Humans predict the sensory consequences of motor commands by learning internal models of the body and of environment perturbations. When facing a sensory prediction error, should we attribute this error to a change in our body, and update the body internal model, or to a change in the environment? In the latter case, should we update an existing perturbation model or create a new model? Here, we propose that a decision-making process compares the models' prediction errors, weighted by their precisions, to select and update either the body model or an existing perturbation model. When no model can predict a perturbation, a new perturbation model is created and selected. When a model is selected, both the prediction's mean estimate and uncertainty are updated to minimize future prediction errors and to increase the precision of the predictions. Results from computer simulations, which we verified in an arm visuomotor adaptation experiment with subjects of both sexes, account for short aftereffects and large savings after adaptation to large, but not small, perturbations. Results also clarify previous data in the absence of errors (error-clamp): motor memories show an initial lack of decay after a large perturbation, but gradual decay after a small perturbation. Finally, qualitative individual differences in adaptation were explained by subjects selecting and updating either the body model or a perturbation model. Our results suggest that motor adaptation belongs to a general class of learning according to which memories are created when no existing memories can predict sensory data accurately and precisely.

Elderly suicide attempters had different psychosocial stressors such as physical illness and more lethal suicide attempts. Our study suggests the need for development of specific preventive strategies and management guidelines for the elderly suicide attempters.

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ObjectiveFew studies have focused on the characteristic features of drug overdose in children and adolescents who have attempted suicide in Korea. The present study examined the characteristics of drug overdose in children and adolescents who visited the emergency room following drug ingestion for a suicide attempt.MethodsThe medical records of 28 patients who were treated in the emergency room following a drug overdose from January 2008 to March 2011 were analyzed. Demographic and clinical variables related to the suicide attempts were examined.ResultsThe mean age of the patients was 16.6±1.7 years (range 11-19 years), and 20 of the patients (71.4%) were female. Most of the patients (n=23, 82.1%) overdosed on a single drug; acetaminophen-containing analgesics were the most common (n=12, 42.9%). Depression was the most common psychiatric disorder (n=22, 78.6%), and interpersonal conflict was the most common precipitating factor of the suicide attempts (n=11, 39.3%). This was the first suicide attempt for approximately 80% of the patients. About one fourth of the patients (n=7, 25%) had follow-up visits at the psychiatric outpatient clinic.ConclusionEarly screening and psychiatric intervention for depression may be an important factor in preventing childhood and adolescent suicide attempts. Developing coping strategies to manage interpersonal conflicts may also be helpful. Moreover, policies restricting the amount and kind of drugs purchased by teenagers may be necessary to prevent drug overdose in this age group.