Neural Representation Of Space Research Articles

How the Human Brain Represents Perceived Dangerousness or "Predacity" of Animals.

Common or folk knowledge about animals is dominated by three dimensions: (1) level of cognitive complexity or "animacy;" (2) dangerousness or "predacity;" and (3) size. We investigated the neural basis of the perceived dangerousness or aggressiveness of animals, which we refer to more generally as "perception of threat." Using functional magnetic resonance imaging (fMRI), we analyzed neural activity evoked by viewing images of animal categories that spanned the dissociable semantic dimensions of threat and taxonomic class. The results reveal a distributed network for perception of threat extending along the right superior temporal sulcus. We compared neural representational spaces with target representational spaces based on behavioral judgments and a computational model of early vision and found a processing pathway in which perceived threat emerges as a dominant dimension: whereas visual features predominate in early visual cortex and taxonomy in lateral occipital and ventral temporal cortices, these dimensions fall away progressively from posterior to anterior temporal cortices, leaving threat as the dominant explanatory variable. Our results suggest that the perception of threat in the human brain is associated with neural structures that underlie perception and cognition of social actions and intentions, suggesting a broader role for these regions than has been thought previously, one that includes the perception of potential threat from agents independent of their biological class. For centuries, philosophers have wondered how the human mind organizes the world into meaningful categories and concepts. Today this question is at the core of cognitive science, but our focus has shifted to understanding how knowledge manifests in dynamic activity of neural systems in the human brain. This study advances the young field of empirical neuroepistemology by characterizing the neural systems engaged by an important dimension in our cognitive representation of the animal kingdom ontological subdomain: how the brain represents the perceived threat, dangerousness, or "predacity" of animals. Our findings reveal how activity for domain-specific knowledge of animals overlaps the social perception networks of the brain, suggesting domain-general mechanisms underlying the representation of conspecifics and other animals.

How environment and self-motion combine in neural representations of space.

Estimates of location or orientation can be constructed solely from sensory information representing environmental cues. In unfamiliar or sensory-poor environments, these estimates can also be maintained and updated by integrating self-motion information. However, the accumulation of error dictates that updated representations of heading direction and location become progressively less reliable over time, and must be corrected by environmental sensory inputs when available. Anatomical, electrophysiological and behavioural evidence indicates that angular and translational path integration contributes to the firing of head direction cells and grid cells. We discuss how sensory inputs may be combined with self-motion information in the firing patterns of these cells. For head direction cells, direct projections from egocentric sensory representations of distal cues can help to correct cumulative errors. Grid cells may benefit from sensory inputs via boundary vector cells and place cells. However, the allocentric code of boundary vector cells and place cells requires consistent head-direction information in order to translate the sensory signal of egocentric boundary distance into allocentric boundary vector cell firing, suggesting that the different spatial representations found in and around the hippocampal formation are interdependent. We conclude that, rather than representing pure path integration, the firing of head-direction cells and grid cells reflects the interface between self-motion and environmental sensory information. Together with place cells and boundary vector cells they can support a coherent unitary representation of space based on both environmental sensory inputs and path integration signals.

Navigating life.

The discoveries of "place cells" in the hippocampus and "grid cells" in the entorhinal cortex are landmark achievements in relating behavior to neural activity, permitting analysis of a powerful system for spatial representation in the brain. The contributions of this work include not only the empirical findings but also the approach this work pioneered of examining neural activity in complex behaviors with real ecological validity in freely moving animals, and of attempting to place the findings in the larger context of how the neural representations of space are used in service of real-world behavior, namely what the Nobel committee described as permitting us to "navigate our way through a complex environment." These discoveries and approaches have had far-ranging impact on and implications for work in human cognitive neuroscience, where we see (1) confirmation in humans that the hippocampus and overlying MTL cortex are critically engaged in supporting a relational representation of space, and that it can be used for flexible spatial navigation and (2) evidence that these regions are also critically involved in aspects of relational memory not limited to space, and in the flexible use of hippocampal memory extending beyond spatial navigation. Recent work, using tasks that emphasize the requirement for the active use of memory in online processing, just as spatial navigation has long placed such a requirement on rodents, suggests that the hippocampus and related MTL cortex can support the navigating of environments even more complex than what is needed in spatial navigation. It allows us to use memory in guiding upcoming actions and choices to act optimally in and on the world, permitting us to navigate life in all its beautiful complexity.

Distributed cognitive maps reflecting real distances between places and views in the human brain.

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.

Global neural pattern similarity as a common basis for categorization and recognition memory.

