Qualitative analysis of verbal fluency decline in amnesic and subcortical vascular mci

Background: We examined two qualitative components of phonemic verbal fluency performance - clustering (i.e. the trend to produce words within phonemic or semantic sub-categories) and switching (i.e. shifting to new clusters when previous ones are exhausted) – in patients with preclinical or established cortical and subcortical vascular dementia. Previous evidence suggests that clustering is related to temporal lobe functioning, while switching is a frontal ability. We hypothesized that the differential involvement of temporal and fronto-subcortical structures would determine a differential impairment of clustering and switching components in Alzheimer’s disease (AD) and in vascular subcortical dementia (VaD) and we also aimed at verifying if these parameters might reveal useful for the early differentiation of these two forms of cognitive impairment. Methods: Four groups of patients were included into the study (30 subjects each): patients with amnesic Mild Cognitive Impairment (aMCI), patients with probable AD, patients with vascular MCI (vMCI) and patients with VaD. A group of 30 age, education and sex-matched normal controls (NC) was also included. All patients received the F, P, L verbal fluency task as part of an extensive neuropsychological battery; controls were administered only the fluency task and the Mini-Mental State Examination (MMSE). The following parameters were computed for each trial: total number of correct words generated, mean clusters’ size and total number of switches. Results: Patients and controls had similar socio-demographic features; severity of cognitive impairment, as defined by the MMSE score, was comparable within the two types of dementia and MCI samples. As to experimental variables (Table 1), all patient groups had significantly reduced total fluency, number of switches and mean cluster size, with respect to normal controls. Total word production was significantly poorer for demented than for MCI patients and for vMCI than for aMCI patients, while there was no difference between AD and VaD patients. The AD group showed a significant decrease in switching with respect to the aMCI group and a trend was also apparent for vMCI patients compared with aMCI patients (p= 0.066), while there was no difference between VaD patients and vMCI and AD patients. Mean cluster size was overlapping among all patient groups. The total number of words generated was also highly and positively correlated with the number of switches in all study groups, while it did not correlate with clusters’ size. Conclusion: Verbal fluency declines earlier and disproportionately in vascular cognitive impairment than in cortical MCI, probably due to a deficit in switching secondary to fronto-subcortical dysfunction. Instead, clustering ability does not appear to be disproportionately affected in aMCI and AD, compared to their vascular counterparts (switching might be more relevant to performance in the phonemic task)