Long‐term modification of synaptic strength is thought to be the basic mechanism underlying the activity‐dependent refinement of neural circuits and the formation of memories engrammed on them. Studies ranging from cell culture preparations to humans subjects indicate that the decision of whether a synapse will undergo strengthening or weakening critically depends on the temporal order of presynaptic and postsynaptic activity. At many synapses, potentiation will be induced only when the presynaptic neuron fires an action potential within milliseconds before (...) the postsynaptic neuron fires, whereas weakening will occur when it is the postsynaptic neuron that fires first. Such processes might be important for the remodeling of neural circuits by activity during development and for network functions such as sequence learning and prediction. Ultimately, this synaptic property might also be fundamental for the cognitive process by which we structure our experience through cause and effect relations. BioEssays 24:212–222, 2002. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/bies.10060. (shrink)

Recent studies on neural pathways in a broad spectrum of vertebrates suggest that, in addition to migration and an increase in the number of certain select neurons, a significant aspect of neural evolution is a “parcellation” (segregation-isolation) process that involves the loss of selected connections by the new aggregates. A similar process occurs during ontogenetic development. These findings suggest that in many neuronal systems axons do not invade unknown territories during evolutionary or ontogenetic development but follow in their (...) ancestors' paths to their ancestral targets; if the connection is later lost, it reflects the specialization of the circuitry.The pattern of interspecific variability suggests (1) that overlap of circuits is a more common feature in primitive (generalized) than in specialized brain organizations and (2) that most projections, such as the retinal, thalamotelencephalic, corticotectal, and tectal efferent ones, were bilateral in the primitive condition. Specialization of these systems in some vertebrate groups has involved the selective loss of connections, resulting in greater isolation of functions. The parcellation process may also play an important role in cell diversification.The parcellation process as described here is thought to be one of several underlying mechanisms of evolutionary and ontogenetic differentiation. (shrink)

Phasic activity of dopaminergic neurons in the ventral tegmental area or substantia nigra compacta has been suggested to encode reward-prediction error signal for reinforcement learning. Recent studies have shown that the lateral habenula neurons exhibit a similar response, but for nonrewarding or punishment signals. Hence, the transient signaling role of LHb neurons is opposite that of DA neurons and also that of several other brain nuclei such as the border region of the globus pallidus internal segment and the rostral medial (...) tegmentum. Previous theoretical models have investigated the neural circuit mechanism underlying reward-based phasic activity of DA neurons, but the feasibility of a larger neural circuit model to account for the observed reward-based phasic activity in other brain nuclei such as the LHb has yet to be shown. Here, we propose a large-scale neural circuit model and show that parallel excitatory and inhibitory pathways underlie the learned neural responses across multiple brain regions. Specifically, the model can account for the phasic neural activity observed in the GPb, LHb, RMTg, and VTA/SNc. Based on sensitivity analysis, the model is found to be robust against changes in the overall neural connectivity strength. The model also predicts that striosomes play a key role in the phasic activity of VTA/SNc and LHb neurons by encoding previous and expected rewards. Taken together, our model identifies the important role of parallel neural circuit pathways in accounting for phasic activity across multiple brain areas during reward and punishment processing. (shrink)

In the dyadic and triadic sharing of emotions, intentions, and behaviors in families, interactive synchrony is important to the early life experiences that contribute to the development of cultural cognition. This synchrony likely depends on neurobiological circuits, currently under study with brain imaging, that involve attention, stress response, and memory.

It is argued that van der Velde and de Kamps employ binding circuitry that effectively constitutes a form of conjunctive binding. Analogies with prior systems are discussed and hypothetical origins of binding circuitry are examined for credibility.

