A central issue of cognitive neuroscience is to understand how a large collection of coupled neurons combines external signals with internal memories into new coherent patterns of meaning. An external stimulus localized at some input spreads over a large assembly of coupled neurons, building up a collective state univocally corresponding to the stimulus. Thus, the synchronization of spike trains of many individual neurons is the basis of a coherent perception. Based on recent investigations of homoclinic chaotic systems and their synchronization, (...) a novel conjecture for the dynamics of single neurons and, consequently, for neuron assemblies is formulated. Homoclinic chaos is proposed as a suitable way to code information in time by trains of equal spikes occurring at apparently erratic times. In order to classify the set of different perceptions, the percept space can be given a metric structure by introducing a distance measure between distinct percepts. The distance in percept space is conjugate to the duration of the perception in the sense that an uncertainty relation in percept space is associated with time-limited perceptions. This coding of different percepts by synchronized spike trains entails fundamental quantum features which are not restricted to microscopic phenomena. It is conjectured that they are related to the details of the perceptual chain rather than depending on Planck's action. (shrink)

Cognitive functions like perception, memory, language, or consciousness are based on highly parallel and distributed information processing by the brain. One of the major unresolved questions is how information can be integrated and how coherent representational states can be established in the distributed neuronal systems subserving these functions. It has been suggested that this so-called ''binding problem'' may be solved in the temporal domain. The hypothesis is that synchronization of neuronal discharges can serve for the integration of distributed neurons into (...) cell assemblies and that this process may underlie the selection of perceptually and behaviorally relevant information. As we intend to show here, this temporal binding hypothesis has implications for the search of the neural correlate of consciousness. We review experimental results, mainly obtained in the visual system, which support the notion of temporal binding. In particular, we discuss recent experiments on the neural mechanisms of binocular rivalry which suggest that appropriate synchronization among cortical neurons may be one of the necessary conditions for the buildup of perceptual states and awareness of sensory stimuli. (shrink)

The concept of representation has been a key element in the scientific study of mental processes, ever since such studies commenced. However, usage of the term has been all but too liberal—if one were to adhere to common use it remains unclear if there are examples of physical systems which cannot be construed in terms of representation. The problem is considered afresh, taking as the starting point the notion of activity spaces—spaces of spatiotemporal events produced by dynamical systems. It is (...) argued that representation can be analyzed in terms of the geometrical and topological properties of such spaces. Several attributes and processes associated with conceptual domains, such as logical structure, generalization and learning are considered, and given analogues in structural facets of activity spaces, as are misrepresentation and states of arousal. Based on this analysis, representational systems are defined, as is a key concept associated with such systems, the notion of representational capacity. According to the proposed theory, rather than being an all or none phenomenon, representation is in fact a matter of degree—that is can be associated with measurable quantities, as is behooving of a putative naturalistic construct. (shrink)

The target paper of Dr. Feinberg is a testimony to an admirable scholarship and deep thoughtfulness. This paper develops a general theoretical framework of nested hierarchy in the brain that allows production of mind with consciousness. The difference between non-nested and nested hierarchies is the following. In a non-nested hierarchy the entities at higher levels of the hierarchy are physically independent from the entities at lower levels and there is strong constraint of higher upon lower levels. In a nested hierarchy, (...) higher levels are physically composed of lower levels, and there is no central control of the system resulting in weak constraint of higher upon lower levels. (shrink)

This article provides a retrospective, current and prospective overview on developments in brain research and neuroscience. Both theoretical and empirical studies are considered, with emphasis in the concept of multivariability and metastability in the brain. In this new view on the human brain, the potential multivariability of the neuronal networks appears to be far from continuous in time, but confined by the dynamics of short-term local and global metastable brain states. The article closes by suggesting some of the implications of (...) this view in future multidisciplinary brain research. (shrink)

