180°两主子午线方向上的对比敏感度。结果：①单眼散光弱视组和单眼非散光弱视组的对侧眼、弱视眼的CS值在所有空间频率均较正常组的CS降低（P〈0.05）,表现为中、高空间频率区CS的明显受损（P〈0.01）。②单眼散光弱视组的弱视眼在90°和180°两主子午线方向上的对比敏感度有显著差异（P〈0.01）。结论：弱视儿童的对侧眼不正常。用计算机Gabor斑检查可以了解弱视散光儿童不同子午线上的CS存在的差异,明确定位弱子午线,并可以针对子午线性弱视,进一步开展知觉学习的治疗。     

The responsiveness of biological motion processing areas to selective attention towards goals

A growing literature indicates that visual cortex areas viewed as primarily responsive to exogenous stimuli are susceptible to top-down modulation by selective attention. The present study examines whether brain areas involved in biological motion perception are among these areas-particularly with respect to selective attention towards human movement goals. Fifteen participants completed a point-light biological motion study following a two-by-two factorial design, with one factor representing an exogenous manipulation of human movement goals (goal-directed versus random movement), and the other an endogenous manipulation (a goal identification task versus an ancillary color-change task). Both manipulations yielded increased activation in the human homologue of motion-sensitive area MT+ (hMT+) as well as the extrastriate body area (EBA). The endogenous manipulation was associated with increased right posterior superior temporal sulcus (STS) activation, whereas the exogenous manipulation was associated with increased activation in left posterior STS. Selective attention towards goals activated a portion of left hMT+/EBA only during the perception of purposeful movement-consistent with emerging theories associating this area with the matching of visual motion input to known goal-directed actions. The overall pattern of results indicates that attention towards the goals of human movement activates biological motion areas. Ultimately, selective attention may explain why some studies examining biological motion show activation in hMT+ and EBA, even when using control stimuli with comparable motion properties.     

Occipitotemporal activity elicited by viewing eye movements: a magnetoencephalographic study

The temporal and spatial processing of viewing eye movements was studied by magnetoencephalography (MEG) in six normal subjects. Three visual stimulus types were studied: (1) moving eyes (EYES), (2) moving simulated eyes (SIM), consisting of checks moving in the same spatial location as EYES, and (3) an inwardly moving radial pattern (RADIAL). A large clear MEG component, 1M, with mean peak latency of approximately 170 ms, was seen in the right hemisphere to RADIAL and EYES in all six subjects. The 1M to EYES was significantly longer in latency and smaller in amplitude than that seen to RADIAL. A left hemisphere 1M to EYES and RADIAL was seen in three of six subjects. In all subjects and both hemispheres the equivalent current dipoles (ECD) for EYES and RADIAL were located near the occipitotemporal border, the MT/V5 homologue in humans. The ECD to EYES was significantly more posterior and inferior than that to RADIAL, with a calculated significant separation distance of around 1 cm. No ECD was estimated in the fusiform gyrus, a structure that plays a main role in static face perception. Although the 1M was detected in SIM in all six subjects, our criteria for a reliable ECD could only be satisfied in only one subject. Our results suggest that the cortex of human MT/V5 and its surrounds is active both in the perception of eye motion and motion in general, particularly in the right hemisphere. The areas responsive to eye motion were separable from those responsive to radial motion. These data suggest that there may be specialization within regions of human cortex previously thought to be sensitive to motion in general.     

Imagery of a moving object: The role of occipital cortex and human MT/V5+

Visual imagery – similar to visual perception – activates feature-specific and category-specific visual areas. This is frequently observed in experiments where the instruction is to imagine stimuli that have been shown immediately before the imagery task. Hence, feature-specific activation could be related to the short-term memory retrieval of previously presented sensory information.Here, we investigated mental imagery of stimuli that subjects had not seen before, eliminating the effects of short-term memory. We recorded brain activation using fMRI while subjects performed a behaviourally controlled guided imagery task in predefined retinotopic coordinates to optimize sensitivity in early visual areas.Whole brain analyses revealed activation in a parieto-frontal network and lateral–occipital cortex. Region of interest (ROI) based analyses showed activation in left hMT/V5+. Granger causality mapping taking left hMT/V5+ as source revealed an imagery-specific directed influence from the left inferior parietal lobule (IPL). Interestingly, we observed a negative BOLD response in V1–3 during imagery, modulated by the retinotopic location of the imagined motion trace.Our results indicate that rule-based motion imagery can activate higher-order visual areas involved in motion perception, with a role for top-down directed influences originating in IPL. Lower-order visual areas (V1, V2 and V3) were down-regulated during this type of imagery, possibly reflecting inhibition to avoid visual input from interfering with the imagery construction. This suggests that the activation in early visual areas observed in previous studies might be related to short- or long-term memory retrieval of specific sensory experiences.     