An understanding of the functional repertoire of neural circuits and their plasticity requires knowledge of neural connectivity diagrams and their dynamical evolution. However, one must additionally take into account the fast and reversible functional effects induced by neuromodulatory mechanisms which do not alter neural circuit diagrams. Neuromodulators contribute crucially to determine the performativity of a neural circuit, that is, its ability to change behavior, and especially behavioral changes occurring under temporal constraints that are incompatible with (...) the longer time scales of Hebbian learning and other forms of neural learning. This paper focuses on two properties of neuromodulatory action that have been relatively neglected so far. These properties are the functional soundness of neuromodulated circuits and the robustness of neuromodulatory action. Both properties are analyzed here as sources of functional specifications for the computational modeling of neural circuit performativity. In particular, taking dynamical systems that are based on CTRNNs as an exemplary class of computational models, it is argued that robustness is suitably modeled there by means of a hysteresis process, and functional soundness by means of a multiplicity of stable fixed points. (shrink)

Powerful ultrastructural tools are providing new insights into neuronal circuits, revealing a wealth of anatomically‐defined synaptic connections. These wiring diagrams are incomplete, however, because functional connectivity is actively shaped by neuromodulators that modify neuronal dynamics, excitability, and synaptic function. Studies of defined neural circuits in crustaceans, C. elegans, Drosophila, and the vertebrate retina have revealed the ability of modulators and sensory context to reconfigure information processing by changing the composition and activity of functional circuits. Each ultrastructural (...) connectivity map encodes multiple circuits, some of which are active and some of which are latent at any given time. (shrink)

Neural circuits linking local operations in the cortex and the basal ganglia confer reiterative capacities, expressed in seemingly unrelated human traits such as speech, syntax, adaptive actions to changing circumstances, dancing, and music. Reiteration allows the formation of a potentially unbounded number of sentences from a finite set of syntactic processes, obviating the need for the hypothetical.

This commentary is intended to illuminate Gold's & Stoljar 's main contentions by exploiting a favorite comparison, namely, that between biology and electronics. Roughly, and leaving out Darwinian theory and the like, biology is physics and chemistry plus natural history just as electronics is physics plus wiring diagrams. Natural history contains generalizations, not laws. Psychology and cognitive science typically give more abstract explanations, as do “block diagrams” in electronics, and are less dispensable.

This paper selectively reviews the neurophysiological evidence for shared neural circuits (supposedly implemented by mirror neurons) as the mechanism underlying empathy. I will argue that while the mirror neuron system plays a role in motor resonance, it is not possible to conclude that this system is critically involved in emotion recognition, and there is little evidence for its role in empathy and sympathy. In addition, there is modest support from neurological observations that lesion of the regions involved in (...) the mirror neuron system leads to dysfunction in empathy, whereas damage of the ventromedial prefrontal cortex is associated with such impairment. To significantly advance our understanding of the mechanisms underlying empathy, research needs finer conceptualization, better designed paradigms, and integration with knowledge from lesion studies. (shrink)

The human brain is the first computer to which all others are compared. Yet we know painfully little about how a brain accomplishes its peculiar computations. In particular, consciousness is at once familiar and mysterious, and needs to be understood both for science and for medicine. Boldly, but gently this book introduces a reader to the neural circuitry that achieves consciousness. This amazing interconnection enables consciousness to flow like a stream, intimately relevant to the outside world; and for this (...) to happen, fundamental cues emerge from mental images to bring forth associated recalls. Alas cues can be inconsistent, causing memory failure; fortunately a subliminal cue editor encourages remembering forgotten items. Furthermore, cues generally address several memories, forcing the brain to make a selection. This necessitates another special circuit whose purpose is subliminal editing. The simplified explanations provided in this book make it clear that neurons do far more than ordinary devices, since a single neuron is capable of remarkably dense combinational and sequential logic. Beginning with their interesting and unexpected logical behavior, the reader will genuinely enjoy Dr. Burger's synthesis of a system for biological consciousness, a system that may someday result in credible artificial consciousness. (shrink)

Reuse is well established in molecular evolution; some analogies from this better understood field may help suggest specific aspects of reuse of neural circuits.

