Psychological Medicine

Memory and verbal learning functions in twins with bipolar-I disorder, and the role of information-processing speed

a1 Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki, Finland; Department of Public Health, University of Helsinki, Helsinki, Finland; Department of Psychology, UCLA, California, USA; Department of Psychiatry and Research Imaging Center, University of Texas, San Antonio, Texas, USA

Article author query
kieseppa t   [PubMed][Google Scholar] 
tuulio-henriksson a   [PubMed][Google Scholar] 
haukka j   [PubMed][Google Scholar] 
van erp t   [PubMed][Google Scholar] 
glahn d   [PubMed][Google Scholar] 
cannon td   [PubMed][Google Scholar] 
partonen t   [PubMed][Google Scholar] 
kaprio j   [PubMed][Google Scholar] 
lonnqvist j   [PubMed][Google Scholar] 


Background. Euthymic bipolar-I disorder (BP I) patients and their siblings have shown impairments in verbal learning and memory functions compared with controls, suggesting that these impairments may be genetic in origin. Reduced information-processing speed has been associated with impaired memory in the elderly, and recently in schizophrenia. The authors compared verbal learning and memory functioning in twins with BP I and co-twins to control twins, and examined whether the observed deficits are related to information-processing speed.

Method. Finnish Medical and Population Registers and Twin Cohorts were used to identify the BP I and control twins. Neuropsychological tests assessing verbal learning and memory, working memory, facial recognition, visual memory, and information-processing speed were administered to 26 BP I twins, 19 non-bipolar co-twins, and 114 controls. Group differences were analyzed by generalized estimation equation modeling.

Results. BP I patients, but not co-twins, showed impairments in all memory tests compared with controls. Female co-twins showed impairment in verbal learning and memory. Information-processing speed had a significant effect on encoding and learning efficiency.

Conclusions. This study showed for the first time that information-processing speed is related to memory functioning and verbal learning in BP I in a population-based, representative and euthymic sample. Furthermore, the data support the view that defects in verbal memory may be related to the genetic factors predisposing to BP I in females.

c1 Dr Tuula Kieseppä, Department of Mental Health and Alcohol Research, National Public Health Institute, Mannerheimintie 166, 00300 Helsinki 30, Finland. (Email: