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Alzheimer's Disease

Executive Function

Choosing one action (or response) over another is based on split second decision. This is called executive function , or being able to plan and initiate a response. Executive function occurs in the frontal lobes, which are the front halves of the cerebral hemispheres . The back halves of the cerebral hemispheres, which contain the parietal, temporal lobes and occipital lobes, collect and identify sensory information that is processed and then routed to the frontal lobes. The frontal lobes analyze this data in order to decide what action is most appropriate.

The frontal lobes are affected by Alzheimer's disease , although it appears that early in the course of the illness there is a lot of frontal lobe activity which attempts to compensate for the damage. In addition, the memory loss that characterizes Alzheimer's disease can also affect executive function: it is hard to make a decision if you cannot remember the important elements that are needed to go into that decision. Persons diagnosed with Alzheimer's disease frontal lobe damage often lose their ability to sequence a task because they can no longer prioritize each segment of an activity. For example, think about the steps involved in taking a shower: remove clothing, turn on shower, adjust the temperature, step into shower, use shampoo to wash hair, use soap to wash the body, rinse off, turn off the water, dry off, and dress. Often times, people with frontal lobe damage are unable to organize these steps and lose the ability to successfully and independently complete the task.

Loss of executive function can be noticed if a person becomes unable to do activities they used to be able to do, like crocheting, crafts, baking, weeding the garden.

Ideas about the involvement of the frontal lobes in ordering behaviour come from studies of people in which the frontal lobes are selectively damaged (say from a car accident, bullet, woodworking wound, tumor or blood vessel problem) characteristically become lose interest in the people and things around them. (Notice that we are not saying that initiative 'rests' in the frontal lobes, or 'takes place' there, because it is more realistic to think about imitative coming about as a result of a very complex circuit, which critically requires the frontal lobes, but which also requires activation of other parts of the brain.) Frontal lobe impairment was classically seen as a late sign of Alzheimer's disease, 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, and edited Kenneth Rockwood and Serge Gauthier.

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Last updated October 23, 2014
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