In medical practice, doctors often reach a diagnosis of a disease within minutes of coming into contact with a patient, and sometimes before the patient has even reported their symptoms. When, for example, a doctor encounters a patient with jaundice (yellowish staining of the skin and the whites of the eyes), a diagnosis related to liver disease or dysfunction comes to mind immediately and automatically.

Diagnosing disease is a specialized type of problem-solving, which is believed to require little or no analytical reasoning. Instead, it is likely based on the rapid retrieval of similar cases from memory and, as such, has been likened to pattern recognition. A new study now provides evidence that medical diagnoses involve the same brain systems that are required for recognizing and naming everyday objects.



Marcio Melo of the University of São Paulo and his colleagues, working in collaboration with Karl Friston and Cathy Price of the Wellcome Trust Centre for Neuroimaging in London, recruited 25 Brazilian radiologists and scanned their brains while they viewed a series of 60 different chest X-rays. 20 of the images contained clearly identifiable and easily diagnosable symptoms of diseases, such as pneumonia, and 20 others had pictures of an animal embedded in the X-ray. The remaining images had a letter embedded in them, and served as controls.

Previous work has shown that radiologists scan X-rays in detail and identify then fixate upon an abnormality within about one second of first seeing the image. They do so by switching from a "search-to-find" strategy to one in which the global properties of the image are assessed. This second strategy is thought to be similar to the process by which face recognition occurs, and improves with experience: the more experienced a radiologist is, the less time they spend scanning an image, and this may contribute to their expertise.

This latest set of experiments were designed in such a way as to prevent the participants from scanning the X-rays in detail, as this would likely have affected the results. The animals and letters were embedded within X-ray images so that all the target stimuli were presented in the same context. Each image was presented for 3.5 seconds, during which the participants were required to locate the target, recognize and then name it.

Brain activation patterns while radiologists diagnose disease from X-rays are very similar to those observed during naming animals and letters. From Melo, M. et al (2011).

Confirming the earlier work, the results showed that the participants could identify abnormalities in the X-rays to reach an accurate diagnosis very rapidly. On average, they did so just 1.3 seconds after first seeing the images, suggesting that the process does indeed occur automatically.

Crucially, all three types of trial produced the same activation pattern in a distributed set of brain regions, albeit at different levels (above). Diagnosing disease produced a higher level of activation than naming animals, which in turn produced a higher level of activation than naming letters. Activation of the prefrontal cortex was highest during the diagnostic trials, which involve more associations between words and meaning, whereas the visual cortex was more active during trials involving naming animals.

This suggests that the brain mechanisms underlying physicians' prompt recognition of abnormalities on an X-ray are very similar to those underlying the naming of everyday objects. The greater activation of prefrontal cortical areas shows that recognizing disease symptoms is more taxing than naming objects, however, and this is probably because making a diagnosis involves selecting from a larger number of appropriate names than does naming an animal.

The researchers note that the X-rays used in the study all showed relatively common abnormalities with which most radiologists are familiar, and that their hypothesis should be tested further in other medical specialities that are based largely on visual clinical symptoms, such as dermatology. Diagnoses that are less dependent upon visual signs may well employ different mechanisms.

Nevertheless, they suggest that their findings could have implications for medical education. In recent years there has been increased interest in how neuroscience might inform the learning process, and the knowledge that visual recognition plays a role in at least some diagnoses could help medical students better learn how to diagnose certain diseases more accurately.

Reference: Melo, M., et al. (2011). How Doctors Generate Diagnostic Hypotheses: A Study of Radiological Diagnosis with Functional Magnetic Resonance Imaging. PLoS ONE 6 (12): e28752. doi: 10.1371/journal.pone.0028752