The neural basis of centre-surround interactions in visual motion processing

Perception of a moving visual stimulus can be suppressed or enhanced by surrounding context in adjacent parts of the visual field. We studied the neural processes underlying such contextual modulation with fMRI. We selected motion selective regions of interest (ROI) in the occipital and parietal lobes with sufficiently well defined topography to preclude direct activation by the surround. BOLD signal in the ROIs was suppressed when surround motion direction matched central stimulus direction, and increased when it was opposite. With the exception of hMT+/V5, inserting a gap between the stimulus and the surround abolished surround modulation. This dissociation between hMT+/V5 and other motion selective regions prompted us to ask whether motion perception is closely linked to processing in hMT+/V5, or reflects the net activity across all motion selective cortex. The motion aftereffect (MAE) provided a measure of motion perception, and the same stimulus configurations that were used in the fMRI experiments served as adapters. Using a linear model, we found that the MAE was predicted more accurately by the BOLD signal in hMT+/V5 than it was by the BOLD signal in other motion selective regions. However, a substantial improvement in prediction accuracy could be achieved by using the net activity across all motion selective cortex as a predictor, suggesting the overall conclusion that visual motion perception depends upon the integration of activity across different areas of visual cortex.     

基于空间ICA和时间相关方法的人脑视觉皮层V5区的功能连通性研究

利用功能磁共振成像技术,将空间ICA和时间相关方法相结合来研究不同活动状态下人脑视觉皮层V5区的功能连通性。首先利用空间ICA处理组块视觉运动刺激的数据,定位V5区;然后分别计算静息和连续视觉运动刺激两种稳态下V5区与其它脑区低频振荡的时间相关,检测出该区的功能连通网络。实验结果表明,静息时V5区的功能连通网络更广泛,且与已知的解剖连通一致;当被试接受连续视觉运动刺激时,与V5区连通的脑区网络局限在视觉皮层,此时的网络特定于处理视觉运动这一任务。     

Vision modulates somatosensory cortical processing

Over 150 years ago, E.H. Weber declared that experience showed that tactile acuity was not affected by viewing the stimulated body part. However, more recent investigations suggest that cross-modal links do exist between the senses. Viewing the stimulated body site improves performance on tactile discrimination and detection tasks and enhances tactile acuity. Here, we show that vision modulates somatosensory cortex activity, as measured by somatosensory event-related potentials (ERPs). This modulation is greatest when tactile stimulation is task relevant. Visual modulation is not present in the P50 component reflecting the primary afferent input to the cortex but appears in the subsequent N80 component, which has also been localized to SI, the primary somatosensory cortex. Furthermore, we replicate previous findings that noninformative vision improves spatial acuity. These results are consistent with a hypothesis that vision modulates cortical processing of tactile stimuli via back projections from multimodal cortical areas. Several neurophysiological studies suggest that primary and secondary somatosensory cortex (SI and SII, respectively) activity can be modulated by spatial and tactile attention and by visual cues. To our knowledge, this is the first demonstration of direct modulation of somatosensory cortex activity by a noninformative view of the stimulated body site with concomitant enhancement of tactile acuity in normal subjects.     

Sustained Spatial Attention to Vibrotactile Stimulation in the Flutter Range: Relevant Brain Regions and Their Interaction

The present functional magnetic resonance imaging (fMRI) study was designed to get a better understanding of the brain regions involved in sustained spatial attention to tactile events and to ascertain to what extent their activation was correlated. We presented continuous 20 Hz vibrotactile stimuli (range of flutter) concurrently to the left and right index fingers of healthy human volunteers. An arrow cue instructed subjects in a trial-by-trial fashion to attend to the left or right index finger and to detect rare target events that were embedded in the vibrotactile stimulation streams. We found blood oxygen level-dependent (BOLD) attentional modulation in primary somatosensory cortex (SI), mainly covering Brodmann area 1, 2, and 3b, as well as in secondary somatosensory cortex (SII), contralateral to the to-be-attended hand. Furthermore, attention to the right (dominant) hand resulted in additional BOLD modulation in left posterior insula. All of the effects were caused by an increased activation when attention was paid to the contralateral hand, except for the effects in left SI and insula. In left SI, the effect was related to a mixture of both a slight increase in activation when attention was paid to the contralateral hand as well as a slight decrease in activation when attention was paid to the ipsilateral hand (i.e., the tactile distraction condition). In contrast, the effect in left posterior insula was exclusively driven by a relative decrease in activation in the tactile distraction condition, which points to an active inhibition when tactile information is irrelevant. Finally, correlation analyses indicate a linear relationship between attention effects in intrahemispheric somatosensory cortices, since attentional modulation in SI and SII were interrelated within one hemisphere but not across hemispheres. All in all, our results provide a basis for future research on sustained attention to continuous vibrotactile stimulation in the range of flutter.     

