Two studies to date have looked at the effects of an additional X chromosome on brain activity in males. In addition to the structural imaging study described earlier, Itti et al. had used single photon emission computed tomography (SPECT) imaging to measure regional cerebral blood flow (rCBF) in nine self-selected adult right-handed 47,XXY males (average age 27.8 ± 6.6) and nine controls matched on age and handedness [Itti et al., 2003]. Cognitive performance was significantly lower in the 47,XXY males than controls, particularly in the verbal domain. The 47,XXY subjects did not show the expected leftward perfusion asymmetries demonstrated in the control subjects, with the exceptions of the a few regions (precentral gyrus, transverse temporal gyrus, and cerebellum). Instead, significant rCBF increase was observed in the 47,XXY subjects in the right hemisphere regions including the prefrontal motor area, parietal associative regions, and temporal language areas. Subcortical areas such as the hippocampi and cerebellum had decreased rCBF. There appeared to be some association between increased right-sided flow and cognitive scores, for example, the increase in rCBF in several right-sided temporal gyri was associated with lower verbal scores, as was lower CBF in the left hippocampus.