Psychoneural reduction has been debated extensively in the philosophy of neuroscience. In this article I will evaluate metascientific approaches that claim direct molecular and cellular explanations of cognitive functions. I will initially consider the issues involved in linking cellular properties to behaviour from the general perspective of neural circuits. These circuits that integrate the molecular and cellular components underlying cognition and behaviour, making consideration of circuit properties relevant to reductionist debates. I will then apply this general perspective (...) to specific systems where psychoneural reduction has been claimed, namely hippocampal long-term potentiation and the Aplysia gill-withdrawal reflex. (shrink)

The growing recognition by cognitive neuroscientists that areas of vertebrate brains may be reused for multiple purposes either functionally during development or during evolution echoes a similar realization made by neuroscientists working on invertebrates. Because of these animals' relatively more accessible nervous systems, neuronal reuse can be examined at the level of individual identified neurons and fully characterized neural circuits.

In this paper we present theoretical and experimental evidence for a set of mechanisms by which intention is understood. We propose that three basic aspects are involved in the understanding of intention. The first aspect to consider is intention recognition, i.e., the process by which we recognize other people’s intentions, distinguishing among different types. The second aspect concerns the attribution of intention to its author: the existence of shared neural representations provides a parsimonious explanation of how we recognize other (...) people’s intentions , but in and of itself, is not sufficient to determine who the agent is. Once the intention has been recognized and attributed to an agent, the reasons for, and the aim of, the intention are to be considered. Hence, the third aspect concerns the aim-intention motivating the execution of a certain action. We discuss the neural basis of these three theoretical aspects suggesting a conceptual synthesis. (shrink)

Development in animals is frequently characterized by periods of heightened capacity for both neural and behavioral change. So‐called sensitive periods of development are windows of opportunity in which brain and behavior are most susceptible to modification. Understanding what factors regulate sensitive periods constitutes one of the main goals of developmental neuroscience. Why is the ability to learn complex behavioral patterns often restricted to sensitive periods of development? Songbirds provide a model system for unraveling the mysteries of neural mechanisms (...) of learning during development. Like many songbirds, zebra finches (Taeniopygia guttata) learn a specific vocal pattern during a restricted period early in life. Young birds must hear songs produced by members of their species; this auditory experience is thought to engender specific changes in the brain to guide the process of vocal learning. Many studies of the songbird system have focused on examining relationships between brain development and learning. One goal of this work is to elucidate mechanisms that regulate basic processes of neural development, and in so doing to shed light on factors governing the emergence of a complex learned behavior. (shrink)

Disruptions in chromatin regulator genes are frequently the cause of neurodevelopmental and neuropsychiatric disorders. Chromatin regulators are widely expressed in the brain, yet symptoms suggest that specific circuits can be preferentially altered when they are mutated. Using Drosophila allows targeted manipulation of chromatin regulators in defined neuronal classes, lineages, or circuits, revealing their roles in neuronal precursor self‐renewal, dendrite and axon targeting, neuron diversification, and the tuning of developmental signaling pathways. Phenotypes arising from chromatin regulator disruption are context (...) dependent – defined by interaction networks between the regulators, transcription factors, and chromatin remodeling complex partners. Future challenges are to determine the complexity of partner interactions, and to ascertain the degree to which cognitive deficits are due to loss of chromatin regulator activity in building a circuit or in maintaining homeostasis and activity within it. (shrink)

Newborn neurons are generated in the adult hippocampus from a pool of self‐renewing stem cells located in the subgranular zone (SGZ) of the dentate gyrus. Their activation, proliferation, and maturation depend on a host of environmental and cellular factors but, until recently, the contribution of local neuronal circuitry to this process was relatively unknown. In their recent publication, Song and colleagues have uncovered a novel circuit‐based mechanism by which release of the neurotransmitter, γ‐aminobutyric acid (GABA), from parvalbumin‐expressing (PV) interneurons, can (...) hold radial glia‐like (RGL) stem cells of the adult SGZ in a quiescent state. This tonic GABAergic signal, dependent upon the activation of γ2 subunit‐containing GABAA receptors of RGL stem cells, can thus prevent their proliferation and subsequent maturation or return them to quiescence if previously activated. PV interneurons are thus capable of suppressing neurogenesis during periods of high network activity and facilitating neurogenesis when network activity is low. (shrink)

Differentiating self from other has been investigated at the neural level, and its incorporation into the model proposed Hurley is necessary for the model to be complete. With an emphasis on the feed-forward model in layer 2, we examine the role that self and other disruptions, including auditory verbal hallucinations (AVHs), may have in expanding the model proposed by Hurley.