The understanding of the interrelationship between brain and mind remains far from clear. It is well established that the brain's capacity to integrate information from numerous sources forms the basis for cognitive abilities. However, the core unresolved question is how information about the "objective" physical entities of the external world can be integrated, and how unifiedand coherent mental states (or Gestalts) can be established in the internal entities of distributed neuronal systems. The present paper offers a unified methodological and conceptual (...) basis for a possible mechanism of how the transient synchronization of brain operations may construct the unified and relatively stable neural states, which underlie mental states. It was shown that the sequence of metastable spatial EEG mosaics does exist and probably reflects the rapid stabilization periods of the interrelation of large neuron systems. At the EEG level this is reflected in the stabilization of quasi-stationary segments on corresponding channels. Within the introduced framework, physical brain processes and psychological processes are considered as two basic aspects of a single whole informational brain state. The relations between operational process of the brain, mental states and consciousness are discussed. (shrink)

Cortex functional connectivity associated with hypnosis was investigated in a single highly hypnotizable subject in a normal baseline condition and under neutral hypnosis during two sessions separated by a year. After the hypnotic induction, but without further suggestions as compared to the baseline condition, all studied parameters of local and remote functional connectivity were significantly changed. The significant differences between hypnosis and the baseline condition were observable (to different extent) in five studied independent frequency bands (delta, theta, alpha, beta, and (...) gamma). The results were consistent and stable after 1 year. Based on these findings we conclude that alteration in functional connectivity of the brain may be regarded as a neuronal correlate of hypnosis (at least in very highly hypnotizable subjects) in which separate cognitive modules and subsystems may be temporarily incapable of communicating with each other normally. (shrink)

The binding problem is to explain how information processed by different sensory systems is brought together to unify perception. The problem has two sides. First, we want to explain phenomenal binding: the fact that we experience a single world rather than separate perceptual fields for each sensory modality. Second, we must solve a functional problem: to explain how a neural net like the brain links instances to types. I argue that phenomenal binding and functional binding require very different treatments. The (...) puzzle of phenomenal binding rests on a confusion and so can be dissolved. So only functional binding deserves explanation. The general solution to that problem is that information to be bound is arrayed along different dimensions. So sensory coding into separate topographic maps facilitates functional binding and there is no need based on the unity of perception for special mechanisms that bring "back together" information in different maps. (shrink)

Laboratoire de Neurosciences Cognitives et Imagerie Ce´re´brale (LENA), Hoˆpital de La Salpeˆtrie`re, Centre National de la Recherche Scientifique (CNRS).

Temporal binding via 40-Hz synchronization of neuronal discharges in sensory cortices has been hypothesized to be a necessary condition for the rapid selection of perceptually relevant information for further processing in working memory. Binocular rivalry experiments have shown that late stage visual processing associated with the recognition of a stimulus object is highly correlated with discharge rates in inferotemporal cortex. The hippocampus is the primary recipient of inferotemporal outputs and is known to be the substrate for the consolidation of working (...) memories to long-term, episodic memories. The prefrontal cortex, on the other hand, is widely thought to mediate working memory processes, per se. This article reviews accumulated evidence for the role of a subcortical matrix in linking frontal and hippocampal systems to select and ''stream'' conscious episodes across time (hundreds of milliseconds to several seconds). ''Streaming'' is hypothesized to be mediated by the selective gating of reentrant flows of information between these cortical systems and the subcortical matrix. The physiological mechanism proposed for this temporally extended form of binding is synchronous oscillations in the slower EEG spectrum (< 8 Hz). (shrink)

Despite its prominent role in cognitive psychology, its relevance for the research of consciousness, and some helpful clarification (e.g., Revonsuo 1999), the binding problem is still surrounded by considerable confusion. In this paper, I first give an informal but systematic overview on the diversity of forms the binding problem can assume, and then attempt to extract, on the basis of "working definitions" of various much-discussed types of binding, a common denominator. I propose that at the heart of the binding problem (...) lies the notion of representing an entity as having a certain property, and discuss several objections that could be raised against the proposed analysis, as well its usefulness and implications. (shrink)

