Introduction
The cognitive disorder in Huntington's disease is considered a "subcortical" syndrome and usually lacks features such as aphasia, amnesia, or agnosia that are associated with dementia of the Aizheimer's type. The most prominent cognitive impairments in Huntington's disease involve the so-called "executive functions" ó abilities such as organization, regulation and perception. These fundamental abilities can affect performance in many cognitive areas, including speed, reasoning, planning, judgment, decision making, emotional engagement, perseveration, impulse control, temper control, perception, awareness, attention, language, learning, memory and timing.

Several studies have suggested that cognitive and behavioral impairments are greater sources of impaired functioning than the movement disorder in persons with Huntington's disease, both in the work place and at home. In addition, family members most often report that placement outside the home is initiated because of cognitive and behavioral deterioration rather than motor symptoms.

This chapter provides an overview of cognitive impairments and the related behavior problems that typically accompany Huntington's disease. In addition, compensation and adaptation strategies are provided, which physicians may recommend to patients, families and other professionals.

Disorganization
Difficulties in planning, organization, sequencing and prioritizing can affect responsibilities at home and at work. Daily tasks, such as attempts to follow a recipe, to maintain a daily planner, to complete a list of household errands, to develop a meeting agenda, or to apply for social security benefits, become daunting.

Many early-stage Huntington's disease patients complain of problems with organization and report that they just "can't get things done." There are several ways to compensate for poor organization, which can be instituted early in the disease. Routines should be established at work or in the home so that the environment can provide structure and organization.

Activities should be organized so that each day is basically the same. For example, 7 a.m. shower, 7:30 a.m. breakfast, 8 a.m. take bus to work, 8:30 a.m. check mail, 9:30 a.m. dictate letters, 10 a.m. coffee, 10:30 a.m. staff meeting, noon lunch, 1 p.m. return phone calls, 2:30 p.m. review accounting, 4 p.m. open meeting to schedule with customers, 5 p.m. take bus home, 6 p.m. dinner, 7 p.m. family time with kids, 8:30 p.m. time with spouse, 9:30 p.m. read, 10 p.m. lights out. A central location could be established for posting a daily schedule. Persons who never before used daily planners or computer calendars may need to start.

A centralized message center can be used to make lists and organize tasks to be accomplished each day. Additional strategies for dealing with poor organization are offered in Table 6.

Lack of initiation
Some family members complain that the person with Huntington's disease "just sits around all day and won't do anything." Regulation of behavior involves getting started, maintaining the desired behavior and stopping unwanted behaviors. The initiation, or starting of an activity, conversation or behavior is often compromised in Huntington's disease. A lack of initiation is often misinterpreted as laziness, apathy or lack of interest, and may be a reason for poor performance at work.

Once started, persons with Huntington's disease may be able to execute the behaviors adequately (i.e., compute taxes, calculate sales, administrate employees, teach school), but may be unable to organize and initiate the behaviors at the appropriate time. External initiation often helps the person with Huntington's disease remain active and participate in both social and work activities. Keeping a daily routine can minimize the need for internal initiation.

Maintaining the desired behavior is usually less of a problem for persons with Huntington's disease. If this aspect of regulation is impaired, however, the Huntington's disease patient may be unable to regulate ongoing behaviors in an appropriate manner.

Perseveration
Perseveration, or being fixed on a specific thought or action, can occur when behaviors are inadequately regulated by the brain. Spouses often report that patients become behaviorally rigid, and tend to get stuck on an idea or task. Established routines and gentle reminders of changing tasks can help avoid problems. An activity that is atypical for the established routine will be particularly stressful and challenging for the person with Huntington's disease.

For instance, travel out of town, or a visit to the doctor or dentist, may disrupt a safe routine. When shifting to a new task, help prepare the person with Huntington's disease and allow plenty of time for him to adapt to the new idea. There is a delicate balance of how much preparation is needed. Telling of a change in plans too early can cause increased anxiety. Typically, inform the Huntington's disease patient only one day prior to an event or a few hours before. Allow plenty of time and frequent gentle cues to allow the shift to take place.

Impulsivity
Some persons with Huntington's disease experience difficulties with impulse control and may develop problem behaviors such as irritability, temper outbursts, sexual promiscuity and acting without thinking. Some degree of impulsivity and dysregulation of behaviors is quite common in Huntington's disease. Some strategies to help family members and caregivers cope with impulsivity are addressed below.

Irritability and temper outbursts
One of the most typical complaints we hear from Huntington's disease families is concern about irritability and temper outbursts. These signs can be present for a couple of reasons. First, it is important to assess for depression when increased irritability is reported. Oftentimes, irritability and temper outbursts diminish when a mood disorder is treated. Many times, however, irritability or outbursts remain even in the absence of a mood disorder.