An emerging class of theories concerning the functional structure of the brain takes the reuse of neural circuitry for various cognitive purposes to be a central organizational principle. According to these theories, it is quite common for neural circuits established for one purpose to be exapted (exploited, recycled, redeployed) during evolution or normal development, and be put to different uses, often without losing their original functions. Neural reuse theories thus differ from the usual understanding of the (...) role of neural plasticity (which is, after all, a kind of reuse) in brain organization along the following lines: According to neural reuse, circuits can continue to acquire new uses after an initial or original function is established; the acquisition of new uses need not involve unusual circumstances such as injury or loss of established function; and the acquisition of a new use need not involve (much) local change to circuit structure (e.g., it might involve only the establishment of functional connections to new neural partners). Thus, neural reuse theories offer a distinct perspective on several topics of general interest, such as: the evolution and development of the brain, including (for instance) the evolutionary-developmental pathway supporting primate tool use and human language; the degree of modularity in brain organization; the degree of localization of cognitive function; and the cortical parcellation problem and the prospects (and proper methods to employ) for function to structure mapping. The idea also has some practical implications in the areas of rehabilitative medicine and machine interface design. (shrink)

Susan Hurley's impressive article about the shared circuit model (SCM) raises two important issues. First, I suggest that the SCM presupposes relational coding rather than translational coding as neural code. Second, the SCM being the basis for self implies that the self may be characterized as format, relational, and embodied and embedded, rather than by specific and isolated higher-order cognitive contents.

Segregated neural circuits that effect particular domain-specific behaviors can be differentiated from neuroanatomical structures implicated in many different aspects of behavior. The basal ganglionic components of circuits regulating nonlinguistic motor behavior, speech, and syntax all function in a similar manner. Hence, it is unlikely that special properties and evolutionary mechanisms are associated with the neural bases of human language.

Chemosensation and mechanosensation cover an enormous spectrum of processes by which animals use information from the environment to adapt their behavior. For pragmatic reasons, these sensory modalities are commonly investigated independently. Recent advances, however, have revealed numerous situations in which they function together to control animals’ actions. Highlighting examples from diverse vertebrates and invertebrates, we first discuss sensory receptors and neurons that have dual roles in the detection of chemical and mechanical stimuli. Next we present cases where peripheral chemosensory and (...) mechanosensory pathways are discrete but intimately packaged to permit coordinated reception of external cues. Finally, we consider how chemical and mechanical signals converge in central neural circuitry to enable multisensory integration. These insights demonstrate how investigation of the interplay between different sensory modalities is key to a more holistic and realistic understanding of sensory‐guided behaviors. (shrink)

The judgement of human ability is ubiquitous, from school admissions to job performance reviews. The exact make-up of ability traits, however, is often narrowly defined and lacks a comprehensive basis. We attempt to simplify the spectrum of human ability, similar to how five personality traits are widely believed to describe most personalities. Finding such a basis for human ability would be invaluable since neuropsychiatric disease diagnoses and symptom severity are commonly related to such differences in performance. Here, we identified four (...) underlying ability traits within the National Institutes of Health Toolbox normative data (n= 1, 369): (1) Motor-endurance, (2) Emotional processing, (3) Executive and cognitive function, and (4) Social interaction. We used the Human Connectome Project young adult dataset (n= 778) to show that Motor-endurance and Executive and cognitive function were reliably associated with specific brain functional networks (r2= 0.305 ± 0.021), and the biological nature of these ability traits was also shown by calculating their heritability (31 and 49%, respectively) from twin data. (shrink)

