In Reply We appreciate the opportunity to discuss further the interesting points raised by Poletti and Raballo in their letter. First, IQ decline between childhood and adulthood is indeed unlikely to reflect an absolute deterioration in cognitive functions because the raw subtest scores increased across all groups during this period. However, since we do not have data on these same subtests for study individuals at age 18 months and 4 years, we cannot establish the process(es) underlying the IQ decline during this period. Clearly, the decline in nonverbal IQ is at least partly owing to the lag in processing speed ability, but we also found a stable verbal IQ deficit despite a lag in working memory. Moreover, our analyses adjusting for other cognitive tests suggest that the lags in processing speed, working memory, and attention reflect at least partially distinct processes.1 Finally, while our findings suggest that lags, rather than deterioration, in cognitive functions underlie cognitive decline between childhood and early adulthood, future studies from early adulthood and beyond are needed to establish whether individuals with psychotic disorders experience cognitive deterioration later in life.
Mollon J, Zammit S, Reichenberg A. Clinical Implications of Slower Cognitive Growth in the Psychosis Spectrum—Reply. JAMA Psychiatry. Published online May 23, 2018. doi:10.1001/jamapsychiatry.2018.0816
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