Wiring the Brain

Is homosexuality a lifestyle choice or an innate biological disposition?   The idea that it is a choice is certainly widespread – a part of several mainstream religious doctrines and political ideologies – and is used to condone significant discrimination against homosexuals and the criminalization of homosexual behaviour.   But what does the science say?   The broad conclusions are that sexual orientation is an innate disposition – no different from whether you are left or right-handed – that it is affected by genetic influences and that it reflects differences in brain structure and function.   I will consider the evidence of genetic effects on sexual orientation here, including some recent additions – a later blog will look at the neurobiological findings. A number of family and twin studies of the heritability of sexual orientation, starting in the 1950’s, found significant genetic influences: the statistical likelihood of an individual being homosexual increased somewhat if t...

Most people know that strawberries are red, lemons are yellow and grass is green.   And practically all adults can correctly identify the name of a colour when visually presented with it (allowing for some disagreements based on retinal pigment gene variants – more on that in a later post – and, yes, your wife is right, it’s green, not blue – just accept it).   The ability to recognise colours and remember which one goes with which object seems so trivial that it is hard to appreciate how specialised a skill it is – one that requires a lot of practice and which involves dedicated brain circuits.   Children are able to visually discriminate between colours from a very young age and will readily separate objects by colour.   However, they learn the names of colours with great difficulty, usually starting around the age of 3.   At this stage, they will still frequently misidentify quite dissimilar colours, like red and blue.   As they learn more colour names, they will only mix up one...

The prevailing model for how the network of the brain is organized is the “small-world” network.   In such a network, most units, or nodes, are very sparsely and only locally connected.   However, a very small proportion of nodes, called hubs, are very highly connected, and over longer distances.   These hubs thus provide an indirect but short pathway of connectivity between any two nodes in the network (like people with thousands of “friends” on Facebook).   This overall architecture is highly efficient and robust and can be observed not just at the level of networks of neurons but also at   a higher level of brain organization, in the pattern of connectivity of cortical areas.   Indeed, it is also typical of genetic, social and many other networks, including the internet.   In the brain, the existence of hub neurons had thus been hypothesised, but these beasts had not actually been observed until a recent study by Rosa Cossart and colleagues.   They were analysing the activity patter...

Organisms with a bilaterally symmetric nervous system face a problem – how to integrate functions across the two sides so that behavioural outputs can be coordinated for the entire body.   In the brain this is important to allow integration of the large number of cognitive “modules” which are differentially lateralised, such as language.   (The importance of this communication is dramatically illustrated by so-called “ split-brain ” patients, who have had the majority of the connections between the two cerebral hemispheres severed in order to treat otherwise intractable epilepsy.   These patients, first studied by Roger Sperry and colleagues, end up in essence with two brains inside the same skull, and it could be argued, two largely independent minds).   The importance of bilateral integration is also evident and very well understood in the control of movement, where motor commands have to be tightly and dynamically coordinated across the two sides of the body.   The integration ...