Structural and functional analyses of the occipital cortex in visual impaired patients with visual loss before 14 years old.

Abstract

Single photon emission tomography (SPECT) perfusion images of the brain of individuals with complete visual loss before the age of 14 were carried out and compared to those of visually normal subjects, in order to assess hypothetical differences in brain structural and metabolism between the two groups. Study group was comprised by 2 females and 3 males, aged 30 +/- 10 years. Controls were composed by 6 females and 5 males aged 41.5 +/- 3.8 years. All individuals were submitted to physical and neurological examinations, and to MRI and to SPECT. Blind subjects presented larger perfusion measurements bilaterally in their medial temporal lobes (p=0.030, right side; p=0.01, left side), but smaller perfusion measurements in their left frontotemporal area than controls (p=0.026). Intragroup analysis of the study group disclosed asymmetric perfusion, lesser in the left temporal and parietal areas (p=0.026 and p<0.0001, respectively) compared to the right side. In the healthy controls, reduced perfusion was also noted at the left parietal areas when compared to the right side (p=0.035). The study revealed that completely blind patients that became visually impaired before the age of 14 in spite of not having MRI detectable changes in their brain's anatomy do present increases in perfusion of their left and right medial temporal lobes, and a reduction in the perfusion of the left frontotemporal area, as compared to normal controls. While the increases in blood flow may reflect compensatory mechanisms for visual deprivation, the significance of the diminished perfusion in the left frontotemporal area remains elusive.