Examination of the underlying causes of irritability and temper outbursts is helpful in diminishing the frequency and severity of these behaviors. Persons with Huntington's disease are continually challenged by previously routine tasks or activities that are experienced as overwhelming. Huntington's disease results in a progressive loss of abilities that often "sneak up" on persons with Huntington's disease. Several patients have confided that "I didn't realize I could no longer do it." Close attention should be paid to the signals, verbal or nonverbal, that patients are upset or wanting something, so that they do not get to the stage of exploding before they receive attention.

Knowledge of the person and sensitivity to his needs means that some situations can be anticipated and potential frustration defused. It may be possible to identify situations which trigger frustration and either avoid them or provide diversional activities. An awareness of the person's capabilities is very important, so that he is encouraged to be as independent as possible and allowed to take risks without risking constant exposure to failure.

Although this encouragement to maintain independence is not always possible at work, it is critical to encourage in the home. The person with Huntington's disease should be encouraged to do things for himself and to participate in primary decision-making as long as possible, except perhaps in situations where safety is an issue (i.e. driving or cooking). Family members should be responsible for providing a safe environment so that no person is ever in danger. Remove dangerous implements, such as guns, from the house and have emergency numbers near the telephone.

Listed below are some general strategies for families to employ to minimize irritability and some coping skills for temper outbursts.

Perceptual problems
H D causes deficits in spatial perception. The mental manipulation of personal space is impaired, even early in the disease. For instance, the judgment of where the body is in relation to walls, corners or tables may be disturbed, resulting in falls and accidents. Precautions might include carpeting the floors and removing furniture with sharp corners to the periphery of the room, where it will be out of the patient's path. Behavior problems reported by family members are often due to another kind of impaired perception, unawareness of changes due to Huntington's disease, which can lead to challenges in providing care.

Unawareness
Denial is commonly considered a psychological inability to cope with distressing circumstances. We often see this in situations such as the loss of a loved one, a terminal disease, or a serious injury. This type of denial typically recedes over time as the individual begins to accept his losses. Individuals with Huntington's disease often suffer from a more recalcitrant lack of insight or self-awareness. They may be unable to recognize their own disabilities or evaluate their own behavior. This type of denial is thought to result from a disruption of the pathways between the frontal regions and the basal ganglia. It is sometimes called "organic denial," or anosognosia, and is a condition that may last a lifetime. We recommend that "unawareness" be used to describe this type of denial in Huntington's disease to distinguish it from the more familiar kind and to avoid thinking of patients with Huntington's disease as suffering from a purely psychological problem.

Unawareness often plays a significant role in seemingly irrational behavior. At first unawareness may be beneficial because it keeps the individual motivated to try things and to avoid labelling himself. In this way it may prevent demoralization.

On the other hand, unawareness may lead to anger and frustration when the individual cannot understand why he cannot work or live independently. The Huntington's disease patient with unawareness sometimes feels that people are unjustifiably keeping him away from activities that he could do, such as driving, working, or caring for children, and may attempt to do these things against the advice of family and friends. This type of unawareness can become dangerous.

Organic denial is also an issue for health professionals, friends, and family members, who may delay making the diagnosis or keep the diagnosis from the affected individual because they are concerned that he "cannot handle it." Some people interpret the unawareness as a sign that the individual does not want to know. We have not found that talking about Huntington's disease to a person with unawareness will cause negative consequences.

In our clinical experience, organic denial is not easily amenable to treatment or change. Nevertheless, there are different degrees of unawareness. It may be that the person can talk about her problems, but not acknowledge that she has Huntington's disease. In such a case, one might try to address the problems while avoiding discussion of the diagnosis. Noncompliance with therapy or nursing care should not automatically be interpreted as intentional. It may be helpful to develop a contract that includes incentives for compliance. Denial can thus be sidestepped, while behavioral goals remain the same.

For example, the goal may be to convince an unsafe driver to stop, rather than to accept the diagnosis, or acknowledge why he must stop driving.

Attention
There are many different types of attention. In persons with Huntington's disease, simple attention often remains intact. In contrast, sustained or complex types of attention become impaired by Huntington's disease. For instance, most persons with Huntington's disease will experience difficulty with what is called "divided attention," or the capacity to do two things at once. For most people, divided attention is impaired when we are tired, sick, or stressed. In Huntington's disease, divided attention is compromised most of the time, regardless of extra stress. Consequently, a person may complain that he can't "pay attention" as well as he used to.

