Dorsal Stream Research Articles

Understanding the concept of a novel tool requires interaction of the dorsal and ventral streams.

The left hemisphere tool-use network consists of the dorso-dorsal, ventro-dorsal, and ventral streams, each with distinct computational abilities. In the dual-loop model, the ventral pathway through the extreme capsule is associated with conceptual understanding. We performed a learning experiment with fMRI to investigate how these streams interact when confronted with novel tools. In session one, subjects observed pictures and video sequences in real world action of known and unknown tools and were asked whether they knew the tools and whether they understood their function. In session two, video sequences of unknown tools were presented again, followed again by the question of understanding their function. Different conditions were compared to each other and effective connectivity (EC) in the tool-use network was examined. During concept acquisition of an unknown tool, EC between dorsal and ventral streams was found posterior in fusiform gyrus and anterior in inferior frontal gyrus, with a functional interaction between BA44d and BA45. When previously unknown tools were presented for a second time, EC was prominent only between dorsal stream areas. Understanding the concept of a novel tool requires an interaction of the ventral stream with the dorsal streams. Once the concept is acquired, dorsal stream areas are sufficient.

Associations Between Autism Spectrum Quotient and Integration of Visual Stimuli in 9-year-old Children: Preliminary Evidence of Sex Differences.

The dorsal stream vulnerability hypothesis posits that the dorsal stream, responsible for visual motion and visuo-motor processing, may be particularly vulnerable during neurodevelopment. Consistent with this, autism spectrum disorder (ASD) has been associated with deficits in global motion integration, though deficits in ventral stream tasks, such as form identification, have also been reported. In the current study, we examined whether a similar pattern of results is found in a cohort of 381 children born with neurodevelopmental risk factors and exhibiting a wide spectrum of caregiver-reported autistic traits. We examined the associations between global motion perception, global form perception, fine motor function, visual-motor integration, and autistic traits (autism spectrum quotient, AQ) using linear regression, accounting for possible interactions with sex and other factors relevant to neurodevelopment. All assessments of dorsal stream function were significantly associated with AQ such that worse performance predicted higher AQ scores. We also observed a significant sex interaction, with worse global form perception associated with higher AQ in boys (n = 202) but not girls (n = 179). We found widespread associations between dorsal stream functions and autistic traits. These associations were observed in a large group of children with a range of AQ scores, demonstrating a range of visual function across the full spectrum of autistic traits. In addition, ventral function was associated with AQ in boys but not girls. Sex differences in the associations between visual processing and neurodevelopment should be considered in the designs of future studies.

Simple shape feature computation across modalities: convergence and divergence between the ventral and dorsal visual streams.

Shape processing, whether by seeing or touching, is pivotal to object recognition and manipulation. Although the low-level signals are initially processed by different modality-specific neural circuits, multimodal responses to object shapes have been reported along both ventral and dorsal visual pathways. To understand this transitional process, we conducted visual and haptic shape perception fMRI experiments to test basic shape features (i.e. curvature and rectilinear) across the visual pathways. Using a combination of region-of-interest-based support vector machine decoding analysis and voxel selection method, we found that the top visual-discriminative voxels in the left occipital cortex (OC) could also classify haptic shape features, and the top haptic-discriminative voxels in the left posterior parietal cortex (PPC) could also classify visual shape features. Furthermore, these voxels could decode shape features in a cross-modal manner, suggesting shared neural computation across visual and haptic modalities. In the univariate analysis, the top haptic-discriminative voxels in the left PPC showed haptic rectilinear feature preference, whereas the top visual-discriminative voxels in the left OC showed no significant shape feature preference in either of the two modalities. Together, these results suggest that mid-level shape features are represented in a modality-independent manner in both the ventral and dorsal streams.

Experience dependent plasticity of higher visual cortical areas in the mouse.