Familiarity, or memory strength, is a central construct in models of cognition. In previous categorization and long-term memory research, correlations have been found between psychological measures of memory strength and activation in the medial temporal lobes (MTLs), which suggests a common neural locus for memory strength. However, activation alone is insufficient for determining whether the same mechanisms underlie neural function across domains. Guided by mathematical models of categorization and long-term memory, we develop a theory and a method to test whether memory strength arises from the global similarity among neural representations. In human subjects, we find significant correlations between global similarity among activation patterns in the MTLs and both subsequent memory confidence in a recognition memory task and model-based measures of memory strength in a category learning task. Our work bridges formal cognitive theories and neuroscientific models by illustrating that the same global similarity computations underlie processing in multiple cognitive domains. Moreover, by establishing a link between neural similarity and psychological memory strength, our findings suggest that there may be an isomorphism between psychological and neural representational spaces that can be exploited to test cognitive theories at both the neural and behavioral levels.

Neural Representation of Space: Relation between one- and two-dimensional Environments.

Neural Representation of Space: Relation between one- and two-dimensional Environments.

Building common high-dimensional models of neural representational spaces

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Which coordinate system for modelling path integration?

Path integration is a navigation strategy widely observed in nature where an animal maintains a running estimate, called the home vector, of its location during an excursion. Evidence suggests it is both ancient and ubiquitous in nature, and has been studied for over a century. In that time, canonical and neural network models have flourished, based on a wide range of assumptions, justifications and supporting data. Despite the importance of the phenomenon, consensus and unifying principles appear lacking. A fundamental issue is the neural representation of space needed for biological path integration. This paper presents a scheme to classify path integration systems on the basis of the way the home vector records and updates the spatial relationship between the animal and its home location. Four extended classes of coordinate systems are used to unify and review both canonical and neural network models of path integration, from the arthropod and mammalian literature. This scheme demonstrates analytical equivalence between models which may otherwise appear unrelated, and distinguishes between models which may superficially appear similar. A thorough analysis is carried out of the equational forms of important facets of path integration including updating, steering, searching and systematic errors, using each of the four coordinate systems. The type of available directional cue, namely allothetic or idiothetic, is also considered. It is shown that on balance, the class of home vectors which includes the geocentric Cartesian coordinate system, appears to be the most robust for biological systems. A key conclusion is that deducing computational structure from behavioural data alone will be difficult or impossible, at least in the absence of an analysis of random errors. Consequently it is likely that further theoretical insights into path integration will require an in-depth study of the effect of noise on the four classes of home vectors.

Dynamic Changes in Brain Activity during Prism Adaptation

Prism adaptation does not only induce short-term sensorimotor plasticity, but also longer-term reorganization in the neural representation of space. We used event-related fMRI to study dynamic changes in brain activity during both early and prolonged exposure to visual prisms. Participants performed a pointing task before, during, and after prism exposure. Measures of trial-by-trial pointing errors and corrections allowed parametric analyses of brain activity as a function of performance. We show that during the earliest phase of prism exposure, anterior intraparietal sulcus was primarily implicated in error detection, whereas parieto-occipital sulcus was implicated in error correction. Cerebellum activity showed progressive increases during prism exposure, in accordance with a key role for spatial realignment. This time course further suggests that the cerebellum might promote neural changes in superior temporal cortex, which was selectively activated during the later phase of prism exposure and could mediate the effects of prism adaptation on cognitive spatial representations.

Dynamics of Parietal Neural Activity during Spatial Cognitive Processing

Dynamic neural processing unrelated to changes in sensory input or motor output is likely to be a hallmark of cognitive operations. Here we show that neural representations of space in parietal cortex are dynamic while monkeys perform a spatial cognitive operation on a static visual stimulus. We recorded neural activity in area 7a during a visual maze task in which monkeys mentally followed a path without moving their eyes. We found that the direction of the followed path could be recovered from neuronal population activity. When the monkeys covertly processed a path that turned, the population representation of path direction shifted in the direction of the turn. This neural population dynamic took place during a period of unchanging visual input and showed characteristics of both serial and parallel processing. The data suggest that the dynamic evolution of parietal neuronal activity is associated with the progression of spatial cognitive operations.

