Amphetamine-related improvement in executive function in patients with chronic
schizophrenia is modulated by practice effects.
Author(s): Pietrzak RH, Snyder PJ, Maruff P.
Affiliation(s): Department of Psychiatry, Yale University School of Medicine, New Haven, CT
06516, USA. robert.pietrzak@yale.edu
Publication date & source: 2010, Schizophr Res. , 124(1-3):176-82
BACKGROUND: Amelioration of cognitive impairment is an important treatment goal
for a broad range of neuropsychiatric disorders, including schizophrenia. One
critical issue in clinical trial design is the extent to which repeated exposure
to cognitive tests (i.e., practice effects) may lead to improvement in
performance on the cognitive tests in the absence of any true treatment effect.
The current study examined the extent to which practice effects on a measure of
executive function may influence the sensitivity of that task to detecting the
cognitive-enhancing effects of a single acute dose of d-amphetamine in
individuals with chronic schizophrenia.
METHODS: Twenty-four men with chronic schizophrenia were randomized to receive a
constant or random/matched alternate form version of a hidden maze learning
measure of executive function (Groton Maze Learning Test; GMLT) on four separate
occasions in one month. They also completed a measure of psychomotor speed. Using
a double-blind, placebo-controlled, parallel groups design, cognitive function
following administration of a single dose of d-amphetamine (20mg p.o) or placebo
was then assessed.
RESULTS: The group who received the constant-pathway version of the GMLT showed a
large practice effect (d = 2.05) over four practice sessions. Consequently, they
did not evidence any improvement on the GMLT following d-amphetamine
administration. In contrast, the group who received the random/matched alternate
version of the GMLT showed a statistically significant and large effect size (d =
.84) improvement on this measure. Both groups showed d-amphetamine-related
improvement on a measure of psychomotor speed.
CONCLUSIONS: Results of this study suggest that practice effects associated with
repeated exposure to a cognitive test could obscure the sensitivity of the test
to detecting true treatment-related cognitive improvement.
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