Experience dependent plasticity in the visual cortex is a key paradigm for the study of mechanisms underpinning learning and memory. Despite this, studies involving manipulating visual experience have largely been limited to the primary visual cortex, V1, across various species. Here we investigated the effects of monocular deprivation (MD) on the ocular dominance (OD) and orientation selectivity of neurons in four visual cortical areas in the mouse: the binocular zone of V1 (V1b), the putative "ventral stream" area LM and the putative "dorsal stream" areas AL and PM. We employed two-photon calcium imaging to record neuronal responses in young adult mice before MD, immediately after MD, and following binocular recovery. OD shifts following MD were greatest in LM and smallest in AL and PM; in LM and AL, these shifts were mediated primarily through a reduction of deprived-eye responses, in V1b and LM through an increase in response through the non-deprived eye. The OD index recovered to pre-MD levels within 2weeks in V1 only. MD caused a reduction in orientation selectivity of deprived-eye responses in V1b and LM only. Our results suggest that changes in OD in higher visual areas are not uniformly inherited from V1.

The neurofunctional network of syntactic processing: cognitive systematicity and representational specializations of objects, actions, and events

Theoretical accounts of syntax are broadly divided into lexicalist or construction-based viewpoints, where lexicalist traditions argue that a great deal of syntactic information is stored in lexical representations, while construction-based views argue for separate representations of multiword syntactic structures. Moreover, a strict autonomy between syntactic and semantic processing has been posited based on the grammatical well-formedness of non-sense sentences such as This round table is square. In this paper, we provide an overview of these competing conceptions of syntactic structure and the role of syntax in grammar. We review converging neuroimaging, electrophysiological, behavioral, electrocorticographic, and computational modeling evidence that challenge these views. In particular, we show that a temporal lobe ventral stream is crucial in processing phrases involving nouns and attributive adjectives, while a dorsal stream involving left parietal regions, including the angular gyrus, is crucial in processing constructions involving verbs and relational adjectives. We additionally support this interpretation by examining divergent pathways in the visual system for processing object information and event/spatial information, on the basis of integration across visual and auditory modalities. Our interpretation suggests that combinatorial operations which combine words into phrases cannot be isolated to a single anatomical location, as has been previously proposed—instead, it is an instantiation of a more general neural computation, one that is implemented across various brain regions and can be utilized in service of constructing linguistic phrases. Based on this orientation, we explore how abstract syntactic constructions, such as the transitive construction, both mirror and could emerge from semantics. These abstract construction representations are argued to be distinct from, and stored in regions functionally downstream from, lexical representations of verbs. Comprehension therefore involves the integration of both representations via feedforward and feedback connections. We implicate the IFG in communicating across the language network, including correctly integrating nominal phrases with the overall event representation and serving as one interface between processing streams. Overall, this approach accords more generally with conceptions of the development of cognitive systematicity, and further draws attention to a potential role for the medial temporal lobe in syntactic behaviors, often overlooked in current neurofunctional accounts of syntactic processing.

Visuomotor interactions in the mouse forebrain mediated by extrastriate cortico-cortical pathways.

The mammalian visual system can be broadly divided into two functional processing pathways: a dorsal stream supporting visually and spatially guided actions, and a ventral stream enabling object recognition. In rodents, the majority of visual signaling in the dorsal stream is transmitted to frontal motor cortices via extrastriate visual areas surrounding V1, but exactly where and to what extent V1 feeds into motor-projecting visual regions is not well known. We employed a dual labeling strategy in male and female mice in which efferent projections from V1 were labeled anterogradely, and motor-projecting neurons in higher visual areas were labeled with retrogradely traveling adeno-associated virus (rAAV-retro) injected in M2. We characterized the labeling in both flattened and coronal sections of dorsal cortex and made high-resolution 3D reconstructions to count putative synaptic contacts in different extrastriate areas. The most pronounced colocalization V1 output and M2 input occurred in extrastriate areas AM, PM, RL and AL. Neurons in both superficial and deep layers in each project to M2, but high resolution volumetric reconstructions indicated that the majority of putative synaptic contacts from V1 onto M2-projecting neurons occurred in layer 2/3. These findings support the existence of a dorsal processing stream in the mouse visual system, where visual signals reach motor cortex largely via feedforward projections in anteriorly and medially located extrastriate areas.

