Background. Several studies have suggested that visual backward masking (VB
M) impairment is present in patients with bipolar disorder, but the clinica
l features, such as current symptoms, treatment status and past burden of i
llness that may contribute to the impairment have not been well described.
This study examined well-characterized enthymic patients on two VBM tasks t
o ascertain the extent of VBM impairment in this group and the clinical cor
relates of this impairment.
Method. Twenty-eight euthymic patients with a DSM-IV diagnosis of bipolar d
isorder were matched by age, sex and IQ with 28 non-psychiatric control sub
jects. Both groups completed two VBM tasks; one required subjects to locate
the target stimulus, one required identification of the target stimulus. R
eaction times and error rates across a range of target-mask inter-stimulus
intervals were assessed.
Results. Patients were significantly slower and had more errors on both VBM
tasks. There was a significant relation between reaction times on the iden
tification task and past burden of illness, particularly past number of dep
ressions. There was no discernible impact of treatment status on reaction t
ime or performance, including no difference in lithium-treated versus not t
reated subjects.
Conclusions. These results are consistent with previous reports of neuropsy
chological deficits in euthymic bipolar disorder patients. The potential be
nefit to employing tasks such as VBM is that it may provide a method for re
lating clinical variables such as illness burden with known neural pathways
in order to elucidate better the pathophysiology leading to impaired cogni
tive performance in patients with bipolar disorder.