GSK239512

A single Baseline magnetic resonance image (MRI) prior to randomization. Following randomization, a total of 8 MRIs at approximate 6 week intervals: Week 6, Week 12, Week 18, Week 24, Week 30, Week 36, Week 42, Week 48. Reference MRI: In order to accommodate variations in MTR images acquired using different scanners, the images must be normalized to eliminate intensity shifts and contrast variations. For each scanner, images from a normal subject will be obtained and processed to serve as a calibration for each scanner prior to initiating scanning for subjects participating in the study

A single Baseline MRI prior to randomization Following randomization, a total of 8 MRIs at approximate 6 week intervals: Week 6, Week 12, Week 18, Week 24, Week 30, Week 36, Week 42, Week 48. Reference MRI: In order to accommodate variations in MTR images acquired using different scanners, the images must be normalized to eliminate intensity shifts and contrast variations. For each scanner, images from a normal subject will be obtained and processed to serve as a calibration for each scanner prior to initiating scanning for subjects participating in the study

The CSSB is a computerized battery with following domains (score range): Verbal memory (0-75), working memory (0-28), motor speed (0-100), verbal fluency, attention and speed of information processing (0-110) and executive functions with higher score representing better performance. Two Baseline CSSB testing were conducted; the first on the day prior to commencing dosing (Day -1) and the other test pre-dose on Day 1: the average of the two tests was used as Baseline. Change from Baseline was calculated as score at a given time minus score at Baseline. For each individual task from the CSSB, the Baseline was calculated as the mean of the second screening assessment and the Day 1 pre-dose assessment. A composite score was calculated by averaging all the measures, and then calculating a z-score of the composite. Higher the composite score, better is the performance. Z-score is the measure of standard deviation away from the mean score.

Executive function/working memory composite score was calculated from the three tasks controlled oral word association (a measure of language fluency, planning and working memory where participants were instructed to generate as many as words as they could think of beginning with a specific letter in one minute. They were then requested to do exactly the same for two furthers letters and a score was given for this activity accuracy), category naming (a measure of semantic fluency, planning and working memory where participants were required to generate as many exemplars of the category 'animals' as they could in one minute), and one-back (a valid measure of working memory where participants were shown a single stimulus of a card in the center of the computer screen and were asked for YES" or "NO" to match the current card with the previous card and the accuracy was noted). Change from Baseline is the value at indicated time point minus the Baseline value.

Episodic memory composite score was calculated from the three tasks International Shopping List Task (ISLT) immediate recall, ISLT delayed recall, and Paired Associate Learning (PAL). The Total Score was calculated by taking the mean of all individual task scores. Change from Baseline is the value at indicated time point minus the Baseline value.