A Brief Report on Mental Rotation of Hands in HIV Infection: Neuropsychological Evidence of Dysfunction in Fronto-striato-parietal Networks

Infection with the human immunodeficiency virus (HIV) often leads to neuropathology, which is diffusely distributed throughout brain parenchyma, but is commonly believed to preferentially disrupt the structure and function of frontostriatal and temporolimbic systems {2}. Understandably, the vast majority of neuropsychological research in HIV has therefore been centered on constructs of direct relevance to these neural systems (e.g., executive functions, working memory, motor skills, and episodic memory). However, very little is currently known about the nature and extent of deficits in spatial cognition in persons living with HIV infection. Spatial cognition refers to the ability to detect, understand, manipulate, and integrate visual stimuli in the context of its environment. Although spatial cognition is primarily linked to the integrity of the posterior parietal cortex (PPC), optimally functioning parieto-striato-cortical pathways are also needed for the integration of visual input {e.g., 3}, as observed in patients with frontostriatal pathology (e.g., Parkinson's disease) {4}. Considering that frontostriatal dysfunction is considered a hallmark of HIV-associated neurocognitive disorders, this overlap suggests that research regarding spatial cognition may in fact be relevant to the neuropsychology of HIV. Early studies of spatial cognition in HIV included limited batteries and did not find much evidence of impairment {e.g., 5, 6}, leading to a temporary neglect of this thread of research. However, recent meta-analyses have produced mixed results regarding the effect to which spatial abilities are affected by HIV infection {e.g., 7, 8}, suggesting that there may be a signal worthy of further examination. Indeed, a closer review of the HIV literature explores the fronto-striatal components of this construct, indicating that subtler differences may exist in the distinct subcategories of spatial cognition (e.g., visuoconstruction, spatial attention) in this cohort. For instance, Poutiainen and colleagues found significant differences between a group of 13 HIV+ individuals and 10 seronegative controls on measures of visuoconstruction, visusospatial skills, and praxis {9}. Furthermore, Martin {10} suggested that HIV infection was associated with impairment on measures of egocentric spatial ability (i.e., spatial tasks that are built around the participant's frame of reference, as opposed to that of an observer). Measures of spatial attention {e.g., 11, 12} and, more recently, number line orientation {e.g., 13} also may be impaired in HIV infection, perhaps demonstrating the particular sensitivity of visuospatial tasks that draw upon complex attention and working memory to the prefrontostriatal pathologies of HIV disease. Mental rotation, the ability to manipulate three-dimensional objects in space, is a widely-studied and neurally-complex area of spatial cognition that has been largely ignored in the neuroAIDS literature. These tasks are sensitive to both the functioning of the posterior parietal cortex and fronto-striato-parietal neural networks {14}. While mental rotation has been studied more extensively in other frontostriatal disorders (i.e., Parkinson's disease) {15}, to our knowledge, only one study to date has examined this construct in HIV infection. Olesen and colleagues {16} used a computerized mental rotation task in which two stimuli appear at different degrees of rotation; participants are asked to evaluate whether the objects are identical (same) or mirror images of each other (different). Impairment between groups presented as a disproportionate increase in errors and reaction time in the HIV+ group (n = 14) as the degree of rotation increased. Although the reaction time analyses showed trend-level group differences overall, this effect was primarily seen in the object condition, as explained by a three-way interaction between stimulus, group, and level of rotation. In conjunction with group differences found on a measure of global versus locally-biased processing, the authors concluded that HIV-related deficits in spatial cognition were likely due to parietal lobe pathology. Although these data support the notion of impaired spatial cognition in HIV infection, the lack of supplemental neuroanatomical and neuropsychological data raise questions about the underlying neural and cognitive mechanisms. Despite relying on the PPC for basic processing of visual input, frontal systems are additionally required to adequately integrate, manipulate, and utilize visual information {e.g., 3}. For instance, the ability to mentally rotate three-dimensional objects requires the external processes of viewing the object as it physically exists pre-rotation, but also simultaneously viewing and manipulating it on the visuospatial scratchpad of the mind's eye {17}. Additionally, the cognitive requirements of the task likely vary based on the relative position of the object to be rotated. In fact, neuroimaging studies have shown that different types of rotations (i.e., object-centered or viewer-centered) rely on discrete neural pathways (i.e., right parietal lobes and intraparietal sulcus, or left parietal and left frontal regions, respectively) {18}. The involvement of frontal regions and the internal manipulation requirements of the task imply that mental rotation not only requires intact visuospatial skills, but also optimally functioning working memory abilities. Considering the overlapping neural networks between mental rotation abilities and HIV-associated neuropathologies, further exploration is needed to determine the neuropsychological correlates of this impairment, thereby elucidating the deficient component processes. In the present study, two tasks of mental rotation were administered within a larger battery containing measures of executive functions, information processing, motor skills, as well as other tasks of spatial cognition. We hypothesized that there would be evidence of HIV-related impairment on tasks of mental rotation, and that poorer performance would be associated with impairment on measures of executive functions and working memory. Furthermore, we hypothesized that mental rotation impairments would be most evident on the hand rotation task, as egocentric spatial tasks tend to rely more heavily on frontal systems {19}, which are particularly affected by HIV infection.