Neurosemantics is not yet a common term and in current neuroscience and philosophy it is used with two different sorts of objectives. One deals with the meaning of the electrical and the chemical activities going on in neural circuits. This way of using the term regards the project of explaining linguistic meaning in terms of the computations done by the brain. This book explores this second sense of neurosemantics, but in doing so, it will address much of the (...) first as well, for we believe that the capacity of neural circuits to support linguistic meaning, hinges on their peculiar role in coding entities and facts of the world. It is an enterprise at the edge of the available state-of-the-art knowledge in neuroscience and specifically, in the growing understanding of brain computational mechanisms. We conceive neurosemantics, however, as the natural evolution of a long standing project that began in the early days of Boole’s logic, the idea that semantics can be construed and explained in mathematical terms. Classical formal semantics, for a very long time, excluded from the analysis of language any account of mental processes, which on the contrary, became the central focus during the cognitive turn. Cognitive semantics, however, failed to provide a rigorous mathematical framework for semantic processes. Today, it is possible to begin explaining language by way of a new mathematical foundation, one that is empirically grounded in how the brain computes: neurosemantics. The way this book intends to contribute is twofold. One is to present a series of existing examples of neurosemantics in practice: early models addressing aspects of linguistic semantics purely in neurocomputational terms. The other is to try to identify the principles upon which models of this kind can be constructed, and their corresponding neural bases. (shrink)

Money is a specifically human incentive. However, functional imaging techniques bring striking evidence that neural circuits pertaining to more “natural” addictive and rewarding processes are involved in response to monetary reward. Main results are evoked here, with specific brain responses demonstrated along the different stages of the process. (Published Online April 5 2006).

The leading hypothesis concerning the “reuse” or “recycling” of neural circuits builds on the assumption that evolution might prefer the redeployment of established circuits over the development of new ones. What conception of cognitive architecture can survive the evidence for this hypothesis? In particular, what sorts of “modules” are compatible with this evidence? I argue that the only likely candidates will, in effect, be the columns which Vernon Mountcastle originally hypothesized some 60 years ago, and which form (...) part of the well-known columnar hypothesis in neuroscience—systems that cannot handle gross cognitive functions as distinct from strictly exiguous subfunctions. This is in stark contrast to the modules postulated by much of cognitive psychology, cognitive neuropsychology, and evolutionary psychology. And yet the fate of this revised notion is unclear. The main issue confronting it is the effect of the neural network context on local function. At some point the effects of context are so strong that the degree of specialization required for modularity is not able to be met. Still, despite indications from neuroimaging that peripheral and central systems deploy shared circuitry, some skills clearly do seem to display modularization and autonomy. This article: provides an in-depth analytical and historical review of the fortunes of modular thinking in cognitive science; offers a systematic calibration of brain regions in terms of degrees of functional specificity and robustness; and suggests another way of accounting for the partially encapsulated character of expertise and other highly practiced skills without having to resort to domain-specific modules. (shrink)

Neural reuse posits development of functional overlap in brain system circuits to accommodate complex evolutionary functions. Evolutionary adaptation evolved neural circuits that have been exploited for many uses. One such use is engaging cognitive processes in memory consolidation during the neurobiological states of sleep. Neural reuse, therefore, should not be limited to neural circuitry, but be extended to include sleep-state associated memory processes.

This article reviews concepts of, as well as neurocognitive and genetic studies on, empathy. Whereas cognitive empathy can be equated with affective theory of mind, that is, with mentalizing the emotions of others, affective empathy is about sharing emotions with others. The neural circuits underlying different forms of empathy do overlap but also involve rather specific brain areas for cognitive (ventromedial prefrontal cortex) and affective (anterior insula, midcingulate cortex, and possibly inferior frontal gyrus) empathy. Furthermore, behavioral and imaging (...) genetic studies provide evidence for a genetic basis for empathy, indicating a possible role for oxytocin and dopamine as well as for a genetic risk variant for schizophrenia near the gene ZNF804A. (shrink)

Neural reuse theories should interest developmental psychologists because these theories can potentially illuminate the developmental relations among psychological characteristics observed across the lifespan. Characteristics that develop by exploiting pre-existing neural circuits can be thought of as developmental homologues. And, understood in this way, the homology concept that has proven valuable for evolutionary biologists can be used productively to study psychological/behavioral development.