Deep learning applied to EEG source-data reveals both ventral and dorsal visual stream involvement in holistic processing of social stimuli

Perception of social stimuli (faces and bodies) relies on “holistic” (i.e., global) mechanisms, as supported by picture-plane inversion: perceiving inverted faces/bodies is harder than perceiving their upright counterpart. Albeit neuroimaging evidence suggested involvement of face-specific brain areas in holistic processing, their spatiotemporal dynamics and selectivity for social stimuli is still debated. Here, we investigate the spatiotemporal dynamics of holistic processing for faces, bodies and houses (adopted as control non-social category), by applying deep learning to high-density electroencephalographic signals (EEG) at source-level. Convolutional neural networks were trained to classify cortical EEG responses to stimulus orientation (upright/inverted), separately for each stimulus type (faces, bodies, houses), resulting to perform well above chance for faces and bodies, and close to chance for houses. By explaining network decision, the 150–200 ms time interval and few visual ventral-stream regions were identified as mostly relevant for discriminating face and body orientation (lateral occipital cortex, and for face only, precuneus cortex, fusiform and lingual gyri), together with two additional dorsal-stream areas (superior and inferior parietal cortices). Overall, the proposed approach is sensitive in detecting cortical activity underlying perceptual phenomena, and by maximally exploiting discriminant information contained in data, may reveal spatiotemporal features previously undisclosed, stimulating novel investigations.

The dorsal stream of visual processing and action-specific domains in parietal and frontal cortex in primates.

This review summarizes our findings obtained from over 15 years of research on parietal-frontal networks involved in the dorsal stream of cortical processing. We have presented considerable evidence for the existence of similar, partially independent, parietal-frontal networks involved in specific motor actions in a number of primates. These networks are formed by connections between action-specific domains representing the same complex movement evoked by electrical microstimulation. Functionally matched domains in the posterior parietal (PPC) and frontal (M1-PMC) motor regions are hierarchically related. M1 seems to be a critical link in these networks, since the outputs of M1 are essential to the evoked behavior, whereas PPC and PMC mediate complex movements mostly via their connections with M1. Thus, lesioning or deactivating M1 domains selectively blocks matching PMC and PPC domains, while having limited impact on other domains. When pairs of domains are stimulated together, domains within the same parietal-frontal network (matching domains) are cooperative in evoking movements, while they are mainly competitive with other domains (mismatched domains) within the same set of cortical areas. We propose that the interaction of different functional domains in each cortical region (as well as in striatum) occurs mainly via mutual suppression. Thus, the domains at each level are in competition with each other for mediating one of several possible behavioral outcomes.

The processing of stress in a foreign language modulates functional antagonism between default mode and attention network regions

Lexical stress is an essential element of prosody. Mastering this prosodic feature is challenging, especially in a free-stress foreign language for individuals native to a fixed-stress language, a phenomenon referred to as stress deafness. By using functional magnetic resonance imaging, we elucidated the neuronal underpinnings of stress processing in a free-stress foreign language, and determined the underlying mechanism of stress deafness. Here, we contrasted behavioral and hemodynamic responses revealed by native speakers of a free-stress (German; N = 38) and a fixed-stress (French; N = 47) language while discriminating pairs of words in a free-stress foreign language (Spanish). Consistent with the stress deafness phenomenon, French speakers performed worse than German speakers in discriminating Spanish words based on cues of stress but not of vowel. Whole-brain analyses revealed widespread bilateral networks (i.e., cerebral regions including frontal, temporal and parietal areas as well as insular, subcortical and cerebellar structures), overlapping with the ones previously associated with stress processing within native languages. Moreover, our results provide evidence that the structures pertaining to a right-lateralized attention system (i.e., middle frontal gyrus, anterior insula) and the Default Mode Network modulate stress processing as a function of the performance level. In comparison to the German speakers, the French speakers activated the attention system and deactivated the Default Mode Network to a stronger degree, reflecting attentive engagement, likely a compensatory mechanism underlying the “stress-deaf” brain. The mechanism modulating stress processing argues for a rightward lateralization, indeed overlapping with the location covered by the dorsal stream but remaining unspecific to speech.

