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"Space perception"
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Coupling of functional connectivity and regional cerebral blood flow reveals a physiological basis for network hubs of the human brain
Human brain functional networks contain a few densely connected hubs that play a vital role in transferring information across regions during resting and task states. However, the relationship of these functional hubs to measures of brain physiology, such as regional cerebral blood flow (rCBF), remains incompletely understood. Here, we used functional MRI data of blood-oxygenation-level–dependent and arterial-spin–labeling perfusion contrasts to investigate the relationship between functional connectivity strength (FCS) and rCBF during resting and an N -back working-memory task. During resting state, functional brain hubs with higher FCS were identified, primarily in the default-mode, insula, and visual regions. The FCS showed a striking spatial correlation with rCBF, and the correlation was stronger in the default-mode network (DMN; including medial frontal-parietal cortices) and executive control network (ECN; including lateral frontal-parietal cortices) compared with visual and sensorimotor networks. Moreover, the relationship was connection–distance dependent; i.e., rCBF correlated stronger with long-range hubs than short-range ones. It is notable that several DMN and ECN regions exhibited higher rCBF per unit connectivity strength (rCBF/FCS ratio); whereas, this index was lower in posterior visual areas. During the working-memory experiment, both FCS–rCBF coupling and rCBF/FCS ratio were modulated by task load in the ECN and/or DMN regions. Finally, task-induced changes of FCS and rCBF in the lateral-parietal lobe positively correlated with behavioral performance. Together, our results indicate a tight coupling between blood supply and brain functional topology during rest and its modulation in response to task demands, which may shed light on the physiological basis of human brain functional connectome.
Journal Article
Serial dependence in visual perception
Visual input is often noisy and discontinuous, even though the physical environment is generally stable. The authors show that the visual system trades off change sensitivity to capitalize on physical continuity via serial dependence: present perception is biased toward past visual input. This bias is modulated by attention and governed by a spatiotemporally-tuned operator, a continuity field.
Visual input often arrives in a noisy and discontinuous stream, owing to head and eye movements, occlusion, lighting changes, and many other factors. Yet the physical world is generally stable; objects and physical characteristics rarely change spontaneously. How then does the human visual system capitalize on continuity in the physical environment over time? We found that visual perception in humans is serially dependent, using both prior and present input to inform perception at the present moment. Using an orientation judgment task, we found that, even when visual input changed randomly over time, perceived orientation was strongly and systematically biased toward recently seen stimuli. Furthermore, the strength of this bias was modulated by attention and tuned to the spatial and temporal proximity of successive stimuli. These results reveal a serial dependence in perception characterized by a spatiotemporally tuned, orientation-selective operator—which we call a continuity field—that may promote visual stability over time.
Journal Article
Dark and magical places : the neuroscience of navigation
\"An illuminating examination of how the brain helps us to understand and navigate space-and why, sometimes, it doesn't work the way it should. Navigation is one of the most complex tasks our brains perform. And we do it countless times a day-as we drive across town to the airport, or traverse the maze of a supermarket, or walk within our own homes. But why is it that some people are lost on their own street and others can seamlessly navigate a new city after visiting it once? Fueled by his own spatial shortcomings, Christopher Kemp describes the brain regions that orient us in space and the specialized neurons-place cells and grid cells-that do it. He explains how the brain plans routes, recognizes landmarks, and makes sure we leave a room through a door instead of a painting. Along the way, he meets the scientists trying to understand the mental maps of modern humans, and Neanderthals, and lost people everywhere. Dark and Magical Places is an informed and entertaining journey into the mysteries of the mind\"-- Provided by publisher.
