Dementia is a clinical phenomenon, which is characterized by a gradually progressive loss of cognitive emotional and behavioral function. From the various diseases that cause dementia, Alzheimer's disease is the commonest, accounting for about 60% of cases (Alzheimer's Association Australia, 2001). Alzheimer's Disease represents one of the most serious health issues of our time, and with the proportion of elderly individuals in our society increasing, it presents a continuous challenge to researchers investigating its nature, cause, diagnosis and treatment possibilities. While the causes of the disease remain relatively unknown, the greatest risk factor is advancing age (Kawas, 2003; Mayeux, 2003; Salman, 2004). Women seem to be more likely than men to develop it (Jorm & Jolley, 1998; Mayeux, 2003), and the chance of developing Alzheimer's Disease doubles every five years after the age of sixty (Kawas, 2003).
In the typical case, dementia of the Alzheimer's type begins with an impairment of recent memory and new learning (Perry & Hodges, 2000). Despite variability in the emergence of symptoms, the disease consists of three broad stages, reflecting progression of symptomatology and underlying neuropathology (Filley, 1995; Forstl & Kurz, 1999; Nagy et al., 1999). In the early stage (between 2 & 4 years before and including diagnosis), patients show relatively subtle symptoms, such as mild forgetfulness, word-finding difficulties and reduced levels of mental efficiency in general (Andresen, 1995). The neuropathology at this stage, referred to as the transentorhinal period seems to involve the accumulation of neurofibrillary tangles in the parahippocampal region (Nagy et al., 1999). In the second and longest stage (between 2 & 12 years), patients show increasing functional impairment in a variety of cognitive domains, and activities of daily living. In the third and terminal stage, most aspects of cognition and emotion are severely impaired (Forstl & Kurz, 1999). The cognitive changes seen in the last two stages, also referred to as the limbic and the isocortical periods respectively, have been shown in neuroimaging studies to be characterized by the spread of atrophy to the limbic system, and then to the neocortex (Nagy et al., 1999). Thus, there is strong support for a relationship between cognitive decline and the staging of the neuropathology in AD (Forstl & Kurz, 1999; Nagy et al., 1999). In the present study, two tasks that are likely to reflect progression of early neuropsychological impairment during the transentorhinal period will be investigated.