Neuropsychological Assessment

Introduction

Neuropsychological assessment is a formalized method of observing and evaluating patients' behaviors. It distinguishes itself from other methods of inquiry regarding behavior in its goals and its methodologies. The core method that neuropsychologists utilize is the administration and interpretation of standardized tests. These tests assess a patient's level of function within different cognitive domains and provide information regarding which aspects of behavior are impaired and which are spared. Based on a patient's performance on these tests, the neuropsychological evaluation provides clinically-relevant information regarding etiologies underlying behavioral impairment, as well as information that can inform patient care and treatment. In this chapter, we present an overview of the practice of clinical neuropsychology, including its definition, goals, the types of patients referred for assessments, the domains of cognitive function assessed, and the types of measures administered.

The science of neuropsychology is dedicated to the study of brain–behavior relationships. Our understanding of how behavior is organized in the brain has been informed by observations of patients with focal brain lesions by studies of cognitive impairment associated with different underlying disease processes, and most recently, by neuroimaging techniques, including magnetic resonance imaging (MRI), functional MRI (fMRI), positron emission tomography (PET), and magneto-encephalography Data from these different sources inform our understanding of the neurological underpinnings of behavior and are utilized by clinical neuropsychologists in linking a patient's neuropsychological test performance with underlying brain dysfunction.

In assessing behavior, the clinical neuropsychologist focuses primarily on cognitive domains that include attention, executive function, language, visual perception, and memory. Examining the nature of a patient's cognitive impairment, as well as the pattern of impaired and spared behaviors, is helpful in distinguishing different underlying neurological conditions, differentiating neurological from psychiatric conditions, and discriminating normal from abnormal performance. A patient's cognitive behaviors are specifically measured or quantified, allowing the neuropsychologist to determine whether a patient is performing “normally” within a particular cognitive domain and, if not, to determine the extent of impairment. The neuropsychologist utilizes the data obtained to address practical questions regarding patient care, including a patient's prognosis and ability to manage various aspects of his or her life (e.g., to live independently, to return to work, to comprehend and to follow medical instructions, and to comprehend legal documents), and to recommend possible treatments, interventions or strategies from which a patient might benefit. Finally, as the information provided is quantified, repeat neuropsychological assessments are used to track the course of a patient's disease.

Referrals for neuropsychological evaluation typically originate from a patient's treating physician (most often a neurologist, neurosurgeon, psychiatrist, or internist), but patients or their family members can also initiate a referral. Referred patients may have known neurological disease or damage, or may display or complain of cognitive dysfunction due to an unknown or unclear etiology. Patients assessed include those with acquired impairments or developmental impairments. Developmental impairments (e.g., learning disabilities, attention-deficit hyperactivity disorder [ADHD], autism spectrum disorder) arise when the brain fails to develop normally, with the cause often unknown. For children with developmental impairments, the neuropsychological evaluation can play an important role in determining diagnosis and in guiding interventions. For adults, it is often the case that a diagnosis has already been assigned, and the neuropsychologist is asked to address questions regarding the impact of the patient's impairment on his/her ability to function within a more challenging setting, for example, in higher education or work settings. This information can help determine whether specific accommodations might help address the areas of difficulty. Acquired impairments (e.g., stroke, head injury, or dementing illnesses) result from neurological disease or damage that often occurs after a period of normal development. The presentation of acquired impairments in childhood often differs from that in adulthood, with localized cerebral pathologies more common in adults and generalized insults to the central nervous system (CNS) more common in childhood. Study findings differ regarding whether the recovery profiles of children are better than those of adults, due to greater brain plasticity, or whether children's developing brains are more vulnerable to the effects of neurological insults than are adults' mature brains.

Given that the goal of a neuropsychological evaluation is to determine whether behavioral function has been altered (and if so, to what extent), a critical issue that arises when characterizing the cognitive status of a patient with an acquired impairment is the determination of his or her pre-morbid level of function. The importance of baseline testing has recently received attention in determining the effects of concussive injuries. Many athletic teams, including professional and school teams, now mandate that players undergo pre-season baseline cognitive evaluations, often using a computerized cognitive screening measure. Repeat testing conducted following an injury is then compared to a player's baseline performance to determine if there has been a change in cognitive functioning. This information is used to monitor a player's recovery and to guide return-to-play decisions. However, in many other contexts, baseline neuropsychological data are not available, and the neuropsychologist consequently has to rely on indirect methods to estimate a patient's pre-morbid level of intellectual function. These include consideration of historical and observational data (such as level of education and occupational history, previous relevant medical history, and examination of a patient's performance on specific cognitive tests). Specifically, certain classes of learned information (for example, knowledge of word meanings, factual information, and word reading are highly correlated with pre-morbid intelligence and are generally resistant to the effects of neurological disease. The neuropsychologist also considers the patient's pattern of performance across an array of cognitive measures, with higher scores typically reflective of pre-morbid function, and lower scores generally indicating impairment, although the role of normal variability (further discussed below) is also taken into account.

