( phemes compared to normal control subj...)New insight into people who 'see' colors in letters and numbers

In fMRI scans, the researchers found that the synesthetes showed greater activation in a color-perception region of the cortex when viewing graphemes, compared to normal control subjects. The researchers found that the strength of this activation influences the strength of the synesthetic colors. In fMRI, harmless radio waves and magnetic fields are used to map regions of higher blood flow in the brain, which reflects higher activity in those regions.

Importantly, the researchers found evidence suggesting that synesthetes may be quite different from one another, which the researchers said "has profound implications for the studies of synesthesia that group together data from multiple synesthetes and treat them as if they all come from a homogeneous population.

"The use of single case studies in synesthesia is also of concern because the results obtained with one synesthete may not generalize to other synesthetes.

The researchers concluded that "Our results suggest that synesthetic colors lead to improved behavioral performance in a manner similar to real colors. Because this study uses both psychophysical and neuroimaging measures in the same subjects in the study of synesthesia, we are able to examine specific aspects of the synesthetic experience that previous studies have not been able to address."

Edward M. Hubbard, A. Cyrus Arman, Vilayanur S. Ramachandran, and Geoffrey M. Boynton: "Individual Differences among Grapheme-Color Synesthetes: Brain-Behavior Correlations"