Data from: Inferring pathobiology from structural MRI in schizophrenia and bipolar disorder: modeling head motion and neuroanatomical specificity

Despite over 400 peer-reviewed structural MRI publications documenting
neuroanatomic abnormalities in bipolar disorder and schizophrenia, the
confounding effects of head motion and the regional specificity of these
defects are unclear. Using a large cohort of individuals scanned on the
same research dedicated MRI with broadly similar protocols, we observe
reduced cortical thickness indices in both illnesses, though less
pronounced in bipolar disorder. While schizophrenia (n = 226) was
associated with wide-spread surface area reductions, bipolar disorder
(n = 227) and healthy comparison subjects (n = 370) did not differ. We
replicate earlier reports that head motion (estimated from time-series
data) influences surface area and cortical thickness measurements and
demonstrate that motion influences a portion, but not all, of the observed
between-group structural differences. Although the effect sizes for these
differences were small to medium, when global indices were covaried during
vertex-level analyses, between-group effects became nonsignificant. This
analysis raises doubts about the regional specificity of structural brain
changes, possible in contrast to functional changes, in affective and
psychotic illnesses as measured with current imaging technology. Given
that both schizophrenia and bipolar disorder showed cortical thickness
reductions, but only schizophrenia showed surface area changes, and
assuming these measures are influenced by at least partially unique sets
of biological factors, then our results could indicate some degree of
specificity between bipolar disorder and schizophrenia.