A new class of visuomotor neuron has been recently discovered in the monkey’s premotor cortex: mirror neurons. These neurons respond both when a particular action is performed by the recorded monkey and when the same action, performed by another individual, is observed. Mirror neurons appear to form a cortical system matching observation and execution of goal-related motor actions. Experimental evidence suggests that a similar matching system also exists in humans. What might be the functional role of this (...) matching system? One possible function is to enable an organism to detect certain mental states of observed conspecifics. This function might be part of, or a precursor to, a more general mind-reading ability. Two different accounts of mind-reading have been suggested. According to “theory theory‘, mental states are represented as inferred posits of a naive theory. According to “simulation theory‘, other people’s mental states are represented by adopting their perspective: by tracking or matching their states with resonant states of one’s own. The activity of mirror neurons, and the fact that observers undergo motor facilitation in the same muscular groups as those utilized by target agents, are findings that accord well with simulation theory but would not be predicted by theory theory. (shrink)

Mirror neurons are widely regarded as an important key to social cognition. Despite such wide agreement, there is very little consensus on how or why they are important. The goal of this paper is to clearly explicate the exact role mirror neurons play in social cognition. I aim to answer two questions about the relationship between mirroring and social cognition: What kind of social understanding is involved with mirroring? How is mirroring related to that understanding? I argue that (...) philosophical and empirical considerations lead us to accord a fairly minimal role for mirror neurons in social cognition. (shrink)

Recently, there has been a resurgence of interest in theories of mindreading. New discoveries in neuroscience have revitalized the languishing debate. The discovery of so-called mirror neurons has revived interest particularly in the Simulation Theory (ST) of mindreading. Both ST proponents and theorists studying mirror neurons have argued that mirror neurons are strong evidence in favor of ST over Theory Theory (TT). In this paper I argue against the prevailing view that mirror neurons are evidence for (...) the ST of mindreading. My view is that on an appropriate construal of their function, mirror neurons do not operate like simulation theorists claim. In fact, mirror neurons are more appropriately understood as one element in an information-rich mindreading process. As such, mirror neurons fit in better with some sort of TT account of mindreading. I offer a positive account, the Model TT, which better explains the role of mirror neurons in social cognition. (shrink)

Lizardo argues that The Social Theory of Practices is refuted by the discovery of mirror neurons. The book argues that the kind of sameness of tacit mental content assumed by practice theorists such as Bourdieu is fictional, because there is no actual process by which the same mental content can be transmitted. Mirror neurons, Lizardo claims, provide such a mechanism, as they imply that bodily automatisms, which can be understood as the basis of habitus and concepts, can be (...) shared and copied from one person to another. This response to Lizardo points out that the Gallese arguments on which Lizardo relies relate to phylogenetic and universal body movements, not to the learned movements characteristic of practices, and that there is no sameness producing mechanism parallel to the genetic one. (shrink)

This article argues that mirror neurons originate in sensorimotor associative learning and therefore a new approach is needed to investigate their functions. Mirror neurons were discovered about 20 years ago in the monkey brain, and there is now evidence that they are also present in the human brain. The intriguing feature of many mirror neurons is that they fire not only when the animal is performing an action, such as grasping an object using a power grip, but (...) also when the animal passively observes a similar action performed by another agent. It is widely believed that mirror neurons are a genetic adaptation for action understanding; that they were designed by evolution to fulfill a specific socio-cognitive function. In contrast, we argue that mirror neurons are forged by domain-general processes of associative learning in the course of individual development, and, although they may have psychological functions, they do not necessarily have a specific evolutionary purpose or adaptive function. The evidence supporting this view shows that mirror neurons do not consistently encode action “goals”; the contingency- and context-sensitive nature of associative learning explains the full range of mirror neuron properties; human infants receive enough sensorimotor experience to support associative learning of mirror neurons ; and mirror neurons can be changed in radical ways by sensorimotor training. The associative account implies that reliable information about the function of mirror neurons can be obtained only by research based on developmental history, system-level theory, and careful experimentation. (shrink)

Questions concerning the nature of representation and what representations are about have been a staple of Western philosophy since Aristotle. Recently, these same questions have begun to concern neuroscientists, who have developed new techniques and theories for understanding how the locus of neurobiological representation, the brain, operates. My dissertation draws on philosophy and neuroscience to develop a novel theory of representational content.

