Right Versus Left Hippocampal Activity as a Biomarker in Schizophrenia

To the Editor: In their article published in the May 2014 issue of the Journal, Jason R. Tregellas, Ph.D., et al. (1), state that their hypothesis “that patients would show greater intrinsic hippocampal activity than healthy subjects” was supported. However, their original hypothesis said nothing about the right or left hippocampus.

The impressive Figure 2, showing the difference between schizophrenia patients and control subjects, is only the data from the right hippocampus. The text states that there were no group differences in the left hippocampus, and since the N was relatively small, I would expect that a test of their original hypothesis, that hippocampal activity would be higher in schizophrenia patients, was probably not supported (i.e., a test comparing schizophrenia patients and control subjects on total hippocampal activity would not have been statistically significant).

Therefore, the comparison that they found to be significant, involving only the right hippocampus, was a post hoc comparison and not a test of their original hypothesis.