Neural codes for one’s own position and direction in a real-world “vista” environment

Humans, like animals, rely on an accurate knowledge of one’s spatial position and facing direction to keep orientated in the surrounding space. Although previous neuroimaging studies demonstrated that scene-selective regions (the parahippocampal place area or PPA, the occipital place area or OPA and the retrosplenial complex or RSC), and the hippocampus (HC) are implicated in coding position and facing direction within small-(room-sized) and large-scale navigational environments, little is known about how these regions represent these spatial quantities in a large open-field environment. Here, we used functional magnetic resonance imaging (fMRI) in humans to explore the neural codes of these navigationally-relevant information while participants viewed images which varied for position and facing direction within a familiar, real-world circular square. We observed neural adaptation for repeated directions in the HC, even if no navigational task was required. Further, we found that the amount of knowledge of the environment interacts with the PPA selectivity in encoding positions: individuals who needed more time to memorize positions in the square during a preliminary training task showed less neural attenuation in this scene-selective region. We also observed adaptation effects, which reflect the real distances between consecutive positions, in scene-selective regions but not in the HC. When examining the multi-voxel patterns of activity we observed that scene-responsive regions and the HC encoded both spatial information and that the RSC classification accuracy for positions was higher in individuals scoring higher to a self-reported questionnaire of spatial abilities. Our findings provide new insight into how the human brain represents a real, large-scale “vista” space, demonstrating the presence of neural codes for position and direction in both scene-selective and hippocampal regions, and revealing the existence, in the former regions, of a map-like spatial representation reflecting real-world distance between consecutive positions

Caloric vestibular stimulation reduces pain and somatoparaphrenia in a severe chronic central post-stroke pain patient: a case study

Central post-stroke pain is a neuropathic syndrome characterized by intolerable contralesional pain and, in rare cases, somatic delusions. To date, there is limited evidence for the effective treatments of this disease. Here we used caloric vestibular stimulation to reduce pain and somatoparaphrenia in a 57-year-old woman suffering from central post-stroke pain. Resting-state functional magnetic resonance imaging was used to assess the neurological effects of this treatment. Following vestibular stimulation we observed impressive improvements in motor skills, pain, and somatic delusions. In the functional connectivity study before the vestibular stimulation, we observed differences in the patient's left thalamus functional connectivity, with respect to the thalamus connectivity of a control group (N = 20), in the bilateral cingulate cortex and left insula. After the caloric stimulation, the left thalamus functional connectivity with these regions, which are known to be involved in the cortical response to pain, disappeared as in the control group. The beneficial use of vestibular stimulation in the reduction of pain and somatic delusion in a CPSP patient is now documented by behavioral and imaging data. This evidence can be applied to theoretical models of pain and body delusions

Functional organization of the caudal part of the human superior parietal lobule

: Like in macaque, the caudal portion of the human superior parietal lobule (SPL) plays a key role in a series of perceptive, visuomotor and somatosensory processes. Here, we review the functional properties of three separate portions of the caudal SPL, i.e., the posterior parieto-occipital sulcus (POs), the anterior POs, and the anterior part of the caudal SPL. We propose that the posterior POs is mainly dedicated to the analysis of visual motion cues useful for object motion detection during self-motion and for spatial navigation, while the more anterior parts are implicated in visuomotor control of limb actions. The anterior POs is mainly involved in using the spotlight of attention to guide reach-to-grasp hand movements, especially in dynamic environments. The anterior part of the caudal SPL plays a central role in visually guided locomotion, being implicated in controlling leg-related movements as well as the four limbs interaction with the environment, and in encoding egomotion-compatible optic flow. Together, these functions reveal how the caudal SPL is strongly implicated in skilled visually-guided behaviors

Functional connectivity between posterior hippocampus and retrosplenial complex predicts individual differences in navigational ability

Individuals vary widely in their ability to orient and navigate within the environment. Previous neuroimaging research has shown that hippocampus (HC) and scene-responsive regions (retrosplenial complex or RSC and parahippocampal gyrus/parahippocampal place area or PPA) are crucial for spatial orienting and navigation. We used resting-state functional connectivity and a self-reported questionnaire of navigational ability to examine the hypothesis that the pattern of reciprocal connections between these regions reflects individual differences in spatial navigation. We found that the functional connectivity between the posterior HC and RSC was significantly higher in good than in poor navigators. These results confirm the crucial role of hippocampal and extra-hippocampal regions in spatial navigation and provide new insight into how spontaneous brain activity may account for individual differences in spatial ability. This article is protected by copyright. All rights reserved

