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Convolutional networks used for computer vision represent candidate models for the computations performed in mammalian visual systems. We use them as a detailed model of human brain activity during the viewing of natural images by constructing predictive models based on their different layers and BOLD fMRI activations. Analyzing the predictive performance across layers yields characteristic fingerprints for each visual brain region: early visual areas are better described by lower level convolutional net layers and later visual areas by higher level net layers, exhibiting a progression across ventral and dorsal streams. Our predictive model generalizes beyond brain responses to natural images. We illustrate this on two experiments, namely retinotopy and face-place oppositions, by synthesizing brain activity and performing classical brain mapping upon it. The synthesis recovers the activations observed in the corresponding fMRI studies, showing that this deep encoding model captures representations of brain function that are universal across experimental paradigms. [Display omitted] •Convolutional network layer image representations explain ventral stream fMRI.•This mapping follows the known hierarchical organisation.•Results from both static images and video stimuli.•A full brain predictive model synthesizes brain maps for other visual experiments.•Only deep models can reproduce observed BOLD activity.

ObjectiveStudies investigating the functional organisation of the medial temporal lobe (MTL) suggest that parahippocampal cortex (PHC) generates representations of spatial and contextual information used by the hippocampus in the formation of episodic memories. However, evidence from animal studies also implicates PHC in spatial binding of visual information held in working memory. This study focussed on elucidating the role of PHC in spatial binding in working memory in humans.MethodWe assessed a 46-year-old man (PJ), after he had recovered from bilateral medial occipitotemporal cortical mOTC strokes resulting in lesions in PHC but sparing the hippocampus, and a group of age-matched healthy controls on a series of visual working memory tasks.ResultsWhen recalling the colour of one of two objects, PJ misidentified the target when cued by its location, but not shape. When recalling the position of one of three objects, he frequently misidentified the target, which was cued by its colour. Increasing the duration of the memory delay had no impact on the proportion of binding errors, but did significantly worsen recall precision in both PJ and controls.ConclusionWe conclude that PHC plays a crucial role in spatial binding during encoding of visual information in working.

Sensory information travels along feedforward connections through a hierarchy of cortical areas, which, in turn, send feedback connections to lower-order areas. Feedback has been implicated in attention, expectation, and sensory context, but the mechanisms underlying these diverse feedback functions are unknown. Using specific optogenetic inactivation of feedback connections from the secondary visual area (V2), we show how feedback affects neural responses in the primate primary visual cortex (V1). Reducing feedback activity increases V1 cells’ receptive field (RF) size, decreases their responses to stimuli confined to the RF, and increases their responses to stimuli extending into the proximal surround, therefore reducing surround suppression. Moreover, stronger reduction of V2 feedback activity leads to progressive increase in RF size and decrease in response amplitude, an effect predicted by a recurrent network model. Our results indicate that feedback modulates RF size, surround suppression and response amplitude, similar to the modulatory effects of visual spatial attention. Feedback modulation of V1 is implicated in functions such as attention yet the precise neural mechanisms are not known. Here the authors report that optogenetic inactivation of V2 projections leads to modulation of V1 receptive field properties such as size, surround suppression and response amplitude.

Mapping the organization of excitatory inputs onto the dendritic spines of individual mouse visual cortex neurons reveals how inputs representing features from the extended visual scene are organized and establishes a computational unit suited to amplify contours and elongated edges. Synapses set the scene Processing a visual stimulus requires various connections between neurons, with each encoding for particular features that integrate and generate the overall representation of a scene. The precise logic of this connectivity and what information an individual neuron receives regarding various parts of the visual field are unknown. Here, Sonja Hofer and colleagues mapped the organization of excitatory inputs onto the dendritic spines of individual mouse visual cortex neurons. Inputs representing similar visual features in similar visual field positions were more likely to cluster on neighbouring spines and inputs beyond the receptive field of the observed neuron were located on higher-order dendritic branches. Connections between neurons with dissimilar receptive fields were more likely when these fields were spatially displaced. These arrangements establish a computational unit suited to amplify contours and elongated edges, features that are common elements of our visual space. How a sensory stimulus is processed and perceived depends on the surrounding sensory scene. In the visual cortex, contextual signals can be conveyed by an extensive network of intra- and inter-areal excitatory connections that link neurons representing stimulus features separated in visual space 1 , 2 , 3 , 4 . However, the connectional logic of visual contextual inputs remains unknown; it is not clear what information individual neurons receive from different parts of the visual field, nor how this input relates to the visual features that a neuron encodes, defined by its spatial receptive field. Here we determine the organization of excitatory synaptic inputs responding to different locations in the visual scene by mapping spatial receptive fields in dendritic spines of mouse visual cortex neurons using two-photon calcium imaging. We find that neurons receive functionally diverse inputs from extended regions of visual space. Inputs representing similar visual features from the same location in visual space are more likely to cluster on neighbouring spines. Inputs from visual field regions beyond the receptive field of the postsynaptic neuron often synapse on higher-order dendritic branches. These putative long-range inputs are more frequent and more likely to share the preference for oriented edges with the postsynaptic neuron when the receptive field of the input is spatially displaced along the axis of the receptive field orientation of the postsynaptic neuron. Therefore, the connectivity between neurons with displaced receptive fields obeys a specific rule, whereby they connect preferentially when their receptive fields are co-oriented and co-axially aligned. This organization of synaptic connectivity is ideally suited for the amplification of elongated edges, which are enriched in the visual environment, and thus provides a potential substrate for contour integration and object grouping.

