Positron Emission Tomography (PET) was once among the most powerful techniques available for researching human brain activity. By injecting a volunteer with a radioactive tracer, such as a glucose derivative, and monitoring the radiation emitted from the brain over the next few hours, neuroscientists could see where in the brain most glucose was being absorbed - and where neural activity was happening. But in recent years, the influence of PET in neuroscience research has fallen dramatically, as shown in a new paper by Neuroimage assistant editor Paul Cumming: PET Neuroimaging: The White Elephant Packs His Trunk? Here's the numbers of research papers published per year (note the exponential scale.)
PET studies of the brain have been declining since about 1985, despite the fact that research about the brain in general has grown. It seems it was fMRI scanning that killed PET. Cheaper, safer (no radiation), and more versatile, the growth of fMRI has been rapid and constant since 1990 in proportional terms. Still, fMRI isn't everything. While PET's role as a measure of brain activity is over, it remains the only method that can probe certain aspects of brain chemistry. Anyway. I'm very fond of these kinds of bibliometric graphs. Some that I've done previously include the rise of the mouse as a laboratory animal, the fall of Freud (and psychoanalysis) and which brain regions are most researched right now.
Cumming P (2013). PET Neuroimaging: The White Elephant Packs His Trunk? NeuroImage PMID: 23959198