Showing posts from February, 2010

Why Johnny can’t read (but Jane can)

Reading is not a skill that comes naturally.   Unlike learning spoken language, which the human brain has evolved to absorb almost effortlessly, learning to read is a protracted and difficult process.   It involves the categorical association of arbitrary visual symbols with phonemes and also the ability to break words down into component phonemes.   It thus relies on an integration between visual and auditory processes, combining spatial and temporal information, within a learned linguistic context. The fact that reading is such a specialized and integrative skill may partly explain why it can be selectively impaired in people of otherwise normal intellectual abilities. Dyslexia, as this type of selective reading difficulty is called, is quite common, affecting anywhere from 5% to 20% of children, depending on the criteria used in its diagnosis.   Cohort studies which directly tested all individuals have found that dyslexia is about twice as common in boys as in girls.   This is n

Psst!… Pass it on! Cortical communication via the thalamus

Many neuroscientists think of the thalamus – a compact structure lying right in the centre of the brain – simply as a relay station, where sensory information from the periphery converges and is then passed on to the cortex.   The cortex is thought to be the site of perception and cognition, with different cortical areas specialized to subserve different functions.   Communication between cortical areas can be mediated by axonal tracts running in the white matter of the cortex.   This leads readily to the view that once information reaches the cortex it is processed and integrated with other information about the external world and internal states entirely within the cortex, resulting in conscious perception or some kind of motor (or emotional) output.   In most neuroimaging studies, for example, the focus is solely on activity in the cortex and the thalamus (and other lower brain areas) are explicitly ignored. A new study by S. Murray Sherman and colleagues demonstrates unequivocall

Noisy genes and the limits of genetic determinism

Why are genetically identical monozygotic twins not phenotypically identical?   They are obviously much more similar than people who do not share all their DNA, but even in outward physical appearance are not really identical.   And when it comes to psychological traits or psychiatric disorders, they can be quite divergent (concordance between monozygotic twins for schizophrenia for example is only around 50%).   What is the source of this phenotypic variance?   Why are the effects of a mutation often variable, even across genetically identical organisms? “Nurture” has been the answer proffered by many, but there is good evidence that environmental or experience-dependent effects can not explain all the extra phenotypic variance and in most cases contribute very little to it.   (See post on “Nature, nurture and noise” on June 24 th , 2009 for more on this: An alternative source of variation is intrinsic to the

What’s in a name? Genetic overlap between major psychiatric disorders

The criteria used to assign patients to specific psychiatric disease categories are set out in the Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association.   (There is also a World Health Organisation equivalent, the International Classification of Disease).   Every so often, these criteria are revised to reflect new research and changing concepts of disease.   The APA has just released a draft of preliminary revisions to the current diagnostic criteria (available at ) as part of the preparations for the fifth release ( DSM-5 ), due out in 2013.   The specific diagnosis given to any patient who shows up with a spectrum of symptoms has major implications not only for their clinical treatment but also for insurance, education, employment and many other aspects of their lives.   Given the authority and influence of this tome for clinical practice as well as research purposes, it is timely to consider how genetics

Bad to the bone; altered connections in the brains of psychopaths

The manipulative con-man.   The guy who lies to your face, even when he doesn’t have to.   The child who tortures animals.   The cold-blooded killer.    Psychopaths are characterised by an absence of empathy and poor impulse control, with a total lack of conscience.   About 1% of the total population can be defined as psychopaths, according to a detailed psychological profile checklist.   They tend to be egocentric, callous, manipulative, deceptive, superficial, irresponsible and parasitic, even predatory.   The majority of psychopaths are not violent and many do very well in jobs where their personality traits are advantageous and their social tendencies tolerated.   However, some have a predisposition to calculated, “instrumental” violence; violence that is cold-blooded, planned and goal-directed.   Psychopaths are vastly over-represented among criminals; it is estimated they make up about 20% of the inmates of most prisons.   They commit over half of all violent crimes and are 3-4 t

Instant Neurons

A new study from Marius Wernig and colleagues at Stanford University  has succeeded in transforming fibroblast cells directly into neurons. In the end, it was far simpler than expected. The identities of different cell types are known to be established during development by particular combinations of transcription factors, which, by controlling the expression of large numbers of target genes, define the genetic and biochemical profile of each cell type. It was thought that this profile of gene expression was then locked into place by chromatin proteins which bind to DNA and fix it into an active or inactive conformation. Over development, the passage from an early embryonic cell, with full potential to generate any cell type, to more differentiated cells, was believed to be unidirectional and irreversible. The ability to clone an animal, by transferring the nucleus of a differentiated cell into a fertilised, enucleated oocyte, showed that, in fact, the profile of gene expression co