This book provides up-to-date, practical information on functional mapping in order to assist neurosurgeons responsible for safely removing lesions in and around eloquent cortex – one of the greatest challenges in neurosurgery. The roles of pre- and intraoperative mapping techniques are clearly explained, highlighting the advantages and limitations of each tool available to the neurosurgeon. The inclusion of treatment algorithms for applications in specific clinical circumstances ensures that the book will serve as a clear guide to this most complex of neurosurgical problems. To further assist the reader, instructive clinical case examples, accompanied by intraoperative photos and other illustrative material, help to explain the applications of functional mapping of eloquent cortex in different pathologies. Practitioners will find the book to be a ready guide to navigation of the practical decisions commonly faced when operating in eloquent cortex.
Functional Anatomy of Visual Processing in the Cerebral Cortex of the Macaque
In this thesis, we examined the monkey cortical regions involved in processing of color, visual motion information, and the recognition of actions done by others. The aim was to gain better insight in the functional organization of the monkey visual cortex using in-house developed functional imaging techniques. Two different functional imaging techniques were used in these studies, the double-label deoxyglucose technique (DG) and functional magnetic resonance imaging (fMRI) in the awake monkey (Chapter 2). Both techniques allow to obtain an overview of stimulus-related neural activity throughout the whole brain, integrated over a limited amount of time. The results of the color experiments (Chapter 3) clearly showed that color related information is processed within a group of areas belonging to the ventral stream, which is involved in the perception of objects. Color-related metabolic activity was observed in visual areas V1, V2, V3, V4 and inferotemporal cortex (area TEO and TE). These findings set to rest the longstanding controversial claims that color would be processed almost selectively in one extrastriate visual area (V4) (Zeki SM, Brain Res 1973 53: 422-427). These results also show the usefulness of whole brain functional mapping techniques, as a complimentary approach to single cell measurements. In Chapter 4, we investigated which regions in the superior temporal sulcus (STS) of the monkey are involved in the analysis of motion. While the caudal part of the STS has been studied extensively, including area MT/V5 and MST, little is known about motion sensitivity in more anterior-ventral STS regions. Using fMRI, we were able to localize and delineate six different motion sensitive regions in the STS. One of these regions, that we termed 1st (lower superior temporal), had not been described so far. We were able to further characterize the six motion sensitive regions, using a wide variety of motion-sensitivity tests. The results of the latter tests suggested that motion related information might be processed along a second pathway within the STS, in addition to the MT-MST path (which is involved in the perception of heading). This second pathway, which includes the more rostral motion sensitive STS regions (FST, 1st and STPm) is possibly involved in the visual processing of biological movements (movements of animate objects) and actions. Finally, we investigated how and where in the monkey brain visual information about actions done is processed (Chapter 5 and 6). We found (Chapter 5) that, in agreement with earlier single unit results, the observation of grasping movements activates several regions in the premotor cortex of the monkey. Remarkable is that these premotor regions predominantly have a motor function, coding different types of higher order motor acts (for instance grasping of an object). These results are in agreement with earlier suggestions that we are able to understand actions done by others, because observation of a particular motor act activates our own motor representation of the same act. Furthermore, these studies suggested that within the frontal cortex of the monkey, there is a distinction between context-dependent (a person grasping) and more abstract (a hand grasping) action representations. In Chapter 6 we studied two other regions which are involved in the processing of visual information of actions done by others, the superior temporal sulcus (STS) and the parietal cortex. In the parietal cortex, we found a similar distinction between context-dependent and more abstract action representations as observed in prefrontal cortex. These results suggest that the parietal cortex is not only involved in the visual control of action planning, but also in the visual processing of actions performed by others. Based upon anatomical connections between the STS, parietal and frontal regions and motion-, form- and action-related functional properties of the former regions, we tentatively suggest how information about actions done by others might be sent from the STS to the frontal cortex along three different pathways. The latter working hypothesis will be tested in the future by additional fMRI control experiments and by combining fMRI, inactivation and microstimulation experiments while monkeys perform grasping tasks and/or view actions performed by others.
Therapeutic Laser Applications and Laser tissue Interactions
As vision is one of the most important sensory modalities present in almost all animal species, the systematic exploration of the visual system has been a major target of neurobiological research in recent years. This research activity has led to increased understanding of the functional, anatomical and biochemical organisation of the primate visual system. This book gives a comprehensive overview of key discoveries relating to the human visual cortex, made possible by new methodologies, such as brain imaging techniques, which have enabled scientists to map the human visual cortex with respect to its functional organisation. Providing a platform for discussion of developments, uncertainties and future exploration in this multidisciplinary field, the book summarises our state-of-the-art knowledge, and gives impetus to comparative studies on the visual systems of humans and other primates.
New Insights Into Functional Mapping in Cerebral Tumor Surgery
The rationale of brain tumour surgery depends on two antagonist goals: on one hand, to optimise the quality of resection, on the other hand, to minimise the risk of permanent postoperative deficit. However, due to the physiological interindividual anatomo-functional variability, increased in cases of cerebral tumours because of the plastic potential of the brain, a study of the interactions between the lesion and the host seems mandatory - in order to understand the individual dynamic organisation of the brain, then with the goal to avoid postsurgical sequelae.In this way, new methods of functional brain mapping can be useful for the neurosurgeon. First, before surgery, non-invasive functional neuroimaging techniques (fMRI, PET, MEG) and invasive extraoperative electrical mapping (subdural grids) may allow to study the cortical organisation for each patient. Furthermore, Diffusion Tensor Imaging can help to understand the brain connectivity. Thus, the relationships between the tumour and the eloquent areas can be estimated, and these data applied to the surgical planning. Second, during surgery, direct intraoperative electrical stimulation permits to detect with accuracy and reliability, both the cortical sites and the white pathways essential for a given function, at each moment and each place of the tumour removal. Moreover, repeated stimulations all along the surgical act also allow to study the mechanisms of short-term plasticity, induced by the resection itself. This on-line mapping is used to tailor the resection according to cortico-subcortical functional boundaries. Third, postoperative neurofunctional imaging, combined to the precise evaluation of the clinical course and the objective assessment of the location and extent of resection, gives the opportunity to study the mechanisms underlying the functional compensation, i.e. the long-term plasticity. This potential may be used to perform a second surgery with a better quality of resection than the first one, thanks to possible brain remapping. Such a pre-, intra- and post-surgical longitudinal study of dynamic interactions between brain and lesion, allows to better apprehend the distinct patterns of functional redistribution for each patient, thus to apply this knowledge in order: to better select the surgical indication in brain tumours; to better inform the patient of the actual risk of transient postoperative deficit; to better plan the resection (surgical approach, cortico-subcortical boundaries); to optimise the quality of tumour removal while preserving the functional areas and tracts; and to plan a specific rehabilitation. Finally, on a fundamental point of view, the association of methods of functional mapping in neurosurgical patients allows to better understand the pathophysiology of brain areas, their connectivity, and the mechanisms of plastic potential of the glio-neurono-synaptic networks.