Year: 2011
Type: dissertation
Study design: Observational Study
Abstract: The ventral fronto-parietal network has been considered to play a crucial role in \nreorienting attention towards significant environmental events, while the dorsal system is \nthought to be dominant in controlling goal-directed behaviour (Corbetta and Shulman \n2002). I begin by reviewing literature which suggests this distinction may not be so clear \ncut and suggest my own scheme which takes into account this evidence (Singh-Curry and \nHusain 2009). Specifically, ventral areas, particularly the right inferior parietal lobe (IPL), \nappear to be activated by tasks involving sustained attention, responding to salient taskrelevant \nevents, detecting novel stimuli and switching between tasks. Accordingly, I \nhypothesise that the right IPL may play a crucial role in reconfiguring behaviour between \na task-engaged state and a more exploratory mode of functioning, which permits the \nidentification of potentially important novel events. \nThe first few chapters of my thesis aimed to test this hypothesis by examining attention \ndeficits in stroke patients with hemispatial neglect, the syndrome which frequently occurs \nfollowing damage to the right IPL. These patients were shown to have difficulty \nsustaining attention over time, even when no spatial shifts of attention were required. This \ndeficit in sustained attention was particularly evident for stimuli of lower perceptual \nsalience. More importantly, however, these deficits were found to interact with each other, \nas well as the direction of spatial attention, suggesting that these functions may be \ndependent on an interrelated brain network. Consistent with this notion, the results of \nlesion-symptom analysis indicated that the Right IPL and ventral attention network appears to be crucial in the mediation of all of these processes, including the processing of \nnovel stimuli, supporting my hypothesis. \nThe detection of novel events has also been found to activate the midbrain dopaminergic \nsystem (Bunzeck and Duzel 2006), while the principal pathological feature of Parkinson’s \ndisease (PD) is degeneration of these neurons (Hornykiewicz 1998). Although PD is \ntraditionally considered a disorder of movement, more recently it has been recognised that \nthere may be associated cognitive deficits, including disorders of impulse control \n(Weintraub 2008). At present, however, the factors which predispose some individuals \nwith PD to develop such problems are unclear. \nAccordingly, in the second part of my thesis, I examined novelty processing and risktaking \nbehaviour in PD in order to identify subgroups which may be particularly \nvulnerable to developing impulse control problems. In addition to PD patients with \nimpulse control disorders (ICD), those who were classified as akinetic-rigid, as opposed to \ntremor dominant – without ICD – were found to process novelty more quickly than nonnovel \nperceptually salient stimuli, unlike tremor dominant PD patients. Novelty seeking \nwas found to be associated with relative preservation of the mesolimbic dopaminergic \nsystem in patients without ICD, while increased risk-taking was associated with \npreservation of the mesolimbic system in ICD patients. Mesolimbic sparing, in addition to \nthe akinetic-rigid motor phenotype of PD may therefore increase susceptibility to impulse \ncontrol problems in PD.
Author: Victoria Singh-Curry
Language: English
Subfield: Cognitive Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W638243331