Semantic fluency performance of patients with cortical and subcortical neurodegenerative diseases

Previous studies using the Animals Fluency Test have shown that dementia patients with Alzheimer's disease (AD), Huntington's disease (HD), or Parkinson's disease (PD) produce fewer correct words and have smaller semantic cluster sizes than controls or PD patients without dementia (PDND). Although the number of correct words generated by the patients with AD was positively correlated with mental status, cluster size, surprisingly, was not. To increase word output and increase the reliability of estimates of cluster size, semantic fluency was reexamined using the Supermarket Fluency Task. Overall, patients with HD or PD with dementia (PDD) exhibited reduced cluster sizes compared to older controls or PDND patients, but cluster sizes were only marginally reduced for patients with AD. These effects were evident only for female participants, because the cluster sizes for elderly control men were substantially smaller than those of elderly women. For the female patients with AD, cluster size was correlated with mental status, but the relationship was nonlinear. Cluster size was normal for mildly demented patients with AD, but much reduced for moderately or severely demented participants. In contrast to a previous report, in the present study the proportion of category labels generated was increased for patients with HD with dementia but not for patients with AD. This finding questions one line of evidence that semantic memory stores undergo "bottom-up" degradation in AD. Together with previous results, these findings indicate that semantic cluster size reflects efficiency of access to semantic knowledge which is similarly compromised in subcortical and cortical diseases.