Saturday, September 12, 2009

Reductionism...the hate word

Now that neurobiology has started to explore the neural correlates of subjective mental states such empathy, love, desire, beauty, reward and much else besides, the hate word “reductionism” is being used to stigmatize and call into question the efforts of neurobiologists in this direction. Our detractors insist on the “holism” of subjective experiences, and some at least seem desperate to find a source other than the brain for these experiences.

Clearly, this kind of research touches a raw nerve among them. Their motives are probably varied, but these motives do not interest me much. What is interesting to consider is the extent to which an unquestioning adherence to holism can impede research and a better understanding of how the brain functions. The visual brain provides an excellent example.

Salomon Henschen (Sweden) was the first to chart the location and extent of the primary visual receiving centre in the brain, followed by Tatsuji Inouye (Japan) and Gordon Holmes (England) who charted it in greater detail, the former in the aftermath of the Russo-Japanese War and the latter in the aftermath of the First World War. Both Henschen and Holmes believed that the primary visual centre (now commonly referred to as V1) in the brain was the only brain area for vision and that vision, being experienced in a wholesome way, was a unitary, wholesome, process. In the service of this doctrine, they and many others dismissed, often contemptuously, evidence that may suggest that, however wholesome our experience may be, the brain processes that lead to these experiences are in fact fractionated. Indeed, Gordon Holmes was even blind to his own evidence, which showed (in one patient) that the faculty to perceive visual motion may be selectively spared (I have reviewed this evidence in detail in my book, now sadly out of print, A Vision of the Brain). Indeed, so forceful was their dismissal that the clinical evidence which may have supported another view simply vanished from the literature. One would find it very hard to find any reference to it in the papers on the visual brain published between 1918 and 1970.

But one of the striking discoveries about vision since 1970 has been that there are many visual areas, each with its own distinctive connections and specialization, of which the areas specialized for visual motion and colour are perhaps the best studied to date. Even perceptually, in very brief time frames, vision is not the wholesome process that many thought it to be. For it turns out that we see colour before we see motion by about 100 ms, an enormously long time in neural terms.

This does not mean that vision is a not a wholesome experience but only that the process leading to that experience are widely distributed in separate areas of the brain. The challenge for neurobiology now is to understand how, in the longer term, that is to say for periods exceeding 100 ms, the brain integrates the results of activities in its separate parts to give us our wholesome experience.

Had we insisted on a holistic approach (as indeed was done for a long time), we would never have undertaken the research that revealed the brain processes that are instrumental in giving us our wholesome visual experience. To stigmatize this research as “reductionist” is silly. The research is simply a step in understanding better the brain process that lead to holistic experiences.

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