Neuropsychological Assessment of Marijuana Users

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Neuropsychological procedures are used in an effort to provide an unbiased estimate of the individual's cognitive capacity. In neurology and psychiatry, these tests have been used to help clinicians to better diagnose patients and to provide them with better treatments. We chose to use a fixed battery in our effort to assess neurobehavioral changes that might be associated with the chronic use of marijuana. That battery included tests of language skills, visual and spatial memory, attention, concentration, executive function, visuo-constructive skills, manual dexterity, simple reaction time, and complex reaction time in subjects in our studies. The various tests used are listed below.

This is a subtest of the Wechsler Adult Intelligence Scales-Revised (WAIS-R). Participants are required to arrange red and white blocks to copy the visual presentation of a printed design. There are time limits for each of the problems; and subjects receive points for each design depending on the time to perfect completion. This is a test of visuoconstructional assembly ability and visuomo-tor coordination. It is sensitive to cortical dysfunction, but primarily parietal lobe dysfunction.

3.1.2. Boston Naming Test (Short Form)

This is a 30-item version of the Boston Naming Task from the Boston Diagnostic Aphasia Battery. In this test, the participant has to name the picture, which is presented.

3.1.3. Controlled Oral Word Association Test (COWAT) (26)

The participant is required to generate as many words as possible that begin with the letters, F, A, and S and animal names within 60 s. This task involves the function of the frontal cortex and is also a test of verbal fluency (language).

3.1.4. California Computerized Assessment Package (Short Form) (CALCAP)

The CALCAP (27) is used to measure simple and choice reaction time and speed of information processing. This test has proven to be sensitive in detecting central nervous system (CNS) changes in studies of acquired immunodeficiency syndrome (AIDS) dementia. This computerized test consists of four individual tests (one test of simple visual reaction time and three tests of choice reaction time) and takes only 10 min to administer.

This is another test of visuoconstruction. The subject is asked to draw the face of the clock, put in all the numbers, and set the hands to 11:10. The drawing is scored for accuracy.

This test is from the WAIS-R digit symbol. It requires the subject to fill in blank spaces with symbols under the numbers 1 to 9. The key of numbers and symbols is in full view. After instruction and a brief practice session, the time allotment is 90 s and the score is the maximum correct in this time period. The task involves several functions: visual memory, learning of nonverbal associates, sustained attention, speed of visual scanning, and visual motor planning and motor coordination. This test was chosen because it has been shown to be very sensitive to neurotoxic-related cognitive change. (test-retest reliability is 0.81).

This is a measure of simple motor speed. The participant is instructed to tap a key with the index finger as rapidly as possible for 10 s. Three trials are obtained for each hand and the mean is used for the analyses. This is a sensitive measure of CNS motor dysfunction.

3.1.8. Grooved Pegboard (30)

Participants are required to place pegs into holes first with their dominant hand and then with their nondominant hand. The amount of time it takes to place all the pegs is the dependent measure.

3.1.9. Immediate Logical Memory (Immediate/Delayed Recall) (31)

A single-paragraph story is read by the examiner, and the subject is asked to recall as many of the details as possible. This tests immediate recall of logical verbal material. Following 30 min of further testing, the participant is asked to recall the previously presented story. The difference between the initial score and the delayed recall score indicates the amount of verbal material that was retained after the delay.

3.1.10. Line Orientation (32)

Participants are presented with the picture of two lines placed at varying angles and required to chose from an array of 11 items that angle the two lines match. This test measures visuospatial ability.

3.1.11. Rey Auditory Verbal Learning Task (RAVLT) (33)

A list of 15 common nouns is read to the subject, who is required to recall as many words as possible, in any order, for five trials. The entire list of words is repeated for each trial. The first trial provides a measure of immediate memory span; the fifth trial provides a measure of the total amount of information that is learned. A total score across all five trial measures the amount of immediate recall and total amount of information learned. Learning curves can be generated over the five trials. The number of perseverations, intrusions, and confabulations are noted (all are types of inaccurate responses). After a 30-min delay, delayed free recall of the list is required. Finally, a recognition form where the original 15 items are visually identified from a list of 50 words completes the test. Specific characteristics of memory such as verbal learning and memory, retention, and recall can be evaluated using the different parts of the RAVLT.

3.1.12. Rey Osterreith Complex Figure (34)

The complex figure task assesses visual memory and visuoconstruction. The subject is shown a complex figure and asked to draw a copy of the figure on a blank piece of paper. Thirty minutes later she or he is asked to reproduce the figure from memory. The drawing is scored for accuracy.

3.1.13. Shipley IQ

This is a brief test that estimates general reasoning and intelligence. It correlates 0.79 with WAIS-R full-scale IQ. It assesses vocabulary, abstract reasoning, and mathematical abilities. As in our pilot data, this score was useful for controlling for individual differences in pre-morbid intellectual ability.

The Stroop task also tests executive function. Words with the names of colors are listed on a page. First, the subject is asked to read the words (names of colors) that are printed in black as fast as he can during a specific time period. Second, the subject is asked to say the color of the ink in which a series of xs are printed with as fast as possible within 45 s. Third, the subject is asked to say name of the color of the ink that the words (color names that do not match the words) are printed with as fast as possible. The number of words correctly read or colors correctly named in the time period is the score.

3.1.15. Symbol Digit-Paired Associate Learning (36)

The subject is shown seven cards, each with an unfamiliar symbol and a single digit, for 3 s each. The symbol is then presented as a cue, and the subject is asked for the corresponding digit. After each response the symbol digit pair is displayed for another 3 s. The test consists of three trials and generates a total score out of 21. It is a test of nonverbal associative learning.

Subjects are required to connect a series of numbers (Trails A) or letters alternating with numbers (Trails B) in order with paper and pencil in timed trials. The time for perfect completion (the administrator of the test corrects any inaccuracies as the test proceeds) is the score on this test. This task assesses speed of visuomotor integration and visuomotor scanning, planning (Trails A and B), and cognitive flexibility (Trails B).

3.1.17. Verbal and Nonverbal Cancellation Test (37)

This is a test of attention and concentration. The participant is required to identify targets (the letter A for verbal, and a specific symbol for nonverbal)

among 374 distractor items. Time to completion and number of missed targets will be analyzed.

3.1.18. WRAT-Reading Test (38)

The test measures language skills. The subject is asked to read a series of 64 words. The correctness of the pronunciation of each word is determined.

3.1.19. WAIS-R-Vocabulary (31)

This is a subtest of the WAIS-R. It correlates highly (r = 0.81) with the full-scale IQ (a composite of 11 individual subtests) and is therefore the single best subtest to estimate general intelligence. Therefore, the WAIS-R vocabulary score is a reasonable choice to control for pre-morbid intellectual capacity. The vocabulary score is resistant to the effects of age and mild brain injury and has been found to control for the effects of educational level and is a reproducible and quantitative test. We have repeatedly shown that this measure is a better predictor than years of education for performance on neurocognitive tests (39).

3.1.20. Wisconsin Card Sorting Test (40)

This test measures complex problem-solving ability, planning, cognitive flexibility, and the ability to use external feedback to monitor decisions. These tests have been shown to be especially sensitive in detecting dysfunction of the dorsolateral portion of the prefrontal lobes.

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