Wiring the Brain

The idea that our genes can affect many of the traits that define us as individuals, including our personality, intelligence, talents and interests is one that some people find hard to accept. That this is the case is very clearly and dramatically demonstrated, however, by a number of genetic conditions, which have characteristic profiles of psychological traits. Genetic effects include influences on perception, sometimes quite profound, and other times remarkably selective. A recent study suggests that differences in perception in two conditions, synaesthesia and Williams syndrome, may share some unexpected similarities. Williams syndrome is a genomic disorder caused by deletion of a specific segment of chromosome 7. Due to the presence of a number of repeated sequences, this region is prone to errors during replication that can result in deletion of the intervening stretch of the chromosome, which contains approximately 28 genes. The disorder is characterised by typical facia

Studies linking some aspect of parental behaviour with some trait in their offspring are depressingly common in the sociological literature. Though these studies typically only report a correlation between parental behaviour and whatever the trait is in the offspring, the implication, and often the explicit conclusion, is that one causes the other. These kinds of stories get huge play in the popular press (and in the blogosphere), where the conclusion of a causative relationship is rarely challenged. For example, the finding that children who grow up with more books in the house are more successful academically is taken as evidence that simply having books around makes kids smarter. This kind of thinking illustrates a common and fundamental flaw in interpreting sociological or epidemiological findings – correlation does not imply causation . Red hair and freckles are highly correlated but one does not cause the other. Both are caused by something else (a mutation in a gene contro

To many people, the term “autism” suggests a specific disorder – one with characteristic and recognizable symptoms, presumably reflecting the same underlying cause.   In fact, no such disorder exists.   Autism refers to a variable spectrum of symptoms – including deficits in social interaction, impaired communication (especially a delay in developing language), narrow, restricted interests and stereotyped behaviours.   Any one child who is diagnosed with autism may show only some of these symptoms.   There is a wide range of IQ in autism, including very high levels seen in what has been known as Asperger’s syndrome, but the average is about 70.   There is also a high incidence of epilepsy (around 10%). Psychiatrists have long recognized this variability and use the term “ autism spectrum disorder ” to encompass the entire range.   Until recently, with a couple of exceptions, they have not had the means to distinguish different subtypes of autism based on their underlying cause.   O

Most neurons in the brain are not born in their final position – they are generated by cell division in one part of the brain and have to migrate, sometimes over long distances, along complicated routes, to finally arrive at their pre-specified destination.   This process entails an incredibly complex and dynamic set of genetic instructions and interactions between different cell types.   A prime example is the migration of interneurons to the cerebral cortex – these inhibitory neurons make up one half of a balancing act that controls all cognitive functions in the cortex, but, unlike the excitatory neurons of the cortex, they are born in a completely different part of the brain (what will become the striatum).   Many researchers have been trying to understand how these neurons find their way specifically to the cortex.   A number of genes have been found which encode guidance cues which can attract or repel the migrating neurons and which mark out their correct pathway.   These cues