Neural representation of scene boundaries

The occipital place area represents the local elements of scenes

Neural responses to visual scenes reveals inconsistencies between fMRI adaptation and multivoxel pattern analysis

The perception and imagery of landmarks activate similar content‐dependent brain areas, including occipital and temporo‐medial brain regions. However, how these areas interact during visual perception and imagery of scenes, especially when recollecting their spatial location, remains unknown. Here, we combined functional magnetic resonance imaging (fMRI), resting‐state functional connectivity (rs‐fc), and effective connectivity to assess spontaneous fluctuations and task‐induced modulation of signals among regions entailing scene‐processing, the primary visual area and the hippocampus (HC), responsible for the retrieval of stored information. First, we functionally defined the scene‐selective regions, that is, the occipital place area (OPA), the retrosplenial complex (RSC) and the parahippocampal place area (PPA), by using the face/scene localizer, observing that two portions of the PPA—anterior and posterior PPA—were consistently activated in all subjects. Second, the rs‐fc analysis (n = 77) revealed a connectivity pathway similar to the one described in macaques, showing separate connectivity routes linking the anterior PPA with RSC and HC, and the posterior PPA with OPA. Third, we used dynamic causal modelling to evaluate whether the dynamic couplings among these regions differ between perception and imagery of familiar landmarks during a fMRI task (n = 16). We found a positive effect of HC on RSC during the retrieval of imagined places and an effect of occipital regions on both RSC and pPPA during the perception of scenes. Overall, we propose that under similar functional architecture at rest, different neural interactions take place between regions in the occipito‐temporal higher‐level visual cortex and the HC, subserving scene perception and imagery.

The parahippocampal place area (PPA) is one of several brain regions that respond more strongly to scenes than to non-scene items such as objects and faces. The mechanism underlying this scene-preferential response remains unclear. One possibility is that the PPA is tuned to low-level stimulus features that are found more often in scenes than in less-preferred stimuli. Supporting this view, Nasr et al. (2014) recently observed that some of the stimuli that are known to strongly activate the PPA contain a large number of rectilinear edges. They further demonstrated that PPA response is modulated by rectilinearity for a range of non-scene images. Motivated by these results, we tested whether rectilinearity suffices to explain PPA selectivity for scenes. In the first experiment, we replicated the previous finding of modulation by rectilinearity in the PPA for arrays of 2-d shapes. However, two further experiments failed to find a rectilinearity effect for faces or scenes: high-rectilinearity faces and scenes did not activate the PPA any more strongly than low-rectilinearity faces and scenes. Moreover, the categorical advantage for scenes vs. faces was maintained in the PPA and two other scene-selective regions—the retrosplenial complex (RSC) and occipital place area (OPA)—when rectilinearity was matched between stimulus sets. We conclude that selectivity for scenes in the PPA cannot be explained by a preference for low-level rectilinear edges.

Perceived egocentric distance sensitivity and invariance across scene-selective cortex

Spatial knowledge about an environment can be cued from memory by perception of a visual scene during active navigation or by imagination of the relationships between nonvisible landmarks, such as when providing directions. It is not known whether these different ways of accessing spatial knowledge elicit the same representations in the brain. To address this issue, we scanned participants with fMRI, while they performed a judgment of relative direction (JRD) task that required them to retrieve real-world spatial relationships in response to either pictorial or verbal cues. Multivoxel pattern analyses revealed several brain regions that exhibited representations that were independent of the cues to access spatial memory. Specifically, entorhinal cortex in the medial temporal lobe and the retrosplenial complex (RSC) in the medial parietal lobe coded for the heading assumed on a particular trial, whereas the parahippocampal place area (PPA) contained information about the starting location of the JRD. These results demonstrate the existence of spatial representations in RSC, ERC, and PPA that are common to visually guided navigation and spatial imagery.

