Dorsal Visual Systems Research Articles

Altered large-scale individual-based morphological brain network in spinocerebellar ataxia type 3.

Accumulating evidences indicate regional gray matter (GM) morphology atrophy in spinocerebellar ataxia type 3 (SCA3); however, whether large-scale morphological brain networks (MBNs) undergo widespread reorganization in these patients remains unclear. To investigate the topological organization of large-scale individual-based MBNs in SCA3 patients. The individual-based MBNs were constructed based on the inter-regional morphological similarity of GM regions. Graph theoretical analysis was taken to assess GM structural connectivity in 76 symptomatic SCA3, 24 pre-symptomatic SCA3, and 54 healthy normal controls (NCs). Topological parameters of the resulting graphs and network-based statistics analysis were compared among symptomatic SCA3, pre-symptomatic SCA3, and NCs groups. The inner association between network properties and clinical variables was further analyzed. Compared to NCs and pre-symptomatic SCA3 patients, symptomatic SCA3 indicated significantly decreased integration and segregation, a shift to "weaker small-worldness", characterized by decreased Cp , lower Eloc, and Eglob (all p < 0.005). Regarding nodal properties, symptomatic SCA3 exhibited significantly decreased nodal profiles in the central executive network (CEN)-related left inferior frontal gyrus, limbic regions involving the bilateral amygdala, left hippocampus, and bilateral pallidum, thalamus; and increased nodal degree, efficiency in bilateral caudate (all pFDR <0.05). Meanwhile, clinical variables were correlated with altered nodal profiles (pFDR ≤0.029). SCA3-related subnetwork was closely interrelated with dorsolateral cortico-striatal circuitry extending to orbitofrontal-striatal circuits and dorsal visual systems (lingual gyrus-striatal). Symptomatic SCA3 patients undergo an extensive and significant reorganization in large-scale individual-based MBNs, probably due to disrupted prefrontal cortico-striato-thalamo-cortical loops, limbic-striatum circuitry, and enhanced connectivity in the neostriatum. This study highlights the crucial role of abnormal morphological connectivity alterations beyond the pattern of brain atrophy, which might pave the way for therapeutic development in the future.

Features of visual, cognitive and neuroimaging changes in Parkinson’s disease patients with freezing of gait

To determine visual and cognitive impairments in relation to MRI changes in patients with freezing of Gait (FOG) in Parkinson's disease (PD). We examined 78 patients with PD without dementia, who were divided into groups according to the presence (FOG«+» group) or absence (FOG«-» group) of «freezing» episodes. A decrease in contrast sensitivity (CS) and retinal photosensitivity was determined in all subjects with PD, but in patients with FOG, the decrease in CS was more pronounced. There was a significant decrease in the volume of the cuneus, lingual gyrus, posterior cingulate gyrus, superior parietal lobe and middle frontal gyrus in the FOG«+» group. It was revealed that patients with FOG had cognitive impairments of both the frontal and posterior cortical subtypes, while in the FOG«-» group, only visuospatial deficit prevailed. A direct correlation was determined between the severity of FOG and part I of the UPDRS scale, between a decrease in CS and cortical areas related to the dorsal and ventral visual information processing systems. The presence of a negative relationship between the scores of the FOG-Q, Timed Up and Go test and the volume of cortical areas of the frontal lobe responsible for planning and programming of movements indicates their role in the development of FOG in PD. Thus, visual impairments associated with PD, along with a heterogeneous profile of cognitive impairment, make a significant contribution to the development of FOG.

Disruption and Compensation of Sulcation-based Covariance Networks in Neonatal Brain Growth after Perinatal Injury.

