Behavioural monitoring disorders in unilateral spatial neglect: productive symptoms and impaired awareness of disease

This doctoral thesis investigates the relationships between disorders of behavioural monitoring (including “productive” behaviours and unawareness of neuropsychological deficits) and unilateral spatial neglect in right-brain-damaged patients. One main monitoring disorder is recurrent perseveration, namely a “productive” motor symptom frequently found in target cancellation tasks: we demonstrate, in two specific tasks (Experiments 1 and 2), that the disposition of the stimuli and the type of target modulate its severity. Neglect patients showing perseveration in visuo-motor exploratory tests perseverate also in drawing tasks. No correlation between omission and perseveration errors is found, supporting the functional independence of the two deficits. In the context of a two-component hypothesis, perseveration (the first component) is a specific disorder that manifests in a variety of tasks, particularly those requiring serial graphic production; unilateral spatial neglect (the second component) may trigger and facilitate the production of perseveration errors. Moreover results indicate that patients with perseveration are not disproportionately impaired in tasks assessing executive, visuo-spatial short-term memory, and attentional functions, suggesting the specificity of the monitoring disorder associated with spatial neglect. Lesion analysis indicates damage to the right insula as a relevant neural correlate of perseverative behaviour. Experiment 3 shows that perseverating patients produce a majority of substitution errors during a word reading task, suggesting that also this type of paralexic neglect error can be considered a “productive” manifestation. The clinical, experimental and neural features of another monitoring deficit and “positive” manifestation referring to the personal space, “somatoparaphrenia”, are reviewed: somatoparaphrenia is a symptom usually associated with right-sided hemispheric lesions, most often characterized by a delusion of disownership of contralesional body parts. Possible pathological factors may include a deranged representation of the body concerned with ownership, mainly right-hemisphere-based, and deficits of multisensory integration. Finally, Experiment 4 investigates anosognosia for unilateral spatial neglect by a quantitative assessment. Results indicate that unawareness for spatial attentional and representational deficits is not a pervasive disorder, and that some tasks can evoke different degrees of awareness. In addition, the scores assigned by neglect patients to their performance in spatial tasks are not modulated by the different conditions of the estimation tasks. In conclusion, we demonstrate that: 1) “productive”, as “defective”, manifestations of unilateral spatial neglect are multifarious; 2) these “positive” phenomena are independent of general executive deficits and of the severity of the spatial neglect syndrome; 3) the neural bases of motor productive disorders included the right insula; 4) neglect patients are not globally anosognosic about their spatial defective performances.