Here Jean-Pierre Changeux elucidates our current knowledge of the human brain, taking an interdisciplinary approach and explaining in layman's terms the complex theories and scientific breakthroughs that have significantly improved our ...

Understanding how biological organisms are autonomous—maintain themselves far from equilibrium through their own activities—requires understanding how they regulate those activities. In multicellular animals, such control can be exercised either via endocrine signaling through the vasculature or via neurons. In C. elegans this control is exercised by a well-delineated relatively small but distributed nervous system that relies on both chemical and electric transmission of signals. This system provides resources to integrate information from multiple sources as needed to maintain the organism. (...) Especially important for the exercise of neural control are neuromodulators, which we present as setting agendas for control through more traditional electrical signaling. To illustrate how the C. elegans nervous system integrates multiple sources of information in controlling activities important for autonomy, we focus on feeding behavior and responses to adverse conditions. We conclude by considering how a distributed nervous system without a centralized controller is nonetheless adequate for autonomy. (shrink)

In this chapter, I aim to examine the two central properties that are said to underlie the theory of mirror neurons, namely action execution and action observation. I shall call these the functional properties of mirror neurons. I will argue that attributing the functional properties of mirror cognition, as many neuroscientists do, to the so-called ‘mirror neurons’ suffers from the problem of misidentification. This is the problem of incorrectly identifying an object or a property of one sort (...) with some other object or property. In light of this, I will propose that the most promising solution for the problem of misidentification is to ground the functional properties of mirror neurons squarely in consciousness and its bearer. (shrink)

The neurological discovery of mirror neurons is of eminent importance for the phenomenological theory of intersubjectivity. G. Rizzolatti and V. Gallese found in experiments with primates that a set of neurons in the premotor cortex represents the visually registered movements of another animal. The activity of these mirror neurons presents exactly the same pattern of activity as appears in the movement of one's own body. These findings may be extended to other cognitive and emotive functions in humans. (...) I show how these neurological findings might be “translated” phenomenologically into our own experienced sensations, feelings and volitions. (shrink)

Despite the impressive body of evidence supporting the existence of a mirror neuron (MN) system for action, the original claim regarding its crucial role in action understanding remains controversial. Emma Borg has recently launched a sharp attack on this claim, with the aim of demonstrating that neither the original version nor the subsequent revisions of the MN hypothesis tell us very much about how intentional attribution actually works. In this article I take up the challenge she issues in the title (...) of her paper (If Mirror Neurons are the Answer, What was the Question?) and argue that what MNs offer is not as Borg claims 'an extremely limited' picture of action understanding but rather an enriched picture that brings to light aspects of social cognition hitherto ignored in the mind-reading literature, showing how intentional motor components of action can shape social cognition prior to and apart from any forms of deliberate mentalizing. (shrink)

The fan effect says that “activation” spreading from a concept is divided among the concepts it spreads to. Because this activation is not a physical entity, but an abstraction of unknown lower‐level processes, the spreading activation model has predictive but not explanatory power. We provide one explanation of the fan effect by showing that distributed neuronal memory networks (specifically, Hopfield networks) reproduce four qualitative aspects of the fan effect: faster recognition of sentences containing lower‐fan words, faster recognition of sentences when (...) more cues are provided, faster acceptance of studied sentences than rejection of probes, and faster recognition of sentences studied more frequently. These are all a natural result of the dynamics of distributed associative memory. (shrink)

In numerous peripheral sense organs, external stimuli are detected by primary sensory neurons compartmentalized within specialized structures composed of cuticular or epithelial tissue. Beyond reflecting developmental constraints, such compartmentalization also provides opportunities for grouped neurons to functionally interact. Here, the authors review and illustrate the prevalence of these structural units, describe characteristics of compartmentalized neurons, and consider possible interactions between these cells. This article discusses instances of neuronal crosstalk, examples of which are observed in the vertebrate tastebuds (...) and multiple types of arthropod chemosensory hairs. Particular attention is paid to insect olfaction, which presents especially well‐characterized mechanisms of functional, cross‐neuronal interactions. These examples highlight the potential impact of peripheral processing, which likely contributes more to signal integration than previously considered. In surveying a wide variety of structural units, it is hoped that this article will stimulate future research that determines whether grouped neurons in other sensory systems can also communicate to impact information processing. (shrink)

Selected contributions to the symposium on "Mirror neurons and the evolution of brain and language" held on July 5-8, 2000 in Delmenhorst, Germany.

