Biomedical subjects
Elizabeth Warburton
Publications and source records attributed to Elizabeth Warburton.
Is motor perseveration in unilateral neglect 'driven' by the presence of neglected left-sided stimuli?
Unilateral spatial neglect refers to a difficulty in detecting or acting on information in a particular region of space. When asked to cross out stimuli distributed across a page, patients with neglect may miss many targets on the left. In addition, they have a tendency to return to, and re-mark, right-sided targets that they have already cancelled. A recent retrospective study has shown this effect to be specific to unilateral neglect rather than a consequence of right hemisphere damage in general. Here, a consecutive group of seven right-hemisphere neglect patients performed five versions of a standard cancellation task, each version differing in the quantity of left-sided information presented. All of the participants showed perseveration on right-sided targets in the basic task. A highly significant and linear reduction in perseverative behaviour was observed as left-sided information was removed. In a second study, left-sided targets were again progressively removed but, in this case, were replaced with an additional distractor item, keeping the total quantity of stimuli presented in each condition constant. Again, a significant reduction in right-sided perseveration was observed, indicating a high degree of selectivity to the effect. The results show that a difficulty in perceiving existing cancellation marks, or a non-spatially specific motoric perseveration, are unlikely to fully account for this behaviour. As the patients omitted almost all targets on the left side of the basic cancellation task, the results suggest a striking influence on apparently intentional behaviour from un-cancelled information within the neglected field.
Speech production: Wernicke, Broca and beyond.
We investigated the brain systems engaged during propositional speech (PrSp) and two forms of non- propositional speech (NPrSp): counting and reciting overlearned nursery rhymes. Bilateral cerebral and cerebellar regions were involved in the motor act of articulation, irrespective of the type of speech. Three additional, left-lateralized regions, adjacent to the Sylvian sulcus, were activated in common: the most posterior part of the supratemporal plane, the lateral part of the pars opercularis in the posterior inferior frontal gyrus and the anterior insula. Therefore, both NPrSp and PrSp were dependent on the same discrete subregions of the anatomically ill-defined areas of Wernicke and Broca. PrSp was also dependent on a predominantly left-lateralized neural system distributed between multi-modal and amodal regions in posterior inferior parietal, anterolateral and medial temporal and medial prefrontal cortex. The lateral prefrontal and paracingulate cortical activity observed in previous studies of cued word retrieval was not seen with either NPrSp or PrSp, demonstrating that normal brain- language representations cannot be inferred from explicit metalinguistic tasks. The evidence from this study indicates that normal communicative speech is dependent on a number of left hemisphere regions remote from the classic language areas of Wernicke and Broca. Destruction or disconnection of discrete left extrasylvian and perisylvian cortical regions, rather than the total extent of damage to perisylvian cortex, will account for the qualitative and quantitative differences in the impaired speech production observed in aphasic stroke patients.