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doctoral thesis

Emergent Connectivity Principles in the Neocortex

Riachi, Imad
2010

The neocortex makes up over 80% of the mammalian brain and is responsible for higher cognitive functions, processing of sensory inputs and orchestration of complex motor outputs. It is a 6-layered structure composed of billions of morphologically and electrically diverse neurons. Functionally, the basic unit is the neocortical column (NCC), a vertical structure of 0.5 mm wide, repeated millions of times across the neocortex and connected in an intricate but consistent way. In this thesis I investigated the role of morphologies (neurogeometry) in shaping the elaborate connectivity scheme within a column. First, I suggest a morphological basis for the higher than expected reciprocal connectivity reported experimentally between connected pairs, using a newly defined measure: the Reciprocity Index (RI), which arises from a purely mathematical concept and can be derived from the morphometric statistics of neurons. Second, I show that most experimentally reported synaptic patterns between different classes of neurons can be directly computed from the statistics of their morphologies, while some pathways would require additional functional mechanisms to refine an even more specific synaptic pattern. My thesis is done within the Blue Brain Project, the first comprehensive attempt to reverse-engineer the mammalian brain, starting with the somatosensory NCC of a P14 rat. I present in this thesis my contribution in constructing the framework for building biologically accurate circuitry. I explain how we start from 3D neuron morphologies obtained in vitro, repair them for slicing artefacts, build circuits and accurately detect potential synapses. I also explore how modelling of the experimental procedures can help us characterize biases and predict in vivo data from in vitro data. I finally present recent exploratory work on how to use the supercomputing power to design novel in silico protocols to investigate the emergent dynamics of the neocortical column.

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Type
doctoral thesis
DOI
10.5075/epfl-thesis-4631
Author(s)
Riachi, Imad
Advisors
Markram, Henry  
Date Issued

2010

Publisher

EPFL

Publisher place

Lausanne

Thesis number

4631

Total of pages

224

Subjects

neocortical column

•

connectivity

•

neurogeometry

•

morphologies

•

emergent properties

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primary somatosensory cortex

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large scale modelling

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simulation driven research

•

synaptic pathways

•

reciprocal connection

•

reciprocity index

•

connection probability profile

•

in silico

•

colonne néocorticale

•

connectivité

•

neurogeometry

•

morphologie

•

propriétés émergentes

•

cortex somatosensoriel primaire

•

modélisation à grande échelle

•

recherche axée sur la simulation

•

connexion réciproque

•

indice de réciprocité

•

in silico

•

voies synaptiques

EPFL units
LNMC  
BBP-CORE  
Faculty
SV  
School
BMI  
Doctoral School
EDNE  
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/45575
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