Perinatal brain injuries in preterm neonates are associated with alterations in structural neurodevelopment, leading to impaired cognition, motor coordination, and behavior. However, it remains unknown how such injuries affect postnatal cortical folding and structural covariance networks, which indicate functional parcellation and reciprocal brain connectivity. Studying 229 magnetic resonance scans from 158 preterm neonates (n = 158, mean age = 28.2), we found that severe injuries including intraventricular hemorrhage, periventricular leukomalacia, and ventriculomegaly lead to significantly reduced cortical folding and increased covariance (hyper-covariance) in only the early (<31weeks) but not middle (31-35weeks) or late stage (>35weeks) of the third trimester. The aberrant hyper-covariance may drive acceleration of cortical folding as a compensatory mechanism to "catch-up" with normal development. By 40weeks, preterm neonates with/without severe brain injuries exhibited no difference in cortical folding and covariance compared with healthy term neonates. However, graph theory-based analysis showed that even after recovery, severely injured brains exhibit a more segregated, less integrated, and overall inefficient network system with reduced integration strength in the dorsal attention, frontoparietal, limbic, and visual network systems. Ultimately, severe perinatal injuries cause network-level deviations that persist until the late stage of the third trimester and may contribute to neurofunctional impairment.

More optimal but less regulated dorsal and ventral visual networks in patients with major depressive disorder

Previous studies indicate that major depressive disorder (MDD) can profoundly modify the visual cortices as well as the visuo-attentional systems of brain. However, little is known on the specific pattern of the whole-network-level abnormalities. In this study, resting-state functional magnetic resonance imaging data were collected from 159 participants, including 86 medication-free MDD patients and 73 matched healthy controls. The dorsal/ventral visual networks were defined based on our previously published brain coordinates from activation likelihood estimation analyses. The static and dynamic network properties were respectively calculated and compared between MDD and control groups. Moreover, the inter-network connectivities quantified using the multivariate distance correlation between the dorsal attention network (DAN) and the two visual networks were also analyzed. Results indicated that both of the two visual networks in MDD were found with significantly increased clustering coefficient (dorsal: p = 0.002; ventral: p = 0.004) and higher small-worldness (dorsal: p = 0.001; ventral: p = 0.002) as compared with control group. A higher mean variability of dynamic functional connectivity was found in both two networks in MDDs (dorsal: p < 0.001; ventral: p = 0.001). Moreover, the two visual networks in MDD group showed decreased inter-network connectivities to DAN (dorsal: p = 0.004; ventral: p = 0.013). Taken together, these results may support that the ventral and dorsal visual systems under the pathological effect of depression are possibly characterized by a status of increased autonomy, i.e., a more optimal, economical, and efficient intra-network organization combining with increased independency and receiving less outside regulation from attention network, thus indicating the increased functional role of the brain visual systems in MDD.

The Distinct Roles of Dorsal and Ventral Visual Systems in Naming of Chinese Characters

We aimed to investigate the role of dorsal and ventral visual systems in rapid naming of simple Chinese characters. Twenty college students (10 female; Mage = 22.5 years) were required to covertly read a character- and a cross-matrix during an fMRI experiment. A basic prosaccade and a prosaccade-naming task were also performed to confirm the functional significance of the findings. The results of whole brain analysis showed that both dorsal and ventral visual systems were activated in the character-matrix reading. The cross-matrix scanning elicited weaker activation in the left middle frontal gyrus, superior temporal gyrus, and ventral occipitotemporal cortex. Next, whereas both top-down and bottom-up effective connectivities (ECs) were found between these two systems in the character-matrix reading, only top-down ECs were observed in the cross-matrix scanning. Moreover, in the character-matrix reading, we found a negative correlation between the reaction time of naming in the prosaccade-naming task and the EC strength from visual word form area to superior temporal gyrus and a positive correlation between the reaction time in the basic prosaccade task and the EC strength from middle frontal gyrus to intraparietal sulcus. The cross-matrix scanning did not show any brain-behavior relationship. These results suggest that while the dorsal visual system is mainly engaged in eye-movement control, the ventral system is associated more with orthographic processing and orthography-phonology mapping.

Neural Mechanisms of Dorsal and Ventral Visual Regions during Text Reading.

