Executive Operations and Abilities

MENTAL CONTROL

Working Memory. The common tests for working memory, such as those for attention, involve serial reversal tasks such as digits backward, spelling words backward, and serial subtraction. They are also part of the evaluation of attention described in Chapter 7 , with the focus here on the “manipulation” involved in the reversal process. The first is the backward digit span in which the patient must repeat digits in reverse order, beginning with the last number. The examiner continues to administer series of digits until the patient incorrectly repeats two strings of digits backward at the same series level. A normal performance is correct backward recitation of two less than the maximum forward digit span. The ability to spell “world” (or other words) backward is another commonly used serial reversal task that overlaps with attention testing. The patient must give the letters placed in the correct place, that is, “d-l-r-o-w.” The serial subtraction tasks include counting backward by 3s from 20, or 7s from 100. For example, the examiner asks the patient to subtract by 7 beginning from 100, for example, 93, 86, 79, 72, 65, et cetera. The number of errors are the number of incorrect subtractions from the prior response. The examiner can also ask the patient to recite the days of the week backward or the months of the year backward beginning with December. Patients should be able to obtain a normal score on these last two serial reversal tasks.

If greater assessment of working memory is needed, there are at least four other tasks that are readily applicable in clinical encounters or at the bedside. These tasks involve greater maintenance or manipulation of online information in the brain. First, there are serial ordering tasks. The simplest is to have the patient rearrange digits in ascending order from smallest to largest. For example, if given the series “2-1-3,” the correct answer would be “1-2-3.” Most people can serially order up to five or more digits. Second is a clinical variation of the classic N-back test of working memory. In the classical test, the participant hears a series of digits or letters and is asked to indicate if a letter was previously presented a set number of places back, e.g., for N-3, the participant would indicate the ones shown in capital letters: n t s j o a J p q s t u S . In a simpler clinical variation, the examiner recites a long series of digits and, once the examiner stops, asks the patient to repeat the next to last digit in the sequence (“N-1”) or, for more challenging testing, two or three back from the last digit in the sequence (“N-2” and “N-3”). A third task is a variation of the Brown-Petersen procedure, which aims to test working memory divorced from the effects of rehearsal. The examiner spells aloud a random, three-letter consonant syllable (“trigram”) that the patient must remember. Immediately afterward, the patient is asked to count backward by threes from a random number. After 10 seconds, the examiner interrupts the counting backward and asks the patient to recall the consonant trigrams. The examiner repeats this procedure at least four times. Fourth are complex span paradigms that require remembering a set of items in order and combined with a concurrent secondary task. One version is the reading span task in which patients read two to six sentences and must remember the last word of each sentence, which they have to repeat back in order at the end of the task.

Complex Attention. Additional mental control tasks involve the ability to sustain, shift, and divide attention. The ability to sustain attention is reflected in many of the fundamental attentional tasks, such as forward digit span, and the ability to shift attention is reflected in tests such as Trailmaking-A (see Chapter 7 ). The ability to divide attention is effectively tested during dual-task or multitasking procedures. One example is the performance of simultaneous tasks, such as having the patient do a forward digit span while manually tracking the examiner’s moving finger with their index finger. The examiner compares the results of this divided attention task to the results from the single task forward digit span. One old task, the face-hands test, may further reflect difficulty dividing attention. In this test, the examiner touches the patient on the hands and cheek simultaneously in 10 trials (4 contralateral, 4 ipsilateral, 2 symmetric). On the last four nonsymmetric trials, any error in recognizing where the patient was touched suggests impairment, most often from dementia or frontal lobe disease.