Research suggests that perception and imagination engage neuronal representations in the same visual areas. However, the underlying mechanisms that differentiate sensory perception from imagination remain unclear. Here, we examine the directed coupling (effective connectivity) between fronto-parietal and visual areas during perception and imagery. We found an increase in bottom-up coupling during perception relative to baseline and an increase in top-down coupling during both perception and imagery, with a much stronger increase during imagery. Modulation of the coupling from frontal to early visual areas was common to both perception and imagery. Furthermore, we show that the experienced vividness during imagery was selectively associated with increases in top-down connectivity to early visual cortex. These results highlight the importance of top-down processing in internally as well as externally driven visual experience.

Study DesignTime-series.ObjectivesTo examine relationships of electroencephalographic(EEG) measures of sensorimotor control and balance outcomes in response to 4 weeks of balance training in chronic ankle instability(CAI) patients.BackgroundBalance training is a common therapeutic intervention for CAI patients, often resulting in improvements in clinician-oriented balance measures. The mechanisms of these improvements are currently unknown in CAI patients, however, cortical activity has not yet been measured in CAI patients during motor tasks. EEG can be used to capture coordination of cortical activity during motor tasks, and how it changes as a result of balance training.Methods and Measures8 CAI patients completed a 4 week balance training protocol(BTP). Balance, measured by the Star Excursion Balance Test(SEBT) and EEG were collected at baseline and after completing the BTP. Cortical activity was measuring using EEG during a dual-to-single limb transition(DSLT) and was quantified using event-related spectral perturbations(ERSP), calculating the change in the power of a signal with respect to the DSLT. ERSP was calculated in the Alpha(8–12 Hz) and Beta(14–25 Hz) bandwidths in the 250 ms prior to and 250 ms following the DSLT(AlphaPre, AlphaPost, BetaPre, BetaPost). Increases in ERSP are indicative of more coordinated activity, whereas decreases indicate more widespread activation of the cerebral cortex. Change scores (posttest-baseline) in EEG and SEBT measures were analysed using Pearson product moment correlations at an alpha of 0.10.ResultsA moderate positive relationship was identified between the change in Alpha ERSP and SEBT in the posteromedial direction(p=0.045). Moderate positive correlations were identified between the change in Beta ERSP and SEBT in the anterior(p=0.071), posteromedial(p=0.049), and posterolateral(p=0.076) directions.ConclusionThe positive relationships identified suggest that patients with greater improvements in dynamic balance have an increased coordination of cortical activity following balance training. Further research is needed to clarify the direction of these results and their functional and clinical significance.

Temporal integration in visual perception is thought to occur within cycles of occipital alpha-band (8–12 Hz) oscillations. Successive stimuli may be integrated when they fall within the same alpha cycle and segregated for different alpha cycles. Consequently, the speed of alpha oscillations correlates with the temporal resolution of perception, such that lower alpha frequencies provide longer time windows for perceptual integration and higher alpha frequencies correspond to faster sampling and segregation. Can the brain’s rhythmic activity be dynamically controlled to adjust its processing speed according to different visual task demands? We recorded magnetoencephalography (MEG) while participants switched between task instructions for temporal integration and segregation, holding stimuli and task difficulty constant. We found that the peak frequency of alpha oscillations decreased when visual task demands required temporal integration compared with segregation. Alpha frequency was strategically modulated immediately before and during stimulus processing, suggesting a preparatory top-down source of modulation. Its neural generators were located in occipital and inferotemporal cortex. The frequency modulation was specific to alpha oscillations and did not occur in the delta (1–3 Hz), theta (3–7 Hz), beta (15–30 Hz), or gamma (30–50 Hz) frequency range. These results show that alpha frequency is under top-down control to increase or decrease the temporal resolution of visual perception.