Starting from the special theory of relativity it is argued that the structure of an experience is extended over time, making experience dynamic rather than static. The paper describes and explains what is meant by phenomenal parts and outlines opposing positions on the experience of time. Time according to he special theory of relativity is defined and the possibility of static experience shown to be implausible, leading to the conclusion that experience is dynamic. Some implications of this for the relationship (...) of phenomenology to the physical world are considered. (shrink)

The binding problem is frequently discussed in consciousness research. However, it is by no means clear what the problem is supposed to be and how exactly it relates to consciousness. In the present paper the nature of the binding problem is clarified by distinguishing between different formulations of the problem. Some of them make no mention of consciousness, whereas others are directly related to aspects of phenomenal experience. Certain formulations of the binding problem are closely connected to the classical philosophical (...) problem of the unity of consciousness and the currently fashionable search for the neural correlates of consciousness. Nonetheless, only a part of the current empirical research on binding is directly relevant to the study of consciousness. The main message of the present paper is that the science of consciousness needs to establish a clear theoretical view of the relation between binding and consciousness and to encourage further empirical work that builds on such a theoretical foundation. (shrink)

(von der Malsburg, 1981), “the binding problem” has with the visual percept of it, so that both are effortlessly captured the attention of researchers across many disci- perceived as being aspects of a single event. I like to plines, including psychology, neuroscience, computa- refer to these sorts of problems as perceptual binding tional modeling, and even philosophy. Despite the is- problems, since they involve unifying aspects of per- sue’s prominence in these fields, what “binding” means cepts. In addition, there are (...) cognitive binding problems: is rarely made explicit. In this paper, I will briefly survey they include relating a concept to a percept, such as the many notions of binding and will introduce some linking the visual representation of an apple to all the issues that will be explored more fully in the reviews semantic knowledge stored about it (it is edible, how it that follow. (shrink)

How do our brains represent distinct objects in consciousness? In order to consciously distinguish between objects, our brains somehow selectively bind together activity patterns of spatially intermingled neurons that simultaneously represent similar and dissimilar features of distinct objects. Gamma-band synchronous oscillations (GSO) of neuroelectrical activity have been hypothesized to be a mechanism used by our brains to generate and bind conscious sensations to represent distinct objects. Most experiments relating GSO to specific features of consciousness have been published only in the (...) last several years. This brief review focuses on a wide variety experiments in which animals, including humans, discriminate between sensory stimuli and make these discriminations evident in their behavior. Performance of these tasks, in humans, is invariably accompanied by conscious awareness of both stimuli and behavior. Results of these experiments indicate that specific patterns of GSO correlate closely with specific aspects of conscious sensorimotor processing. That is, GSO appear to be closely correlated with neural generation of our most paradigmatic cognitive state: consciousness. (shrink)

Recent experiments have shown that the amplitudes of cortical gamma band oscillatory activities that occur during anesthesia are often greater than amplitudes of similar activities that occur without anesthesia. This result is apparently at odds with the hypothesis that synchronized oscillatory activities constitute the neural correlate of consciousness. We argue that while synchronization and oscillatory patterning are necessary conditions for consciousness, they are not sufficient. Based on the results of a binocular rivalry study of Fries et al. (1997), we propose (...) that the degrees of oscillatory strength and synchronization of neuronal activities determine the degree of awareness those activities produce. On the other hand, the overal firing rates of neurons in cortical sensory areas are not correlated with the degree of awareness the activities of those neurons produce. The results of the experiment of Fries et al. (1997) appear to conflict with the results of another binocular rivalry experiment, in which monkeys were trained to pull a lever in order to report which stimulus object was being perceived (Leopold & Logothetis, 1996). In the latter experiment, it was demonstrated that the firing rates of neurons in striate cortex did not change during perceptual alterations, while 90% of neurons in inferior and superior temporal cortices changed their firing rate when the perceived image changed. This result led to the conclusion that activities in temporal cortex are correlated with visual awareness, but those in striate cortex are not. We argue that activities in temporal cortex contribute little, if anything, to perceptual awareness, and that their primary function is computational. Thus the correlation between the firing rates of neurons in these areas and the responses of the monkeys is due to the recognition of a particular stimulus object, which in turn is due to the computations made there. (shrink)