Artikel-Schlagworte: „Neuroimaging“

Slashdot reported on Sunday Sept 20 the outcome of a new study on the apropriateness of fMRI research which can be read in much more detail on Wired. This study can be seen as a serious warning to ‚blindly‘ believe results of fMRI research without doing proper quality management. Craig M. Bennett and colleagues realized an experiment which is quite close to a gag of ‚Monthy Python’s Flying Circus.‘ However, the experiment is serious. They scanned a mature, but dead atlantic salmon. The experimental task is worth to be mentioned in its original language:

„The salmon was shown a series of photographs depicting human individuals in social situations with a specified emotional valence. The salmon was asked to determine what emotion the individual in the photo must have been experiencing.“

Several photos of human beings were shown to the salmon and reactions were measured. Reviewing the results – surprise, surprise – they showed clear activity in the dead salmon’s brain:

„Several active voxels were discovered in a cluster located within the salmon’s brain cavity.“

bennett-salmon-figure1

The dead salmon and its emotional reactions (Photo courtesy Craig Bennett)

The dead salmon’s ‚emotional reactions‘ look quite impressive at it can be seen in the figure right next to this text. It seems the (dead) salmon reacted to photos of human beings. Unfortunately, the study was turned down by several publications. However, a poster is available. Thinking about the mass of research in the field of fMRI, it seems a little bit confusing what we can believe and what not. What is needed is a good control of random but significant voxels. Additionally, we should not take brain research too serious. But false positives should be taken very seriously. At last, I want to point also to an older posting on this blog about the works of Ed Vul and his colleagues at the MIT. Further infos dedicated to fMRI and the dead salmon are available on Craig Bennett’s personal blog.

References:

Bennett CM, Baird AA, Miller MB, and Wolford GL. (submitted) Neural Correlates of Interspecies Perspective Taking in the Post-Mortem Atlantic Salmon: An Argument For Multiple Comparisons Correction.

This is the ‚first‘ blog and I knew at once what it should be about: The new findings that heavily criticize the general findings of neuroimaging studies. A summary in German can be found in one of the lastes issues of ‚Gehirn und Geist‘ (04-09, p.69) by Prof. Fritz Strack. Let’s look what is problematic besides the fact that neuroimaging studies do permanently perform a false logical conclusion, because they attribute characteristics of ‚whole‘ human beings solely to their brains and neglect the rest of the body (and the mind)??

Telepolis published a short summary of the research of Edward Vul, a PhD student at the MIT in cambridge (USA) on ‚voodoo correlations‘ and ’non-independence error.‘  In a first article he and colleagues write about artifical exaggerated correlations between voxels and external variables. These correlations are sometimes higher than the reliabilities 😉 which is far from being realistic! This was found not only in one, but in many studies that were re-analyzed … and not to mention all those articles that were published in high rated journals (but not re-analyzed). Additionally, in another article Edward Vul and colleagues concentrate on the selection of the analyzed brain areas (voxels). These were not independent from the behavior measurements that were done at the very same time. This means that from thousands of voxels those were selected for further analyses that showed a maximum correlation with the external behaviour measurements. Of course all further statistical relationships were high – but are they real or a methodological artefact? – that’s another story to be told.

Another article from Sirotin & Das (Nature 457) questions one of the most basic assumptions of neuroimaging studies: the covariation of local brain activity and blood flow. In an experimental study with animals the authors compared the neuronal firing of cells (direct measurement of cell firing) with the intensity of the blood flow. The results showed that both parameters did not correlate continuously with each other.

So what now? At first we should congratulate the cited researchers for their courage and the journals also for their courage to publish these important findings. What is needed in neurobiology and neuroimaging studies is a methodological discussion. Results should not or even must not be discussed without giving importance to methodological questions. Other disciplines like psychology or sociology have regular discussions of this kind (although sometimes the discipline does not considers change, e.g. ask a German psychologist why nobody does  Bayesian statistics?). I don’t like the last sentence of so many articles like ‚further research is needed,‘ but this time I think – yes – these findings have to be understood properly and the experiments that led to their results have to be repeated.

References:

Sirotin, B. Y. & Das, A. (2009). Anticipatory Haemodynamic Signals in Sensory Cortex not Predicted by Local Neuronal Activity. Nature 457, 475–479.

Vul, E., Harris, C., Winkielman, P. & Pashler, H. (in press/ 2009). Voodoo correlations in social neuroscience. Perspectives on Psychological Science.

Vul, E. & Kanwisher, N. (in press/ 2009). Begging the question: The non-independence error in fMRI data analysis. To appear in Hanson, S. & Bunzl, M. (Eds.). Foundations and Philosophy for Neuroimaging.