Differential working memory impairment in bipolar disorder and schizophrenia: effects of lifetime history of psychosis.
BACKGROUND
Although bipolar disorder and schizophrenia have long been viewed as distinct illnesses, there is growing evidence that these two complex diseases share some common genes, which may manifest as overlapping neuropsychological impairments. Although working memory dysfunction has been proposed to be central to the pathophysiology of schizophrenia, it has received less attention in studies of bipolar disorder.


METHODS
We applied measures of working memory to patients with schizophrenia (n = 15), patients with schizoaffective disorder (n = 15), patients with psychotic (n = 11) and non-psychotic (n = 15) bipolar disorder, and demographically matched healthy subjects (n = 32), in order to determine the extent to which these groups show common or unique impairments.


RESULTS
While patients with bipolar disorder (with and without psychotic features) and those with schizophrenia/schizoaffective disorder were impaired on backward digit span, only patients with a lifetime history of psychotic features, regardless of diagnosis, were impaired on spatial delayed response task.


CONCLUSIONS
Backward digit span performance is comparable in bipolar disorder and schizophrenia, and may be an appropriate endophenotypic marker that cuts across diagnostic categories. In contrast, spatial working memory performance clearly distinguishes non-psychotic bipolar disorder patients from patients with functional psychosis.
Division of Schizophrenia and Related Disorders, Department of Psychiatry, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229-3900, USA. glahn@uthscsa.edu
David C
DC
Glahn
Carrie E
CE
Bearden
Sibel
S
Cakir
Jennifer A
JA
Barrett
Pablo
P
Najt
E
E
Serap Monkul
Natalie
N
Maples
Dawn I
DI
Velligan
Jair C
JC
Soares
D000328:Adult; D001714:Bipolar Disorder / Q000150:complications / Q000523:psychology*; D003863:Depression / Q000175:diagnosis / Q000209:etiology; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005260:Female; D006801:Humans; D008297:Male; D008569:Memory Disorders / Q000175:diagnosis / Q000209:etiology*; D009483:Neuropsychological Tests; D011618:Psychotic Disorders / Q000150:complications*; D012559:Schizophrenia; D012565:Schizophrenic Psychology; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires