Hippocampus and homing in pigeons: left and right hemispheric differences in navigational map learning.

One-month-old, inexperienced homing pigeons, prior to any opportunity to learn a navigational map, were subjected to either right or left unilateral ablation of the hippocampal formation (HF). These pigeons were then held together with a group of age-matched control birds in an outdoor aviary, where they were kept for about 3 months with the opportunity to learn a navigational map. When subsequently tested for navigational map learning at about 4 months of age posthatching, control and right HF-ablated pigeons were equally good at orienting homeward from distant, unfamiliar locations, indicating successful navigational map learning. By contrast, left HF-ablated pigeons were impaired in orienting homeward, indicating a failure to learn a navigational map. Interestingly, both right and left HF-ablated pigeons displayed impaired homing performance relative to controls. These results suggest that different aspects of homing pigeon navigation may be lateralized to different hemispheres, and in particular, the HF of the different hemispheres. The left HF appears critical for navigational map learning, i.e. determining an approximate direction home from distant, unfamiliar locations. The right HF, and possibly the left HF as well, appear to play an important role in local navigation near the loft, which is likely based on familiar landmarks.