Neural correlates of vibrissa resonance; band-pass and somatotopic representation of high-frequency stimuli

The array of vibrissae on a rat's face is the first stage of a high-resolution tactile sensing system. Recently, it was discovered that vibrissae (whiskers) resonate when stimulated at specific frequencies, generating several-fold increases in motion amplitude. We investigated the neural correlates of vibrissa resonance in trigeminal ganglion and primary somatosensory cortex (SI) neurons (regular and fast spiking units) by presenting low-amplitude, high-frequency vibrissa stimulation. We found that somatosensory neurons showed band-pass tuning and enhanced sensitivity to small amplitude stimuli, reflecting the resonance amplification of vibrissa motion. Further, a putative somatotopic map of frequency selectivity was observed in SI, with isofrequency columns extending along the representations of arcs of vibrissae, in agreement with the gradient in vibrissa resonance across the vibrissa pad. These findings suggest several parallels between frequency processing in the vibrissa system and the auditory system and have important implications for detection and discrimination of tactile information.     

Dynamic Changes in Brain Activations and Functional Connectivity during Affectively Different Tactile Stimuli

In the present study, we compared brain activations produced by pleasant, neutral and unpleasant touch, to the anterior lateral surface of lower leg of human subjects. It was found that several brain regions, including the contralateral primary somatosensory area (SI), bilateral secondary somatosensory area (SII), as well as contralateral middle and posterior insula cortex were commonly activated under the three touch conditions. In addition, pleasant and unpleasant touch conditions shared a few brain regions including the contralateral posterior parietal cortex (PPC) and bilateral premotor cortex (PMC). Unpleasant touch specifically activated a set of pain-related brain regions such as contralateral supplementary motor area (SMA) and dorsal parts of bilateral anterior cingulated cortex, etc. Brain regions specifically activated by pleasant touch comprised bilateral lateral orbitofrontal cortex (OFC), posterior cingulate cortex (PCC), medial prefrontal cortex (mPFC), intraparietal cortex and left dorsal lateral prefrontal cortex (DLPFC). Using a novel functional connectivity model based on graph theory, we showed that a series of brain regions related to affectively different touch had significant functional connectivity during the resting state. Furthermore, it was found that such a network can be modulated between affectively different touch conditions.     

Ontogeny of corticocortical projections of the rat somatosensory cortex.

Rhodamine-coated microspheres (RCMs) were injected into the primary somatosensory cortex (SI) of rats ranging in age from postnatal (PN) day 1 to adulthood. Ipsilateral corticocortical and callosal projections within the SI were identified as early as PN day 1. At the end of the first PN week, ipsilaterally projecting neurons located in sublayer VIb were the first to assume an adult-like pattern of connectivity. Injections at subsequent postnatal ages revealed that an adult pattern of lamination of ipsilateral corticocortical projections within the SI is established between PN weeks 2 and 3, comprising projection neurons from layers II/III, layer V, and sublayer VIb. Therefore, local interactions in the rat SI are mediated not only by pyramidal neurons of layers III and V, derived from the cortical plate, but also by a subpopulation of ontogenetically older neurons located in the sublayer VIb, which may correspond to the subplate neurons of other species. Overall, these results suggest the existence of three independent short-range corticocortical systems of projections within the rat SI, which differ in terms of the laminar distribution and ontogenetic origin of their cells.     

Prefrontal cortex and somatosensory cortex in tactile crossmodal association: an independent component analysis of ERP recordings

Our previous studies on scalp-recorded event-related potentials (ERPs) showed that somatosensory N140 evoked by a tactile vibration in working memory tasks was enhanced when human subjects expected a coming visual stimulus that had been paired with the tactile stimulus. The results suggested that such enhancement represented the cortical activities involved in tactile-visual crossmodal association. In the present study, we further hypothesized that the enhancement represented the neural activities in somatosensory and frontal cortices in the crossmodal association. By applying independent component analysis (ICA) to the ERP data, we found independent components (ICs) located in the medial prefrontal cortex (around the anterior cingulate cortex, ACC) and the primary somatosensory cortex (SI). The activity represented by the IC in SI cortex showed enhancement in expectation of the visual stimulus. Such differential activity thus suggested the participation of SI cortex in the task-related crossmodal association. Further, the coherence analysis and the Granger causality spectral analysis of the ICs showed that SI cortex appeared to cooperate with ACC in attention and perception of the tactile stimulus in crossmodal association. The results of our study support with new evidence an important idea in cortical neurophysiology: higher cognitive operations develop from the modality-specific sensory cortices (in the present study, SI cortex) that are involved in sensation and perception of various stimuli.     