Abstract Introduction Rapid Eye Movement (REM) sleep Behavior Disorder (RBD) is a REM sleep parasomnia known to be strongly associated with the development of neurodegenerative disorders. Cognitive deterioration has been shown to be a common issue in RBD patients, in particular impairments in visuo-spatial abilities. However, little is known about the effect of RBD on visual processing. The aim of this study was to evaluate the basic mechanisms of stimulus analysis in RBD patients by a visual search paradigm. Methods 12 RBD patients (mean age: 68.25 ± 9.63, 9 males) and 12 age-matched healthy controls (HC) were enrolled in the study. After a nocturnal video-polysomnographic recording, patients performed a visual search task in which they had to detect the presence/absence of a target (letter T) embedded in the 50% of trials into a set of distractors (letters Os, Xs, or Ls). Target’s salience and distractors’ numerosity were manipulated as independent variables, whereas accuracy and reaction times (RT) were recorded as dependent variables. Results Typical effects of visual search were confirmed: RT increased with distractors’ number and decreased with targets’ salience. RBD patients showed significantly slower RT in comparison with HC. Furthermore, analyzing RT of stimuli containing the target in comparison to RT of stimuli in which the target was absent, patients differed from controls only in the condition of target absent. This result indicates a perceptual impairment specifically related to the exhaustive visual analysis, according to the Sternberg’s model. Conclusion These results experimentally demonstrates a perceptual impairment revealed by the more demanding conditions of the visual search task. This impairment seems to be in line with previous neuropsychological researches that showed the presence of a visuo-spatial deficit in RBD patients. Support (If Any) none.

Normal and abnormal differences in sustained visual attention have long been of interest to scientists, educators, and clinicians. Still lacking, however, is a clear understanding of how sustained visual attention varies across the broad sweep of the human life span. In the present study, we filled this gap in two ways. First, using an unprecedentedly large 10,430-person sample, we modeled age-related differences with substantially greater precision than have prior efforts. Second, using the recently developed gradual-onset continuous performance test (gradCPT), we parsed sustained-attention performance over the life span into its ability and strategy components. We found that after the age of 15 years, the strategy and ability trajectories saliently diverge. Strategy becomes monotonically more conservative with age, whereas ability peaks in the early 40s and is followed by a gradual decline in older adults. These observed life-span trajectories for sustained attention are distinct from results of other life-span studies focusing on fluid and crystallized intelligence.

While parietal cortex is thought to be critical for representing numerical magnitudes, we recently reported an event-related potential (ERP) study demonstrating selective neural sensitivity to numerosity over midline occipital sites very early in the time course, suggesting the involvement of early visual cortex in numerosity processing. However, which specific brain area underlies such early activation is not known. Here, we tested whether numerosity-sensitive neural signatures arise specifically from the initial stages of visual cortex, aiming to localize the generator of these signals by taking advantage of the distinctive folding pattern of early occipital cortices around the calcarine sulcus, which predicts an inversion of polarity of ERPs arising from these areas when stimuli are presented in the upper versus lower visual field. Dot arrays, including 8–32dots constructed systematically across various numerical and non-numerical visual attributes, were presented randomly in either the upper or lower visual hemifields. Our results show that neural responses at about 90ms post-stimulus were robustly sensitive to numerosity. Moreover, the peculiar pattern of polarity inversion of numerosity-sensitive activity at this stage suggested its generation primarily in V2 and V3. In contrast, numerosity-sensitive ERP activity at occipito-parietal channels later in the time course (210–230ms) did not show polarity inversion, indicating a subsequent processing stage in the dorsal stream. Overall, these results demonstrate that numerosity processing begins in one of the earliest stages of the cortical visual stream. •We tested for early visual cortical involvement in magnitude processing.•Subjects viewed dot arrays presented in upper or lower visual field.•This manipulation resulted in ERP polarity inversion, occurring in V2/V3.•The ERPs were selectively sensitive to numerosity and less to non-numerical cues.•This demonstrates that numerosity processing starts in very early visual areas.