Vision, attention and action in posterior cortical atrophy and other dementias
Item statusRestricted Access
Embargo end date02/07/2020
Ingle, Harriet Elizabeth
Posterior Cortical Atrophy (PCA) is a rare, progressive dementia characterised by visuospatial and visuoperceptual deficits (often with intact visual acuity), and a generally younger age of onset than typical Alzheimer’s disease (AD) (Aresi & Giovagnoli, 2009; Caixeta, Taleb, Ghini, Dias Soares, de Melo Caizera & Vargas, 2013; Mendez, Ghjarania & Perryman, 2002). Patients with PCA typically present with fewer memory deficits, better verbal fluency, and better insight into their diagnosis compared with typical AD, although PCA and AD tend to converge clinically at advanced stages of disease progression (Lehmann et al., 2012). Despite being identified by Benson and colleagues three decades ago, there are still no widely agreed clinical diagnostic criteria for PCA and it remains relatively poorly understood (Benson, Davis & Snyder, 1988; Crutch et al., 2017). This PhD study was comprised of two phases. The initial screening phase involved a diverse battery of assessments with two main aims. First, this battery was intended to investigate the sensitivity and specificity of different screening tests in discriminating PCA patients (n = 6) from patients with other neurodegenerative dementias (n = 21) (typical Alzheimer’s disease, frontotemporal dementia, Lewy body dementia, corticobasal degeneration, and primary progressive aphasia). The Modified Luria Alternating Square and Triangles (M-LAST) task achieved the highest sensitivity and specificity, closely followed by target cancellation and bisection tasks. The M-LAST task has not been reported previously in the assessment of PCA patients, but may have considerable potential for use in diagnostic settings. Similarly, an unusual variant of the bisection task (gap bisection, McIntosh et al., 2004) yielded the most impressive sensitivity for PCA. The secondary aim of the screening phase was to identify whether patients with other neurodegenerative diseases demonstrated deficits on the assessments which were specific to early visual function, as this is an area that has not been addressed previously in the literature. There was evidence of significant impairment for patients other than PCA on a number of measures. However, the most striking results from patients with dementias other than PCA were obtained on the second phase of assessment. The second laboratory-based phase aimed to more fully characterise the visuoattentional deficits associated with PCA (n = 5) and other dementias (n = 13), through the use of eye-tracking and motion-tracking technology. The PCA patients proved difficult to test under these conditions, as their visual impairments were so advanced and generalised that they appeared almost functionally blind on some tests. The most exciting novel results were obtained from patients with AD, in whom evidence of optic ataxia (misreaching to peripheral targets) was found for three of the four AD patients tested on a pointing task. These results, discussed in context with other recently published evidence (Gordon et al., 2018), suggest that screening for optic ataxia may have potential as a behavioural symptom potentially sensitive to early neuronal changes associated with AD. A systematic review of the literature was conducted in order to investigate the use of visual attention or visuomotor-specific assessments in the evaluation of patients with PCA. A case study was conducted of visual form agnosic patient DF, in whom recent evidence of optic ataxia has been found (Rossit et al., 2018; Hesse, Ball & Schenk, 2012, 2014). Strong evidence of optic ataxic-like pointing errors was observed in patient DF, with preserved grip scaling, implicit avoidance of obstacles and perceptual matching. An additional study on healthy participants was conducted in order to test whether attentional demands modulate performance on a visuomotor pointing task. The results indicated that increasing attentional demands led to optic ataxic-like pointing errors, thus the experimental manipulation appeared to serve as a model of optic ataxia in the healthy brain.