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Abstract:
Studies of patients with Parkinson disease (PD) and amnesia
have suggested that independent neural systems subserve declarative
memory and habit learning. The gradual formation of associations
likened to habit learning appears to depend on the basal ganglia.
To test the involvement of cortical structures, 8 patients with
Alzheimers disease (AD) were tested on a probabilistic
classification task. AD patients are impaired on implicit learning
tasks that require cortical association areas. We hypothesized that
the AD patients would exhibit intact habit learning if the system
depends primarily on the basal ganglia. In the probabilistic
classification task subjects viewed between 1 and 3 cues on a
computer screen and decided for each trial if the cues predicted
one of two outcomes. The cues were probabilistically associated
with the outcomes, thereby forcing subjects to gradually abstract
the associations across multiple trials. The AD patients showed
intact learning over the course of 60 trials. A main effect of
trial block (1-way ANOVA F(1,7) = 4.771, p<.05) was found to be
due to the AD patients significant improvement in performance from
the first block to the last block (paired t-test t = -2.344,
p<.05). The same patients were at chance on a test of memory for
the training episode, performing significantly more poorly than
controls. These results are consistent with the idea that the human
habit learning system is independent of cortical structures and
depends on the basal ganglia.
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