Visuo-spatial attention and semantic memory competition in the parietal cortex

Abstract Neuroimaging studies associate specific functional roles to distinct brain regions investigating separate cognitive processes using dedicated tasks. For example, using both correlative (i.e., fMRI) and causal (i.e., TMS) approaches it has been shown the involvement of intra-parietal sulcus (IPS), as part of the dorsal attention network, in spatial attentional tasks as well as the importance of the angular gyrus (AG), as part of the default mode network, during the selection of relevant information in semantic memory. Nonetheless, in our daily life attention and semantic memory are rarely needed in isolation. In the present TMS study we investigate how the brain combines attentional and semantic memory demands in a single task. Results showed that, compared to a pseudo-TMS, stimulation of IPS, but not AG, affects behavioral performance, thus suggesting its preponderant role in such a combined task. Moreover, the lack of difference between the effect of IPS and AG stimulations seems to suggest that the two regions may be coactivated or that a third-party source might indirectly mediate the interaction between the two networks

Functional connectivity between posterior hippocampus and retrosplenial complex predicts individual differences in navigational ability

Individuals vary widely in their ability to orient and navigate within the environment. Previous neuroimaging research has shown that hippocampus (HC) and scene-responsive regions (retrosplenial complex or RSC and parahippocampal gyrus/parahippocampal place area or PPA) are crucial for spatial orienting and navigation. We used resting-state functional connectivity and a self-reported questionnaire of navigational ability to examine the hypothesis that the pattern of reciprocal connections between these regions reflects individual differences in spatial navigation. We found that the functional connectivity between the posterior HC and RSC was significantly higher in good than in poor navigators. These results confirm the crucial role of hippocampal and extra-hippocampal regions in spatial navigation and provide new insight into how spontaneous brain activity may account for individual differences in spatial ability. This article is protected by copyright. All rights reserved

Implicit coding of location and direction in a familiar, real-world "vista" space

Keeping oriented in the surrounding space requires an accurate representation of one's spatial position and facing direction. Although previous studies provided evidence of specific spatial codes for position and direction within room-sized and large-scale navigational environments, little is known about the mechanisms by which these spatial quantities are represented in a real small-scale environment. Here, we used two spatial tasks requiring participants to encode their own position and facing direction on a series of pictures taken from a familiar circular square. Crucially, directions and positions were incidentally manipulated, so that when participants were required to encode their current position in the square, the perceived direction across consecutive trials was the same, and vice versa. We found a behavioral advantage (priming effect: reduced reaction times and increased accuracy) for repeated directions and positions, even in the absence of any explicit demand to encode either of them. The advantage was higher for repeated directions, indicating that representation of one's own direction is more automatic than representation of one's own location. Furthermore, priming effects were partially mediated by gender: females (but not males) showed a stronger priming effect for repeated directions than for repeated positions. Finally, although priming effects were not linearly related to the physical distances between consecutive positions and directions, they revealed a rough preservation of real-world distance relationships

Interhemispheric interplay between the left and right premotor cortex during grasping as assessed by dynamic causal modelling

Abstract Research on the contribution of the ipsilateral hemisphere to unilateral movements, and how it is mediated by transcallosal connections, has so far provided contradictory findings. By using dynamic causal modelling (DCM) and Parametric Empirical Bayes analyses applied to fMRI data, we sought to describe effective connectivity during pantomimed and imagined right-hand grasping within the grasping network, namely the anterior intraparietal sulcus, ventral and dorsal (PMd) premotor cortex, supplementary motor area and primary motor cortex (M1). The two-fold aim of the present work was to explore a) whether right and left parieto-frontal areas show similar connectivity couplings, and b) the interhemispheric dynamics between these regions across the two hemispheres. We detected a network architecture comparable across hemispheres during executed but not imagined grasping movements. Furthermore, during pantomimed grasping the interhemispheric crosstalk was mainly driven by premotor areas: we found an inhibitory influence from the right PMd toward the left premotor and motor areas and excitatory couplings between homologous ventral premotor and supplementary motor regions. Overall, our results support the view that dissociable components of unilateral grasping execution are encoded by a non-lateralized set of brain areas complexly intertwined by interhemispheric dynamics, whereas motor imagery obeys different principles