Bird brains

Humans and birds share a few commonalities: we both like the sound of our own voices, we tend to follow the crowd, we like to preen, we have a fraught relationship with mirrors and we occasionally pick at our food. Now a new study has found a connection that may offend your sense of the place of humanity in the evolutionary hierarchy: it seems the human brain is wired in a similar way to the avian brain.

When you look at a bird brain it appears quite different to a human brain but it is in the organisation that there are similarities.

In this new study researchers looked at 34 previous studies that examined the anatomy of a pigeon’s brain. In particular they looked at the anatomy of the pigeon hippocampus, the part of the brain that is involved in long term memory and navigation in both birds and mammals.

The finding was that bird brains, just like human brains, are organised around areas known as “hub nodes”. In the brain most neurons are functionally connected with only a small number of other neurons. However, a small number of neurons are very highly connected and these neurons behave like hubs in the network of the brain so that via these few “hub nodes” the whole brain is connected. This is an example of the “small-world” model in action.

A small-world network is a model in which most nodes are not neighbours of one another, but most nodes can be reached from every other by a small number of hops or steps. This is the principle that drives the theory of “six degrees” of separation that everyone and everything is six or fewer steps away, by way of introduction, from any other person in the world, so that a chain of “friends” can be made to connect any two people in a maximum of six steps. You also see it embodied on Facebook for instance, by people who have thousands of friends and so become a “hub node” connecting many other people.

Maybe it should not surprise us that bird brains and human brains are organised around this small-world model. The brains of mammals from cats to monkeys are also organised in this way. Indeed most of the universe seems to operate around a principle of infinite connectivity through a small number of crucial points, be those points Kevin Bacon (see “six degrees of Kevin Bacon”) or a neuron cluster.

On a medical front there is a theory that conditions like Alzheimers and schizophrenia are disorders of this connectivity. This understanding may lead to new and effective treatments.

In the short term though, the next time someone calls you a “bird brain” there’s not much you can but shrug and say “fair enough”.