Functional brain imaging—the missing link?

Abstract

There is now a consistent picture of the perceptual deficit in amblyopia derived from detailed psychophysics over the last three decades. It is not complete, but it is comprehensive. Concurrently, animal models have been developed in which the behavioral deficit is quite similar to that in the human condition. Is it the correct model however? What has been missing is a noninvasive method for assessing the nature of the neural loss in humans with amblyopia that could provide the link between animals and man. That is where functional brain imaging comes in. It could potentially provide this missing link. Does it? This study by Connor and colleagues, 1 a team that includes a person with established credentials in brain imaging, is just what is needed. The authors take a measured approach, using a number of possible indices of dysfunction and set out to compare functions that we know from the psychophysics are relevant to human amblyopia, namely, different cortical regions, visual field regions, and types of amblyopia. Indices of Dysfunction The following three different indices were used: (1) magnitude of blood oxygen level dependent response; (2) relative number of voxels monocularly activated; and (3) relative number of voxels binocularly activated. The response magnitude differences between normal and amblyopic eyes were found to be modest, showing a trend for reduced responses from amblyopic activation but no overall significant effects. This is very much in line with previous studies. 2-4 It was found that significantly more voxels were activated by the fellow fixing eye, also in line with previous reports. 2,5 Finally, less voxels showed binocular activation in amblyopes. 6