Recovery of vision in fish after optic nerve crush: a behavioral and electrophysiological study.

Recovery of the visual field was studied during regeneration of the retinotectal projection in bluegill sunfish (Lepomis macrochirus) using a behavioral perimetry technique. Fish were trained to orient ballistically to brief light flashes along the horizontal meridian. After crushing the right optic nerve intraorbitally, orienting to stimuli in the right visual field in different fish reappeared between 32 and 56 days postcrush. On average, recovery of the field center (30 to 150 degrees) occurred in 3 days, the most temporal 30 degrees requiring a further 7 days. Orientation accuracy, measured by the mean absolute error angle, returned to normal 10 to 15 days from the start of recovery. Perimetry was terminated at different times to 152 days postcrush, and the retinotectal projection was mapped electrophysiologically using an automated procedure to characterize multiunit receptive fields (MURFs). At early stages of visual recovery, MURFs associated with strong multiunit discharges were found in the same field regions responsive in behavioral perimetry. The 10- to 15-day recovery of normal orienting accuracy was associated with an increase in the amplitude of multiunit activity, attaining a plateau of 75% of normal. There was also evidence of a long-term decline in MURF area. Early maps showed a roughly normal visutopic order, although abnormalities in MURF size and shape persisted to as much as 152 days postcrush.