Dynamic Neural Network Reconfiguration During the Generation and Reinstatement of Mnemonic Representations.

Mnemonic representations allow humans to re-experience the past or simulate future scenarios by integrating episodic features from memory. Theoretical models posit that mnemonic representations require dynamic processing between neural indexes in the hippocampus and areas of the cortex providing specialized information processing. However, it remains unknown whether global and local network topology varies as information is encoded into a mnemonic representation and subsequently reinstated. Here, we investigated the dynamic nature of memory networks while a representation of a virtual city is generated and reinstated during mental simulations. We find that the brain reconfigures from a state of heightened integration when encoding demands are highest, to a state of localized processing once representations are formed. This reconfiguration is associated with changes in hippocampal centrality at the intra- and inter-module level, decreasing its role as a connector hub between modules and within a hippocampal neighborhood as encoding demands lessen. During mental simulations, we found increased levels of hippocampal centrality within its local neighborhood coupled with decreased functional interactions between other regions of the neighborhood during highly vivid simulations, suggesting that information flow vis-à-vis the hippocampus is critical for high fidelity recapitulation of mnemonic representations.

Mental simulation of routes during navigation involves adaptive temporal compression.

Mental simulation is a hallmark feature of human cognition, allowing features from memories to be flexibly used during prospection. While past studies demonstrate the preservation of real-world features such as size and distance during mental simulation, their temporal dynamics remains unknown. Here, we compare mental simulations to navigation of routes in a large-scale spatial environment to test the hypothesis that such simulations are temporally compressed in an adaptive manner. Our results show that simulations occurred at 2.39× the speed it took to navigate a route, increasing in compression (3.57×) for slower movement speeds. Participant self-reports of vividness and spatial coherence of simulations also correlated strongly with simulation duration, providing an important link between subjective experiences of simulated events and how spatial representations are combined during prospection. These findings suggest that simulation of spatial events involve adaptive temporal mechanisms, mediated partly by the fidelity of memories used to generate the simulation.

Efficacy of identifying neural components in the face and emotion processing system in schizophrenia using a dynamic functional localizer.

Schizophrenia is associated with deficits in face perception and emotion recognition. Despite consistent behavioural results, the neural mechanisms underlying these cognitive abilities have been difficult to isolate, in part due to differences in neuroimaging methods used between studies for identifying regions in the face processing system. Given this problem, we aimed to validate a recently developed fMRI-based dynamic functional localizer task for use in studies of psychiatric populations and specifically schizophrenia. Previously, this functional localizer successfully identified each of the core face processing regions (i.e. fusiform face area, occipital face area, superior temporal sulcus), and regions within an extended system (e.g. amygdala) in healthy individuals. In this study, we tested the functional localizer success rate in 27 schizophrenia patients and in 24 community controls. Overall, the core face processing regions were localized equally between both the schizophrenia and control group. Additionally, the amygdala, a candidate brain region from the extended system, was identified in nearly half the participants from both groups. These results indicate the effectiveness of a dynamic functional localizer at identifying regions of interest associated with face perception and emotion recognition in schizophrenia. The use of dynamic functional localizers may help standardize the investigation of the facial and emotion processing system in this and other clinical populations.

Functional activation abnormalities during facial emotion perception in schizophrenia patients and nonpsychotic relatives.

BACKGROUND: Deficits in facial emotion perception in schizophrenia may be a marker of disorder liability. Previous functional magnetic resonance imaging (fMRI) studies investigating these deficits have been limited by task demands that may recruit other impaired cognitive processes in schizophrenia. METHODS: We used a family study design along with a passive viewing task during fMRI to investigate brain activation abnormalities underlying facial emotion perception in schizophrenia and examine whether such abnormalities are associated with the genetic liability to the disorder. Twenty-eight schizophrenia patients, 27 nonpsychotic relatives, and 27 community controls passively viewed images of facial emotions during an fMRI scan. RESULTS: Analyses revealed hypoactivation in face processing areas for both patients and relatives compared to controls, and hyperactivation in relatives compared to both patients and controls for frontal regions implicated in emotion processing. CONCLUSIONS: Results suggest that activation abnormalities during facial emotion perception are manifestations of the genetic liability to schizophrenia, and may be accompanied by compensatory mechanisms in relatives. Studying mechanisms in nonpsychotic relatives is a valuable way to examine effects of the unexpressed genetic liability to schizophrenia on the brain and behaviour.

Spatial and temporal functional connectivity changes between resting and attentive states.

Remote brain regions show correlated spontaneous activity at rest within well described intrinsic connectivity networks (ICNs). Meta-analytic coactivation studies have uncovered networks similar to resting ICNs, suggesting that in task states connectivity modulations may occur principally within ICNs. However, it has also been suggested that specific "hub" regions dynamically link networks under different task conditions. Here, we used functional magnetic resonance imaging at rest and a continuous visual attention task in 16 participants to investigate whether a shift from rest to attention was reflected by within-network connectivity modulation, or changes in network topography. Our analyses revealed evidence for both modulation of connectivity within the default-mode (DMN) and dorsal attention networks (DAN) between conditions, and identified a set of regions including the temporoparietal junction (TPJ) and posterior middle frontal gyrus (MFG) that switched between the DMN and DAN depending on the task. We further investigated the temporal nonstationarity of flexible (TPJ and MFG) regions during both attention and rest. This showed that moment-to-moment differences in connectivity at rest mirrored the variation in connectivity between tasks. Task-dependent changes in functional connectivity of flexible regions may, therefore, be understood as shifts in the proportion of time specific connections are engaged, rather than a switch between networks per se. This ability of specific regions to dynamically link ICNs under different task conditions may play an important role in behavioral flexibility.

