Early stage @entity191 XXXX and normal volunteers: comparative mechanisms of sequence learning.

@entity1 @entity1625 @entity146 @entity191 @entity1726
Early-stage nondemented @entity191 ( @entity1726 (es)) @entity1 can learn short but not long sequences as well as controls. We have previously shown that to achieve normal performance, @entity1726 (es) @entity1 activated the same right-sided cortical regions as controls plus the homologous left sided cortex and bilateral cerebellum. In this study, we evaluated two related hypotheses to explain the @entity146 and the increased bilateral brain activation observed in the @entity1726 (es) group. Hypothesis 1 proposed that @entity1726 (es) @entity1 recruit regions from a normal bilateral network specialized for sequence learning that healthy controls would activate if performing difficult tasks. Thus, @entity1726 (es) @entity1 can learn short sequences as well as controls. Hypothesis 2 proposed that information processing within the network in the @entity1726 (es) group is impaired. Thus, @entity1726 (es) @entity1 cannot learn as difficult a sequence as controls. To test hypothesis 1, we increased task difficulty and statistical power in the control group and showed that the control and the @entity1726 (es) groups activated the same regions. To test hypothesis 2, we analyzed the equal performance data using two @entity1625 ( @entity1625 ) multivariate analyses. The task- @entity1625 analysis showed that to perform equally with controls, the @entity1726 (es) group expressed the normal bilateral network more than the control group. The behavior- @entity1625 analysis showed that the correlation between learning performance and regional activation was significantly different between the groups. We conclude that @entity1726 (es) @entity1 have near normal learning if task difficulty is moderate because they can recruit additional regions from a normal bilateral network specialized for sequence learning. However, when a difficult task would normally require bilateral activation, @entity1726 (es) @entity1 fail to learn because information processing within the network is impaired. Hum. Brain Mapp. 20:246-258, 2003.