Divided attention is needed to drive a car while listening to the radio, talking to the kids in the back seat, or talking on the cell phone. When divided attention is impaired it is recommended that patients try to do only one thing at a time. For instance, an HD-affected person should turn off radios, television, and telephones, and limit conversations while cooking dinner. When swallowing becomes a problem, mealtime distractions should be minimized and the patient should concentrate on chewing and swallowing to limit choking.

Language
Communication, or the transfer of information from one person to another, requires a complex integration of thought, muscle control, and breathing. Huntington's disease can impair all three of these functions. There are two main aspects to communication: getting the information IN (understanding) and getting the information OUT (talking). Both of these aspects can be impaired by Huntington's disease, making communication a difficult task.

The most prominent language difficulties in people with Huntington's disease are (1) speaking clearly (articulation), (2) starting conversation (initiation), and (3) organizing what's coming in and going out.

Impaired initiation of speech
Word finding is often impaired, while knowledge of vocabulary is retained, because it takes the brain much longer to search and retrieve the desired object. Listeners sometimes fail to wait long enough for the brain to do its job.

In addition to speed limitations, the brain fails to regulate the sequence and amount of traveling information, resulting in impairments in starting and stopping. When language initiation is compromised by Huntington's disease, techniques such as phrasing questions with alternate choice answers (e.g., yes or no; lasagna or spaghetti) may help someone get started or retrieve the desired response.

Disorganization of language content
In contrast to the basic impairments in language output, the basic capacity to understand language remains relatively intact in HD. Even in later stages of the disease, language comprehension may remain when the ability to speak is significantly diminished. This fact is important to communicate to family members, staff at care facilities and other professionals involved. Even if a patient cannot express herself, it is likely that she can understand what is being said. Difficulties with word usage are rare in persons with Huntington's disease, as are frank aphasia or impairments in semantic memory. The trouble that occurs in persons with Huntington's disease is an inability to organize the outgoing and incoming language, resulting in miscommunication. To aid the person with Huntington's disease in organizing language output and input it is best to rely on short simple sentences and to assess understanding frequently during important conversations.

Learning and memory
The type of memory impairments found in Huntington's disease consist mostly of difficulties in learning new information, and in retrieving acquired information, but not in storage of information. Problems occur in getting information in and out, due to the slowed speed of processing and the poor organization of information. Several studies have found that Huntington's disease patients can demonstrate normal memory for information if offered in a recognition format. If, rather than asking "can you tell me what time your doctor's appointment is today?," one inquires "is your doctor's appointment at 10 a.m. or 11 a.m. today?," persons with Huntington's disease can often answer correctly. Similarly, if patients with Huntington's disease are given a long list of words to learn and are required to say the words back freely they perform poorly. But if they are given a list of words and asked to recognize which ones were on the earlier list they demonstrate good memory.

It has been observed that persons with severe amnesia such as that associated with Korsakoff's syndrome, herpes encephalitis, or Alzheimer's disease can experience defective explicit memory, such as for names and dates, and intact implicit, or unconscious memory, such as the ability to tie one's shoes. In contrast, persons with Huntington's disease typically have impairments in skills that depend on implicit memory. Driving, playing a musical instrument, or riding a bike are all motor memories that can be considered implicit, or unconscious. Huntington's disease impairs this motor memory system, making Huntington's disease sufferers reliant on more effortful conscious memory systems to drive a car. Consequently, driving will take much more concentration and effort, resulting in increased fatigue and irritability.

Timing
Some recent findings have suggested that persons with Huntington's disease have difficulty with the estimation of time. For instance, persons with Huntington's disease may be less able to judge how much time has elapsed. Spouses often complain that their once-punctual spouse becomes frequently late and mis-estimates how long activities will take. Frequent reminders may be needed to keep on schedule. It is helpful to allow extra time and avoid time pressure when possible.

The progression of cognitive impairments
Although performance in IQ tests often remains within the normal range in the early stages of the disease, cognitive deficits are evident in speed of processing, cognitive flexibility (or the ability to shift topics readily) and the organization of complex information.

The most sensitive indicator of early Huntington's disease on the Mini-Mental State Examination is serial sevens (the ability to subtract 7 from 100 serially) and the most sensitive subscale on the Mattis Dementia Rating Scale is initiation (the ability to begin and maintain verbal and motor behaviors).

There exist few longitudinal studies of the cognitive decline in HD. Based upon the information available, speed, organization, and initiation of behavior are impaired in early Huntington's disease, constructional impairments worsen in mid-stage Huntington's disease, and some abilities remain relatively spared (memory, language comprehension) even in the later stages of the disease. Clinically, as the disease progresses, the severity of cognitive impairments increases and patients are often unable to speak or communicate their views in late stages.