TASK SETTING AND MONITORING

Verbal Fluency. Word list generation, which declines with language (see Chapter 8), is also compromised with executive impairment as it requires setting and maintaining a task. The examiner instructs the patient to name, as quickly as possible, as many English words that begin with the letter “F” (or “A” or “S”) and as many names of animals (or some other category) as they can in 1 minute. Ask the patient to avoid proper names or multiple versions or variations of the same word. Do not count close word variations of the same word, such as “six,” “sixth,” “sixtieth,” but do count word variations with a different meaning, e.g., “sixteen.” In a timed performance, normal subjects can list 15 ± 5 “F” words per minute and 18 ± 6 animals per minute without cueing. When the patient is impaired due to language, both lexical (letter) and category (e.g., animals) word generation declines, but when the patient is impaired due to executive operations, there is a discrepancy between impairment on the more effortful lexical word generation and an often normal performance on the more visualizable category list. A discrepancy of less than three between lexical versus category word lists can be a major clue to executive dysfunction.

Design Fluency. A further measure of executive task performance is design fluency, or the number of freeform designs generated in 1 minute. One easily administered version is the Five-Point test ( Fig. 13.2 ). This test measures the ability to inhibit previously drawn responses and the ability to generate and create different visual patterns. The examiner presents the patient with squares (typically 40) containing five dots and asks the patient to make as many unique designs as possible in 1 minute by connecting the dots within each square with straight lines. The patient does not need to use all the dots in the designs. The lines must be straight ones that connect dots, and the designs should not be repeated. The examiner can start with two examples. There are several variations of this design fluency test. One counts the number of unique designs in five minutes. Another restricts the total number of lines/squares to four. A third version restricts to continuously connected straight lines. The examiner scores the total number of correct designs, the number of rule violations, and the number of repeated designs.

SET-CHANGE DETECTION AND SET-SHIFTING

The Trailmaking-B test is a classic measure of set-shifting, which is heavily dependent on the anterior cingulate cortex. The Trailmaking tests are timed tests that measure the time required to draw a line between scattered items. On part A of the Trailmaking test, the patient must draw a line connecting a series of randomly arrayed numbers in numerical sequence (1-2-3, etc.). Part A is more of an attentional task and is described in Chapter 7 . On part B of the Trailmaking test, the patient must draw a line connecting numbers and letters in alternating sequence, that is, 1 to A then A to 2 then 2 to B, et cetera. Begin by demonstrating the test to the patient using an abbreviated sample. There are more difficult variations of the Trailmaking-B, which change letters into Roman numerals, days of the week, or months of the year ( Fig. 13.3 ). For the numbers-months variation, tell the patient: “On this page are both numbers and months of the year. Begin at number 1 and draw a line from 1 to January, then January to 2, then 2 to February, and so on. Remember, first you have a number, then a month, then a number, and so on. Draw the lines as fast as you can. Begin.” If the patient makes a mistake on the practice sample, point to the error immediately and explain it. If the patient makes an error on the real test, point to the error and return the patient’s pen to the last correct circle and continue from that point. Since these tests are formally timed, there are normative values available. One good measure of the task that accounts for attention is to look at the timing difference between Trailmaking-B and Trailmaking-A. The examiner, however, can also administer the Trailmaking-B test, or a modification of it, untimed and simply count the patient’s errors in completing the alternating sequence. Performance on these Trailmaking-B tasks can be very informative. They not only measure the ability to shift response sets among predetermined options but may also reveal problems with perseveration or even stimulus-boundedness, an environment-dependent behavior.

The Wisconsin Card Sort test is among the best set-shifting tests in neuropsychology and among the most used executive functions tests for assessing the presence of preservation errors. Mental status examiners have considered a number of clinical variations that do not risk a potential compromise of the subsequent neuropsychological administration of this test. One easy to implement alternative involves alternating a coin between the examiner’s hands and having the patient guess the hand that has the coin. The examiner starts with hands held behind the back, then brings them forward and asks the patient to state which hand has the coin. Then the examiner uncovers his hands indicating the correct response. The examiner repeats this procedure, moving the location of the coin out-of-sight behind his or her back according to different strategies. The first strategy is a right hand–left hand alternation of the coin. Once the patient determines the correct alternating strategy for three times in a row, the examiner then switches to a two right-hand two left-hand strategy until the patient gets several in a row. This is followed by a three right-hand three left-hand strategy until the patient gets several in a row. The inability to get the set within the number of trials constitutes an abnormal response.