When reading a narrative text, both the dorsal and ventral visual systems are activated. To illustrate the patterns of interactions between the dorsal and ventral visual systems in text reading, we conducted analyses of functional connectivity (FC) and effective connectivity (EC) in a left-hemispheric network for reading-driven functional magnetic resonance imaging (fMRI) and resting-state fMRI (rs-fMRI) data. In reading-driven fMRI (Experiment 1), we found significant FCs among the left middle frontal gyrus (MFG), the left intraparietal sulcus (IPS), and the visual word form area (VWFA), and there were top–down effects from the left MFG to the left IPS, from the left MFG to the VWFA, and from the left IPS to the VWFA. In rs-fMRI (Experiment 2), we identified FCs and ECs for MFG-IPS and IPS-VWFA connections. In addition, the brain–behavior relationship in resting states showed that the dorsal connection was more associated with reading fluency relative to lexical decision. The combination of two experiments revealed that the MFG-IPS and the VWFA-IPS connections were shared connections both in reading-driven fMRI and rs-fMRI, and that the MFG-VWFA was specific connectivity in reading-driven fMRI. These results suggest that top–down effects from the dorsal visual system to ventral visual system play an important role in text reading.

Insular cortex: structural and functional neuroanatomy.

Insular cortex: structural and functional neuroanatomy.

Finding and recognizing objects in natural scenes: complementary computations in the dorsal and ventral visual systems.

Searching for and recognizing objects in complex natural scenes is implemented by multiple saccades until the eyes reach within the reduced receptive field sizes of inferior temporal cortex (IT) neurons. We analyze and model how the dorsal and ventral visual streams both contribute to this. Saliency detection in the dorsal visual system including area LIP is modeled by graph-based visual saliency, and allows the eyes to fixate potential objects within several degrees. Visual information at the fixated location subtending approximately 9° corresponding to the receptive fields of IT neurons is then passed through a four layer hierarchical model of the ventral cortical visual system, VisNet. We show that VisNet can be trained using a synaptic modification rule with a short-term memory trace of recent neuronal activity to capture both the required view and translation invariances to allow in the model approximately 90% correct object recognition for 4 objects shown in any view across a range of 135° anywhere in a scene. The model was able to generalize correctly within the four trained views and the 25 trained translations. This approach analyses the principles by which complementary computations in the dorsal and ventral visual cortical streams enable objects to be located and recognized in complex natural scenes.

Widespread disruption of functional brain organization in early-onset Alzheimer's disease.

Early-onset Alzheimer’s disease (AD) patients present a different clinical profile than late-onset AD patients. This can be partially explained by cortical atrophy, although brain organization might provide more insight. The aim of this study was to examine functional connectivity in early-onset and late-onset AD patients. Resting-state fMRI scans of 20 early-onset (<65 years old), 28 late-onset (≥65 years old) AD patients and 15 “young” (<65 years old) and 31 “old” (≥65 years old) age-matched controls were available. Resting-state network-masks were used to create subject-specific maps. Group differences were examined using a non-parametric permutation test, accounting for gray-matter. Performance on five cognitive domains were used in a correlation analysis with functional connectivity in AD patients. Functional connectivity was not different in any of the RSNs when comparing the two control groups (young vs. old controls), which implies that there is no general effect of aging on functional connectivity. Functional connectivity in early-onset AD was lower in all networks compared to age-matched controls, where late-onset AD showed lower functional connectivity in the default-mode network. Functional connectivity was lower in early-onset compared to late-onset AD in auditory-, sensory-motor, dorsal-visual systems and the default mode network. Across patients, an association of functional connectivity of the default mode network was found with visuoconstruction. Functional connectivity of the right dorsal visual system was associated with attention across patients. In late-onset AD patients alone, higher functional connectivity of the sensory-motor system was associated with poorer memory performance. Functional brain organization was more widely disrupted in early-onset AD when compared to late-onset AD. This could possibly explain different clinical profiles, although more research into the relationship of functional connectivity and cognitive performance is needed.