Recent research suggests that human memories are stored not between neurons as synaptic weights, but within individual neurons themselves. This opens the possibility to replace the dominant paradigm of brain function – neural networks – with a new one. In this article, I explore how “identified neurons” could explain how memories are stored, and how human traits are implemented in the brain.

The aim of the article is to show how mirror neurons, a recent discovery in neurology, might play a vital role in the creation of unity in our lives. This unity is a formal one. But since we all share the illusion that there is more to personal identity than only a formal unity, and that deep in ourselves the inner essence of our true self lies hidden, this same mechanism should also be able to shed some light on (...) the inescapability of this illusion. I begin by elaborating on the parallel Wittgenstein saw between the problem of the Self and the problem of mental processes. I continue by focusing on the problem of mental processes, first by looking at the philosophy-of-mind-debate where the understanding of the other is studied, then by looking at developmental psychology studies of how a child understands itself. With the help of Sartre's being-for-the-other, the conclusion will lead us to the formal unity in our lives that Wittgenstein described with his limit-concept. (shrink)

Are there universals of reading? There are three ways of construing this question. Is the region of the brain where reading is implemented identical regardless of what writing system the reader uses? Is the mental information-processing system used for reading the same regardless of what writing system the reader uses. Do the word's writing systems share certain universal features? Dehaene offers affirmative answers to all three questions in his book. Here I suggest instead that the answers should be negative. And (...) I ask: if reading is not universal in any sense, what does this imply about Dehaene's Neuronal Recycling hypothesis for reading? (shrink)

This paper explores a remarkable convergence of ideas and evidence, previously presented in separate places by its authors. That convergence has now become so persuasive that we believe we are working within substantially the same broad framework. Taylor's mathematical papers on neuronal systems involved in consciousness dovetail well with work by Newman and Baars on the thalamocortical system, suggesting a brain mechanism much like the global workspace architecture developed by Baars (see references below). This architecture is relational, in the sense (...) that it continuously mediates the interaction of input with memory. While our approaches overlap in a number of ways, each of us tends to focus on different areas of detail. What is most striking, and we believe significant, is the extent of consensus, which we believe to be consistent with other contemporary approaches by Weiskrantz, Gray, Crick and Koch, Edelman, Gazzaniga, Newell and colleagues, Posner, Baddeley, and a number of others. We suggest that cognitive neuroscience is moving toward a shared understanding of consciousness in the brain. (shrink)

1. Properties of mirror neurons in monkeys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (...) . . . . 000 1.1. Action types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 1.2. Context effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 2. Is there a human ‘mirror neuron system’? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 2.1. Monkeys versus humans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 2.2. Action understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 3. The development of mirroring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 3.1. Imitation in newborns? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 3.2. Effects of experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 3.3. Effects of sensorimotor experience . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. (shrink)

Mirror neurons are neurons which fire in two distinct conditions: (i) when an agent performs a specific action, like a precision grasp of an object using fingers, and (ii) when an agent observes that action performed by another. Some theorists have suggested that the existence of such neurons may lend support to the simulation approach to mindreading (e.g. Gallese and Goldman, 1998, 'Mirror neurons and the simulation theory of mind reading'). In this note I critically examine (...) this suggestion, in both its original and a revised form (due to Iacoboni et al., 2005, 'Grasping the intentions of others with one's own mirror neuron system'), and argue that the existence of mirror neurons can in fact tell us very little about how intentional attribution actually proceeds. (shrink)

Considering the properties of mirror neurons (MNs) in terms of development and phylogeny, we offer a novel, unifying, and testable account of their evolution according to the available data and try to unify apparently discordant research, including the plasticity of MNs during development, their adaptive value and their phylogenetic relationships and continuity. We hypothesize that the MN system reflects a set of interrelated traits, each with an independent natural history due to unique selective pressures, and propose that there are (...) at least three evolutionarily significant trends that gave raise to three subtypes: hand visuomotor, mouth visuomotor, and audio–vocal. Specifically, we put forward a mosaic evolution hypothesis, which posits that different types of MNs may have evolved at different rates within and among species. This evolutionary hypothesis represents an alternative to both adaptationist and associative models. Finally, the review offers a strong heuristic potential in predicting the circumstances under which specific variations and properties of MNs are expected. Such predictive value is critical to test new hypotheses about MN activity and its plastic changes, depending on the species, the neuroanatomical substrates, and the ecological niche. (shrink)

