There are many reasons that a person might have difficulty with shopping, because it is a complex task that requires many different brain functions to be operating properly. Importantly, too, in mild dementia, people lack the motivation to start the task, or the insight to know that it is time to get started, or the ability to plan, or to the judgment to choose what is needed.

These complex behaviours often reflect more problems with planning, sequencing, insight and judgment, which are known as executive function Executive function
Includes the behaviors associated with judgment, agitation and social behavior - not memory. These behaviors are affected in all dementias, but especially in frontotemporal dementia.. Such functions are importantly dependent on the frontal lobes. We know that because people who have localized damage to their frontal lobes (say from a car accident, bullet, tumor Tumor
An abnormal mass of tissue that is the result of excessive cell division. They are not useful to the body and can be benign (non-cancerous) or malignant (cancerous). or blood vessel problem) characteristically have these types of problems. Frontal lobe impairment was classically seen as a late sign Sign
In medicine a sign is what a physician finds by examining a patient. For example, a patient with the symptom of pain might have signs of a fast heart rate, a pale face, a clammy touch and tenderness. of Alzheimer's disease Alzheimer's disease
A neurological disease that affects memory and behaviour. It is characterized by beta-amyloid plaques and neurofibrillary tangles in the brain. There is no known cause but genetics and lifestyle are thought to play a role., but thinking about this has changed in two ways. Now that there is better testing of the frontal lobes, we see that there is involvement early. Also, brain imaging studies suggest that early on, the brain is able to compensate for damage in the frontal lobes, but the ability to compensate becomes less as the disease progresses. This is an important insight, because it suggests that strategies to treat Alzheimer's disease need not just focus on countering the disease process, but can also enhance the repair process.

This issue is explored in considerable detail in the chapter on 'executive function' by Sarah Voss and Roger Bullock, in the book Trial Designs and Outcomes in Dementia Therapeutic Research, published in London in 2005 by Taylor & Francis, 2005, and edited Kenneth Rockwood and Serge Gauthier. The assessment of function in anti-dementia drug trials is discussed in detail in another chapter in that book, by Serge Gauthier.