An examination of somatosensory area SIII in ferret cortex

A somatotopically organized region on the suprasylvian gyrus of the ferret was examined using multiunit recordings and anatomical tracer injections. This area, which contains a representation of the face, was bordered by the primary somatosensory area (SI), anteriorly, and by the visually responsive rostral posterior parietal cortex (PPr), posteriorly. Anatomical tracers revealed connections to this region from cortical areas MI, SI, MRSS, PPr, and the thalamic posterior nucleus. These results are consistent with previous work in ferrets as well as with the location, physiology, and connectivity of area SIII in cats. Given its associations, functional properties, location, and homology, it is proposed that this region represents the third cortical somatosensory area (SIII) in ferrets.     

Referral of Touch and Ownership between the Hands and the Role of the Somatosensory Cortices

Recent studies have shown that the feeling of body ownership can be fooled by simple visuo-tactile manipulations. Perceptual illusions have been reported in which participants sense phantom touch seen on a rubber hand (rubber hand illusion). While previous studies used homologous limbs for those experiments, we here examined an illusion where people feel phantom touch on a left rubber hand when they see it brushed simultaneously with brushes applied to their right hand. Thus, we investigated a referral of touch from the right to the left hand (across the body midline). Since it is known from animal studies that tactile illusions may alter early sensory processing, we expected a modulation of the primary somatosensory cortex (SI) corresponding to this illusion. Neuromagnetic source imaging of the functional topographic organization in SI showed a shift in left SI, associated with the strength of the referral of touch. Hence, we argue that SI seems to be closely associated with this perceptual illusion. The results suggest that the transfer of tactile information across the body midline could be mediated by neurons with bilateral tactile receptive fields (most likely BA2).     

Optogenetic Patterning of Whisker-Barrel Cortical System in Transgenic Rat Expressing Channelrhodopsin-2

The rodent whisker-barrel system has been an ideal model for studying somatosensory representations in the cortex. However, it remains a challenge to experimentally stimulate whiskers with a given pattern under spatiotemporal precision. Recently the optogenetic manipulation of neuronal activity has made possible the analysis of the neuronal network with precise spatiotemporal resolution. Here we identified the selective expression of channelrhodopsin-2 (ChR2), an algal light-driven cation channel, in the large mechanoreceptive neurons in the trigeminal ganglion (TG) as well as their peripheral nerve endings innervating the whisker follicles of a transgenic rat. The spatiotemporal pattern of whisker irradiation thus produced a barrel-cortical response with a specific spatiotemporal pattern as evidenced by electrophysiological and functional MRI (fMRI) studies. Our methods of generating an optogenetic tactile pattern (OTP) can be expected to facilitate studies on how the spatiotemporal pattern of touch is represented in the somatosensory cortex, as Hubel and Wiesel did in the visual cortex.     

See me, hear me, touch me: multisensory integration in lateral occipital-temporal cortex

Our understanding of multisensory integration has advanced because of recent functional neuroimaging studies of three areas in human lateral occipito-temporal cortex: superior temporal sulcus, area LO and area MT (V5). Superior temporal sulcus is activated strongly in response to meaningful auditory and visual stimuli, but responses to tactile stimuli have not been well studied. Area LO shows strong activation in response to both visual and tactile shape information, but not to auditory representations of objects. Area MT, an important region for processing visual motion, also shows weak activation in response to tactile motion, and a signal that drops below resting baseline in response to auditory motion. Within superior temporal sulcus, a patchy organization of regions is activated in response to auditory, visual and multisensory stimuli. This organization appears similar to that observed in polysensory areas in macaque superior temporal sulcus, suggesting that it is an anatomical substrate for multisensory integration. A patchy organization might also be a neural mechanism for integrating disparate representations within individual sensory modalities, such as representations of visual form and visual motion.     

Functional imaging of perceptual learning in human primary and secondary somatosensory cortex

Cellular mechanisms underlying synaptic plasticity are in line with the Hebbian concept. In contrast, data linking Hebbian learning to altered perception are rare. Combining functional magnetic resonance imaging with psychophysical tests, we studied cortical reorganization in primary and secondary somatosensory cortex (SI and SII) and the resulting changes of tactile perception before and after tactile coactivation, a simple type of Hebbian learning. Coactivation on the right index finger (IF) for 3 hr lowered its spatial discrimination threshold. In parallel, blood-oxygen level-dependent (BOLD) signals from the right IF representation in SI and SII enlarged. The individual threshold reduction was linearly correlated with the enlargement in SI, implying a close relation between altered discrimination and cortical reorganization. Controls consisting of a single-site stimulation did not affect thresholds and cortical maps. Accordingly, changes within distributed cortical networks based on Hebbian mechanisms alter the individual percept.     

