Visual discrimination learning in the water maze: a novel test for visual acuity

Learning about space, the environment and specific objects comprising three -dimensional arrangements requires processing of visual information. As lea rning and memory experiments in mammals rely heavily on normal processing o f visual cues, drug-induced disruption of acquisition learning or memory fo rmation necessitates the important control for visual acuity. A popular tas k used frequently for rats is the Morris water maze. However, previously us ed visual tasks in the water maze only control for gross visual disturbance s. Here we describe a new training procedure enabling visual acuity to be t ested in the water maze. Animals were trained to discriminate between two c ue cards containing a pattern of vertical black and white stripes. Cards we re presented in two adjacent quadrants separated by a barrier with the esca pe platform located in front of the smaller stripes (1 cm wide). Once 80% c orrect responses were attained, the wider cue card (normally 5 cm wide stri pes) was randomly changed to gratings of 1,2, 3, 4, 5, and 10 em width. Ani mals learned the discrimination with acuity of 1.5 c/deg. A detailed analys is of the swim patterns further suggests that, independent of the grating u sed, animals make a choice immediately after release and swim along the wal ls towards the cue. In a further acuity test taken a few weeks later when a nimals were given saline infusions, performance was better than in the firs t test suggesting an effect of learning. This novel test may prove useful i n determining subtle drug-induced deficits in visual acuity that may contri bute to disruption of spatial performance in the water maze. (C) 2001 Elsev ier Science B.V. All rights reserved.