A History of Human Brain Mapping

The reviewed article is ‘A Brief History of Human Brain Mapping’ by Marcus Raichle. Raichle sets out to provide a brief overview of the field of human brain mapping in this review article.

Raichle emphasises that the build up to functional brain imaging has been achieved over the last century rather than the past few decades. He also notes that evidence for the relationship between blood flow and brain function was noted as far back as the nineteenth century. This relationship was forgotten and rediscovered several times subsequently. Raichle then discusses the re-emergence of evidence that increases in blood flow to an area were not related to an increase in oxygen consumption and how this finding challenged convention. He covers the advent of the CT scan in the Atkinson Morley and then the development of the PET scan.

The discussion of Magnetic Resonance Imaging (MRI) is particularly interesting as it covers the early research in Nuclear Magnetic Resonance.  Raichle discusses how this was used to examine the chemistry, blood flow and metabolism and then looks at functional MRI and the effects that blood oxygenation had on contrast (Blood Oxygenation Level Dependent Contrast or BOLD). Raichle goes onto to give a fascinating account of how stereotaxy has played a prominent role in brain mapping using different approaches and how there has been a more recent development of probabilistic brain mapping. The apparent success of averaging across subjects and producing recognisable images in the process is discussed. In light of recent papers in neuroimaging, Raichle’s discussion of how statistical analysis of the complex image data developed is particularly interesting and he notes the contemporary use of a wide range of approaches. Raichle then identifies the importance of the cognitive psychologists and their use of information theory in advancing the methodology used in fMRI studies where phenomenon could be distinguished in time in contrast with PET scans where activity is averaged over a longer period of time.

Raichle comments on the complexity of the research that is now taking place incorporating as it does cellular information, genetics, modelling, neurophysiology and clinical pathology, cautioning the reader thus

‘..it is tempting to retreat into the narrow confines of one’s own area of expertise; a pathway, however that will ultimately limit the potential of one’s work’

Finally Raichle tells us that evoked responses account for only about 1% of the brain’s use of energy and that aerobic glycolysis should be focused on in more detail in interpreting imaging findings. Raichles relative short review article contains lots of useful information and he references a number of further articles for the reader to pursue. Placing current events in a historical context can be useful in anticipating future trends as well as reflecting on contemporary practice.

References

Raichle M. A Brief History of Human Brain Mapping. Trends in Neurosciences. Vol 32. No 2. p118-126.

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