Perceptual Visual Inversion Secondary to Inhalation of Fumes of Sulfuryl Chloride (P4-12.003)

<h3>Objective:</h3> To describe a case of alteration of visual perception of objects and faces following Inhalation of Sulfuryl Chloride. <h3>Background:</h3> The neural pathways for object perception and recognition include two information-processing streams originating in occipital cortex. Dorsal stream extends to parietal lobe, and Ventral stream extends to inferior temporal lobe. Damage to each pathway can affect elements of visual perception affecting object recognition (what) and spatial perception (where and how). <h3>Design/Methods:</h3> Case report/literature review. <h3>Results:</h3> Fifty-three-year-old woman presented following inhalation of toxic fumes. Over the following hours and days, she lost the ability to speak her native tongue and could only communicate in her second language. She complained that most objects in her visual field were inverted, but not the whole scene. There are few reports of subjective visual field inversion without robust testing. We formulated novel experiments to probe deficits unique to her. On shape from shading (eggs vs. cavities) test, the light on top looked like cavities, unlike neurotypicals - implying that for her, the sun shines from below. She recognized upside-down faces faster than the correct way up and could easily read upside down. Prosopagnosics identify inverted faces more accurately than neurotypicals. We suggest there is a selective injury to the ventral stream,” What Pathway,” in the inferior temporal lobe (associated with object recognition). The insult relatively spared the dorsal stream “How and Where” in the posterior parietal cortex. This may explain why she exhibited mild Balint syndrome (optic ataxia, simultagnosia, oculomotor apraxia). Alternatively, the initial Balint may have been progressively corrected via visual feedback during reaching. Such correction does not occur for the ventral stream because we do not usually palpate people’s faces. <h3>Conclusions:</h3> Inversion of vision is rare but using stimuli designed to probe specific symptoms, we gain insight into cascade of neural signals that culminate in perception. <b>Disclosure:</b> Dr. Ramachandran has nothing to disclose. Dr. Kakawand has nothing to disclose. Dr. McGeoch has nothing to disclose. Mr. Ahern has nothing to disclose. Dr. Tobias has nothing to disclose.

The domain-separation language network dynamics in resting state support its flexible functional segregation and integration during language and speech processing

Modern linguistic theories and network science propose that language and speech processing are organized into hierarchical, segregated large-scale subnetworks, with a core of dorsal (phonological) stream and ventral (semantic) stream. The two streams are asymmetrically recruited in receptive and expressive language or speech tasks, which showed flexible functional segregation and integration. We hypothesized that the functional segregation of the two streams was supported by the underlying network segregation. A dynamic conditional correlation approach was employed to construct framewise time-varying language networks and k-means clustering was employed to investigate the temporal-reoccurring patterns. We found that the framewise language network dynamics in resting state were robustly clustered into four states, which dynamically reconfigured following a domain-separation manner. Spatially, the hub distributions of the first three states highly resembled the neurobiology of speech perception and lexical-phonological processing, speech production, and semantic processing, respectively. The fourth state was characterized by the weakest functional connectivity and was regarded as a baseline state. Temporally, the first three states appeared exclusively in limited time bins (∼15%), and most of the time (> 55%), state 4 was dominant. Machine learning-based dFC-linguistics prediction analyses showed that dFCs of the four states significantly predicted individual linguistic performance. These findings suggest a domain-separation manner of language network dynamics in resting state, which forms a dynamic “meta-network” framework to support flexible functional segregation and integration during language and speech processing.

STNet: A novel spiking neural network combining its own time signal with the spatial signal of an artificial neural network.

