New research is shedding light on exactly what is wrong with the brains of people with several genetic disorders that lead to mental retardation – Down syndrome (a chromosomal abnormality where there are three copies of chromosome 21 instead of the usual two), Fragile X (a mutation of the Fmr1 gene on the X-chromosome) and certain types of autism. The problem seems to be in the way new connections, or synapses, are made.

Daniel Madison, PhD, associate professor of molecular and cellular physiology at Stanford University School of Medicine, and his colleagues have been looking at the connections that brain neurons make with each other. These synapses are largely responsible for the “hardwiring” of the brain, the pattern of information processing that results in memories and mental function. They looked at the brains of Fmr1 mosaic mice (so some neurons are normal and some contain the Fmr1 mutation), and discovered that affected neurons were less likely to form new synapses with other neurons.

The result is fewer connections, and fewer neurons responsible for most of the connections that are present. Therefore the entire neural network is reduced in complexity and robustness – and the result is decreased mental capability.

This type of research, in my opinion, demonstrates one fruitful new direction for neuroscience research – looking at the pattern and robustness of connections between neurons in the brain as a model for both healthy brain function and brain disorders. I have written before about the fact that brain function is not only dependent upon the health of the cells that make up the brain, but on the functional neuronal connections that are made.

Research into patterns of neuronal connections has been going on for years, but really seems to be coming into its own and even taking off. As technology is making such research more feasible researchers are using the new tools to ask the countless questions that have been there in neuroscience but have just been waiting for the technology to address. I think we will see more exciting discoveries like those coming from Dr. Madison’s lab.

Also, this type of research may lead to a closer merger of the fields of psychiatry and neurology. As we learn more about how the connections in the brain manifest as thoughts, mood, and behavior, traditionally psychiatric disorders, like schizophrenia, major depression, and ADHD, will be understood and treated more as neurological disorders. (This is not to minimize the role of psychology and therapy in dealing with some of the symptoms of such disorders.)

These advances will also make the “mental illness denial” position (including scientologists, followers of Thomas Szasz, and others) more difficult to maintain. Right now deniers rely heavily upon the argument that we cannot see anything wrong with the brains of those who have such disorders – therefore they must be healthy. I and other critics of this position have argued that we do not expect to see the kinds of pathology the deniers are talking about. As I said above, the brain cells can look healthy. But brain function is more subtle, and now our technology has a resolution and subtlety equal to investigating brain function at a level that can see these disorders.

Another strategy of those who, for some reason, do not like the concept that any aspect of mental function should be viewed within the “medical model,” is to deny that they are disorders at all, regardless of what is going on inside the brain. The term “neurotypical” has become vogue within some autism circles to refer to people who do not have autism spectrum disorder (ASD). The implication is that those with autism are just in the minority, they are different than those who are more “typical.” The term is deliberately sterilized of any implication that having ASD is unhealthy, or a disorder, or represents a brain dysfunction.

Although I have no problem with using terminology that respects the emotional sensitivity of people with such disorders and their families, I strongly disagree with changing our conceptual models to avoid implications that some are ideologically opposed to. If your heart cannot pump enough blood to keep your organs working then you don’t just have atypical heart function, you have a cardiac dysfunction. If your neurons contain a gene mutation that causes them to make far fewer connections than neurons without the mutation, resulting in decreased mental capability, then the mutation represents a brain disorder and a genetic disease.