During sensory stimulation, visual cortical neurons undergo massive synaptic bombardment. This increases their input conductance, and action potentials mainly result from membrane potential fluctuations. To understand the response properties of neurons operating in this regime, we studied a model neuron with synaptic inputs represented by transient membrane conductance changes. We show that with a simultaneous increase of excitation and inhibition, the firing rate first increases, reaches a maximum, and then decreases at higher input rates. Comodulation of excitation and (...) inhibition, therefore, does not provide a straightforward way of controlling the neuronal firing rate, in contrast to coding mechanisms postulated previously. The synaptically induced conductance increase plays a key role in this effect: it decreases firing rate by shunting membrane potential fluctuations, and increases it by reducing the membrane time constant, allowing for faster membrane potential transients. These findings do not depend on details of the model and, hence, are relevant to cells of other cortical areas as well. (shrink)

The functional role of mirror neurons has been assessed in many different ways. They have been regarded, inter alia, as the core mechanism of mind reading, the mechanism of language understanding, the mechanism of imitation. In this paper we will discuss the thesis according to which MNs are a conceptual mechanism. This hypothesis is attractive since it could accommodate in an apparently simple way all the above-mentioned interpretations. We shall take into consideration some reasons suggesting the conceptualist characterization of (...) MNs, as well as some possible replies. We shall figure out how an argument for the conceptualist hypothesis could be deployed, focusing on the notion of off-line processes, which turns out to be the crucial property necessary to ascribe concept possession. Our conclusion will be that, despite of there being some evidence for the conceptualist account, the issue cannot be definitely settled, because there are both experimental shortages and conceptual difficulties. In particular, there are three distinct senses in which MNs can be regarded as a conceptual mechanism, but we shall argue that only one of these interpretations can be defended. (shrink)

Traditionally, the impairment of cognitive functions in Alzheimeŕs disease (AD) is thought to result from a reduction in neuronal and synaptic activities, and ultimately cell death. Here, we review recent in vivo evidence from mouse models and human patients indicating that, particularly in early stages of AD, neuronal circuits are hyperactive instead of hypoactive. Functional analyses at many levels, from single neurons to neuronal populations to large‐scale networks, with a variety of electrophysiological and imaging techniques have revealed two forms (...) of AD‐related hyperactivity and provided first insights into the synaptic mechanisms. The unexpected finding that hyperactivity is an early neuronal dysfunction represents a major conceptual shift in our understanding of AD that may have important implications for the development of therapeutic approaches. (shrink)

Given that many in neuroscience believe all human experience will eventually be accounted for in terms of the activity of the brain, does the concept of moral or values education make sense? And, are we not headed for a singly deterministic notion of the self, devoid of even the possibility of making choices? One obvious objection is that this does not tally with our experience? we can espouse values and do make choices. But perhaps this is simply appearance and the (...) language of values and choices belongs to a previous age and is no longer sustainable. Perhaps the way in which we encounter other selves and account for their actions as moral agents is simply outdated. We need to begin to address others, including the children we teach, as neuronal selves and account for their actions as neuronally determined. This paper will argue that espousing the notion that we are neuronal selves need not lead to such pessimistic reductionistic conclusions. If we can no longer believe in Cartesian dualism we do not have take a leap into materialism that threatens to reduce our being to that of robots. A neuroscience that recognises that we are multileveled psychosomatic neuronal selves can point the way out of this dilemma. Values in education then not only make sense: they are more pivotal than hitherto imagined. (shrink)

When circumscribed brain regions are damaged in humans, highly specific iimpairments in language, memory, problem solving, and cognition are observed. Neurosurgery such as "split brain " or hemispherectomy, for example has shown that encompassing regions, the left and right cerebral hemispheres each control human behavior in unique ways. Observations stretching over 100 years of patients with unilateral focal brain damage have revealed, withouth the theoretical benefits of "cognitive neuroscience" or "cognitive psychology," that human behavior is indeed controlled by the brain (...) and its neurons. (shrink)