This article proposes a novel hybrid network that combines the temporal signal of a spiking neural network (SNN) with the spatial signal of an artificial neural network (ANN), namely the Spatio-Temporal Combined Network (STNet). Inspired by the way the visual cortex in the human brain processes visual information, two versions of STNet are designed: a concatenated one (C-STNet) and a parallel one (P-STNet). In the C-STNet, the ANN, simulating the primary visual cortex, extracts the simple spatial information of objects first, and then the obtained spatial information is encoded as spiking time signals for transmission to the rear SNN which simulates the extrastriate visual cortex to process and classify the spikes. With the view that information from the primary visual cortex reaches the extrastriate visual cortex via ventral and dorsal streams, in P-STNet, the parallel combination of the ANN and the SNN is employed to extract the original spatio-temporal information from samples, and the extracted information is transferred to a posterior SNN for classification. The experimental results of the two STNets obtained on six small and two large benchmark datasets were compared with eight commonly used approaches, demonstrating that the two STNets can achieve improved performance in terms of accuracy, generalization, stability, and convergence. These prove that the idea of combining ANN and SNN is feasible and can greatly improve the performance of SNN.

Motion and form coherence processing in individuals with cerebral visual impairment.

Using a visual psychophysical paradigm, we sought to assess motion and form coherence thresholds as indices of dorsal and ventral visual stream processing respectively, in individuals with cerebral visual impairment (CVI). We also explored potential associations between psychophysical assessments and brain lesion severity in CVI. Twenty individuals previously diagnosed with CVI (mean age = 17 years 11 months [SD 5 years 10 months]; mean Verbal IQ = 86.42 [SD 35.85]) and 30 individuals with neurotypical development (mean age = 20 years 1 month [SD 3 years 8 months]; mean Verbal IQ = 110.05 [SD 19.34]) participated in the study. In this two-group comparison, cross-sectional study design, global motion, and form pattern coherence thresholds were assessed using a computerized, generalizable, self-administrable, and response-adaptive psychophysical paradigm called FInD (Foraging Interactive D-prime). Consistent with dorsal stream dysfunction, mean global motion (but not form) coherence thresholds were significantly higher in individuals with CVI compared to controls. No statistically significant association was found between coherence thresholds and lesion severity. These results suggest that the objective assessment of motion and form coherence threshold sensitivities using this psychophysical paradigm may be useful in helping to characterize perceptual deficits and the complex clinical profile of CVI. In participants with cerebral visual impairment (CVI), motion (but not form) coherence thresholds were significantly higher compared to controls. These psychophysical results support the notion of dorsal stream dysfunction in CVI.

Altered resting-state functional connectivity in the prefrontal cortex is related to the development of dyscalculia in patients with Turner syndrome.

Patients with Turner syndrome have a high rate of developmental dyscalculia, but the underlying neurocognitive mechanisms are not well-understood. Some studies have implicated visuospatial impairments in patients with Turner syndrome, but others have focused on poor procedural skills in patients with Turner syndrome. This study used brain imaging data to test these two alternative views. This study recruited 44 girls with Turner syndrome (mean age, 12.91 years; SD, 2.02), with 13 (29.5%) of them meeting the criterion for developmental dyscalculia, and 14 normally developing girls (mean age, 14.26 years; SD, 2.18) as a comparison group. All participants were given basic mathematical ability tests and an intelligence test and were scanned using magnetic resonance imaging. We compared patients with Turner syndrome who had dyscalculia, patients with Turner syndrome who did not have dyscalculia, and the normal controls in terms of brain structures and resting-state functional activity. Compared with normal controls, both groups of patients with Turner syndrome (with or without dyscalculia) showed similarly altered functional connectivity in the occipitoparietal dorsal stream. Importantly, compared with patients with Turner syndrome without dyscalculia and normal controls, patients with Turner syndrome with dyscalculia showed decreased functional connectivity between the prefrontal and the lateral occipital cortex. We concluded that both groups of patients with Turner syndrome shared visual deficits, and patients with Turner syndrome with dyscalculia had a deficit in frontal cortex-based higher cognitive processing. It is not their visuospatial deficits but rather their deficits in higher cognitive processing that are responsible for the development of dyscalculia in patients with Turner syndrome.

Distinct dorsal and ventral streams for binocular rivalry dominance and suppression revealed by magnetoencephalography.

