NEUROGENESIS IN MENTAL HEALTH PROBLEMS: THE CRITICAL ROLE OF FORGETTING

The neurogenesis hypothesis of affective and anxiety disorders (1) suggests that the reduced generation of neurons in the postnatal hippocampal dentate gyrus (decreased neurogenesis) is involved in the etiology of different mental health problems. Even if this hypothesis is highly attractive, two of its key postulates - decreased adult neurogenesis results in depressive or anxious phenotypes; effective treatments for these disorders require intact hippocampal neurogenesis – have, in general, been rejected (1). The recent paper by Akers and colleagues (2), however, suggests a new link between neurogenesis and mental health problems: decreased neurogenesis in these patients may reduce their ability in forgetting and/or inhibiting trauma/disorder-related information. When simple objects or events remind a person a negative memory, individuals try to exclude the unwanted experience from mind. However, if their ability of forgetting it is impaired, they are locked to a negative experience that they have to cope with indefintely. For example, in PTSD the patient continuously relives the initial event which caused the disorder. The impossibility of forgetting it, fixes the patient on the traumatic event, with negative alterations in cognitions and mood (3). A similar path can be found in depression: the impossibility of directly forgetting mood-congruent material may induce a prolonged processing of negative, goal-irrelevant aspects of presented information, hindering recovery from negative mood (4). In anorexia, too, a puzzling symptom such as body image distortion, may be explained with the impossibility of forgetting/updating a previously stored negative image of the body (5, 6). These examples suggest that considering the effects of neurogenesis on the different forms of forgetting – directed forgetting (inhibition), long-term forgetting, retrieval-induced forgetting, etc. - may offer a new perspective in the search to develop and test novel mental health drugs and treatments, and perhaps even prevent or at least diminish the severity of these disorders.