In his article “Beyond Point-and-Shoot Morality,” Joshua Greene argues that the empirical findings of cognitive neuroscience have implications for ethics. Specifically, he contends that we ought to trust our manual, conscious reasoning system more than our automatic, emotional system when confronting unfamiliar problems; and because cognitive neuroscience has shown that consequentialist judgments are generated by the manual system and deontological judgments are generated by the automatic system, we ought to trust the former more than the latter when facing unfamiliar moral (...) problems. In the present article, I analyze one of the premises of Greene’s argument. In particular, I ask what exactly an unfamiliar problem is and whether moral problems can be classified as unfamiliar. After exploring several different possible interpretations of familiarity and unfamiliarity, I conclude that the concepts are too problematic to be philosophically compelling, and thus should be abandoned. (shrink)

Registration of a series of the two-dimensional electron microscope images of the brain tissue into volumetric form is an important technique that can be used for neuronal circuit reconstruction. However, complex appearance changes of neuronal morphology in adjacent sections bring difficulty in finding correct correspondences, making serial section neural image registration challenging. To solve this problem, we consider whether there are such stable "markers" in the neural images to alleviate registration difficulty. In this paper, we employ the spherical deformation model (...) to simulate the local neuron structure and analyze the relationship between registration accuracy and neuronal structure shapes in two adjacent sections. The relevant analysis proves that regular circular structures in the section images are instrumental in seeking robust corresponding relationships. Then, we design a new serial section image registration framework driven by this neuronal morphological model, fully utilizing the characteristics of the anatomical structure of nerve tissue and obtaining more reasonable corresponding relationships. Specifically, we leverage a deep membrane segmentation network and neural morphological physical selection model to select the stable rounded regions in neural images. Then, we combine feature extraction and global optimization of correspondence position to obtain the deformation field of multiple images. Experiments on real and synthetic serial EM section neural image datasets have demonstrated that our proposed method could achieve more reasonable and reliable registration results, outperforming the state-of-the-art approaches in qualitative and quantitative analysis. (shrink)

Musical improvisation is a sophisticated activity in which a performer realizes, real-time, melodic, and rhythmic sequences in harmony with those from other musicians. The study of musical improvisation helps one to understand not only the cognition of creativity, but also the complex neuronal basis of executive functions, the relation between conscious and unconscious action, and even more. So far, the prevailing models, founded on the brain imaging method, have focused on the connection between the cortical areas and their cognitive processes. (...) Little attention, on the other hand, has been given to the huge variety of subcortical activities, especially in the basal ganglia. This fundamental subcortical component, through its implicit procedures and the role it plays in memory, is responsible to produce new information all the time, allowing the prefrontal cortex to transform a huge and disordered amount of data in explicit creative acts. The basal ganglia are strongly related to the activation of chemical signals generated by dissonance or lack of symmetry between perception and expectation, participating even in the responses to environmental demands according to the circumstances. Thus, they interact with the frontal cortex and with the limbic system, playing a key role in planning and selecting appropriate actions and in decision making. In this text, we try to explain in which sense improvisation is connected to the processes of executive functions, to creativity and to the integrated activity of cortical–subcortical areas controlling the free flow of ideas and to expressive spontaneity. Eventually, we purpose a model according to which structure and process take part at the centrencephalic space of functional integration, which, through both competing and cooperating dynamics, gives way to spontaneous composition. (shrink)

Impossible Minds: My Neurons, My Consciousness has been written to satisfy the curiosity each and every one of us has about our own consciousness. It takes the view that the neurons in our heads are the source of consciousness and attempts to explain how this happens. Although it talks of neural networks, it explains what they are and what they do in such a way that anyone may understand. While the topic is partly philosophical, the text makes no (...) assumptions of prior knowledge of philosophy; and so contains easy excursions into the important ideas of philosophy that may be missing in the education of a computer scientist. The approach is pragmatic throughout; there are many references to material on experiments that were done in our laboratories. The first edition of the book was written to introduce curious readers to the way that the consciousness we all enjoy might depend on the networks of neurons that make up the brain. In this second edition, it is recognized that these arguments still stand, but that they have been taken much further by an increasing number of researchers. A post-script has now been written for each chapter to inform the reader of these developments and provide an up-to-date bibliography. A new epilogue has been written to summarize the state-of-the art of the search for consciousness in neural automata, for researchers in computation, students of philosophy, and anyone who is fascinated by what is one of the most engaging scientific endeavours of the day. This book also tells a story. A story of a land where people think that they are automata without much in the way of consciousness, a story of cormorants and cliffs by the sea, a story of what it might be like to be a conscious machine... (shrink)

