This 2014 UK/German human study involved fMRI scans of the subjects inferior temporal cortex while viewing images:

“Brain representational idiosyncrasies accessible to fMRI are expressed in an individual’s perceptual judgments.

We found evidence for an individually unique representation predictive of perceptual idiosyncrasies in hIT [human inferior temporal cortex] (but not in early visual areas) and for personally meaningful (but not for unfamiliar) objects.”

Citing other studies, the researchers said:

“The size of primary visual cortex varies across individuals by a factor of about 2.5.

Although other areas might vary by smaller factors, many parts of the brain, including cortical and subcortical structures, show gross anatomical variation across individuals that is predictive of cognitive and behavioral differences.”

The researchers asserted:

“Functional differences as reported here ultimately must arise from differences in the physical structure of each individual brain.”

However, no evidence was provided for this assertion.

The researchers acknowledged this lack of evidence, but in a way that required further evidence:

“Our study demonstrates individual differences in high-level semantic representations but cannot address their structural basis. Our current interpretation is that the representational idiosyncrasies might arise from the microstructural plasticity of cortex, which is driven by individual experience.”

---

The researchers’ assertion beyond the study’s supporting data was at best a statement of their goal. Further, their bias to focus on the inferior temporal cortex area of the cerebrum led them to not investigate other areas of the brain that may have been involved with the “personally meaningful (but not for unfamiliar) objects” finding, such as the subjects’ limbic systems.

I hope that researchers won’t think that their research is complete when they reach their goal of finding “differences in the physical structure of each individual brain.” It would be far more informative to understand the causes for these effects.

http://www.pnas.org/content/111/40/14565.full “Unique semantic space in the brain of each beholder predicts perceived similarity”