Neural Correlates of Spatial Judgement during Object Construction in Parietal Cortex

We recorded the activity of parietal area 7a neurons in monkeys performing an object construction task. In each trial, a model object consisting of a variable arrangement of squares was presented, followed after a delay by a copy of the model object that was missing a single square. Monkeys replaced the missing square to reconstruct the model configuration. Activity of many 7a neurons varied systematically with the position of the missing square and predicted where monkeys were going to add parts to the object they were building. The location of the missing square was a computed spatial datum important to object construction which did not correlate with the retinal location of a visual stimulus or the direction of the required motor response. The population of cells coding this coordinate was generally inactive when the same spatial locations were made relevant by visual targets to which monkeys either planned saccades or directed attention in other behavioral contexts. The data suggest that some parietal neurons participate in neural representations of space that reflect spatial cognitive as opposed to sensorimotor processing, coding the results of spatial computations performed on visual stimuli to meet cognitive objectives.

THE HIPPOCAMPAL AND PARIETAL FOUNDATIONS OF SPATIAL COGNITION.: By N. Burgess, K. J. Jeffrey and J. O'Keefe. 1999. Oxford: Oxford University Press. Price 29.50. Pp. 490. ISBN 0-19-852452-8.

A considerable amount of work has been carried out investigating the neural mechanisms underlying spatial memory. This is a timely and well-constructed book that brings together work from influential researchers investigating the hippocampal and parietal contributions to spatial learning and memory. What is important about this book is that it attempts to integrate these fields and explore how these brain regions may interact during memory processing. The work is clearly described and presented at a level that will be appreciated both by researchers in the area and postgraduate students who are new to the field. The book is divided into three sections: the first two outline the roles of the parietal cortex and hippocampal formation in processing spatial information, respectively; the third section explores the interactions between the parietal cortex and hippocampus in spatial information processing. Damage to the human parietal cortex results in disturbances of spatial perception and action in space. The best-characterized deficit in (predominantly right) parietal lobe patients is a failure to explore the part of space located contralateral to the lesion. Different mechanisms and neural representations of space have been offered to explain parietal neglect. The first series of chapters consider two main themes in parietal research: first, characterization of parietal lobe impairments in spatial learning; and secondly, the potential neuronal mechanisms underlying the parietal representation of space. The chapters by Vallar and Karnath provide contrasting characterizations of parietal neglect. Vallar presents evidence that the parietal deficit in spatial cognition may reflect a translation in the egocentric frame of reference. In contrast, Karnath proposes that neglect may be characterized by a rotation of the egocentric reference frame. Driver discusses whether the spatial neglect shown by parietal patients extends to the processing of individual objects. This view is complemented by the chapter from Olsen et al . …

Multiple perceptual distortions and their modulation in leftsided visual neglect

There is an ongoing debate concerning the perception and neural representation of space in neglect. Four experiments are here reported designed to further investigate the nature of perceptual distortions and their modifiability in patients with neglect. In Experiment 1 it was found that neglect patients, in contrast to left- or right-hemisphere lesioned control patients and normal subjects, show similar distortions of perceived visual space when judging the extension of horizontal distances ( space distortion) as compared to the horizontal size of objects ( size distortion). Similar deficits were present in most neglect patients in a newly developed space bisection task. These results attest that neglect patients have perceptual distortions related to within-object (size) and between-object (distance) spatial processing in their horizontal plane. Objects were oversized by 33% and distances by 19% horizontally in neglect patients, whereas all control groups showed nearly veridical spatial coding (deviations<5%). In Experiment 2 the modifiability of these distortions was tested by the use of slow visual background motion. Leftward, coherent background motion transiently restored normal horizontal size and distance coding in neglect patients, whereas rightward motion aggravated the deficit significantly in the distance task, but not in the size task. None of the other subject groups showed any influence of background motion on spatial judgments. Experiment 3 evaluated possible effects of simultaneous vs successive stimulus presentation in perceptual distortions, thus modulating attentional factors. Neglect patients performed significantly better — although not normal — with a successive presentation of the spatial stimuli (2 s, 10 s delay) as compared to the simultaneous condition in the size judgment task, but not in the distance task. In contrast, this manipulation had no effects in any of the control groups. Experiment 4 reports more detailed results of subject J.S., a neglect patient with a right mediotemporal lesion, who showed a marked horizontal size distortion, but normal horizontal distance judgments. Despite some fluctuation in J.S.’s size judgments he showed a significant overestimation of horizontal object size by +22% to +40% across several test blocks and testing sessions. Thus, performance fluctuations due to attentional or other reasons cannot fully account for J.S.’s dissociation in size vs distance judgments. He thus shows that the visual coding of horizontal spatial extension within an object can be dissociated from that of the spatial extension between objects along the horizontal plane. Finally, performance in the three spatial tasks (used in Experiment 1) was found to correlate significantly with three typical tests of spatial neglect (line bisection, cancellation, copying, r=0.42–0.77), thereby indicating a significant relationship to the neglect syndrome. Together, the results of the four experiments are interpreted in support of multiple spatial–perceptual distortions in visual neglect, which are influenced by visual motion and attention. Perceptual distortions relating to objects and space between objects are present in most neglect patients, but may dissociate, as in case J.S. It is argued that these might reflect the existence of several, partially overlapping and diverging neural maps for the representation of different spatial attributes in the horizontal plane. Furthermore, it is hypothesized that these perceptual distortions constitute an important element of the spatial–perceptual deficits encountered in the syndrome, contribute to its severity, but are not the key deficit of the disorder.

