Impaired Reproduction of Three-Dimensional Objects by Cocaine-Dependent Subjects

C ocaine dependence is a resurgent public health problem that afflicts over 1.5 million American citizens; cocaine is the most prevalent illicit drug detected on blood and urine toxicology screens performed in U.S. emergency rooms. 1 Neuropsychologically, cocaine-dependent patients demonstrate a mild to moderate degree of impairment in such cognitive areas as attention, working memory, learning and memory, and executive functions. 2 – 12 These impairments have been linked in some, 8, 11 but not in all, 7 studies to functional and morphological alterations in (pre)frontal brain regions. 6, 9, 11

Constructional tasks, such as drawing various figures and shapes, are other neuropsychological assessment tools that are particularly sensitive for detection of early or subtle brain damage. 13 Although constructional ability is traditionally assessed within the context of a neurological examination, 13 it is a high-level cognitive function, integrating a complex system of interrelated visual, motor and executive capacities, each of which exhibits a unique role within the context of perceptual/motor behavior. To our knowledge, this has not yet been attempted in cocaine-dependent individuals.

A routine way of assessing constructional ability is through the Copy Figure Test, comprising two- and three-dimensional figures. Such a design offers a more precise interpretation of the findings, that is to say, if a subject inadequately copies both two- and three-dimensional images, it may be inferred that failed performance is not secondary to impaired perception of tridimensionality, and a case for a basic constructional deficit is supported. On the other hand, a control level performance on two-dimensional figures suggests that both eyesight and the ability to translate visual images into kinesthetic concepts and then into motor actions 13 are preserved, and that performance differences are due to three-dimensional processing. In addition, the Copy Figure Test eliminates memory involvement by having the figure to be copied in front of the subject at all times. 13, 14 Furthermore, the test is relatively independent of age, educational status, and intelligence: the ability to copy the figures is fully acquired by the age of 12; older age brackets (ages 40–60) retain normal and unaltered results. 13

Consistent with prior reports on neurocognitive impairments, 4, 7, 8, 11, 12 including visuoperceptual deficits, 3, 5, 10 we hypothesized that individuals with cocaine dependence, relative to healthy comparison subjects, would display compromised Copy Figure Test performance. As a second comparison group, we enrolled subjects with marijuana abuse or dependence, who also were not expected to be impaired. 15

Twenty-seven subjects meeting DSM-IV-TR criteria for cocaine dependence, 26 subjects meeting DSM-IV-TR criteria for marijuana dependence or abuse, and 33 mentally healthy subjects were recruited by advertisement and participated in this study after giving written informed consent. The protocol was approved by the McLean Hospital Institutional Review Board. All subjects were in good physical health and had no history of head injury, loss of consciousness, brain tumor, seizures, or cerebrovascular accident, as determined by neurological screening and by the Cornell Medical Index Health Questionnaire. 16 Education about the effects of the drugs was provided, and referral to drug treatment programs was offered, when appropriate.

Each subject underwent the Structured Clinical Interview for DSM-IV-TR Axis I Disorders. 17 Active cocaine or marijuana use was confirmed by urinalysis; subjects with urine toxicology screens positive for other substances were excluded. Cocaine dependent subjects with a history of any other axis I psychiatric diagnosis, including other substance dependence (but not abuse), were also excluded. Of the 26 marijuana dependence (n=12) or abuse (n=14) subjects, five had a comorbid diagnosis of major depression and four were alcohol dependent. Number of drinks in the week before the study appears in Table 1 . Cocaine-dependent subjects were not seeking or participating in addiction treatment. They had used cocaine for a mean duration±standard deviation (SD) 15.1±6.9 years, with a frequency of 4.4±2.2 times in the week before the study, and last use was at least 24 hours prior to the study. Marijuana abuse/dependence subjects had smoked this substance for 7.0±5.9 years, with a frequency of 6.6±0.7 times in the week before the study.

Subjects were instructed to copy each figure ( Figure 1 ) exactly as it looked to them with a pen. They were further told to make only one attempt at each figure, even if they were not completely satisfied with the result, and not to erase any lines or draw any additional lines that did not appear in the original figure. There were no time limits. A dually trained psychiatrist and neurologist (TVG), who not only was blind to the diagnosis but had never seen the subjects, scored each figure on the following Likert-type scale: 0=near perfect reproduction; 1=mild distortion or rotation; 2=moderate distortion or rotation, micropsy, or loss of three-dimensionality; and 3=gross distortion of the basic gestalt (i.e., figure virtually unrecognizable).

Demographic variables were analyzed with analyses of variance (ANOVAs) or chi-square. Overall Copy Figure Test results were analyzed by means of a two-factor analysis of covariance (ANCOVA), with diagnosis (cocaine dependence, marijuana dependence/abuse, or mentally healthy) as a between-subjects factor; figure type (diamond, cross, Necker cube, smoking pipe, hidden line elimination cube, pyramid and dissected pyramid) as a within-subjects factor; and age, education, current number of drinks per week, and race (white or black) as covariates. Additionally, one-factor ANCOVAs were performed separately for each figure, followed by post hoc Scheffe tests when the group effect was significant. The Pearson correlation coefficient was used for correlative analyses. All analyses were two-tailed, and significance was defined as p<0.05.

The rationale for combining marijuana dependence and abuse data was as follows: a higher diagnostic threshold for marijuana dependence due to the lack of a DSM-IV-TR marijuana withdrawal criterion, and no significant differences between marijuana dependence and abuse subgroups on any of the figures (p>0.35).