Genetic Support for the Dual Nature of Attention Deficit Hyperactivity Disorder: Substantial Genetic Overlap Between the Inattentive and Hyperactive–impulsive Components

Objective Attention deficit hyperactivity disorder (ADHD) is a common, complex and highly heritable disorder, characterised by inattentive, impulsive and overactive behaviour. Evidence for the heritability of ADHD measures in twin population samples has come from the analysis of total scores that combine inattentive and hyperactive–impulsive symptoms subscales. This study investigated, in a community sample, the aetiology of ADHD-like traits and the aetiological overlap between the two dimensions that define the ADHD disorder. Materials and Methods Parents of 6,222 approximately 8-year-old twin pairs from the Twins Early Development Study (TEDS) population sample completed the two subscales of the Conners’ 18-item DSMIV checklist, a screening instrument for ADHD symptoms. Results Both subscales were highly heritable (hyperactive–impulsive: 88%; inattentive: 79%). Bivariate genetic modelling indicated substantial genetic overlap between the two components; however, there were significant independent genetic effects. Conclusions These findings suggest that many genes associated with the hyperactivity–impulsivity dimension will also be associated with the inattentive dimension but that there is significant genetic heterogeneity as well. These results provide genetic support for combining the two behavioural dimensions that define ADHD, but also suggest that some symptom-specific genes will also be identified. Correspondence and reprint requests to Gráinne McLoughlin, SGDP Centre, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, Tel: +44(0) 207-848-5261; Email: g.mcloughlin@iop.kcl.ac.uk.     

Hinge versus twist: the effects of 'reference surfaces' and discontinuities on stereoscopic slant perception

Stereoscopic slant perception around a vertical axis (horizontal slant) is often found to be strongly attenuated relative to geometric prediction. Stereo slant is much greater, however, when an adjacent surface, stereoscopically in the frontal plane, is added. This slant enhancement is often attributed to the presence of a 'reference surface' or to a spatial change in the disparity gradient (introducing second and higher derivatives of disparity). Gillam, Chambers, and Russo (1988 Journal of Experimental Psychology: Human Perception and Performance 14 163-175) questioned the role of these factors in that placement of the frontal-plane surface in a direction collinear with the slant axis (twist configuration) sharply reduced latency for perceiving slant whereas placing the same surface in a direction orthogonal to the slant axis (hinge configuration) had little effect. We here confirm these findings for slant magnitude, showing a striking advantage for twist over hinge configurations. We also examined contrast slant measured on the frontal-plane surface in the hinge and twist configurations. Under conditions where test and inducer surfaces have centres at the same depth for twist and hinge, we found that twist configurations produced strong negative slant contrast, while hinge configurations produced significant positive contrast or slant assimilation. We conclude that stereo slant and contrast effects for neighbouring surfaces can only be understood from the patterns and gradients of step disparities present. It is not adequate to consider the second surface merely as a reference slant for the first or as having its effect via a spatial change in the disparity gradient.     

A note on ROC analysis and non-parametric estimate of sensitivity

In the signal detection paradigm, the non-parametric index of sensitivity A′, as first introduced by Pollack and Norman (1964), is a popular alternative to the more traditional d′ measure of sensitivity. Smith (1995) clarified a confusion about the interpretation of A′ in relation to the area beneath proper receiver operating characteristic (ROC) curves, and provided a formula (which he called A′′) for this commonly held interpretation. However, he made an error in his calculations. Here, we rectify this error by providing the correct formula (which we call A) and compare the discrepancy that would have resulted. The corresponding measure for bias b is also provided. Since all such calculations apply to “proper” ROC curves with non-decreasing slopes, we also prove, as a separate result, the slope-monotonicity of ROC curves generated by likelihood-ratio criterion.This revised article was published online in August 2005 with the PDF paginated correctly.     

A continuous smooth map of space in the primary visual cortex of the common marmoset

We examined the fine-scale mapping of the visual world within the primary visual cortex of the marmoset monkey (Callithrix jacchus) using differential optical imaging. We stimulated two sets of complementary stripe-like locations in turn, subtracting them to generate the cortical representations of continuous bands of visual space. Rotating this stimulus configuration makes it possible to map different spatial axes within the primary visual cortex. In a similar manner, shifting the stimulated locations between trials makes it possible to map retinotopy at an even finer scale. Using these methods we found no evidence of any local anisotropies or distortions in the cortical representation of visual space. This is despite the fact that orientation preference is mapped in a discontinuous manner across the surface of marmoset V1. Overall, our results indicate that space is mapped in a continuous and smooth manner in the primary visual cortex of the common marmoset.     

Strength of affective reaction as a signal to think carefully

Analytic processes reduce biases, but it is not known how or when these processes will be deployed. Based on an affective signal hypothesis, relatively strong affective reactions were expected to result in increased analytic processing and reduced bias in judgement. The valence and strength of affective reactions were manipulated through varying outcomes in a game or evaluative conditioning of a stimulus. Relatively strong positive or negative affective reactions resulted in less desirability bias. Bias reduction only occurred if participants had time to deploy analytic processes and indicators of the degree of analytic processing (in the form of attentional control) predicted less bias. Affective processes have long been acknowledged as a source of bias, but these findings suggest affective processes are also integral to bias reduction.     

The Developmental Trajectory from Amodal Perception to Empathy and Communication: The Role of Mirror Neurons in This Process

In a recent paper entitled “Mirror Neurons. Procedural Learning and the Positive New Experience” (Wolf et al., 2000), data were presented about a special type of neuron, the mirror neuron, originally located by Rizzolatti and his colleagues (1995). These neurons were discussed as they related to a particular developmental view of psychoanalysis, developmental systems self psychology (Shane, Shane, and Gales. 1997).

In this paper, we focus on how this mirror neuron system might contribute to the development of communicative abilities in humans. First we summarize the research findings about mirror neurons and how they apply to humans. We then attempt to demonstrate how the mirror neuron system might be involved in a developmental sequence hypothesized by Kohut (1984), Stern (1985), and others to begin in infancy. We postulate that this trajectory starts with the onset of “amodal perception” (Stern, 1985) and then proceeds to affect resonance, joint attention, and ultimately to symbolization of language. In this paper, we attempt to integrate these concepts with a formulation of empathy and demonstrate what might go awry in developmental disorders when the normative sequence of development described above does not take place.     

Psychoanalysis Unbound: A Contextual Consideration of Boundaries From a Developmental Systems Self Psychology Perspective

Each individual analyst has a unique way of evolving and developing over the years, in theory and in style of working with analysands. Different environmental conditions as well as one's personal inner life are significant influences. My analytic journey started in 1950 in Los Angeles and the turmoil of the psychoanalytic institutes had a significant impact on me. Often difficulties in the institutes were said to be about theory and ideas in psychoanalysis, but power issues were always present. The American Psychoanalytic Association was also involved in these matters with their attitude on “correct” theory. This paper discusses the interplay of these events and other aspects of my own evolution—from ego to self.