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 le arn a navigational map, were subjected to either right or left unilateral a blation of the hippocampal formation (HF). These pigeons were then held tog ether 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 navigati onal map. When subsequently tested for navigational map learning at about 4 months of age posthatching, control and right HF-ablated pigeons were equa lly good at orienting homeward from distant, unfamiliar locations, indicati ng successful navigational map learning. By contrast, left HF-ablated pigeo ns were impaired in orienting homeward, indicating a failure to learn a nav igational map. Interestingly, both right and left HF-ablated pigeons displa yed impaired homing performance relative to controls. These results suggest that different aspects of homing pigeon navigation may be lateralized to d ifferent hemispheres, and in particular, the HF of the different hemisphere s. The left HF appears critical for navigational map learning, i.e. determi ning an approximate direction home from distant, unfamiliar locations. The right HF, and possibly the left HF as well, appear to play an important rol e in local navigation near the loft, which is likely based on familiar land marks.