Is the principle of minimization of secondary moments validated during various fingertip force production conditions?

During the application of fingertip forces with simultaneous flexion of the four fingers, namely index, middle, ring, and little fingers, a stable force sharing among fingers is adopted. Several studies have hypothesized that this stable force sharing is established to minimize unnecessary rotational moments (different from the main flexion moments). This principle labeled "minimization of secondary moments" is presented in the literature as a principle used by the central nervous system to solve musculoskeletal redundancy. However, this principle has only been tested with one solicited degree of freedom and in one finger posture. Our study tests this principle with various degrees of freedom solicited as secondary moments and in two different finger postures. Participants (n=6) were asked to apply a downward vertical force using their four fingers with the forearm placed in two different configurations: a "horizontal" condition (involving flexion/extension and pronation/supination at the wrist joint) and a "vertical" condition (involving flexion/extension and radial/ulnar deviation at the wrist joint). Additionally, two finger postures were tested in each forearm configuration: in the first, the distal inter-phalangeal joints (DIP) were extended and the proximal inter-phalangeal joints (PIP) highly flexed. In the second finger posture, both DIP and PIP joints were flexed. The resultant four-finger force and the relative involvement of each finger in the resultant four-finger force (force sharing) were analyzed. Results showed that the finger postures did not influence the finger force sharing, showing that the minimization of the secondary moment principle was stable among the finger joint angle configurations. Nonetheless, the relative involvement of each finger was dependent on the secondary degree of freedom solicited (pronation/supination vs. radial/ulnar). The modifications of the finger force sharing between the "horizontal" and "vertical" conditions were in accordance with the principle of minimization of the secondary moments.     

Physicians' understanding of patients' personal representations of their diabetes: accuracy and association with self-care

The degree of accuracy with which physicians understand their patients' views may be of central importance for promoting self-care in the majority of chronic illnesses and in type 2 diabetes in particular. The objectives of this study were to measure the accuracy of the general practitioners' understanding of the patients' views and relate it to health behavioural outcomes in patients with non-complicated type 2 diabetes. The participants in this cross-sectional study consisted of 14 clinicians and 78 of their patients from Paris, France. The predictors were levels of accuracy in understanding the patients' views derived from the illness perception questionnaire-revised (IPQ-R). The outcomes were patient-reported self-care measures. In regression models controlling for clinical and personal variables, higher accuracy on chronicity beliefs was associated with an improved diet and increased blood glucose self-testing and higher accuracy in identifying treatment control beliefs was associated with better dietary self-care. Accuracy was higher with regard to beliefs about causes, treatment control and consequences. These results suggest that accuracy may impact self-care in specific domains of illness perception but not others. The results may help identify useful avenues of communication training designed for professionals.     

Physiological evidence for response inhibition in choice reaction time tasks

Inhibition is a widely used notion proposed to account for data obtained in choice reaction time (RT) tasks. However, this concept is weakly supported by empirical facts. In this paper, we review a series of experiments using Hoffman reflex, transcranial magnetic stimulation and electroencephalography to study inhibition in choice RT tasks. We provide empirical support for the idea that inhibition does occur during choice RT, and the implications of those findings for various classes of choice RT models are discussed.     

Being the agent: memory for action events

Whoever paid the bill at the restaurant last night, will clearly remember doing it. Independently from the type of action, it is a common experience that being the agent provides a special strength to our memories. Even if it is generally agreed that personal memories (episodic memory) rely on separate neural substrates with respect to general knowledge (semantic memory), little is known on the nature of the link between memory and the sense of agency. In the present paper, we review results from two experiments investigating the effects of agency on both explicit and implicit memory traces. Performance of normal subjects is compared to that of schizophrenic patients in order to explore the role of awareness of action on memory. It is proposed that reliable first-person information is necessary to create a stable and coherent motor memory trace.     

Does training have consequences for the walk-run transition speed?

A number of authors when studying the walk-run transition phenomenon focused either on the mechanical or energy expenditure whilst only a few used both parameters concurrently. Moreover the literature demonstrates that the contribution of these variables changes along with the level and method of training. Consequently the purpose of this study is to find, by analyzing concurrently these two variables, if the walk-run transition speed is linked to the type of training. To this end we calculated two theoretical transition speeds: one based on the metabolic energy expenditure St(1) and the second one based on the internal work St(2). Subjects were divided into three groups (untrained, sprint and endurance-trained men) who were required to walk and run on a treadmill at increasing speeds. Firstly we show that the relationship between St(1) and St(2) differs depending on the groups. Sprinters have a significantly lower St(2) than St(1) whereas the opposite is found for untrained subjects. We also show that the transition speed is linked to the subject's type of training. To conclude it seems that acquiring running techniques through specific training has consequences for the walk-run transition phenomenon.     

Mental rotation in schizophrenia

Motor imagery provides a direct insight into action representations. The aim of the present study was to investigate the level of impairment of action monitoring in schizophrenia by evaluating the performance of schizophrenic patients on mental rotation tasks. We raised the following questions: (1) Are schizophrenic patients impaired in motor imagery both at the explicit and at the implicit level? (2) Are body parts more difficult for them to mentally rotate than objects? (3) Is there any link between the performance and the hallucinating symptom profile? The schizophrenic patients (n = 13) displayed the same pattern of performance as the control subjects (n = 13). More particularly, schizophrenic patients’ reaction time varied as a function of the angular disparity of the stimuli. On the other hand, they were significantly slower and less accurate. Interestingly, patients suffering from hallucinations made significantly more errors than non-hallucinatory patients. We discussed these latter results in terms of deficit of the forward model. We emphasized the necessity to distinguish different levels of action, more or less impaired in schizophrenia.