视知觉学习疗法治疗学龄前儿童屈光不正性弱视的效果

目的探讨视知觉学习疗法治疗学龄前屈光不正性弱视的效果。方法选取3—8岁屈光不正性弱视患儿611名1177眼,给予视知觉学习疗法治疗,比较治疗前后患儿视力情况。结果611例1177眼戴镜视力由治疗前的（0．34±0．23）提高到（0．81±0．15）,差异有统计学意义（t=5．63,P〈0．05）。视力提高2行及以上的眼数为1040只,占总眼数的88．4％。结论视知觉学习治疗是一种安全、有效的治疗学龄前屈光不正性弱视的新方法,在患儿进行视知觉学习训练治疗时给予个性化的护理措施,能提高患儿的治疗依从性和生活质量。     

Neural correlates of spontaneous direction reversals in ambiguous apparent visual motion

Looking at bistable visual stimuli, the observer experiences striking transitions between two competing percepts while the physical stimulus remains the same. Using functional imaging techniques, it is therefore possible to isolate neural correlates of perceptual changes that are independent of the low-level aspects of the stimulus. Previous experiments have demonstrated distributed activations in human extrastriate visual cortex related to switches between competing percepts. Here we asked where extrastriate responses still occur with a bistable stimulus that minimizes the cognitive difference between the two percepts. We used the "spinning wheel illusion," a bistable apparent motion stimulus of which both possible percepts correspond to the same object, share the same center, and are perceived as identically patterned stimuli moving at the same speed and changing only in direction. Using functional magnetic resonance imaging, we analyzed the spatial distribution of event-related activations occurring during spontaneous reversals of perceived direction of motion. In accordance with earlier neuroimaging findings for bistable percepts, we observed event-related activations in several frontal and parietal areas, including the superior parietal cortex bilaterally, the right inferior parietal cortex, and the premotor and inferior frontal cortex of both hemispheres. Furthermore, we found bilateral activations in the occipitotemporal junction (hMT+/V5) and in the lateral occipital sulcus ("KO") posterior to hMT+/V5, but not in areas of the "ventral stream" of cortical visual processing. Our data suggest that, while a frontoparietal network subserves more general aspects in bistable visual perception, the activations in functionally specialized extrastriate visual cortex are highly category- or attribute-specific.     

Bistable illusory rebound motion: Event-related functional magnetic resonance imaging of perceptual states and switches

The neural correlates of a recently discovered visual illusion that we call 'illusory rebound motion' (IRM) are described. This illusion is remarkable because motion is perceived in the absence of any net motion energy in the stimulus. When viewing bars alternating between white and black on a gray background, the percept alternates between one of flashing bars (veridical) and the IRM illusion, where the bars appear to shoot back and forth rather like the opening and closing of a zipper. The event-related functional magnetic resonance imaging (fMRI) data reported here reveal that (1) the blood-oxygen-level-dependent (BOLD) signal in the human analog of macaque motion processing area MT (hMT+) increases when there is a perceptual change from "no-IRM" to "see-IRM" and decreases when there is a perceptual change from "see-IRM" to "no-IRM," although the stimulus remains constant; and (2) the BOLD signal in early retinotopic areas (V1, V2, and V3d) shows switch-related activation whenever there is a perceptual change, regardless whether from IRM to no-IRM or vice versa. We conclude that hMT+ is a neural correlate of this novel illusory motion percept because BOLD signal in hMT+ modulates with the perception of IRM.     

Cortical activation during perception of a rotating wide-field acoustic stimulus.

We describe sound stimuli that produce the perception of complete rotation around the head. Such stimuli are analogous to wide-field motion stimuli used in visual research, though auditory stimuli, unlike visual stimuli, can be perceived at any point around the head; they are the only cues for spatial perception behind the subject. Using PET on six subjects, we have compared regional brain activity during the perception of such motion stimuli, with the perception of a control stimulus producing equivalent amplitude changes without rotation. Rotation produced activation of the premotor cortex bilaterally and the right superior parietal cortex. The premotor activation involved the frontal eye fields and ventral premotor areas. The bifrontal and right parietal activation is consistent with previous demonstrations of activation within a frontoparietal network of areas during perception of a linear motion stimulus. The inferior premotor activation in this experiment may reflect preparation for head turning in response to auditory targets that cannot be tracked visually.     