Learning to detect but not to grasp suppressed visual stimuli

A central implication of the two-visual-systems hypothesis (TVSH) is that the dorsal visuomotor system (vision-for-action) can make use of invisible information, whereas the ventral system (vision-for-perception) cannot (Milner & Goodale, 1995). Therefore, actions such as grasping movements should be influenced by invisible information while conscious reports remain unaffected. To test this assumption, we used a dichoptic stimulation technique – continuous flash suppression (CFS) – which has the potency to render stimuli invisible for up to seconds (Tsuchiya & Koch, 2005). In two experiments using CFS, participants were asked to grasp for invisible bars of different sizes (Experiment 1) or orientations (Experiment 2), or to report both measures verbally. Target visibility was measured trial-by-trial using the perceptual awareness scale (PAS). We found no evidence for the use of invisible information by the visuomotor system despite extensive training (600 trials) and the availability of haptic feedback. Participants neither learned to scale their maximum grip aperture to the size of the invisible stimulus, nor to align their hand to its orientation. Careful control of stimulus visibility across training sessions, however, revealed a robust tendency towards decreasing perceptual thresholds under CFS. We discuss our results within the framework of the TVSH and with respect to alternative models which emphasize the close functional interaction between the dorsal and ventral visual systems.

Spatial Frequency Tuning Reveals Interactions between the Dorsal and Ventral Visual Systems

It is widely argued that the ability to recognize and identify manipulable objects depends on the retrieval and simulation of action-based information associated with using those objects. Evidence for that view comes from fMRI studies that have reported differential BOLD contrast in dorsal visual stream regions when participants view manipulable objects compared with a range of baseline categories. An alternative interpretation is that processes internal to the ventral visual pathway are sufficient to support the visual identification of manipulable objects and that the retrieval of object-associated use information is contingent on analysis of the visual input by the ventral stream. Here, we sought to distinguish these two perspectives by exploiting the fact that the dorsal stream is largely driven by magnocellular input, which is biased toward low spatial frequency visual information. Thus, any tool-selective responses in parietal cortex that are driven by high spatial frequencies would be indicative of inputs from the ventral visual pathway. Participants viewed images of tools and animals containing only low, or only high, spatial frequencies during fMRI. We find an internal parcellation of left parietal "tool-preferring" voxels: Inferior aspects of left parietal cortex are driven by high spatial frequency information and have privileged connectivity with ventral stream regions that show similar category preferences, whereas superior regions are driven by low spatial frequency information. Our findings suggest that the automatic activation of complex object-associated manipulation knowledge is contingent on analysis of the visual input by the ventral visual pathway.

Independent Objective Timing Tests Designed to Measure Processing Rates of the Dorsal and Ventral Visual Systems

Th is study introduces new objective psychophysical measures for assessing speed thresholds of two levels of te m- poral processing: One measure occurs at a lower perceptual level designed to test functional limits of the dorsal how or where system; and the second measure occurs at a higher cognitive level designed to test functional limits of the ventral what system. The tests are objective because each trial has a correct answer, as opposed to relying on participants subjectively indicating the point at wh ich they experience the transition fro m an indistinct and blurry percept to a d istinct and clear one. Twenty six par- ticipants performed three rate threshold tests: (1) An objective psychophysical rate o f apparent motion measure, as a test of the dorsal system, (2) an objective psychophysical rate of serial shape-change measure, as a test of the ventral system, and (3) a traditional method-of-limits crit ical flicker fusion threshold measure, as a comparison control test . We hypothesized that indi- viduals' maximu m rate of apparent motion would correlate with thresholds of crit ical flicker fusion (CFF), and that their maximu m rate of serial shape-change would be much slower and uncorrelated with the CFF measure. Results confirmed both hypotheses, revealing a strong correlation between CFF thresholds and threshold rates on the apparent motion test, as well as marked ly slower threshold rates for recognizing direction of shape change. The findings support the apparent motion test as a promising, reliable, objective psychophysical measure associated with the dorsal how or where processing system, and the serial shape-change test as a pro mising, reliab le, objective psychophysical measure associated with the ventral what processing system.

