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SCIENTIFIC ACTIVITIES - Fields Institute - University of Toronto

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Brain<br />

Neuromechan<br />

BRAIN TISSUE IS AN INHOMOGENEOUS, MULTIscaled,<br />

multi-layered, and inter-connected set <strong>of</strong> neurons, glial<br />

cells, and vascular networks. So far, the biophysics and dynamics<br />

<strong>of</strong> the cell types within these networks have been studied<br />

individually, as well as their network interactions.<br />

On the other hand, the macroscopic mechanical response<br />

<strong>of</strong> the brain to traumatic injuries has also been the object <strong>of</strong><br />

intense experimental and computational studies. However, a<br />

full understanding <strong>of</strong> brain physics and dynamics can only be<br />

achieved by linking biomechanical and biochemical processes<br />

taking place in the brain at different length and time scales, and<br />

by accounting for the interactions <strong>of</strong> and feedback among the<br />

brain’s networks.<br />

The aim <strong>of</strong> this first interdisciplinary workshop on<br />

Brain Neuromechanics was to bring together experts from<br />

different areas <strong>of</strong> brain research, such as applied mathematics,<br />

neuroscience, engineering, neurosurgery, to present the latest<br />

developments in their fields and discuss opportunities for longterm<br />

research collaborations.<br />

The first speaker, James Drake, Chief Neurosurgeon<br />

at the Hospital for Sick Children in <strong>Toronto</strong>, set the tone<br />

for the workshop by delivering a talk on the inseparability<br />

<strong>of</strong> neurosurgery and neuromechanics. Improved medical<br />

diagnoses, treatment strategies and clinical protocols can be<br />

achieved only through discoveries in fundamental brain science.<br />

In particular, hydrocephalus, a brain condition known from<br />

the time <strong>of</strong> Hippocrates and characterized by an abnormal<br />

accumulation <strong>of</strong> spinal fluid within the fluid-containing<br />

spaces <strong>of</strong> the brain, remains a puzzle for neurosurgeons even<br />

today; the two surgical treatments currently used display no<br />

statistical difference with regard to the efficacy <strong>of</strong> treating<br />

hydrocephalus. Some <strong>of</strong> the subsequent talks showed<br />

promising new advances in the understanding <strong>of</strong> the underlying<br />

mechanisms that give rise to hydrocephalus. Miles Johnston<br />

(Sunnybrook) showed that, in the rat brain, interstitial fluid<br />

pressures increased after antibody administration into a lateral<br />

16 FIELDSNOTES | FIELDS INSTITUTE Research in Mathematical Sciences<br />

ventricle, suggesting that capillary absorption might play a<br />

pivotal role in the onset <strong>of</strong> hydrocephalus. This finding provides<br />

the exciting possibility that some forms <strong>of</strong> hydrocephalus<br />

may be treatable with pharmacological agents rather than<br />

through surgical interventions. Richard Penn (Chicago)<br />

presented a novel macroscopic biomechanical model <strong>of</strong><br />

fluid-structure interactions in the brain which could explain<br />

the onset <strong>of</strong> hydrocephalus. So far, the model appears to be<br />

in agreement with preliminary experiments on dog brains.<br />

Kathleen Wilkie (Waterloo) introduced a new age-dependent<br />

fractional viscoelastic model for the brain and showed that the<br />

natural pulsations <strong>of</strong> the brain cannot be the primary cause<br />

<strong>of</strong> either infant or adult hydrocephalus. Almut Eisentrager<br />

(Oxford) presented a novel multi-fluid poro-elastic model<br />

<strong>of</strong> hydrocephalus which incorporates blood pulsations on<br />

the cardiac cycle time scale and thus can be used to simulate<br />

spinal fluid pressure fluctuations in clinical infusion tests.<br />

Finally, Corina Drapaca (Penn State) presented the first<br />

neuro-mechanical models that couple the biomechanics and<br />

biochemistry <strong>of</strong> the brain. One model, based on the triphasic<br />

theory, shows that normal pressure hydrocephalus (NPH) can<br />

be caused by an ionic imbalance in the absence <strong>of</strong> increased<br />

intracranial pressure. This represents a significant finding in<br />

NPH research, opening the door to the possibility <strong>of</strong> treating<br />

hydrocephalus using pharmaceutical agents. The other model<br />

can incorporate non-invasive neuro-imaging measurements<br />

and can then be used to investigate the brain’s mechanics<br />

under different clinical scenarios. Although Martin Ostoja-<br />

Starzewski’s (Urbana-Champaign) talk did not focus on<br />

hydrocephalus, his MRI-based finite element approach to<br />

study traumatic brain injuries could also be used in computer<br />

simulations <strong>of</strong> hydrocephalus. In addition, a novel extension <strong>of</strong><br />

continuum mechanics to fractal porous media was introduced to<br />

address the random fractal geometry <strong>of</strong> the brain.<br />

The talks given by Alan Wineman (UMichigan) and<br />

Katerina Papoulia (Waterloo) served to remind the audience

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