The connectivity patterns of many neural circuits are highly ordered and often impressively complex. The intricate order and complexity of neuronal wiring remain not only a challenge for questions related to circuit functions but also for our understanding of how they develop with such an apparent precision. The chemotropic guidance of the growing axon by target‐derived cues represents a central paradigm for how neurons get connected with the correct target cells. However, many studies reveal a remarkable variety of (...) important target‐independent wiring mechanisms. These mechanisms include axonal sorting, axonal tiling, growth cone polarization, as well as cell‐intrinsic mechanisms underlying growth cone sprouting, and neurite branching. Our review focuses on target independent wiring mechanisms and in particular on recent progress emerging from studies on three different sensory systems: olfactory, visual, and somatosensory. We discuss molecular mechanisms that operate during axon‐axon interactions or constitute axon‐intrinsic functions and outline how they complement the well‐known target‐dependent wiring mechanisms. (shrink)

This book examines the concept of “ Neurosemantics”, a term currently used in two different senses: the informational meaning of the physical processes in the neural circuits, and semantics in its classical sense, as the meaning of language, explained in terms of neural processes. The book explores this second sense of neurosemantics, yet in doing so, it addresses much of the first meaning as well. Divided into two parts, the book starts with a description and analysis of (...) the mathematics of the brain, including computational units, representational mechanisms and algorithmic principles. This first part pays special attention to the neural architecture which has been used in developing models of neurosemantics. The second part of the book presents a collection of models, and describes each model reproducing specific aspects of the semantics of language. Some of these models target one of the core problems of semantics, the reference of nouns, and in particular of nouns with a strong perceptual characterization. Others address the semantics of predicates, with a detailed analysis of colour attributes. While this book represents a radical shift from traditional semantics, it still pursues a line of continuity that is based on the idea that meaning can be captured, and explained, by a sort of computation. (shrink)

In this paper, I argue that looking at the concept of neural function through the lens of cognition alone risks cognitive myopia: it leads neuroscientists to focus only on mechanisms with cognitive functions that process behaviorally relevant information when conceptualizing “neural function”. Cognitive myopia tempts researchers to neglect neural mechanisms with noncognitive functions which do not process behaviorally relevant information but maintain and repair neural and other systems of the body. Cognitive myopia similarly affects philosophy of (...) neuroscience because scholars overlook noncognitive functions when analyzing issues surrounding e.g., functional decomposition or the multifunctionality of neural structures. I argue that we can overcome cognitive myopia by adopting a patchwork approach that articulates cognitive and noncognitive “patches” of the concept of neural function. Cognitive patches describe mechanisms with causally specific effects on cognition and behavior which are likely operative in transforming sensory or other inputs into motor outputs. Noncognitive patches describe mechanisms that lack such specific effects; these mechanisms are enabling conditions for cognitive functions to occur. I use these distinctions to characterize two noncognitive functions at the mesoscale of neural circuits: subsistence functions like breathing are implemented by central pattern generators and are necessary to maintain the life of the organism. Infrastructural functions like gain control are implemented by canonical microcircuits and prevent neural system damage while cognitive processing occurs. By adding conceptual patches that describe these functions, a patchwork approach can overcome cognitive myopia and help us explain how the brain’s capacities as an information processing device are constrained by its ability to maintain and repair itself as a physiological apparatus. (shrink)