Has brain imaging discovered anything new about how the brain works?

There have now been roughly 130,000 papers on fMRI. While these have clearly contributed to our understanding of the functional anatomy of the human brain, it is less clear that they have changed the way in which we think about the brain. The issue, in other words, is whether they have established new principles about how the brain works. In this paper we offer as an example one new principle, partly to lay down the criteria that are required for establishing a new principle, and partly to encourage others to offer other principles. Our example concerns the flexible flow of information through the cortex that must occur according to the demands of the task or current context. We suggest that this flexibility is achieved by feedback connections from the prefrontal and parietal cortex, and that these include connections to sensory and motor areas. However, the nature of the selective effect differs. The parietal cortex can select both within and across processing streams. By across streams we mean that it can have the same influence on different streams, for example the dorsal and ventral visual systems. However, only the prefrontal cortex can also select between processing streams. The difference between the prefrontal and parietal effects is due to their different positions within the processing hierarchy.

Distinct task-independent visual thresholds for egocentric and allocentric information pick up

The dominant view of the ventral and dorsal visual systems is that they subserve perception and action. De Wit, Van der Kamp, and Masters (2011) suggested that a more fundamental distinction might exist between the nature of information exploited by the systems. The present study distinguished between these accounts by asking participants to perform delayed matching (perception), pointing (action) and perceptual judgment responses to masked Müller-Lyer stimuli of varying length. Matching and pointing responses of participants who could not perceptually judge stimulus length at brief durations remained sensitive to veridical stimulus length (egocentric information), but not the illusion (allocentric, context-dependent information), which was effective at long durations. Distinct thresholds for egocentric and allocentric information pick up were thus evident irrespective of whether perception (matching) or action (pointing) responses were required. It was concluded that the dorsal and ventral systems may be delineated fundamentally by fast egocentric- and slower allocentric information pick up, respectively.

Significance of the context of cognitive activity in the formation of unconscious visual sets

Experimental data from healthy humans on the context dependence of cognitive activity involved in the process of substituting a previously formed unconscious set with a new set appropriate to the altered conditions are discussed. The mobility/rigidity property of the visual set changes depending on the nature of the additional task introduced into the context (stimulus recognition or identification of the spatial position of a stimulus). It is hypothesized that the process of set substitution is facilitated when the context of cognitive activity includes alternation of the involvement of the ventral and dorsal visual systems in information processing.

Neural substrates of knowledge of hand postures for object grasping and functional object use: Evidence from fMRI

A number of lines of evidence suggest that computation of hand posture differs for object grasping as compared to functional object use. Hand shaping for grasping appears to rely strongly upon calculations of current object location and volume, whereas hand shaping for object use additionally requires access to stored knowledge about the skilled manipulation specific to a given object. In addition, the particular hand postures employed for functional object use may be either prehensile (clenching, pinching) or non-prehensile (e.g., palming, poking), in contrast to the prehensile postures that are obligatory for grasping. In this fMRI study, we assessed the hypothesis that a left-hemisphere-lateralized system including the inferior parietal lobe is specifically recruited for the computation and recognition of hand postures for functional object use. Fifteen subjects viewed pictures of manipulable objects and determined whether they would be grasped with a pinch or clench (Grasp condition), functionally used with a pinch or clench (Prehensile Use condition), or functionally used with a palm or poke hand posture (Non-prehensile Use condition). Despite the fact that the conditions were equated for behavioral difficulty, significantly greater activations were observed in the left inferior frontal gyrus (IFG), posterior superior temporal gyrus (STG), and inferior parietal lobule (IPL) in Non-prehensile Use trials as compared to Grasp trials. Comparison of Non-prehensile Use and Prehensile Use activations revealed significant differences only in the left IPL. These data confirm the importance of the left IPL in storing knowledge of hand postures for functional object use, and have implications for understanding the interaction of dorsal and ventral visual processing systems.