Selective fovea-related deprived activation in retinotopic and high-order visual cortex of human amblyopes

Amblyopia is a visual disorder starting at early childhood and characterized by reduced visual acuity not of optical origin or due to any eye disease. One expression of such an anomalous early visual experience is abnormal foveal vision. In a previous fMRI study, faces that were presented to amblyopic eyes evoked little response compared to houses in high-order visual areas. Patients also demonstrated reduced recognition of facial expression, raising the possibility that these face-selective abnormalities are related to foveal vision deficit. Whether this deficit originates in low-level processing or is mediated by compromised activation in high-order visual areas is unresolved. In the present functional magnetic resonance imaging (fMRI) study, we explored the impact of amblyopia on the representation of object images presented in foveally biased central versus peripheral retinotopic eccentricities through manipulation of object size. Small and large pictures were correlated to visual acuities of 6/6 and 6/60, respectively. In low-level visual areas, the amblyopic eye showed significantly reduced activation for centrally placed, small pictures than the sound eye, while activation to large pictures was only slightly reduced. Similarly, in high-order visual areas, the amblyopic eye showed marked reduction in activation in the fusiform gyrus, with normal activation in the collateral sulcus. The center/periphery size-related amblyopic outcomes of this study support a "bottom-up" nature of the center-periphery effect observed in high-order visual areas. Taken together, these findings point to the regional extent and functional selectivity of fovea-related cortical reorganization that is related to abnormal visual development of one eye.     

Extra-classical receptive field effects measured in striate cortex with fMRI

The aim of this study was to measure the contextual influence of globally coherent motion on visual cortical responses using functional magnetic resonance imaging. Our motivation was to test a prediction from representational theories of perception (i.e. predictive coding) that primary visual responses should be suppressed by top-down influences during coherent motion. We used a sparse stimulus array such that each element could not fall within the same classical receptive field of primary visual cortex neurons (i.e. precluding lateral interactions within V1). This enabled us to attribute differences, in striate cortex responses, to extra-classical receptive field effects mediated by backward connections. In accord with theoretical predictions we were able to demonstrate suppression of striate cortex activations to coherent relative to incoherent motion. These results suggest that suppression of primary visual cortex responses to coherent motion reflect extra-classical effects mediated by backward connections.     

Neuromagnetic activity in medial parietooccipital cortex reflects the perception of visual motion during eye movements

We usually perceive a stationary, stable world despite coherent visual motion induced by eye movements. This astonishing example of perceptual invariance results from a comparison of visual information with internal reference signals (nonretinal signals) predicting the visual consequences of an eye movement. The important consequence of this concept is that our subjective percept of visual motion reflects the outcome of this comparison rather than retinal image slip. To localize the cortical networks underlying this comparison, we compared magnetoencephalography (MEG) responses under two conditions of pursuit-induced retinal image motion, which were identical physically but--due to different calibrational states of the nonretinal signal prompted under our experimental conditions--gave rise to different percepts of visual motion. This approach allows us to demonstrate that our perception of self-induced visual motion resides in comparably "late" parts of the cortical hierarchy of motion processing sparing the early stages up to cortical area MT/V5 but including cortex in and around the medial aspect of the parietooccipital cortex as one of its core elements.     

Integration of multiple motion vectors over space: an fMRI study of transparent motion perception

Visual scenes are frequently composed of objects that move in different directions. To segment such scenes into distinct objects or image planes, local motion cues have to be evaluated and integrated according to criteria of global coherence. When several populations of coherently moving random dots penetrate each other, the visual system tends to assign them to different planes-perceived as transparent motion. This process of integration was studied by changing the angle of motion trajectories with which groups of dots penetrate each other or by varying the spatial constellation of dots moving in opponent directions. Psychophysical testing revealed that stimuli providing almost identical local motion cues could be perceived in three very different ways: (1) as a matrix of stationary flickering dots, (2) as a single surface of coherently moving dots, and (3) as two transparent dot matrices moving in different directions. Behaviorally controlled functional magnetic resonance imaging (fMRI) was used to identify brain regions that contribute to the integration of local motion cues into coherently moving surfaces. Activation of the human motion complex (hMT+/V5) and of areas in the fusiform gyrus (FG) as well as in the intraparietal sulcus (IPS-occ) was correlated with the perception of coherent motion and especially hMT+/V5 took a central role in differentiating transparent motion from single-surface coherent motion.     

