Impairment in the control of coupled cyclic movements of ipsilateral hand and foot after total callosotomy

Integrity of both cerebral hemispheres is required to control in-phase or anti-phase coupling of ipsilateral hand and foot oscillations, as shown by the impairment of these tasks when performed on the healthy side of hemiplegic patients. On this basis, coupling of hand–foot movements was analysed in a right-handed subject (ME) who underwent a total resection of the corpus callosum. Oscillations of the prone hand and foot, paced by a metronome at different frequencies, as well as EMG activity in extensor carpi radialis (ECR) and tibialis anterior (TA) muscles were analysed by measuring the average phase difference between the hand and foot movements and EMG cycles.

ME performed in-phase movements (right-hand extension coupled to right-foot dorsal flexion) at frequencies up to 3 Hz, though the hand cycle progressively lagged the foot cycle as the frequency increased. At 3 Hz the hand lag reached −142° (as compared to about 25° in healthy subjects). The lag increased even further after application of an inertial load to the hand, reaching 180° at 1.8 Hz (about 50° in healthy subjects). ME's hand lag is caused by the lack of any anticipatory reaction in hand movers. In contrast to healthy subjects, which activate the ECR earlier than the TA when the frequency increases, ME activated the ECR later than TA at all frequencies higher than 0.9 Hz.

Anti-phase movements (hand extension coupled to foot plantar flexion) were performed only upto 1 Hz in unloaded conditions. At 0.6 Hz, movements were in tight phase-opposition (3°), but at 1 Hz, the hand lag reached −34° because of a delayed ECR activation. After hand loading ME was unable to couple movements in anti-phase. In contrast, normal subjects maintain a tight anti-phase coupling up to 2.0 Hz, both with an unloaded or loaded hand. Similar deficits were observed by ME when performing in-phase and anti-phase coupling on the left side, as well as when he was blindfolded.

In normal subjects, an anticipated muscular activation of hand movers compensates for hand loading. Since this compensation must depend on monitoring the hand delay induced by loading, the absence in ME of such compensatory reaction suggests that callosal division had apparently compromised the mechanisms sustaining feedback compensation for differences in the biomechanical limb properties. They also confirm and reinforce the idea that elaboration of the afferent message, aiming at controlling the phase of the movement association, needs the co-operation of both cerebral hemispheres.     

A longitudinal study of "intrusion-based reasoning" and posttraumatic stress disorder after exposure to a train disaster

Previously, we found that chronic PTSD relates to “intrusion-based reasoning” (IR), i.e. the tendency to interpret distressing intrusions themselves as evidence that danger is impending, regardless of objective danger information (Engelhard et al., Behav. Res. Ther. 39 (2001) 1139). This study was intended to elucidate the causal status of this relation. Twenty-nine residents of a Belgian town witnessed a train crash and were assessed for IR and PTSD symptoms within 1 month and were re-assessed for PTSD at 3.5 months. Fourteen control residents did not witness the crash and were also tested for IR. The IR paradigm involved rating the danger of brief scenarios in which objective danger and presence of intrusions about the crash were systematically varied. The directly exposed residents showed greater danger ratings to scenarios in which intrusions were included than did the controls. IR was strongly related to both acute and chronic PTSD symptoms. It did not significantly predict chronic PTSD symptoms after controlling for acute symptoms, although the partial correlation (r=0.26, p=0.09) was in the expected direction. The data suggest that IR is involved in the onset and maintenance of PTSD symptoms, but more clarity about causality awaits future larger and experimental studies.     

A simulation study of the degrees of freedom of movement in reaching and grasping

The question of independently controlled components in the act of reaching and grasping has attracted interest experimentally and theoretically. Data from 35 studies were recently found consistent with simulated kinematic finger and thumb trajectories optimised for minimum jerk. The present study closely reproduces those trajectories using a discrete-time model based on minimum acceleration. That model was further used to generate two-dimensional trajectories for finger and thumb to reach and grasp an elliptical object with varying position and/or orientation. Orthogonalisation of these four trajectories revealed one degree of freedom when direction of reach was constant and two degrees of freedom when direction of reach varied, irrespective of object distance and orientation. These simulations indicate that reach and grasp movements contain redundancy that is removable by formation of task-dependent synergies. As skilled movement can be planned and executed in a low dimension workspace, control of these independent components lessens central workload.     