Binocular rivalry is an example of bistable visual perception extensively examined in neuroimaging. Magnetoencephalography can track brain responses to phasic visual stimulations of predetermined frequency and phase to advance our understanding of perceptual dominance and suppression in binocular rivalry. We used left and right eye stimuli that flickered at two tagging frequencies to track their respective oscillatory cortical evoked responses. We computed time-resolved measures of coherence to track brain responses phase locked with stimulus frequencies and with respect to the participants' indications of alternations of visual rivalry they experienced. We compared the brain maps obtained to those from a non-rivalrous control replay condition that used physically changing stimuli to mimic rivalry. We found stronger coherence within a posterior cortical network of visual areas during rivalry dominance compared with rivalry suppression and replay control. This network extended beyond the primary visual cortex to several retinotopic visual areas. Moreover, network coherence with dominant percepts in primary visual cortex peaked at least 50 ms prior to the suppressed percept nadir, consistent with the escape theory of alternations. Individual alternation rates were correlated with the rate of change in dominant evoked peaks, but not for the slope of response to suppressed percepts. Effective connectivity measures revealed that dominant (respectively, suppressed) percepts were expressed in dorsal (respectively ventral) streams. We thus demonstrate that binocular rivalry dominance and suppression engage distinct mechanisms and brain networks. These findings advance neural models of rivalry and may relate to more general aspects of selection and suppression in natural vision.

An efficiently working brain characterizes higher mental flow that elicits pleasure in Chinese calligraphic handwriting.

The mental flow that commonly emerges during immersion in artistic activities is beneficial for maintaining mental health. However, there is not that much converging neurobiological evidence about how flow emerges and elicits pleasure in arts. Using an imitation task of Chinese calligraphic handwriting with self-rated subjective flow experience, we investigated the neural interactions supporting flow. Our results show that calligraphic handwriting requires cooperation between widespread multimodal regions that span the visual and sensorimotor areas along the dorsal stream, the top-down attentional control system, and the orbito-affective network. We demonstrate that higher flow is characterized by an efficiently working brain that manifests as less activation particularly in the brain regions within dorsal attention network and functional connectivity between visual and sensorimotor networks in calligraphy. Furthermore, we also propose that pleasure during calligraphy writing arises from efficient cortical activity in the emergence of flow, and the orbito-caudate circuit responsible for feelings of affection. These findings provide new insight into the neuropsychological representations of flow through art, and highlight the potential benefits of artistic activities to boost well-being and prosperity.

Functional connectivity fingerprints of the frontal eye field and inferior frontal junction suggest spatial versus nonspatial processing in the prefrontal cortex.

Neuroimaging evidence suggests that the frontal eye field (FEF) and inferior frontal junction (IFJ) govern the encoding of spatial and nonspatial (such as feature- or object-based) representations, respectively, both during visual attention and working memory tasks. However, it is still unclear whether such contrasting functional segregation is also reflected in their underlying functional connectivity patterns. Here, we hypothesized that FEF has predominant functional coupling with spatiotopically organized regions in the dorsal ('where') visual stream whereas IFJ has predominant functional connectivity with the ventral ('what') visual stream. We applied seed-based functional connectivity analyses to temporally high-resolving resting-state magnetoencephalography (MEG) recordings. We parcellated the brain according to the multimodal Glasser atlas and tested, for various frequency bands, whether the spontaneous activity of each parcel in the ventral and dorsal visual pathway has predominant functional connectivity with FEF or IFJ. The results show that FEF has a robust power correlation with the dorsal visual pathway in beta and gamma bands. In contrast, anterior IFJ (IFJa) has a strong power coupling with the ventral visual stream in delta, beta and gamma oscillations. Moreover, while FEF is phase-coupled with the superior parietal lobe in the beta band, IFJa is phase-coupled with the middle and inferior temporal cortex in delta and gamma oscillations. We argue that these intrinsic connectivity fingerprints are congruent with each brain region's function. Therefore, we conclude that FEF and IFJ have dissociable connectivity patterns that fit their respective functional roles in spatial versus nonspatial top-down attention and working memory control.