低频振幅算法功能磁共振成像观察屈光参差性弱视患者脑活动

目的 应用基于低频振幅(ALFF)算法的功能磁共振成像(fMRI)观察屈光参差性弱视患者脑活动的变化。方法 对9例左眼单眼屈光参差性弱视患者(弱视组)和12名健康志愿者(对照组)在黑白棋盘格刺激下行fMRI,应用t检验对ALFF脑图进行组间和组内统计学分析。结果 1例弱视组患者数据在预处理后被剔除。左眼接受刺激时,弱视组较对照组左侧舌回、右侧枕中回、右侧中央前回、左侧后扣带回、左侧顶上小叶、左侧楔前叶和楔叶等区域ALFF减弱,左侧额中间回、左侧额上回、左侧颞上回、右侧杏仁体和右侧壳核等区域ALFF显著增强;右眼接受刺激时,弱视组较对照组胼胝体和左侧颞中回ALFF减弱,双侧枕叶、右侧额中回和右侧尾状核等区域ALFF显著增强。弱视组中,与右眼接受视觉刺激时比较,左眼接受视觉刺激时右侧额下回、左侧尾状核、丘脑及前扣带回等脑区ALFF显著增强,双侧枕叶ALFF显著减弱。结论 任务状态下基于ALFF算法的fMRI不仅可反映弱视患者视皮层的功能损害,还可反映多脑区神经活动的变化。     

Altered motion perception in migraineurs: evidence for interictal cortical hyperexcitability

Much research on visual functions in migraine has pinpointed the existence of abnormal visual processing between attacks. However, it is not clear if this is due to cortical hyper- or hypoexcitability. We aimed to clarify this issue by comparing motion perception thresholds of subjects with migraine with (MA) or without aura (MoA) and control subjects. Two types of dot kinetograms were used: in the first experiment coherently moving dots were presented in an incoherent environment, while in the second only coherent motion was seen. Subjects with migraine displayed significantly impaired motion perception compared with controls when they had to detect the direction of the coherently moving dots in an incoherent environment, while they were slightly better in a direction discrimination task, where only coherent motion was presented. This pattern of results is comparable to those achieved by an external excitability enhancement of V5 induced in healthy human subjects in a former study of our group. According to this, a cortical excitability enhancement can result in an impaired focusing on a given signal against a noisy background, but improves perception of non-ambiguous stimuli. Thus we conclude that migraineurs display enhanced visual cortical excitability between attacks in V5.     

Evidence of a direct influence between the thalamus and hMT+ independent of V1 in the human brain as measured by fMRI

In the present study we employed Conditional Granger Causality (CGC) and Coherence analysis to investigate whether visual motion-related information reaches the human middle temporal complex (hMT+) directly from the Lateral Geniculate Nucleus (LGN) of the thalamus, by-passing the primary visual cortex (V1). Ten healthy human volunteers underwent brain scan examinations by functional magnetic resonance imaging (fMRI) during two optic flow experiments. In addition to the classical LGN-V1-hMT+ pathway, our results showed a significant direct influence of the blood oxygenation level dependent (BOLD) signal recorded in LGN over that in hMT+, not mediated by V1 activity, which strongly supports the existence of a bilateral pathway that connects LGN directly to hMT+ and serves visual motion processing. Furthermore, we evaluated the relative latencies among areas functionally connected in the processing of visual motion. Using LGN as a reference region, hMT+ exhibited a statistically significant earlier peak of activation as compared to V1. In conclusion, our findings suggest the co-existence of an alternative route that directly links LGN to hMT+, bypassing V1. This direct pathway may play a significant functional role for the faster detection of motion and may contribute to explain persistence of unconscious motion detection in individuals with severe destruction of primary visual cortex (blindsight).     

Pattern-motion selectivity in the human pulvinar

On the basis of anatomical and physiological data obtained on animal models, we recently proposed that neurons in the main visual extrageniculate nuclei complex, the pulvinar, are actively involved in higher-order visual processing. Pulvinar neurons have been shown to integrate the component signals of a plaid pattern into a coherent global percept (pattern-motion selectivity). Using positron emission tomography (PET), we have investigated the possibility that the human pulvinar is also involved in plaid-defined higher-order motion integration. Plaid patterns were presented to normal observers in two conditions (coherent vs. transparent) created by varying the relative spatial frequency of the two gratings comprising the plaid. Regions of interest analysis revealed a significant activation of the pulvinar in the coherent condition supporting the notion that the human pulvinar nucleus is involved in higher-order motion processing. Plaid pattern activation was also observed in the medial temporal gyrus (area MT/V5), a motion area with strong anatomical connections to the pulvinar. These data provide the first direct evidence that the human pulvinar is involved in complex motion integration, as previously shown in animal models, and further support the existence of cortico-thalamo-cortical computational networks involved in higher-order visual processing.     