Perception of horizontal distances in patients with spatial neglect.

Two different models have argued that neglect of contralateral stimuli following brain damage might be associated with either a compressed or an anisometric neural representation of space along the earth-horizontal axis. We tested these models by determining neglect patients' perception of spatial distances in the horizontal plane. We found no evidence for any compression or expansion or for anisometry along the earth-horizontal axis. The findings argue against a distortion of subjective space along the horizontal axis in patients with neglect, which could account for their failure to orient towards and to explore the contralesional parts of space.

Effects of eye position on auditory localization and neural representation of space in superior colliculus of cats.

The maps of visual and auditory space within the superior colliculus are in approximate register both with each other and with the underlying motor maps associated with orienting responses. The fact that eyes and ears can move independently poses a problem for the sensorimotor organization of these two modalities. By monitoring eye and pinna positions in alert, head-fixed cats, we showed that the accuracy of saccadic eye movements to auditory targets was little affected by eye eccentricity (range +/- 15 deg) at the onset of the sound. A possible neural basis for this behavioral compensation was suggested by recordings from superior colliculus neurons. The preferred sound directions of some neurons in the deep layers of this midbrain nucleus exhibited a shift with the direction of gaze, while in others the response throughout the auditory receptive field was either increased or decreased, suggesting that changes in eye position alter the gain of the auditory response.

Disturbed coordinate transformation in the neural representation of space as the crucial mechanism leading to neglect

Abstract Karnath (1988) and Gainotti, D'Erme and De Bonis (1989). suggested that the typical and severe neglect symptomology that is seen predominantly after lesions of the right hemisphere, is due to the combined effect of at least two different components: (1) an imbalance of lateral orienting tendencies with spontaneously primary orienting towards the ipsilesional side; together with (2) a deficit in orienting attention (from this primary focus), as well as eye or limb movements, to the contralesional side of the sagittal midplane.

Monaural and binaural spectrum level cues in the ferret: acoustics and the neural representation of auditory space

1. The role of the structures of the outer ear in producing monaural and binaural spectral cues to sound location was examined acoustically in the ferret. A probe microphone was introduced across the wall of the external auditory canal and its responses to digitally constructed wideband signals were recorded for a large number of free field locations. 2. In the intact animal the patterns of both monaural and binaural cues were asymmetrical for horizontal locations about the interaural axis. For anterior sound locations the monaural transformations demonstrated relative gains at middle and high frequencies and a location-dependent frequency notch. Changing elevation resulted in variations in the corner frequencies of these spectral features. Additionally, there was greater front-back asymmetry in the binaural spectral cues for locations in lateral space when compared with locations near the midline. 3. Surgical removal of the pinna and concha (pinnectomy) eliminated all the major front-back asymmetrical features in the horizon monaural and binaural spectral transformations as well as the elevation-dependent variations in the monaural spectra. Thus the residual transformations were ambiguous for sound locations in lateral space, resulting in "cones of confusion" centered on the interaural axis. 4. These cues were reflected in the topographic representation of auditory space in the deeper layers of the superior colliculus (SC). Previous studies have shown that spatial tuning at near-threshold sound levels is based on monaural pinna cues, whereas binaural inputs are utilized at higher levels that stimulate both ears. In the intact ferret we examined statistically the topography of the representation of sound azimuth for near-threshold and suprathreshold stimuli and the alignment of the auditory and visual representations in the SC. The distributions of auditory best positions within the SC for near- and suprathreshold stimulus levels were statistically indistinguishable, suggesting that both monaural and binaural cues are integrated in this neural representation of space. 5. Pinnectomy resulted in a large increase in the number of auditory units that responded best to two distinct locations in space. One lobe of the response was tuned appropriately in terms of the position of the unit within the SC, demonstrating that the residual acoustical cues are sufficient for the construction of a topographic representation of auditory space. However, the second region of space, thereby producing an ambiguous representation.(ABSTRACT TRUNCATED AT 400 WORDS)