Human cortical regions involved in extracting depth from motion

We used functional magnetic resonance imaging (fMRI) to investigate brain regions involved in extracting three-dimensional structure from motion. A factorial design included two-dimensional and three-dimensional structures undergoing rigid and nonrigid motions. As predicted from monkey data, the human homolog of MT/V5 was significantly more active when subjects viewed three-dimensional (as opposed to two-dimensional) displays, irrespective of their rigidity. Human MT/V5+ (hMT/V5+) is part of a network with right hemisphere dominance involved in extracting depth from motion, including a lateral occipital region, five sites along the intraparietal sulcus (IPS), and two ventral occipital regions. Control experiments confirmed that this pattern of activation is most strongly correlated with perceived three-dimensional structure, in as much as it arises from motion and cannot be attributed to numerous two-dimensional image properties or to saliency.     

Areal distributions of cortical neurons projecting to different levels of the caudal brain stem and spinal cord in rats

Distributions of corticospinal and corticobulbar neurons were revealed by tetramethylbenzidine (TMB) processing after injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA:HRP) into the cervical or lumbar enlargements of the spinal cord, or medullary or pontine levels of the brain stem. Sections reacted for cytochrome oxidase (CO) allowed patterns of labeled neurons to be related to the details of the body surface map in the first somatosensory cortical area (SI). The results indicate that a number of cortical areas project to these subcortical levels: (1) Projection neurons in granular SI formed a clear somatotopic pattern. The hindpaw region projected to the lumbar enlargement, the forepaw region to the cervical enlargement, the whisker pad field to the lower medulla, and the more rostral face region to more rostral brain stem levels. (2) Each zone of labeled neurons in SI extended into adjacent dysgranular somatosensory cortex, forming a second somatotopic pattern of projection neurons. (3) A somatotopic pattern of projection neurons in primary motor cortex (MI) paralleled SI in mediolateral sequence corresponding to the hindlimb, forelimb, and face. (4) A weak somatotopic pattern of projection neurons was suggested in medial agranular cortex (Agm), indicating a premotor field with a rostromedial-to-caudolateral representation of hindlimb, forelimb, and face. (5) A somatotopic pattern of projection neurons representing the foot to face in a mediolateral sequence was observed in medial parietal cortex (PM) located between SI and area 17. (6) In the second somatosensory cortical area (SII), neurons projecting to the brain stem were immediately adjacent caudolaterally to the barrel field of SI, whereas neurons projecting to the upper spinal cord were more lateral. No projection neurons in this region were labeled by the injections in the lower spinal cord. (7) Other foci of projection neurons for the face and forelimb were located rostral to SII, providing evidence for a parietal ventral area (PV) in perirhinal cortex (PR) lateral to SI, and in cortex between SII and PM. None of these regions, which may be higher-order somatosensory areas, contained labeled neurons after injections in the lower spinal cord. Thus, more cortical fields directly influence brain stem and spinal cord levels related to sensory and motor functions of the face and forepaw than the hindlimb. The termination patterns of corticospinal and corticobulbar projections were studied in other rats with injections of WGA:HRP in SI.(ABSTRACT TRUNCATED AT 400 WORDS)     

Neural Basis of Limb Ownership in Individuals with Body Integrity Identity Disorder

Our body feels like it is ours. However, individuals with body integrity identity disorder (BIID) lack this feeling of ownership for distinct limbs and desire amputation of perfectly healthy body parts. This extremely rare condition provides us with an opportunity to study the neural basis underlying the feeling of limb ownership, since these individuals have a feeling of disownership for a limb in the absence of apparent brain damage. Here we directly compared brain activation between limbs that do and do not feel as part of the body using functional MRI during separate tactile stimulation and motor execution experiments. In comparison to matched controls, individuals with BIID showed heightened responsivity of a large somatosensory network including the parietal cortex and right insula during tactile stimulation, regardless of whether the stimulated leg felt owned or alienated. Importantly, activity in the ventral premotor cortex depended on the feeling of ownership and was reduced during stimulation of the alienated compared to the owned leg. In contrast, no significant differences between groups were observed during the performance of motor actions. These results suggest that altered somatosensory processing in the premotor cortex is associated with the feeling of disownership in BIID, which may be related to altered integration of somatosensory and proprioceptive information.     

