Combined effects of aging and HIV infection on semantic verbal fluency: a view of the cortical hypothesis through the lens of clustering and switching

Abstract

The profile of HIV-associated neurocognitive disorders (HAND) has classically been characterized as "subcortical," but questions have arisen as to whether aging with HIV in the antiretroviral therapy era has subtly shifted the expression of HAND into a more "cortical" disorder (e.g., decay of semantic memory stores). We evaluated this hypothesis by examining semantic fluency and its component processes (i.e., clustering and switching) in 257 individuals across four groups stratified by age (<40 and ≥50 years) and HIV serostatus. Jonckheere-Terpstra tests revealed significant monotonic trends for the combined effects of HIV and aging on overall semantic (and letter) fluency and switching, but not cluster size, with greatest deficits evident in the older adults with HIV infection. Within the older HIV-infected cohort, poorer switching was uniquely associated with self-reported declines in instrumental activities of daily living and deficits in learning and executive functions, but not semantic memory. Results suggest that HIV infection and aging may confer adverse additive effects on the executive components of semantic fluency (i.e., switching), rather than a degradation of semantic memory stores (i.e., cluster size), which is a profile that is most consistent with combined frontostriatal neuropathological burden of these two conditions.

Figure 1

Z-scores displaying the effects of HIV infection and aging on category and letter fluency overall performance. Error bars in this figure represent standard errors. Y = younger (< 40 years); O = older (≥ 50 years).

Figure 2

Z-scores displaying the effects of HIV infection and aging on category and letter fluency component processes (i.e., switching and clustering). Error bars in these figures represent standard errors. Y = younger (< 40 years); O = older (≥ 50 years).