Behind the faces: Alzheimer’s disease and emotional blindness

Abstract

F ace emotional recognition (FER), empathy, emotional inference, decision-making, theory of mind are some of the various aspects of social cognition 1 . FER is involved in other aspects of social cognition and its impairment would interfere in the performance of other components of the social network. The six emotions commonly studied are: happiness, surprise, anger, disgust, fear and sadness.The expression of emotions and their recognition by others was already addressed by the naturalist Charles Darwin in his famous book "The Expression of the Emotions in Man and Animals" 2 . Darwin showed that the expression of emotions is evolutionarily conserved among species and that this fact should have an adaptive and survival implication. The American psychologist Paul Ekman, not without controversy, devoted to the systematic and exhaustive study of facial expressions of the different emotions in the last decades of the twentieth century . He says that the appearance of mirror neurons, first detected in the ventral premotor area of macaque monkeys, led to the discovery of expressed emotion (''read mind"), anticipating the most appropriate response for social interaction and the success of community living. Ultimately, mirror neurons would be the anatomical substrate for empathy. Therefore, it is easy to understand that the loss of this essential skill for our entire social and emotional performance can be quite problematic.The study of social cognition runs parallel to the study of traditional cognitive tasks in the field of dementia. It is possible that the different performance on tests that evaluate social cognition may be of clinical utility to differentiate the causes of dementia, especially in the initial phase of the main dementia of degenerative etiology 6,7,8 . The distinction between the two main forms of primary dementia in pre-senile age, frontotemporal dementia (FTD) and Alzheimer's disease (AD), can be difficult in clinical practice. The impairment of episodic memory, which is considered a hallmark in AD, may occur in FTD, even in the beginning of the disease 9 . In contrast, social cognition is impaired markedly in the behavioral variant of FTD (bvFTD), progressive disease characterized by changes in behavior and personality, with decreased empathy, disinhibition, inappropriate behavior, difficulty in social interaction, loss of insight, hyperorality and impulsivity. Usually, behavioral changes precede the traditional cognitive deficits.Few studies address the involvement of social cognition in patients with AD. The results are contradictory and can be explained by the small number of patients and different forms of assessment. Some studies of patients with amnestic mild cognitive impairment point to the maintenance of integrity in the FER 10 or mild difficulty especially in the detection of negative emotions (anger, fear and sadness) 11,12 . However, these same studies indicate a greater impairment in FER and mild difficulty in socioemotional battery in patients diagnosed with mild AD 6,13 . A comparati...