A new fMRI data analysis method using cross validation: Negative BOLD responses may be the deactivations of interneurons
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Although functional magnetic resonance imaging (fMRI) is widely used for the study of brain functions, the blood oxygenation level dependent (BOLD) effect is incompletely understood. Particularly, negative BOLD responses(NBRs) is controversial. This paper presents a new fMRI data analysis method, which is more accurate than the typical conventional method. The authors conducted the experiments of simple repetition, and analyzed the data by the new method. The results strongly suggest that the deactivations(NBRs) detected by the new method are the deactivations of interneurons, because the deactivation ratios obtained by the new method approximately equals the deactivation ratios of interneurons obtained by the study of interneurons. The (de)activations detected by the new method are largely different from those detected by the conventional method. The new method is more accurate than the conventional method, and therefore the (de)activations detected by the new method may be correct and the (de)activations detected by the conventional method may be incorrect. A large portion of the deactivations of inhibitory interneurons is also considered to be activations. Therefore, the right-tailed t-test, which is usually performed in the conventional method, does not detect the whole activation, because the right-tailed t-test only detects the activations of excitatory neurons, and neglect the deactivations of inhibitory interneurons. A lot of fMRI studies so far by the conventional method should be re-examined by the new method, and many results obtained so far will be modified.
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