A number of regions in the human brain are known to be involved in processing natural scenes, but the field has lacked a unifying framework for understanding how these different regions are organized and interact. We provide evidence from functional connectivity and meta-analyses for a new organizational principle, in which scene processing relies upon two distinct networks that split the classically defined parahippocampal place area (PPA). The first network of strongly connected regions consists of the occipital place area/transverse occipital sulcus and posterior PPA, which contain retinotopic maps and are not strongly coupled to the hippocampus at rest. The second network consists of the caudal inferior parietal lobule, retrosplenial complex, and anterior PPA, which connect to the hippocampus (especially anterior hippocampus), and are implicated in both visual and nonvisual tasks, including episodic memory and navigation. We propose that these two distinct networks capture the primary functional division among scene-processing regions, between those that process visual features from the current view of a scene and those that connect information from a current scene view with a much broader temporal and spatial context. This new framework for understanding the neural substrates of scene-processing bridges results from many lines of research, and makes specific functional predictions.

The human entorhinal-hippocampal circuitry is characterized by an information-specific functional organization where two routes, that are preferentially connected to the parahippocampal cortex or the perirhinal and retrosplenial cortices, divide the entorhinal cortex as well as hippocampal subiculum and CA1 subregions.

Keeping oriented in the environment is a multifaceted ability that requires knowledge of at least three pieces of information: one’s own location (“place”) and orientation (“heading”) within the environment, and which location in the environment one is looking at (“view”). We used functional magnetic resonance imaging (fMRI) in humans to examine the neural signatures of these information. Participants were scanned while viewing snapshots which varied for place, view and heading within a virtual room. We observed adaptation effects, proportional to the physical distances between consecutive places and views, in scene-responsive (retrosplenial complex and parahippocampal gyrus), fronto-parietal and lateral occipital regions. Multivoxel pattern classification of signals in scene-responsive regions and in the hippocampus allowed supra-chance decoding of place, view and heading, and revealed the existence of map-like representations, where places and views closer in physical space entailed activity patterns more similar in neural representational space. The pattern of hippocampal activity reflected both view- and place-based distances, the pattern of parahippocampal activity preferentially discriminated between views, and the pattern of retrosplenial activity combined place and view information, while the fronto-parietal cortex only showed transient effects of changes in place, view, and heading. Our findings provide evidence for the presence of map-like spatial representations which reflect metric distances in terms of both one’s own and landmark locations.

Human adults flawlessly and effortlessly navigate boundaries and obstacles in the immediately visible environment, a process we refer to as guided navigation. Neuroimaging work in adults suggests this ability involves the occipital place area (OPA) [1, 2]-a scene-selective region in the dorsal stream that selectively represents information necessary for visually guided navigation [3-9]. Despite progress in understanding the neural basis of visually guided navigation, however, little is known about how this system develops. Is navigationally relevant information processing present in the first few years of life? Or does this information processing only develop after many years of experience? Although a handful of studies have found selective responses to scenes (relative to objects) in OPA in childhood [10-13], no study has explored how more specific navigationally relevant information processing emerges in this region. Here, we do just that by measuring OPA responses to first-person perspective motion information-a proxy for the visual experience of actually navigating the immediate environment-using fMRI in 5- and 8-year-old children. We found that, although OPA already responded more to scenes than objects by age 5, responses to first-person perspective motion were not yet detectable at this same age and rather only emerged by age 8. This protracted development was specific to first-person perspective motion through scenes, not motion on faces or objects, and was not found in other scene-selective regions (the parahippocampal place area or retrosplenial complex) or a motion-selective region (MT). These findings therefore suggest that navigationally relevant information processing in OPA undergoes prolonged development across childhood.

