Monthly Archives: December 2009

We May Be Born With an Urge to Help

By Darren Schreiber

Nicholas Wade had a recent article in the NY Times asking whether it is in our nature to be helpful.  He discusses new books by Michael Tomasello (Why We Cooperate?) and Frans de Waal (The Age of Empathy).

Comparing spectral centrality measures and community detection methods

by Yunkyu Sohn

Santo Fortunato ( wrote several interesting articles on the objective evaluation of spectral centrality measures and community detection methods. Particularly, the authors conclude that infomap is the most accurate community detection method for any kind of network presented.

infomap code:


Spectral centrality measures in complex networks:

compares PageRank, eigenvector centrality, and the hub and authority scores in regard to their relationship with in degree and node ranking.

Community detection algorithms: A comparative analysis:

compares several popular community detection algorithms by testing them on weighted or directed benchmark networks with heterogeneous distribution of degree and community size, and overlapping community structure.

Causation in networks?

by Robert Bond

Here is an interesting new article from PNAS about distinguishing between peer-influenced contagion and homophily in networks. This could be interesting reading for anyone thinking about collecting dynamic network data… op-ed: Facebook, friends and getting fat

by Nicholas A. Christakis and James H. Fowler (crossposted from

The bonds we renew in person between friends and family as we visit during the holiday season get reactivated online after we all go home. This is the time when feast and Facebook go hand-in-hand.

And as it turns out, these two activities are more related than you might imagine.

Continue reading

Connectomics and network analysis of connectome

By Yunkyu Sohn

3D reconstruction of wiring diagram in rabbit retina

Seung demostrates how the connectomics approach, dense mapping of all neuro-synaptic connections in a single specimen, will eventually substitute the existing methodological means of neuroanatomical data mining, sparse sampling of neuro-synaptic pairs from many specimens, and leads to the understanding of functional properties of neurons through computational analysis.

Reading the Book of Memory: Sparse Sampling versus Dense Mapping of Connectomes

A review article on the graph theoretical analysis of structural and functional brain connectivity data: Complex brain networks: graph theoretical analysis of structural and functional systems

The presence of pace makers in Hippocampal networks

By Yunkyu Sohn

Bonifazi et al. introduces the first direct evidence for the presence of pace makers (functional hubs) in the neuro-synaptic level network of Hippocampus. They developed a novel method to construct functional connectivity matrix in real time in living brain slices. Through the dynamic analysis of this network they found out that there exists role-differentiation of the neurons for the synfire activity of the overall network: High Connectivity pace maker neurons and Low Connectivity follower neurons.

GABAergic Hub Neurons Orchestrate Synchrony in Developing Hippocampal Networks

DARPA Network Challenge

by Jason J. Jones

Wherever you are this Saturday – look up.  If you see a giant red orb, don’t be alarmed.  It just means you are part of the Defense Advanced Research Projects Agency‘s latest experiment.

The DARPA Network Challenge is

a competition that will explore the roles the Internet and social networking play in the timely communication, wide-area team-building, and urgent mobilization required to solve broad-scope, time-critical problems. The challenge is to be the first to submit the locations of 10 moored, 8-foot, red, weather balloons at 10 fixed locations in the continental United States.

A $40,000 prize will be awarded to whomever first submits the correct location (latitude and longitude) of all ten balloons.

Naturally, people are forming teams with varying strategies and varying success.  Many are offering bounties for each balloon location (e.g. Red Balloon Race).  Some are hoping people will participate just for the fun or challenge, and plan to donate the prize money to charity (e.g. Project Red Baloon).

Personally, I plan to sit at my computer in my pajamas all day Saturday and “watch” as it were.  I’ll be checking the Facebook groups and some of the bigger challenge-specific sites.   I may even have to join Twitter (shudder).

Keep watching the skies.  The balloons are out there…