A perfectly matched layer (PML) absorbing material composed of a uniaxial anisotropic material is presented for the truncation of finite-difference time-domain (FDTD) lattices. It is shown that the uniaxial PML material formulation is mathematically equivalent to the perfectly matched layer method published by Berenger (see J. Computat. Phys., Oct. 1994). However, unlike Berenger's technique, the uniaxial PML absorbing medium presented in this paper is based on a Maxwellian formulation. Numerical examples demonstrate that the FDTD implementation of the uniaxial PML medium (...) is stable, equal in effectiveness as compared to Berenger's PML medium, while being more computationally efficient. (shrink)

One of science's greatest intellects examines how people and animals display fear, anger, and pleasure. Darwin based this 1872 study on his personal observations, which anticipated later findings in neuroscience. Abounding in anecdotes and literary quotations, the book is illustrated with 21 figures and seven photographic plates. Its direct approach, accessible to professionals and amateurs alike, continues to inspire and inform modern research in psychology.

The target articles by Dixon (2012), Scarantino (2012), and Mulligan and Scherer (2012) explore the nature of emotion from philosophical and psychological perspectives. I discuss how neuroscience can also contribute to debates about the nature of emotion. I focus on the aspects of emotion that usually fall within the topic of basic emotions, but conclude that we may need to revise how we conceive and study these kinds of emotional states in relation to the brain.

Among discrete emotions, basic emotions are the most elemental; most distinct; most continuous across species, time, and place; and most intimately related to survival-critical functions. For an emotion to be afforded basic emotion status it must meet criteria of: (a) distinctness (primarily in behavioral and physiological characteristics), (b) hard-wiredness (circuitry built into the nervous system), and (c) functionality (provides a generalized solution to a particular survival-relevant challenge or opportunity). A set of six emotions that most clearly meet these criteria (enjoyment, (...) anger, disgust, fear, surprise, sadness) and three additional emotions (relief/contentment, interest, love) for which the evidence is not yet quite as strong is described. Empirical approaches that are most and least useful for establishing basic-emotion status are discussed. Basic emotions are thought to have a central organizing mechanism and to have the capacity to influence behavior, thoughts, and other fundamental processes. (shrink)

A model of the neuropsychology of anxiety is proposed. The model is based in the first instance upon an analysis of the behavioural effects of the antianxiety drugs in animals. From such psychopharmacologi-cal experiments the concept of a “behavioural inhibition system” has been developed. This system responds to novel stimuli or to those associated with punishment or nonreward by inhibiting ongoing behaviour and increasing arousal and attention to the environment. It is activity in the BIS that constitutes anxiety and that (...) is reduced by antianxiety drugs. The effects of the antianxiety drugs in the brain also suggest hypotheses concerning the neural substrate of anxiety. Although the benzodiazepines and barbiturates facilitate the effects of γ-aminobutyrate, this is insufficient to explain their highly specific behavioural effects. Because of similarities between the behavioural effects of certain lesions and those of the antianxiety drugs, it is proposed that these drugs reduce anxiety by impairing the functioning of a widespread neural system including the septo-hippocampal system, the Papez circuit, the prefrontal cortex, and ascending monoaminergic and cholinergic pathways which innervate these forebrain structures. Analysis of the functions of this system suggests that it acts as a comparator: it compares predicted to actual sensory events and activates the outputs of the BIS when there is a mismatch or when the predicted event is aversive. Suggestions are made as to the functions of particular pathways within this overall brain system. The resulting theory is applied to the symptoms and treatment of anxiety in man, its relations to depression, and the personality of individuals who are susceptible to anxiety or depression. (shrink)

Historically, the hypothesis driving emotion research has been that emotion’s data-base—in language, physiology, and behavior— is organized around specific mental states, as reflected in evaluative language. It is suggested that this approach has not greatly advanced a natural science of emotion and that the developing motivational model of emotion defines a better path: emotion is an evolved trait founded on motivational neural circuitry shared by mammalian species, primitively prompting heightened perceptual processing and reflex mobilization for action to appetitive or threatening (...) survival cues. As the field moves forward with increasingly sophisticated measurement technology and assessing more complex affective functioning, scientific understanding of human emotion will proceed best within the framework of this mammalian brain model. (shrink)

Competing perspectives on the nature of emotion are illustrated with latent and emergent variable models. Latent variable models draw from classical test theory, assuming that the measured indicators of emotion covary by virtue of some common executive, organizing neural circuit or network in the brain. By contrast, emergent variable models draw from a theory-driven, operational definition tradition, positing that emotions do not cause, but rather are caused by, the measured indicators of emotion, assuming no executive neural circuit or network, and (...) requiring no covariation among indicators. I suggest that the emergent variable model may be more compatible with the extant literature on the nature of emotion, especially in the age of affective neuroscience. (shrink)

The Bayesian brain hypothesis provides an attractive unifying framework for perception, cognition, and action. We argue that the framework can also usefully integrate interoception, the sense of the internal physiological condition of the body. Our model of entails a new view of emotion as interoceptive inference and may account for a range of psychiatric disorders of selfhood.