INTRODUCTION: Obesity is a common medical illness that is increasingly 
recognised as conferring risk of decline in cognitive performance, independent 
of other comorbid medical conditions. Individuals with mood disorders (bipolar 
disorder (BD) or major depressive disorder (MDD)) display an increased 
prevalence of both obesity and risk factors for cardiovascular diseases. 
Moreover, BD and MDD are associated with impairment in cognitive functioning 
across multiple domains. The independent contribution of obesity to cognitive 
decline in this population has not been explored. This study examines the impact 
of obesity on cognition by comparing neuropsychological performance in obese 
individuals, with or without a mood disorder before and after undergoing 
bariatric surgery.
METHODS AND ANALYSIS: This study compares measures of declarative memory, 
executive functioning and attention in obese individuals (body mass index >35 
kg/m(2)) with BD or MDD, and 2 control populations (obese individuals without a 
psychiatric illness and healthy non-obese controls) prior to and following 
bariatric surgery. Participants (ages 18-60) receive a psychiatric diagnosis via 
the Structured Clinical Interview for the Diagnostic and Statistical Manual of 
Mental Disorders, Fourth Edition (DSM-IV; SCID). Mood ratings, physical 
measurements, nutritional and health questionnaires are also administered. A 
standardised battery of neuropsychological tests aimed at establishing 
performance in areas of declarative memory, executive functioning and attention 
are administered. Warrington's Recognition Memory Task (RMT) and an N-Back Task 
are performed in a 3 T functional MRI to investigate patterns of neural 
activation during cognitive performance. Additionally, anatomical MRI data are 
obtained to investigate potential changes in neural structures. Baseline data 
will be analysed for between-group differences and later compared with 
postsurgical data to investigate cognitive change.
ETHICS AND DISSEMINATION: This study has been approved by the Hamilton 
Integrated Research Ethics Board (09-3254). Results will be available in 
peer-reviewed scientific publications and scientific meetings presentations, and 
released in lay form to media.