The Neurocognitive Basis of Spatial Reorientation

Texture provides crucial information about the category or identity of a scene. Nonetheless, not much is known about how the texture information in a scene is represented in the brain. Previous studies have shown that the parahippocampal place area (PPA), a scene-selective part of visual cortex, responds to simple patches of texture ensemble. However, in natural scenes textures exist in spatial context within a scene. Here we tested two hypotheses that make different predictions on how textures within a scene context are represented in the PPA. The Texture-Only hypothesis suggests that the PPA represents texture ensemble (i.e., the kind of texture) as is, irrespective of its location in the scene. On the other hand, the Texture and Location hypothesis suggests that the PPA represents texture and its location within a scene (e.g., ceiling or wall) conjointly. We tested these two hypotheses across two experiments, using different but complementary methods. In experiment 1, by using multivoxel pattern analysis (MVPA) and representational similarity analysis, we found that the representational similarity of the PPA activation patterns was significantly explained by the Texture-Only hypothesis but not by the Texture and Location hypothesis. In experiment 2, using a repetition suppression paradigm, we found no repetition suppression for scenes that had the same texture ensemble but differed in location (supporting the Texture and Location hypothesis). On the basis of these results, we propose a framework that reconciles contrasting results from MVPA and repetition suppression and draw conclusions about how texture is represented in the PPA.NEW & NOTEWORTHY This study investigates how the parahippocampal place area (PPA) represents texture information within a scene context. We claim that texture is represented in the PPA at multiple levels: the texture ensemble information at the across-voxel level and the conjoint information of texture and its location at the within-voxel level. The study proposes a working hypothesis that reconciles contrasting results from multivoxel pattern analysis and repetition suppression, suggesting that the methods are complementary to each other but not necessarily interchangeable.

BackgroundLittle is known about the structural neural connectivity between the primary auditory cortex and cognition-related brain areas in the human brain. This study aimed to evaluate the structural neural connectivity between the primary auditory cortex and cognition-related brain areas in normal subjects, using diffusion tensor tractography (DTT).Material/MethodsForty-three healthy subjects with no prior history of audiological, neurological, physical, or psychiatric illnesses were recruited for this study. Diffusion tensor imaging data analysis was performed using the Oxford Centre for Functional Magnetic Resonance Imaging of Brain (FMRIB) Software Library. In each subject, a region of interest was set on the primary auditory cortex, including the subcortical white matter. We assessed the neural connectivity between the primary auditory cortex and cognition-related brain areas (the dorsolateral prefrontal cortex [DLPFC]; ventrolateral prefrontal cortex [VLPFC]; orbitofrontal cortex [OFC]; hippocampus; parahippocampal cortex; amygdala, anterior and posterior cingulate gyrus; and fornix).ResultsAccording to the results of DTT, the primary auditory cortex showed neural connectivity (over 50%) with the following areas: the threshold of 1 streamline – the VLPFC (94.2%), OFC (84.9%), fornix (80.2%), hippocampus (76.7%), parahippocampal cortex(74.4%) and DLPFC (58.1%); the threshold of 5 streamlines – the VLPFC (88.4%), OFC (81.4%), fornix (66.3%), hippocampus (55.8%), and parahippocampal cortex (53.5%); and the threshold of 15 streamlines – the VLPFC (82.6%), OFC (74.4%), and fornix (53.5%).ConclusionsIn normal human subjects, DTT showed that the primary auditory cortex had a high degree of neural connectivity with the prefrontal cortex, fornix, hippocampus, and parahippocampal cortex, which are brain areas associated with cognition and memory.

Diffusion-weighted imaging features of brain in obesity

The human parahippocampal gyrus forms a large part of the limbic lobe along the ventromedial part of the temporal cortical mantle. It is a variable and complicated cortex in terms of structure, and the latter is aggravated further by interfaces with the anterior insula anteriorly and the cingulate gyrus and occipital lobe posteriorly. Additional complications relate to its lateral border with the temporal cortex and especially the sulcal configurations that define this junction. The rhinal sulcus, which separates parahippocampal and temporal cortices in other species, including the anthropoid apes, is either lacking or rudimentary in the human brain. Thus, defining this junction requires cytoarchitectural examination and precludes the use of mere inspection of sulcal existing patterns. The cortical areas that form the parahippocampal gyrus are vulnerable to pathological changes in Alzheimer's disease (AD), and its entorhinal and perirhinal subdivisions are both the most heavily damaged cortical areas and the focus for disease onset. The neurons that acquire neurofibrillary tangles (NFTs) occupy the junction of the isocortical mantle with the limbic cortical mantle, but share, or partially share, a vulnerability phenotype with large neurons in both domains. The differential expression of this phenotype across time creates the false impression of NFT spread in cross-sectional comparisons of AD brains. The questions of what this phenotype is and why it is expressed first in the perirhinal and entorhinal cortices of the parahippocampal gyrus are the central molecular biological/neuroanatomical questions in understanding the etiology of AD.