The role of the cognitive activity context in the conservatism of unconscious visual sets

Studies in healthy adults were performed to compare measures of the rigidity of a verbal set in three series of experiments: in series 1, pseudowords were presented at the set-forming stage of the experiment, while common words were presented in the test stage; series 2 used the pseudoword/word conditions of series 1 with the additional task of identifying the position of a target stimulus in a matrix, requiring discrimination from other symbols in terms of two characteristics; in series 3, the pseudoword/word test was followed by an initial task consisting of identifying the matrix position of a target stimulus in conditions in which the need to discriminate was minimized. The results supported the hypothesis that the rigidity of a visual set depends on the cognitive activity context. This property is significantly dependent on the loading applied to working memory and the cognitive tasks solved by the subject, particularly the ratio of involvement of the ventral and dorsal visual systems in the cortical processing of sequentially acting verbal and non-verbal visual stimuli. The cognitive set paradigm serves as a model for experimental studies of the roles of the ventral and dorsal visual systems in organizing recognition functions.

Dependence of the cognitive set on the involvement of the ventral and dorsal visual systems in cognitive activity

Measures of the stability of a non-verbal visual set were compared in healthy human subjects in three series of experiments: 1) controls, in which a pair of set-forming stimuli (images of circles) were presented; 2) in the context of a test with a non-verbal set, subjects were presented with an additional task consisting of recognition of pseudowords (words); and 3) as before, but the additional task consisted of identifying the position of a target stimulus in a matrix of letters. There was a significant decrease in the stability (rigidity) of the non-verbal set on introduction of the additional task consisting of identifying the spatial position of a target stimulus; conversely, there was an increase in rigidity when the task consisted of recognizing the quality of a stimulus. Coherence analysis of cortical potentials in the alpha range showed that changes in the spatial organization of cortical electrical activity were significantly different, depending on the nature of the additional task: when the additional task involved recognition of a verbal stimulus, coherence connections were strengthened in the frontal-temporal-parietal areas of the right hemisphere; presentation in the context of a visuospatial task resulted in greater changes being observed in the anterior areas of the right hemisphere. It is suggested that the successful performance of mental functions requiring relatively rapid shifts in unconscious sets on changes in situation occurs in conditions of alternation of different types of cognitive tasks when cortical processing of visual information is mediated predominantly by one of the visual systems - either the ventral ("what?") or the dorsal ("where?") and, correspondingly, with the involvement of the anterior and posterior cortical selective attention systems.

Control of Visuotemporal Attention by Inferior Parietal and Superior Temporal Cortex

The human cortical visual system is organized into two major pathways: a dorsal stream projecting to the superior parietal lobe (SPL), considered to be critical for visuospatial perception or on-line control of visually guided movements, and a ventral stream leading to the inferotemporal cortex, mediating object perception [1–3]. Between these structures lies a large region, consisting of the inferior parietal lobe (IPL) and superior temporal gyrus (STG), the function of which is controversial. Lesions here can lead to spatial neglect [4, 5], a condition associated with abnormal visuospatial perception [6, 7] as well as impaired visually guided movements [8, 9], suggesting that the IPL+STG may have largely a “dorsal” role. Here, we use a nonspatial task [10] to examine the deployment of visuotemporal attention in focal lesion patients, with or without spatial neglect. We show that, regardless of the presence of neglect, damage to the IPL+STG leads to a more prolonged deployment of visuotemporal attention compared to lesions of the SPL. Our findings suggest that the human IPL+STG makes an important contribution to nonspatial perception, and this is consistent with a role that is neither strictly “dorsal” nor “ventral” [11]. We propose instead that the IPL+STG has a top-down control role, contributing to the functions of both dorsal and ventral visual systems.

Direct information on the cutting room floor

Norman's assigning of the constructivist percept-percept coupling approach and the ecological affordances approach to the ventral and dorsal visual systems, respectively, makes a more workable metatheory than each taken separately, but brings both under closer inspection.