Intraparietal sulcus activity and functional connectivity supporting spatial working memory manipulation.

The intraparietal sulcus (IPS) is recruited during tasks requiring attention, maintenance and manipulation of information in working memory (WM). While WM tasks often show broad bilateral engagement along the IPS, topographic maps of contralateral (CL) visual space have been identified along the IPS, similar to retinotopic maps in visual cortex. In the present study, we asked how these visuotopic IPS regions are differentially involved in the maintenance and manipulation of spatial information in WM. Visuotopic mapping was performed in 26 participants to define regions of interest along the IPS, corresponding to previously described IPS0-4. In a separate task, we showed that while maintaining the location of a briefly flashed target in WM preferentially engaged CL IPS, manipulation of spatial information by mentally rotating the target around a circle engaged bilateral IPS, peaking in IPS1 in most participants. Functional connectivity analyses showed increased interaction between the IPS and prefrontal regions during manipulation, as well as interhemispheric interactions. Two control tasks demonstrated that covert attention shifts, and nonspatial manipulation (arithmetic), engaged patterns of IPS activation and connectivity that were distinct from WM manipulation. These findings add to our understanding of the role of IPS in spatial WM maintenance and manipulation.

A critical review of the allocentric spatial representation and its neural underpinnings: toward a network-based perspective.

While the widely studied allocentric spatial representation holds a special status in neuroscience research, its exact nature and neural underpinnings continue to be the topic of debate, particularly in humans. Here, based on a review of human behavioral research, we argue that allocentric representations do not provide the kind of map-like, metric representation one might expect based on past theoretical work. Instead, we suggest that almost all tasks used in past studies involve a combination of egocentric and allocentric representation, complicating both the investigation of the cognitive basis of an allocentric representation and the task of identifying a brain region specifically dedicated to it. Indeed, as we discuss in detail, past studies suggest numerous brain regions important to allocentric spatial memory in addition to the hippocampus, including parahippocampal, retrosplenial, and prefrontal cortices. We thus argue that although allocentric computations will often require the hippocampus, particularly those involving extracting details across temporally specific routes, the hippocampus is not necessary for all allocentric computations. We instead suggest that a non-aggregate network process involving multiple interacting brain areas, including hippocampus and extra-hippocampal areas such as parahippocampal, retrosplenial, prefrontal, and parietal cortices, better characterizes the neural basis of spatial representation during navigation. According to this model, an allocentric representation does not emerge from the computations of a single brain region (i.e., hippocampus) nor is it readily decomposable into additive computations performed by separate brain regions. Instead, an allocentric representation emerges from computations partially shared across numerous interacting brain regions. We discuss our non-aggregate network model in light of existing data and provide several key predictions for future experiments.

Developmental topographical disorientation and decreased hippocampal functional connectivity.

Developmental topographical disorientation (DTD) is a newly discovered cognitive disorder in which individuals experience a lifelong history of getting lost in both novel and familiar surroundings. Recent studies have shown that such a selective orientation defect relies primarily on the inability of the individuals to form cognitive maps, i.e., mental representations of the surrounding that allow individuals to get anywhere from any location in the environment, although other orientation skills are additionally affected. To date, the neural correlates of this developmental condition are unknown. Here, we tested the hypothesis that DTD may be related to ineffective functional connectivity between the hippocampus (HC; known to be critical for cognitive maps) and other brain regions critical for spatial orientation. A group of individuals with DTD and a group of control subjects underwent a resting-state functional magnetic resonance imaging (rsfMRI) scan. In addition, we performed voxel-based morphometry to investigate potential structural differences between individuals with DTD and controls. The results of the rsfMRI study revealed a decreased functional connectivity between the right HC and the prefrontal cortex (PFC) in individuals with DTD. No structural differences were detected between groups. These findings provide evidence that ineffective functional connectivity between HC and PFC may affect the monitoring and processing of spatial information while moving within an environment, resulting in the lifelong selective inability of individuals with DTD to form cognitive maps that are critical for orienting in both familiar and unfamiliar surroundings.

Neuroticism and self-evaluation measures are related to the ability to form cognitive maps critical for spatial orientation.