Neurons of organisms with complex and flexible behavior, especially humans, must precisely control protein localization and activity to support higher brain functions such as learning and memory. In contrast, simpler organisms generally have simpler individual neurons, less complex nervous systems and display more limited behaviors. Strikingly, however, many key neuronal proteins are conserved between organisms that have very different degrees of behavioral complexity. Here we discuss a possible mechanism by which conserved neuronal proteins acquired new attributes that were (...) crucial in the evolution of complexity of nervous system structure and function. Specifically, we hypothesize that vertebrate‐specific post‐translational palmitoylation sites and PDZ‐binding protein‐protein interaction motifs act as gain‐of‐function mutations, increasing the regulatory potential of conserved proteins without affecting their core functions. We further hypothesize that the additional regulation of neurotransmitter receptors and other membrane proteins made possible by these sites and motifs is critical for the function of complex nervous systems. (shrink)

The neuroanatomical substrates controlling and regulating sleeping and waking, and thus consciousness, are located in the brain stem. Most crucial for bringing the brain into a state conducive for consciousness and information processing is the mesencephalic part of the brain stem. This part controls the state of waking, which is generally associated with a high degree of consciousness. Wakefulness is accompanied by a low-amplitude, high-frequency electroencephalogram, due to the fact that thalamocortical neurons fire in a state of tonic depolarization. (...) Information can easily pass the low-level threshold of these neurons, leading to a high transfer ratio. The complexity of the electroencephalogram during conscious waking is high, as expressed in a high correlation dimension. Accordingly, the level of information processing is high. Spindles, and alpha waves in humans, mark the transition from wakefulness to sleep. These phenomena are related to drowsiness, associated with a reduction in consciousness. Drowsiness occurs when cells undergo moderate hyperpolarizations. Increased inhibitions result in a reduction of afferent information, with a lowered transfer ratio. Information processing subsides, which is also expressed in a diminished correlation dimension. Consciousness is further decreased at the onset of slow wave sleep. This sleep is controlled by the medullar reticular formation and is characterized by a high-voltage, low-frequency electroencephalogram. Slow wave sleep becomes manifest when neurons undergo a further hyperpolarization. Inhibitory activities are so strong that the transfer ratio further drops, as does the correlation dimension. Thus, sensory information is largely blocked and information processing is on a low level. Finally, rapid eye movement sleep is regulated by the pontine reticular formation and is associated with a ''wake-like'' electroencephalographic pattern. Just as during wakefulness, this is the expression of a depolarization of thalamocortical neurons. The transfer ratio of rapid eye movement sleep has not yet been determined, but seems to vary. Evidence exists that this type of sleep, associated with dreaming, with some kind of perception and consciousness, is involved in processing of ''internal'' information. In line with this, rapid eye movement sleep has higher correlation dimensions than slow-wave sleep and sometimes even higher than wakefulness. It is assumed that the ''near-the-threshold'' depolarized state of neurons in the thalamus and cerebral cortex is a necessary condition for perceptual processes and consciousness, such as occurs during waking and in an altered form during rapid eye movement sleep. (shrink)

Neuronal growth and remodelling are guided by both intracellular gene programs and extracellular stimuli. The growth cone is one site where the effects of these extrinsic and intrinsic factors converge upon the mechanical determinants of cell shape. We review the growth cone as a transduction device, converting extracellular signals into mechanical forces. A variety of soluble, extracellular matrix and membrane bound molecules control growth cone behavior. In addition, GAP‐43 is discussed as a possible component of the Intraneuronal gene program which (...) modulates growth cone activity. The GTP‐binding protein, Go, is a major growth cone membrane protein that may transduce signals not only from outside the cell, but from within as well. This may provide a molecular site in the growth cone for the coordination of a genetic growth program with environmental signals. (shrink)

Neurophysiological evidence showing that some neurons in the macaque inferior temporal visual cortex and cortex in the superior temporal sulcus have responses that are invariant with respect to the position, size, and in some cases view of faces, and that these neurons show rapid processing and rapid learning. This chapter provides a whole area of research which show how taste, olfactory, visual, and somatosensory reward is decoded and represented in the orbitofrontal cortex and has led to a theory (...) of emotion, of how and why the brain implements emotion, of some emotional disorders produced by brain damage, of the reward systems involved in appetite control, and of the brain mechanisms of decision-making. The responses of these neurons reflect solution of some of the major problems of visual perception. (shrink)