The Importance of Child and Adolescent Psychopathy

In commenting on the five articles in this special issue, this paper discusses (1) the concept of child and adolescent psychopathy, and whether adolescent psychopaths are qualitatively distinct from other young people; (2) the measurement of adolescent psychopathy; (3) the relationship between psychopathy and other personality dimensions; (4) childhood risk factors for psychopathy; (5) psychopathy in the context of risk factors for delinquency; and (6) the prevention and treatment of adolescent psychopathy. It is argued that the three dimensions of an arrogant, deceitful interpersonal style, deficient affective experience, and an impulsive or irresponsible behavioral style are most important at present in the definition of psychopathy. An ambitious research agenda is recommended, investigating the concept of adolescent psychopathy, developing new measures, conducting new longitudinal studies on development and risk factors, and mounting new randomized experiments on prevention and treatment.     

Trajectories of Peer-Nominated Aggression: Risk Status,Predictors and Outcomes

Developmental trajectories of peer-nominated aggression, risk factors at baseline, and outcomes were studied. Peer nominations of aggression were obtained annually from grades 1 to 3. Three developmental trajectories were identified: an early-onset/increasers trajectory with high levels of peer-nominated aggression at elementary school entry and increasing levels throughout follow-up; a moderate-persistent trajectory of aggression in which children were characterized by moderate levels of physical aggression at baseline; and a third trajectory with stable low levels of aggression. Children following the early-onset/increasers trajectory showed physical forms of aggression at baseline. Male gender and comorbid attention deficit/hyperactivity problems, oppositional defiant problems and poor prosocial behavior plus negative life events predicted which children would follow the early-onset/increasers trajectory of aggression. The outcomes associated with the early-onset/increaser children suggest high risk for chronically high levels of aggressive behavior.     

The planning and execution of sequential eye movements: saccades do not show the one target advantage

The present experiment examined the one-target advantage (OTA) with regard to saccadic eye movements. The OTA, previously found with manual pointing responses, refers to the finding that movements are executed faster when the limb is allowed to stop on the target compared to the situation where it has to proceed and hit a second target. Using an adapted limb movement OTA task, saccades of 5 degrees and 15 degrees were made to (a) a single target (one-target), (b) one target and immediately to another target without a change in direction (two-target-extension), and (c) one target and immediately back to the start location (two-target-reversal). Unlike manual movements, the movement times for the initial saccade in the two-target-extension condition were not prolonged compared to either of the other two conditions. Moreover, this pattern of results was found for both the shorter and longer amplitude saccades. The results indicate that the OTA does not occur in the oculomotor system and therefore is not a general motor control phenomenon.     

Learning from the law to address uncertainty in the precautionary principle

Environmentalists have advocated the Precautionary Principle (PP) to help guide public and private decisions about the environment. By contrast, industry and its spokesmen have opposed this. There is not one principle, but many that have been recommended for this purpose. Despite the attractiveness of a core idea in all versions of the principle—that decision-makers should take some precautionary steps to ensure that threats of serious and irreversible damage to the environment and public health do not materialize into harm—even one of the most widely endorsed principles needs considerable specification and refinement before it can be used. Moreover, the PP is an approach or guide to utilizing scientific evidence in social or legal decision-making contexts. In this it does not differ in kind from other approaches to using factual information such as in the law. The law provides some models for different strategies to guide decision-making under uncertainty when factual issues cannot be resolved with certainty. These in turn can help guide the formulation of different versions of PP and help clarify some presuppositions of the principle. Once some plausible versions of PP are articulated, I suggest some applications to existing environmental problems.     

Global VOR gain adaptation during near fixation to foveal targets

Long-term rotational vestibulo-ocular (VOR) adaptation occurs during systematic dysmetria between visual and vestibular afferents, adjusting eye-rotation angular velocity to re-establish retinal stability of the visual field. Due to translational motion of the eyes during head rotation, VOR gain is higher when fixating near objects. The current study measures VOR in humans before and after 6 min of exposure to a foveal near-target during sinusoidal whole-body rotation at 0.45 Hz. All of six participants showed post-exposure increases in open-loop VOR gain after fixating near targets, demonstrating a mean modulation increase of open-loop VOR gain from 0.86 before adaptation to 1.2 after adaptation. We discuss a number of theoretical and applied implications.     

The Ethics of Type 1 Diabetes Prediction and Prevention Research

There are approximately one million cases oftype 1 diabetes in the US, and the incidenceis increasing worldwide. Given that two-thirdsof cases present in childhood, it is criticalthat prediction and prevention research involvechildren. In this article, I examine whethercurrent research methodologies conform to theethical guidelines enumerated by the NationalCommission for the Protection of Human Subjectsof Biomedical and Behavioral Research, andadopted into the federal regulations thatprotect research subjects. I then offer twopolicy recommendations to help researchersdesign studies that conform to these ethicalrequirements.