Book
Exercise training increases size of hippocampus and improves memory
The hippocampus shrinks in late adulthood, leading to impaired memory and increased risk for dementia. Hippocampal and medial temporal lobe volumes are larger in higher-fit adults, and physical activity training increases hippocampal perfusion, but the extent to which aerobic exercise training can modify hippocampal volume in late adulthood remains unknown. Here we show, in a randomized controlled trial with 120 older adults, that aerobic exercise training increases the size of the anterior hippocampus, leading to improvements in spatial memory. Exercise training increased hippocampal volume by 2%, effectively reversing age-related loss in volume by 1 to 2 y. We also demonstrate that increased hippocampal volume is associated with greater serum levels of BDNF, a mediator of neurogenesis in the dentate gyrus. Hippocampal volume declined in the control group, but higher preintervention fitness partially attenuated the decline, suggesting that fitness protects against volume loss. Caudate nucleus and thalamus volumes were unaffected by the intervention. These theoretically important findings indicate that aerobic exercise training is effective at reversing hippocampal volume loss in late adulthood, which is accompanied by improved memory function.
Journal Article
The representation of serial order in working memory: A matter of space or time?
•Similar neural codes for temporal position and serial position in verbal WM.•Only left IPSa overlap between spatial position and serial position in verbal WM.•Shared neural codes mainly during encoding into WM.
The representation of serial order information is a fundamental aspect of verbal working memory (WM). However, the way our brain represents serial order information remains an open question. The spatial hypothesis considers that auditory-verbal serial order information is recoded using spatial codes, according to a left-to-right dimension for left-to-right readers. The temporal hypothesis considers the intervention of temporal codes for representing serial order information. This fMRI study contrasted the spatial and temporal hypotheses of WM serial order coding by administering an implicit spatial processing task involving the end-of-movement detection of a dot that stabilized on leftward, central or rightward endpoints, an implicit temporal processing task involving the detection of a target sound that occurred at early, middle and late timepoints of an auditory sequence, and a verbal WM task involving the encoding and retention of the serial order of 6-letter lists. We observed shared multivariate neural activity patterns for the encoding of WM serial position information and corresponding timepoints in the temporal processing task, and this in several frontal and parietal areas. Moreover, neural activity patterns in the left anterior IPS also distinguished the different spatial endpoints in the spatial processing task and predicted robustly corresponding serial position information in the WM task. These results provide support for implicit temporal and to a lesser extent, implicit spatial encoding of serial order information in verbal WM.
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Journal Article
Spatial cognition, spatial perception : mapping the self and space
How does knowledge of the body in space relate to an understanding of space itself? Spatial cognition is discussed from two closely related perspectives: the internal mapping of external stimuli (e.g., landmarks and sensory perception of environmental information) and the internal mapping of internally perceived stimuli (e.g., kinesthetic and visual imagery), and their subsequent effects on behaviour. Clarification of what spatial information is present in most perceptual processes and how this is used cognitively in relation to the self in space is then established. Major points and controversies of the various models are discussed, along with evolutionary perspectives of spatial perception and object recognition and comparisons between human and non-human spatial cognitive abilities and behaviours. Written for postgraduate students and researchers, the authors present theoretical and experimental accounts at multiple levels of analysis - perceptual, behavioural and cognitive - providing a thorough review of the mechanisms of spatial cognition.
Book
Distinct roles of forward and backward alpha-band waves in spatial visual attention
Previous research has associated alpha-band [8–12 Hz] oscillations with inhibitory functions: for instance, several studies showed that visual attention increases alpha-band power in the hemisphere ipsilateral to the attended location. However, other studies demonstrated that alpha oscillations positively correlate with visual perception, hinting at different processes underlying their dynamics. Here, using an approach based on traveling waves, we demonstrate that there are two functionally distinct alpha-band oscillations propagating in different directions. We analyzed EEG recordings from three datasets of human participants performing a covert visual attention task (one new dataset with N = 16, two previously published datasets with N = 16 and N = 31). Participants were instructed to detect a brief target by covertly attending to the screen’s left or right side. Our analysis reveals two distinct processes: allocating attention to one hemifield increases top-down alpha-band waves propagating from frontal to occipital regions ipsilateral to the attended location, both with and without visual stimulation. These top-down oscillatory waves correlate positively with alpha-band power in frontal and occipital regions. Yet, different alpha-band waves propagate from occipital to frontal regions and contralateral to the attended location. Crucially, these forward waves were present only during visual stimulation, suggesting a separate mechanism related to visual processing. Together, these results reveal two distinct processes reflected by different propagation directions, demonstrating the importance of considering oscillations as traveling waves when characterizing their functional role.
Journal Article