Magnetoencephalography in the study of human somatosensory cortical processing.

Magnetoencephalography (MEG) is a totally non-invasive research method which provides information about cortical dynamics on a millisecond time-scale. Whole-scalp magnetic field patterns following stimulation of different peripheral nerves indicate activation of an extensive cortical network. At the SI cortex, the responses reflect mainly the activity of area 3b, with clearly somatotopical representations of different body parts. The SII cortex is activated bilaterally and it also receives, besides tactile input, nociceptive afference. Somatically evoked MEG signals may also be detected from the posterior parietal cortex, central mesial cortex and the frontal lobe. The serial versus parallel processing in the cortical somatosensory network is still under debate.     

Interhemispheric connections shape subjective experience of bistable motion

The right and left visual hemifields are represented in different cerebral hemispheres and are bound together by connections through the corpus callosum. Much has been learned on the functions of these connections from split-brain patients [1-4], but little is known about their contribution to conscious visual perception in healthy humans. We used diffusion tensor imaging and functional magnetic resonance imaging to investigate which callosal connections contribute to the subjective experience of a visual motion stimulus that requires interhemispheric integration. The "motion quartet" is an ambiguous version of apparent motion that leads to perceptions of either horizontal or vertical motion [5]. Interestingly, observers are more likely to perceive vertical than horizontal motion when the stimulus is presented centrally in the visual field [6]. This asymmetry has been attributed to the fact that, with central fixation, perception of horizontal motion requires integration across hemispheres whereas perception of vertical motion requires only intrahemispheric processing [7]. We are able to show that the microstructure of individually tracked callosal segments connecting motion-sensitive areas of the human MT/V5 complex (hMT/V5+; [8]) can predict the conscious perception of observers. Neither connections between primary visual cortex (V1) nor other surrounding callosal regions exhibit a similar relationship.     

Somatotopic Organization of the Third Somatosensory Area (SIII) in Cats

Multiunit microelectrode recording techniques were used to study the location and organization of the third somatosensory area (SIII) in cats. Representations of all major contralateral body parts were found in a small region of cortex along the lateral wing of the ansate sulcus and between the lateral sulcus and the suprasylvian sulcus. The systematic map of the body surface included forepaw and face regions previously identified as parts of SIII. The forepaw representation was generally buried on the rostral bank of the lateral wing of the ansate sulcus. The representations of the face and mystacial vibrissae were largely exposed on the rostral suprasylvian gyrus, but part of the representation of the face was also buried in the lateral wing of the ansate sulcus. Representations of the trunk and hindlimb extended from the suprasylvian gyrus onto the medial bank of the suprasylvian sulcus. We had expected to find these latter body parts in more medial cortex just caudal to the representation of these parts in the first somatosensory area (SI). Instead, neurons in penetrations in cortex caudal to the SI trunk and hindlimb representations were unresponsive to tactile stimulation. The unexpected location of the hindlimb in SIII led us to determine whether the proposed parts of SIII had similar cortical and thalamic connections. Injected anatomical tracers revealed that the representations of both the forelimb and hindlimb were interconnected with SI and a region of the thalamus just dorsal to the ventroposterior nucleus. Similarities in patterns of connections of forelimb and hindlimb portions of SIII supported the conclusion that SHI as presented here is a functional unit of cortex. We conclude that SIII has a somatotopic organization that does not parallel that in SI, and that SIII is not entirely coextensive with either area 5 or area 5a of Hassler and Muhs-Clement (1964).     

研究报告: 大鼠感觉运动系统静息态脑网络研究

为了理解啮齿类动物的脑功能连接,本文利用9.4T fMRI获得轻度麻醉状态下大鼠静息状态及刺激激活的数据,通过互相关分析构建节点之间的相关系数矩阵并计算相应的网络参数．结果发现：给予前爪电刺激时,刺激对侧初级感觉皮层(S1)、丘脑(Tha)有较强的正激活,双侧尾状壳核(CPu)有较强的负激活．静息状态时大鼠感觉/运动皮层内部、丘脑内部的连接性较强,而感觉/运动皮层与丘脑之间的连接较弱,双侧感觉运动系统之间存在较强的同步低频振荡,感觉运动系统在静息态时的脑网络具有小世界属性．结果提示,啮齿类动物在大脑信息处理中的功能分离和整合可能与人类存在某些相似性,支持哺乳动物中枢神经系统的基本功能存在遗传保守性的观点．