Parkinson's disease (PD) is becoming increasingly recognized for its non-motor features, including cognitive difficulties. For people with Parkinson's, these problems can be distressing and among the most difficult to discuss with their doctors and families. Cognition is difficult to define, but it generally refers to the brain processes through which we can discover and understand the world around us. These include: making sense of perceptions, storing and remembering events, learning things, forming concepts, solving problems, planning activities, using language, acquiring information, and having the capacity for abstract thoughts.

Cognitive changes in Parkinson's

Understanding exactly how many people with Parkinson's experience cognitive changes is difficult, because the changes themselves are difficult to measure and because researchers have used different means to identify and define the changes. It is estimated that, at any given time, of all people with Parkinson's, approximately a quarter to a third have mild cognitive impairment while another group of a quarter to a third have dementia.

The symptoms of mild cognitive impairment are minimal and do not interfere with a person's ability to care for themselves. The first changes may not be noticeable, but they can be detected through some testing. Once mild cognitive impairment is diagnosed, symptoms may become more apparent. Recent research suggests that mild changes may occur as early as diagnosis. Dementia is a decline in multiple mental abilities that is severe enough to cause problems at home, work, or in social situations. It may include, but is not limited to, problems with memory. If one follows a large number of individuals with Parkinson's over time, many will go on to develop dementia.

Causes of cognitive changes

One cause of cognitive problems is a decrease in the level of dopamine, the neurotransmitter that is involved in regulating body movements. Scientists are looking at changes in two other chemical messengers, acetylcholine and norepinephrine, as possible additional causes of attention difficulties, memory loss and executive function in PD.

Effects of cognitive changes

The cognitive changes that accompany Parkinson's at onset tend to be limited to one or two domains and their severity can vary from person to person. Most often they include:

1.Executive functions

Analogous to the problem-solving tasks of an executive in a company, these include forming concepts, making plans, formulating goals, anticipating consequences, strategizing to achieve goals, and evaluating progress.

2.Attention difficulties

Cognitive changes in PD can make it difficult to pay attention. In situations such as a party, where several conversations are happening at once, this problem can become acute.

3.Slowing of thoughts

People with PD say their brains feel “slow.” They take longer to complete tasks and put in more effort than usual to complete them.

4.Word search.

People with PD may have difficulty finding the right words due to slowed thinking. The words are available, but they can be difficult to access. If you think of vocabulary as a dictionary, the person with PD has to look up the dictionary before opening it to find the words, whereas for a person with Alzheimer's, the dictionary may be available, but many of its pages are blank.

5.Learn and remember information

About two-thirds of people with Parkinson's report having memory problems. There are two types of memory, the first of which is declarative memory (for example, remembering events from a specific time, place, or fact). The second type of memory is non-declarative, which is demonstrated through the performance of tasks (for example, riding a bicycle). Using memory involves encoding, storing, and retrieving. Just like a filing cabinet, you first have to acquire the information, then organize and save it, and finally find it. People with PD have trouble collecting information and organizing it well, so it becomes difficult for them to remember it later. Another specific type of memory is prospective memory. Failures in prospective memory bother most of us, but seem to be more common in PD. For example, you take out a package overnight to mail it in the morning, but then you leave home without mailing it.

6.Mental images and spatial processes

The ability to form a mental image and determine where things are in space can be affected by PD. An example of this problem occurs when one is driving a car, trying to form a mental map of a route to the store.

Seeking help for cognitive changes

Cognitive change is a sensitive topic. The doctor is often as hesitant in discussing this topic as the patient is in asking about it. The doctor may postpone any conversation about the possibility of cognitive impairment for people who are dealing with a new diagnosis or struggling with motor symptoms. For this reason, the person with PD often needs to be the one to start the conversation. If the person is experiencing problems that are bothering the family or causing problems at work, one should discuss them with the doctor. Your doctor can help, perhaps by referring you to a psychiatrist, neuropsychologist, speech therapist, or occupational therapist. Neuropsychological evaluation can be helpful, especially in the early stages of the cognitive problem. Having this initial test can help the doctor determine if future changes are related to medication, PD, or other factors such as depression.

Treatment of cognitive changes in PD

When a person reports having mild symptoms of cognitive impairment, the doctor will first want to rule out causes unrelated to PD, such as a vitamin B-12 deficiency, depression, fatigue, or sleep disorders. PD does not cause sudden changes in mental functioning. If someone feels a sudden change, the cause is probably something different.

If cognitive changes are traced back to PD, there are drug therapies available that were developed for Alzheimer's, but have been found to have some effect on Parkinson's. One is rivastigmine, the only medication approved by the US Food and Drug Administration (FDA) for dementia in PD. Doctors may also prescribe donepezil and galantamine. Additionally, a person with attention difficulties that are caused by daytime sleepiness may benefit from the use of stimulants.

Research directions

Much remains to be learned about the biology behind cognitive changes in PD. Our greatest hopes are that we will be able to detect cognitive development early and then we will have more therapies to treat it.