P104. Two methods for one network: Toward an understanding of the left lateralized pathways for tool use

Abstract

Introduction This project investigates the neural networks involved in the daily use of tools, a fundamental human activity that may be impaired in patients who have suffered strokes, particularly in the middle cerebral artery, resulting in apraxia. Previous experiments with healthy young adults and brain damaged patients have employed various paradigms to address the neural representations of manipulation and employment of tools; but important factors, such as aging or side of brain injury, have not been addressed. Our goal is test the same task, the use of individual tools, using two fundamentally different methods of brain imaging to determine the consistency of findings and to discover the nature of the different components of tool use. Method The methodology comprised fMRI in healthy subjects and lesion analysis in brain damaged patients. Both approaches employed a similar version of the tool carousel, an apparatus built for the presentation of single tools and objects. Twelve tools in the lesion experiment and 10 in the fMRI were presented with the instruction, “Use the tool presented the way you know”. An event-related fMRI experiment was conducted on 17 young and 17 elderly controls. In the lesion study 31 left brain damaged patients and 19 patients with right brain injuries were tested. FMRI-data was analyzed with SPM8 in a factorial design (tool vs. non-tool and use vs. transport) during the planning- and execution-phase. In the lesion study Voxel Lesion Symptom Mapping was applied to the behavioral scoring of patients and VOIs damaged to analyze the following factors: score parameter, damaged side (left, right) and tools used; in addition a ROI analysis specified the findings. Results A left-lateralized network that includes the superior and inferior parietal lobes, the dorsal and ventral premotor cortex and the middle frontal gyrus, the temporal cortex and the lateral occipital complex is similarly involved in tool use in young and elderly controls and in left-brain damaged patients. A difference can be observed in the elderly subjects, who recruit a wider and less focused network during action planning but a smaller, weaker activation pattern during actual motion execution. Despite moderate performance errors in patients with right brain damage, these pathways were not detected, suggesting a more widely-spread distribution of responsible networks and different sources for failure in the correct use of the tools. Conclusions The correspondence of the areas revealed by fMRI in healthy subjects and left-side areas damaged in the patient group demonstrates the role of dorsal and ventral pathways in complex actions like tool use, with particular importance for the frontal and parietal areas. The carousel benefits to test single tool use in patients and healthy participants; this fact and, in addition, the employment of this two different populations validate the findings of the project.