SCIENTIFIC ACTIVITIES - Fields Institute - University of Toronto

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Brain Neuromechan BRAIN TISSUE IS AN INHOMOGENEOUS, MULTIscaled, multi-layered, and inter-connected set of neurons, glial cells, and vascular networks. So far, the biophysics and dynamics of the cell types within these networks have been studied individually, as well as their network interactions. On the other hand, the macroscopic mechanical response of the brain to traumatic injuries has also been the object of intense experimental and computational studies. However, a full understanding of brain physics and dynamics can only be achieved by linking biomechanical and biochemical processes taking place in the brain at different length and time scales, and by accounting for the interactions of and feedback among the brain’s networks. The aim of this first interdisciplinary workshop on Brain Neuromechanics was to bring together experts from different areas of brain research, such as applied mathematics, neuroscience, engineering, neurosurgery, to present the latest developments in their fields and discuss opportunities for longterm research collaborations. The first speaker, James Drake, Chief Neurosurgeon at the Hospital for Sick Children in Toronto, set the tone for the workshop by delivering a talk on the inseparability of neurosurgery and neuromechanics. Improved medical diagnoses, treatment strategies and clinical protocols can be achieved only through discoveries in fundamental brain science. In particular, hydrocephalus, a brain condition known from the time of Hippocrates and characterized by an abnormal accumulation of spinal fluid within the fluid-containing spaces of the brain, remains a puzzle for neurosurgeons even today; the two surgical treatments currently used display no statistical difference with regard to the efficacy of treating hydrocephalus. Some of the subsequent talks showed promising new advances in the understanding of the underlying mechanisms that give rise to hydrocephalus. Miles Johnston (Sunnybrook) showed that, in the rat brain, interstitial fluid pressures increased after antibody administration into a lateral 16 FIELDSNOTES | FIELDS INSTITUTE Research in Mathematical Sciences ventricle, suggesting that capillary absorption might play a pivotal role in the onset of hydrocephalus. This finding provides the exciting possibility that some forms of hydrocephalus may be treatable with pharmacological agents rather than through surgical interventions. Richard Penn (Chicago) presented a novel macroscopic biomechanical model of fluid-structure interactions in the brain which could explain the onset of hydrocephalus. So far, the model appears to be in agreement with preliminary experiments on dog brains. Kathleen Wilkie (Waterloo) introduced a new age-dependent fractional viscoelastic model for the brain and showed that the natural pulsations of the brain cannot be the primary cause of either infant or adult hydrocephalus. Almut Eisentrager (Oxford) presented a novel multi-fluid poro-elastic model of hydrocephalus which incorporates blood pulsations on the cardiac cycle time scale and thus can be used to simulate spinal fluid pressure fluctuations in clinical infusion tests. Finally, Corina Drapaca (Penn State) presented the first neuro-mechanical models that couple the biomechanics and biochemistry of the brain. One model, based on the triphasic theory, shows that normal pressure hydrocephalus (NPH) can be caused by an ionic imbalance in the absence of increased intracranial pressure. This represents a significant finding in NPH research, opening the door to the possibility of treating hydrocephalus using pharmaceutical agents. The other model can incorporate non-invasive neuro-imaging measurements and can then be used to investigate the brain’s mechanics under different clinical scenarios. Although Martin Ostoja- Starzewski’s (Urbana-Champaign) talk did not focus on hydrocephalus, his MRI-based finite element approach to study traumatic brain injuries could also be used in computer simulations of hydrocephalus. In addition, a novel extension of continuum mechanics to fractal porous media was introduced to address the random fractal geometry of the brain. The talks given by Alan Wineman (UMichigan) and Katerina Papoulia (Waterloo) served to remind the audience
ics of the continuum mechanics framework and some important mathematical concepts that any researcher should be aware of when designing biomechanical models of the brain. Another talk of pedagogical nature was given by K. Unnikrishnan (UMichigan) on computational methods and associated statistical significance tests used to detect patterns in multineuronal spike trains which can uncover the functional connectivity of the underlying neuronal networks. Whilst the talks given by Joseph Francis (SUNY Downstate) and Jürgen Germann (Toronto Phenogenomics) presented novel experimental approaches to investigate the plasticity of the brain, the lectures given by Paul Janmey (UPenn) and Kristian Franze (Cambridge) focused on the mechanosensitivity of healthy and diseased brain cells and the experimental settings required to estimate mechanical parameters at such small length and time scales. The mechanics of individual cells and their networks are essential in understanding the brain damage seen in deep brain stimulation studies performed on animal brains. The talks of Bruce Gluckman (Penn State) and Andrew Sharp (Southern Illinois) served to raise awareness in the neuroscience community of the damaging effects of electrode implants. In particular, Gluckman’s experimental results showed not only local damage near insertion locations, but also unexpected non-local damage of brain tissue. Patrick Drew (Penn State) presented a novel technological approach of imaging single vessel vascular dynamics in the mouse cortex that provides the first non-controversial link between functional signals and their vascular origin. The talk of Leslie Loew (Connecticut Health Center) presented yet another technological discovery that uses voltage sensitive dyes to image neuronal physiology. Loew also introduced briefly the Virtual Cell, a software system used to simulate neuronal cell biology. All these technological advancements can provide valuable data for mathematical models of the brain. Corina Drapaca (Penn State) FIELDS INSTITUTE Research in Mathematical Sciences | FIELDSNOTES 17
Page 1 and 2: OCTOBER 2010 | VOLUME 11:1 FIELDS N
Page 3 and 4: This summer, 20 undergraduate stude
Page 5 and 6: Combinatorial Games Group #2 Matthe
Page 7 and 8: First Montreal Spring School in Gra
Page 9 and 10: Extended Workshop on Groups and Gro
Page 11 and 12: 010 ections in Geometry and Physics
Page 13 and 14: Directed Polymers and Random Growth
Page 15: Optimization and Data Analysis in B
Page 19 and 20: Richard Cerezo: From my understandi
Page 21 and 22: ‘Schubert Calculus’ continued f
Page 23 and 24: FIELDS ACTIVITIES Bridging Research

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