DEPRESSION IN THE ELDERLY SUBJECT: Depression is diagnosed to a varying extent in the elderly. In subjects with Alzheimer's disease, the most specific signs involve mood disorders, loss of energy, a feeling of hopelessness, and sometimes body discomfort or pain. DEFINITION OF APATHY: Apathy is defined as a loss of motivation, expressed by a loss of interest in activities, lack of productivity, loss of will and initiative, as well as limited affective response to positive or negative elements. TWO DIFFERENT SYNDROMES: The differential diagnosis is difficult, but studies have demonstrated that depression and apathy are two relatively different syndromes, which may be intertwined. Lack of volition and initiative are suggestive of apathy. Neuropsychology, particularly the capacity to divide attention, may be useful. FUNCTIONAL CONSEQUENCES: Apathy and depression both have functional effects which may accelerate institutionalization (altered capacity for initiative, adaptation to the environment). FUNCTIONAL ANATOMY AND NEUROCHEMICAL CONSEQUENCES: Apathy and to a lesser degree depression, involve prefrontal cortical areas. Involvement of the prefrontal pathways is a common feature of apathy and depression, but the other pathways are affected specifically. Cholinesterase inhibitors and selective serotonine reuptake inhibitors as well as serotoninergic antidepressants have been found to be effective for certain components of apathy.