Casa, Rio de Janeiro Carta de apresentação

Tomei julho para tirar uma espécie de semi-férias cosmológicas do meu ano sabático neurológico da minha carreira como físico. Se vc acha isto confuso, não se preocupe. É confuso para mim também.

O fato é que estou no momento trabalhando com o Reza (meu colaborador Anglo-Iraniano, que está aqui no Rio) em um paper de topologia cósmica (qua anda parado a *muito* tempo), e estou indo na 3a feira para Paris, para um colóquio de cosmologia. Pouco depois de voltar, irei para Mangaratiba para assistir a XIIIa Escola Brasileira de Cosmologia e Gravitação e andar de caiaque.

A minha vida anda meio corrida...

Assim, na falta de um post realmente original, eu reproduzo abaixo (na mais completa cara de pau) uma carta de apresentação que escrevi para me inscrever em um outro encontro no final do ano, explicando o que diabos estou fazendo da vida. Não tenho tempo de traduzi-la (se tivesse, escreveria um post decente!).

One of the most instigating fields of scientific research nowadays is the study of complex biological system and processes as emergent phenomena, that can be modelled theoretically from a few simple principles of efficiency and adaptation. Such studies of course may greatly benefit from the application of methods developed for the physical sciences; but only if firmly grounded on a firm understanding of biology.

A classically-trained physicist alone will create beautiful and elegant models using the extensive and powerful theoretical toolbox at her disposal; such models however will likely fail to capture essential features of biological phenomena*.

It takes the intuition and knowledge of a proficient biologist to identify the critical features required for a successful model, and to test and validate it experimentally. Such research is therefore by necessity multi-disciplinar.

My interest in complex phenomena was kindled as an physics undergrad, when I took a course in chaotic dynamical systems, and organized seminars with other students about topics as diverse as self-organized criticality and allometric scaling rules. My career however has focused on more traditional areas of theoretical physics; first mathematical physics, and later cosmology (although the subject of my PhD, cosmic topology, is somewhat unorthodox).

I met Prof. Suzana Herculano-Houzel, head of the comparative neuroanatomy laboratory in UFRJ almost by chance, while still working towards my PhD. We became friends long before we started working together. She had then recently developed a method of accurately and quickly counting the number of neurons and glia cell in the brain, or any structure thereof. Comparisons between various rodent species (that vary in body mass by several orders of magnitude) showed some intriguing regularities, in the form of power laws relating the various quantities. She wanted some help in figuring out what such regularity meant. And what began as a quick discussion developed into a collaboration that eventually resulted in several simple yet interesting results, and a paper publisehd in PNAS.

After I earned my PhD, I wanted to broaden my experience, and needed a change of airs. At the same time, Suzana's lab was producing a wealth of data in need of analysis (mostly related to cell number counting in various structures of the central nervous system [CNS], of several species of mammals and in different stages of development). This data could potentially yield significant insights into CNS organization, development and evolution. As long as someone could fit them into workable models. I of course eagerly accepted her invitation, and took a position as a postdoctoral fellow there.

In the past months we have shown that the ratio between neuron and glial total mass remains constant across both species and brain structures; used the variational method to study how the spinal cord is organized to minimize total signal propagation time (this may later be generalized to other axonal bundles, and to include the simultaneous optimization of several different quantities); and sought the rules that determine how the extent of folding in cerebral grey matter (the brain's "circuit board") is related to the the scaling of signal propagation time in the white matter (the "wiring"). All these works are currently being prepared for submission to publication. We are now looking into the possibility that brain networks are organized as small-world networks, and that moreover this is an emergent phenomenon which comes as consequence of the extensive processes of neuron generation and death at the early post-natal brain development (the optimal circuit might perhaps correspond to a critical point toward which the network self-organizes). This might help explain why the early rat brain kills off about 70% of all the neurons it generates: nature is not usually wasteful. This latter line of inquiry, although instigating, remains incipient.

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* Proverbially, it is told that a farmer once hired a group of physicists to help increase the milk productivity of his cows. The physicists measured the bovines with all sorts of instruments; filled acres of blackboard space with elaborate calculations, and wrote thousands of lines of code to simulate the cows' every aspect. After months of research, the farmer finally received a ponderous document relating the scientist's findings. He eagerly opened it in the first page, in which he read: "Consider a spherical cow, with homogeneous distribution of milk, embedded in an isotropic and homogeneous pasture... "