Activation of human visual area V6 during egocentric navigation with and without visual experience

V6 is a retinotopic area located in the dorsal visual stream that integrates eye movements with retinal and visuo-motor signals. Despite the known role of V6 in visual motion, it is unknown whether it is involved in navigation and how sensory experiences shape its functional properties. We explored the involvement of V6 in egocentric navigation in sighted and in congenitally blind (CB) participants navigating via an in-house distance-to-sound sensory substitution device (SSD), the EyeCane. We performed two fMRI experiments on two independent datasets. In the first experiment, CB and sighted participants navigated the same mazes. The sighted performed the mazes via vision, while the CB performed them via audition. The CB performed the mazes before and after a training session, using the EyeCane SSD. In the second experiment, a group of sighted participants performed a motor topography task. Our results show that right V6 (rhV6) is selectively involved in egocentric navigation independently of the sensory modality used. Indeed, after training, rhV6 of CB is selectively recruited for auditory navigation, similarly to rhV6 in the sighted. Moreover, we found activation for body movement in area V6, which can putatively contribute to its involvement in egocentric navigation. Taken together, our findings suggest that area rhV6 is a unique hub that transforms spatially relevant sensory information into an egocentric representation for navigation. While vision is clearly the dominant modality, rhV6 is in fact a supramodal area that can develop its selectivity for navigation in the absence of visual experience.

The structural basis of age-related decline in global motion perception at fast and slow speeds

A decrease in global motion perception (GMP) has been reported in older adults, and this age-related decline in GMP varies with the speed of global motion. However, no studies have investigated whether the asynchronous age-related decline in GMP is related to degenerative changes in brain structure. In this study, the random dot kinematogram paradigm and structural magnetic resonance imaging were used to investigate the asynchronous aging of GMP at fast and slow speeds (called fast GMP and slow GMP, respectively) and their relationships with brain structure. Ninety-four older adults (65.74 ± 4.50 yrs) and 90 younger adults (22.83 ± 4.84 yrs) participated in the experiment. The results showed that older adults had higher motion coherence thresholds (MCT) than younger adults at both fast and slow speeds. Brain-behavior correlation analyses of younger adults revealed that none of the correlations between morphological measures and MCTs survived correction for multiple comparisons. For older adults, slow MCT was correlated with cortical thickness in the bilateral V4v, V5/MT+, left V7, V8, LO, and surface area in the right V7. Fast MCT was significantly correlated with gray matter volume in the right V7 and thickness in the left V5/MT+. These results support the view that global motion extraction occurs within two speed-tuned systems that are at least partially independent in terms of their neural substrates, which deteriorate with age at different speeds. Aging of GMP is also associated with morphological changes in the visual cortex. Age-related cerebral atrophy in the dorsal stream may impair both fast and slow GMP, whereas aging of the ventral stream specifically impairs slow GMP.

Neural mechanisms of musical structure and tonality, and the effect of musicianship.

The neural basis for the processing of musical syntax has previously been examined almost exclusively in classical tonal music, which is characterized by a strictly organized hierarchical structure. Musical syntax may differ in different music genres caused by tonality varieties. The present study investigated the neural mechanisms for processing musical syntax across genres varying in tonality - classical, impressionist, and atonal music - and, in addition, examined how musicianship modulates such processing. Results showed that, first, the dorsal stream, including the bilateral inferior frontal gyrus and superior temporal gyrus, plays a key role in the perception of tonality. Second, right frontotemporal regions were crucial in allowing musicians to outperform non-musicians in musical syntactic processing; musicians also benefit from a cortical-subcortical network including pallidum and cerebellum, suggesting more auditory-motor interaction in musicians than in non-musicians. Third, left pars triangularis carries out online computations independently of tonality and musicianship, whereas right pars triangularis is sensitive to tonality and partly dependent on musicianship. Finally, unlike tonal music, the processing of atonal music could not be differentiated from that of scrambled notes, both behaviorally and neurally, even among musicians. The present study highlights the importance of studying varying music genres and experience levels and provides a better understanding of musical syntax and tonality processing and how such processing is modulated by music experience.