The temporal characteristics of motion processing in hMT/V5+: combining fMRI and neuronavigated TMS

Functional imaging has demonstrated the specific involvement of the human middle-temporal complex (hMT/V5+) during processing of moving stimuli. Some studies applied transcranial magnetic stimulation (TMS) to investigate the causal relevance of hMT/V5+ for motion perception. Although the studies used similar visual stimuli and TMS parameters, the critical time point of functionally relevant hMT/V5+ activity differed by 100 ms and more. The present study aimed to elucidate further the temporal characteristics of motion processing in hMT/V5+ by investigating all critical time windows currently debated in the literature. In contrast to previous studies, we used TMS neuronavigation based on individual fMRI results of five participants to target hMT/V5+, applying single-pulse TMS at 24 different time windows (-50 till +200 ms relative to stimulus onset). We revealed that TMS significantly impaired motion perception when applied over hMT/V5+ at 40 to 30 ms before as well as 130 to 150 ms after onset of the moving stimuli. While the late effective time window conforms to results from previous experiments, we did not find evidence for an early time window around 0 ms that has been reported in other studies. Our neuronavigation approach enabled us to quantify the interindividual variance in the exact location of hMT/V5+ and the respective TMS target position on the skull of the participants. Considering that shifting the TMS coil position only by a few millimeters can already lead to a complete loss of TMS effects, our study clearly demonstrates the utility of neuronavigated TMS when investigating specific neuronal effects as in the case of motion processing.     

Neural changes associated with speech learning in deaf children following cochlear implantation

Brain plasticity was investigated, which underlies the gaining of auditory sensory and/or auditory language in deaf children with an early onset deafness after cochlear implantation (CI) surgery. This study examined both the glucose metabolism of the brain and the auditory speech learning using 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and the Central Institute of Deaf (CID) test, respectively, both before and after the CI surgery. In a within analysis comparing the pre-CI and the post-CI PET results, CI itself resulted in an increase in the glucose metabolism in the medial visual cortex, the bilateral thalamus, and the posterior cingulate. Compared with the normal hearing controls, the brain activity of the deaf children was greater in the medial visual cortex and bilateral occipito-parietal junctions after the CI. The better speech perception ability was associated with increases in activity in the higher visual areas such as middle occipito-temporal junction (hMT/V5) and posterior inferior temporal region (BA 21/37) in the left hemisphere and associated with decreases in activity in the right inferior parieto-dorsal prefrontal region. These findings suggest that the speech learning resulted in a greater demand of the visual and visuospatial processings subserved by the early visual cortex and parietal cortices. However, only those deaf children who successfully learned the auditory language after CI used more visual motion perception for mouth movement in the left hMT/V5 region and less somatosensory function in the right parieto-frontal region.     

Dorsal stream development in motion and structure-from-motion perception

Little is known about the neural development underlying high order visual perception. For example, in detection of structures by coherently moving dots, motion information must interact with shape-based information to enable object recognition. Tasks involving these different motion-based discriminations are known to activate distinct specialized brain areas in adults. Here, we investigate neural development of normally developing children using functional magnetic resonance imaging (fMRI) during perception of randomly moving point-light dots (RM), coherently moving dots that formed a 3D rotating object (SFM) and static dots. Perception of RM enhanced neural activity as compared with static dots in motion processing-related visual areas, including visual area 3a (V3a), and middle temporal area (hMT+) in 10 adults (age 20-30 years). Children (age 5-6 years) showed less pronounced activity in area V3a than adults. Perception of SFM induced enhanced neural activity as compared to RM in adults in the left parietal shape area (PSA), whereas children increased neural activity within dorsal (V3a) and ventral brain areas (lingual gyrus) of the occipital cortex. These findings provide evidence of neural development within the dorsal pathway. First, maturation was associated with enhanced activity in specialized areas within the dorsal pathway during RM perception (V3a) and SFM perception (PSA). Secondly, high order visual perception-related neural development was associated with a shift in neural activity from low level shape and motion specialized areas in children, including partially immature area V3a, to high order areas in the parietal lobule (PSA) in adults.