Imitation, deliberation, and mindreading are characteristically human sociocognitive skills. Research on imitation and its role in social cognition is flourishing across various disciplines. Imitation is surveyed in this target article under headings of behavior, subpersonal mechanisms, and functions of imitation. A model is then advanced within which many of the developments surveyed can be located and explained. The shared circuits model (SCM) explains how imitation, deliberation, and mindreading can be enabled by subpersonal mechanisms of control, mirroring, and simulation. It (...) is cast at a middle, functional level of description, that is, between the level of neural implementation and the level of conscious perceptions and intentional actions. The SCM connects shared informational dynamics for perception and action with shared informational dynamics for self and other, while also showing how the action/perception, self/other, and actual/possible distinctions can be overlaid on these shared informational dynamics. It avoids the common conception of perception and action as separate and peripheral to central cognition. Rather, it contributes to the situated cognition movement by showing how mechanisms for perceiving action can be built on those for active perception.;>;>The SCM is developed heuristically, in five layers that can be combined in various ways to frame specific ontogenetic or phylogenetic hypotheses. The starting point is dynamic online motor control, whereby an organism is closely attuned to its embedding environment through sensorimotor feedback. Onto this are layered functions of prediction and simulation of feedback, mirroring, simulation of mirroring, monitored inhibition of motor output, and monitored simulation of input. Finally, monitored simulation of input specifying possible actions plus inhibited mirroring of such possible actions can generate information about the possible as opposed to actual instrumental actions of others, and the possible causes and effects of such possible actions, thereby enabling strategic social deliberation. Multiple instances of such shared circuits structures could be linked into a network permitting decomposition and recombination of elements, enabling flexible control, imitative learning, understanding of other agents, and instrumental and strategic deliberation. While more advanced forms of social cognition, which require tracking multiple others and their multiple possible actions, may depend on interpretative theorizing or language, the SCM shows how layered mechanisms of control, mirroring, and simulation can enable distinctively human cognitive capacities for imitation, deliberation, and mindreading. (shrink)

How do minds emerge from developing brains? According to the representational features of cortex are built from the dynamic interaction between neural growth mechanisms and environmentally derived neural activity. Contrary to popular selectionist models that emphasize regressive mechanisms, the neurobiological evidence suggests that this growth is a progressive increase in the representational properties of cortex. The interaction between the environment and neural growth results in a flexible type of learning: minimizes the need for prespecification in accordance with (...) recent neurobiological evidence that the developing cerebral cortex is largely free of domain-specific structure. Instead, the representational properties of cortex are built by the nature of the problem domain confronting it. This uniquely powerful and general learning strategy undermines the central assumption of classical learnability theory, that the learning properties of a system can be deduced from a fixed computational architecture. Neural constructivism suggests that the evolutionary emergence of neocortex in mammals is a progression toward more flexible representational structures, in contrast to the popular view of cortical evolution as an increase in innate, specialized circuits. Human cortical postnatal development is also more extensive and protracted than generally supposed, suggesting that cortex has evolved so as to maximize the capacity of environmental structure to shape its structure and function through constructive learning. (shrink)

A fundamental characteristic of human visual perception is the ability to group together disparate elements in a scene and treat them as a single unit. The mechanisms by which humans create such groupings remain unknown, but grouping seems to play an important role in a wide variety of visual phenomena, and a good understanding of these mechanisms might provide guidance for how to improve machine vision algorithms. Here, we build on a proposal that some groupings are the result of connections (...) in cortical area V2 that join disparate elements, thereby allowing them to be selected and segmented together. In previous instantiations of this proposal, connection formation was based on the anatomy (e.g., extent) of receptive fields, which made connection formation obligatory when the stimulus conditions stimulate the corresponding receptive fields. We now propose dynamic circuits that provide greater flexibility in the formation of connections and that allow for top-down control of perceptual grouping. With computer simulations we explain how the circuits work and show how they can account for a wide variety of Gestalt principles of perceptual grouping, texture segmentation tasks, amodal illusory contours, and ratings of perceived groupings. We propose that human observers use such top-down control to implement task-dependent connection strategies that encourage particular groupings of stimulus elements in order to promote performance on various visual tasks. (shrink)

LeDoux (1996) has identified a sub-cortical neural circuit that mediates fear responses in rats. The existence of this neural circuit has been used to support the claim that emotion is a non-cognitive process. In this paper I argue that this sub-cortical circuit cannot have a role in the explanation of emotions in humans. This worry is raised by looking at the properties of this neural pathway, which does not have the capacity to respond to the types of (...) stimuli that are generally taken to trigger emotion responses. In particular, the neurons in this pathway cannot represent the stimulus as a complete object or event, rather they represent the simple information that is encoded at the periphery. If it is assumed that an object or event in the world is what, even in simple cases, causes an emotion, then this sub-cortical pathway has limited use in a theory of emotion. (shrink)