Showing posts from March, 2010

Synesthesia: crossed wires or free association?

For millennia, philosophers have mused over the nature of perception, how closely it mirrors “reality” and whether different people might, quite without knowing it, subjectively perceive the world in very different ways.   We might agree that an apple is “red”, but is the quality of your experience of its redness the same as mine?   This has seemed an almost impossible nut to crack, but the fascinating condition of synesthesia provides a stark example where the quality of subjective experience is very definitively and demonstrably different.   This may be due to genetic variants which affect the functional segregation of specialized circuits in the brain which makes synesthesia even more interesting.     The following is a book review I recently wrote for the American Journal of Human Biology, of: Wednesday is Indigo Blue: Discovering the Brain of Synesthesia . By Richard E. Cytowic and David Eagleman. X + 309 pp. Cambridge, MA: MIT Press. 2009.  For people with synesthesia, parti

Intelligence a matter of the right connections


LRR proteins help neurons find a partner

Matching 100 billion neurons with their appropriate partners is a daunting task, especially when each neuron can make synaptic contact with about 1,000 other cells. Nevertheless, the developing brain accomplishes this feat with remarkable specificity – neurons from each area of the brain send out axons which follow a stereotyped pathway to find their appropriate targets, guided by signpost proteins along the way. Once in the right general area they have to select specific cell types with which to form a synapse, often limited to a certain layer or sub-region. Many cells will even form synapses specifically with distinct subcellular compartments of their target cells – on distal or proximal parts of the dendrites or directly on to the cell body, for example. Specifying this level of connectivity, with the numerical complexity of the mammalian brain, obviously requires a large number of labels that can be used to match synaptic partners (even allowing for some level of combinator

Wired for Music

Music has a bizarre power to engage and affect us – to move us emotionally or literally, whether it’s foot-tapping, finger-drumming or booty-shaking.   It seems to have properties that make it automatically and powerfully salient for human beings.   An obvious question is whether this reflects some innate properties of the human brain or whether it emerges over time due to experience with types of music.   Put another way, does the brain shape the music or the other way around?   Does music show particular structures because those are inherently salient and pleasant to humans or is this reaction caused by the brain’s tendency to specialise in processing stimuli that occur with some statistical regularity in its environment?   A new study by Perani and colleagues demonstrates very convincingly that the human newborn brain already shows strong functional specialisation for music processing.   By performing functional magnetic resonance imaging on newborns, all under 3 days old, they fo

Is Mental Illness Good For You?

Mental illness is surprisingly common.   About 10% of the population is affected by it at any one time and up to 25% suffer some kind of mental illness over their lifetime.   This has led some people (many people in fact) to surmise that it must exist for a reason – in particular that it must be associated with some kind of evolutionary advantage.   Indeed, this is a popular and persistent idea both in scientific circles and in the general public.   (See the recent article “ Depression’s Upside ” from the New York Times Magazine, for example). Such theories come in two main varieties – the first, that mental illness confers some specific advantage to those afflicted; and second, that the mutations which cause mental illness in one person’s genetic background may confer an advantage when they are in a different genetic background (balancing selection).   Both of these suffer from some misconceptions about how evolution by natural selection works.   The intuitive appeal of the “surv