Trait neuroticism is suggested to be related to measures of volume and function of the hippocampus, a brain structure located in the medial temporal lobe that is critical for human navigation and orientation. In this study, we assessed whether measures of trait neuroticism and self-concept are correlated with the human ability to orient by means of cognitive maps (i.e. mental representations of an environment that include landmarks and their spatial relationships). After controlling for gender differences, which are well-known in spatial orientation abilities, we found that measures of neuroticism (i.e. negative affect, emotional stability) and self-concept (i.e. self-esteem) were correlated with individual differences in the rate at which cognitive maps were formed; the same measures were generally unrelated to the ability to make use of cognitive maps, as well as the ability to orient using visual path integration. The relationships (and lack thereof) between personality traits and the spatial orientation skills, as reported in the present study, are consistent with specific neural correlates underlying these factors, and may have important implications for treatment of disorders related to them.

Differential neural network configuration during human path integration.

Path integration is a fundamental skill for navigation in both humans and animals. Despite recent advances in unraveling the neural basis of path integration in animal models, relatively little is known about how path integration operates at a neural level in humans. Previous attempts to characterize the neural mechanisms used by humans to visually path integrate have suggested a central role of the hippocampus in allowing accurate performance, broadly resembling results from animal data. However, in recent years both the central role of the hippocampus and the perspective that animals and humans share similar neural mechanisms for path integration has come into question. The present study uses a data driven analysis to investigate the neural systems engaged during visual path integration in humans, allowing for an unbiased estimate of neural activity across the entire brain. Our results suggest that humans employ common task control, attention and spatial working memory systems across a frontoparietal network during path integration. However, individuals differed in how these systems are configured into functional networks. High performing individuals were found to more broadly express spatial working memory systems in prefrontal cortex, while low performing individuals engaged an allocentric memory system based primarily in the medial occipito-temporal region. These findings suggest that visual path integration in humans over short distances can operate through a spatial working memory system engaging primarily the prefrontal cortex and that the differential configuration of memory systems recruited by task control networks may help explain individual biases in spatial learning strategies.

Neural network configuration and efficiency underlies individual differences in spatial orientation ability.

Spatial orientation is a complex cognitive process requiring the integration of information processed in a distributed system of brain regions. Current models on the neural basis of spatial orientation are based primarily on the functional role of single brain regions, with limited understanding of how interaction among these brain regions relates to behavior. In this study, we investigated two sources of variability in the neural networks that support spatial orientation--network configuration and efficiency--and assessed whether variability in these topological properties relates to individual differences in orientation accuracy. Participants with higher accuracy were shown to express greater activity in the right supramarginal gyrus, the right precentral cortex, and the left hippocampus, over and above a core network engaged by the whole group. Additionally, high-performing individuals had increased levels of global efficiency within a resting-state network composed of brain regions engaged during orientation and increased levels of node centrality in the right supramarginal gyrus, the right primary motor cortex, and the left hippocampus. These results indicate that individual differences in the configuration of task-related networks and their efficiency measured at rest relate to the ability to spatially orient. Our findings advance systems neuroscience models of orientation and navigation by providing insight into the role of functional integration in shaping orientation behavior.

Structural connectivity of visuotopic intraparietal sulcus.

The intraparietal sulcus (IPS) contains topographically organized regions, similar to retinotopic maps in visual cortex. These regions, referred to as IPS1-4, show similar functional responses to the mapping tasks used to define them, yet differing responses to tests of other posterior parietal cortex (PPC) functions such as short-term memory, eye movements and object viewing, suggesting that they may have distinct patterns of structural connectivity to other parts of the brain. The present study combined functional magnetic resonance imaging (fMRI) mapping with diffusion tensor imaging (DTI) to describe white matter connections of visuotopic regions along the IPS, in 25 neurotypical young-adult participants. We found that posterior IPS more likely connects to retinotopically defined visual regions, and superior temporal gyrus, relative to anterior IPS. Anterior IPS regions 3 and 4 had higher connection probabilities to prefrontal regions, relative to posterior IPS. All four IPS regions showed inter-hemispheric connections to analogous regions in the opposite hemisphere, as well as consistent connections to the thalamus and regions of the striatum. Multivariate pattern classification at the group level reliably distinguished IPS regions from one another on the basis of connectivity patterns, especially for the most distal pairs of regions; occipital and prefrontal regions provided the most discriminating information. These findings advance our understanding of the structure of visuotopic IPS, with implications for functional differences between regions, and possible homologies between humans and macaques. Visuospatial functions dependent on the parietal cortex are frequently impaired in individuals with developmental disorders and those afflicted by cerebrovascular disease; the findings described here can be used as a basis for comparing connectivity differences in these populations.

Cognitive mapping in humans and its relationship to other orientation skills.

Human orientation in novel and familiar environments is a complex skill that can involve numerous different strategies. To date, a comprehensive account of how these strategies interrelate at the behavioural level has not been documented, impeding the development of elaborate systems neuroscience models of spatial orientation. Here, we describe a virtual environment test battery designed to assess five of the core strategies used by humans to orient. Our results indicate that the ability to form a cognitive map is highly related to more basic orientation strategies, supporting previous proposals that encoding a cognitive map requires inputs from multiple domains of spatial processing. These findings provide a topology of numerous primary orientation strategies used by humans during orientation and will allow researchers to elaborate on neural models of spatial cognition that currently do not account for how different orientation strategies integrate over time based on environmental conditions.