How well does it actually work to surgically reroute the optical nerve?

Question

Two publications, Roe et al, 1992^[1] and Metin & Frost, 1989^[2], describe results pertaining to the ability of a region of cortex to process information from a different sensory mode than the one that it normally does.

Specifically, they describe studies in which:

1. input from the retinas of newborn rodents was rerouted, by surgical methods, to parts of the cortex other than the visual;
2. the rodents were allowed to mature;
3. the responses of cortical cells in the new target region to visual stimuli were assess.

Now it's 20 years later, so I'm sure there have been many others.

Something of which these publications seem to make no mention is the behavior that developed in the test subjects. For example, did they appear to be completely blind from a behavioral standpoint?

Is anyone aware of any publication, relating to these studies or other, similar experiments, which addresses this question?

1. Roe AW, Pallas SL, Kwon YH, Sur M. 1992. Visual projections routed to the auditory pathway in ferrets: receptive fields of visual neurons in primary auditory cortex. Journal of Neuroscience, 12(9): 3651-64.
2. Métin C, Frost DO. 1989. Visual responses of neurons in somatosensory cortex of hamsters with experimentally induced retinal projections to somatosensory thalamus. Proceedings of the National Academy of Sciences USA, 86(1): 357-361.

Answer 1

At least two follow-up studies have investigated the behavioral consequences of the re-routing of the optic nerve to the auditory cortex. In these animals the visual cortices were ablated, and the optic nerve re-routed by combined lesions of the superior colliculus and ascending auditory pathways to the thalamus. These lesions induce retinal axons to form permanent ectopic (i.e., re-routed) projections to the auditory thalamus and cortex. These ectopic visual projections result in the formation of retinotopic maps in the auditory cortex and in visually responsive neurons with receptive field properties reminiscent of cells in the visual cortex.

These re-wired ferrets and hamsters were shown to have functional vision, as shown by their ability to tell light from dark and to recognize simple visual patterns. Visual pattern recognition was absent in control animals that were blinded, but not re-wired. Visual function, as measured by grating visual acuity in re-wired hamsters and rats, was however not as good as in control animals with normal vision (Frost et al., 2000; Melchner et al., 2000).

<sub>References
- Frost et al., PNAS (2000); 97(20): 11068–73
- Melchner et al., Nature (2000); 404: 971-6</sub>