Retention of the original topographic polarity by the 180 degrees rotated tectal reimplant in young adult goldfish.

1. The pattern of visual projection from the retina on to the optic tectum was studied with neurophysiological mapping methods following reimplantation of the optic tectum in young adult goldfish.2. When a rectangular piece of the tectum was dissected out and then reimplanted to the same tectum in situ, the restored visual projection showed a normal retinotopic order over the area of the tectal reimplant.3. If the tectal tissue was reimplanted after rotation by 180 degrees , the visual projection from that part of the retina which innervated the 180 degrees rotated tectal reimplant was found to be organized in a completely reverse retinotopic order within the reimplanted area in contrast to the normal projection from the other part of the retina on to the intact surrounding area of the same optic tectum.4. The results indicate that a piece of reimplanted tectal tissue retains its original topographic polarity regardless of whether the tectal tissue was rotated or not.5. The retention of original topographic polarity by a small fraction of the tectal tissue suggests that the optic tectum is not a passive receiver of incoming optic fibres but an active accommodator which selects appropriate optic fibres to make proper synaptic connexions in a consistent topographic order.