[Neurological features of decision-making deficit: Korinai syndrome in Parkinson disease and fearlessness in dementia].

For patients with Parkinson disease, falls are generally attributed to postural instability. However, closer examination often shows that parkinsonian patients tend to keep falling at the same spot in their home on performing the same actions such as standing up from a chair, starting to walk, or turning at the corner and hitting the same part of the head. Each time the patients fall, their treating physicians explain the reasons for falling and tell them how to avoid falls in daily life. In spite of the repeated advice given by physicians, these patients fall in the same manner and location. When physicians question them regarding the reason for repeating the same risky actions that they had been asked to avoid, the patients answer that they clearly remembered their physician's advice but had thought that they would be able to successfully accomplish the risky actions at that time. Thus, it seems that this type of fall is partly caused by decision-making deficit. Negative-reward motor learning is known to be defective in parkinsonian patients who are being treated with dopamine agonists and are liable to indulge in risky behavior and tend to be involved in pathological gambling. The behavioral abnormalities that are caused by defective decision making and are common to pathological gambling and repeated falling in parkinsonian patients could be termed as "Korinai syndrome, " which means "syndrome involving the inability to learn by experience." In contrast, patients with dementia often show loss of fear reaction, which may result in the life-threatening inability to perceive crises. The present author performed a series of studies just after the Great East Japan Earthquake in March 2011; these studies were based on the behavior of patients with dementia during this large earthquake. The results showed that both intellectually normal elderly people and patients with mild dementia had shown evident fear reactions and could remember their own fearful experience, whereas patients with moderate or severe dementia had not shown any fear reactions during the earthquake and had remained calm in spite of the highly confused behavior of their caregivers. Moreover, those who had remained calm without showing any fear reaction also did not show any trace of memory of the recently experienced large earthquake.