Behavioural, physiological, and anatomical consequences of monocular deprivation in the golden hamster (Mesocricetus auratus).

Abstract

The effects of long-term monocular deprivation (MD) on the visual acuity, cortical physiology and dLGN anatomy of the golden hamster were assessed in adult animals which had undergone unilateral eyelid suture at the time of natural eyelid opening. Acuity was measured in a two-alternative forced-choice task in a Y-maze, using a modified method of constant stimuli to vary the spatial frequency of a high-contrast square-wave grating which had the same mean luminance (5 cd/m2) as a uniform grey card. The acuity of the normal (non-deprived) eye of each of two early-MD hamsters was within the normal range (about 0.5 cycles per degree of visual angle), but the acuity of the deprived eyes was reduced by about 0.6 octaves at the 70%-correct criterion. A second reversal of eyelid suture and retesting through the "normal" eye demonstrated that this acuity difference was not attributable to surgical artifacts. Another hamster undergoing prolonged MD beginning in adulthood had normal acuity in both eyes, indicating a "sensitive period" in the development of the hamster's visual system. Single-unit recording from area V1 of the cortex of four early-MD hamsters revealed a shift in ocular dominance favouring the normal eye. The deprived eye's loss of excitatory influence was greater in the ipsilateral hemisphere, but even here 57% of cells were binocularly driven. Only small differences were observed in other receptive field properties. In the dLGN, cell areas in the deprived "lamina" were about 4% smaller than in the non-deprived areas after 5-7.5 months of MD, a difference which was statistically non-significant. However, this difference increased to 19.5% in one hamster in which MD lasted 17 months (p less than 0.025). The relatively small MD effect observed in the hamster is interpreted as being consistent with the absence of a sensitive "detail-analysing" mechanism in the hamster's visual system.