While an estimation of pre-morbid level of function is necessary for the interpretation of normally-distributed behaviors ( Figure 8-1 ), for behaviors that are more even across individuals (i.e., “species-wide” behaviors), such methods are unnecessary (with any behavioral dysfunction indicative of impairment).

Within the class of normally-distributed behaviors, individuals display a range of abilities. For these behaviors, the neuropsychologist compares a patient's performance (i.e., raw score) to that of a normative sample. Tests that are most reliable are those for which there is a large normative sample against which a patient's performance can be compared, and for which the normative sample is stratified according to age, level of education, and sometimes gender. Recently, increasing attention has been paid to developing test instruments and normative data that are appropriate for the specific patient's cultural background. In interpreting a patient's test performance, the neuropsychologist converts a patient's raw scores to “standard scores,” expressed according to the normative mean and standard deviation (see Figure 8-1 ). Scores vary in the types of standard scores expressed (e.g., standard scores, T-scores, scaled scores, or Z-scores). Scores that fall within the mean of the normative sample are considered to fall within the “average” range, while those that fall significantly above or below the mean are considered areas of strength or weakness, respectively. Scores that fall two or more standard deviations below the mean are generally considered “impaired” (see Figure 8-1 ). In interpreting test scores, the neuropsychologist considers how the patient's performance compares not only to the mean but also to the patient's own profile of scores. A patient who scores well above the mean on most tests, and below the mean on selective measures may be considered to exhibit “impaired” performance ( relative to the patient's pre-morbid level of function), even though level of performance may not fall strictly in the “impaired” range on any measure. While the neuropsychologist considers differences in patient scores as a means to identify impairment, the neuropsychologist also considers normal variability. Specifically, because neuropsychological evaluations typically yield a large quantity of scores, it is important to consider the extent to which variable performances are typical vs. atypical. In fact, research on this topic finds that it is not uncommon for healthy adults to obtain some low test scores and, moreover, that individuals with higher IQ levels display greater variability among scores than do those with lower IQ levels. For this reason, the neuropsychologist considers the patient's pattern of performance within the context of his/her history, behavior, and diagnosis when determining what aspects of performance are clinically relevant.

Neuropsychological tests are also characterized by standardized administration, with all patients presented with test questions in the same way, and with patients' responses to stimuli scored in a standardized manner. Given that the neuropsychologist relies on normative data to interpret patients' performances, this interpretation is meaningful only if the examiner adheres to standardized test administration and scoring procedures.

While patients' performances (i.e., “scores”) on a set of neuropsychological tests are the core set of data obtained from a neuropsychological evaluation, their behavior on tests can only be understood within the context of their developmental and medical history, as well as their current cognitive complaints. In addition, test data also need to be interpreted within the context of clinical (i.e., qualitative) observations regarding the patient's mood, motivation to perform, attention-to-task, and comprehension of task instructions. In interpreting test behavior, a neuropsychologist relies not only on the specific score that a patient obtains on a test, but also on the patient's response style (for example, whether it is very slow, impulsive, concrete, or perseverative in nature). This careful analysis of patient behavior provides the most meaningful information regarding a patient's level of competence, as well as how different performance variables impact a patient's ability to express that competence. These observations are of particular importance when assessing the validity of test performance (especially when assessing questions of possible malingering). In considering performance validity, the neuropsychologist relies on the administration of specific “symptom validity tests” as well as embedded measures of effort. These methods typically involve examining patterns of performances that are rarely seen in neurological or psychiatric patients (e.g., performance at or below chance on a forced-choice recognition memory measure). In cases where effort is less than optimal, test scores are interpreted cautiously, if at all.

Dimensions of Behavior Assessed

In the following sections, we describe the domains that are typically assessed within a neuropsychological evaluation. It should be noted that these descriptions are by no means exhaustive, but instead are presented as an overview of the types of questions and methodologies that are employed in a neuropsychological evaluation in addressing questions regarding diagnosis and patient care.