What could homing pigeons tell us about navigational impairments in Alzheimer’s patients? Activational effects of odors

Abstract

Navigation by path integration has been demonstrated in species as diverse as ants, homing pigeons, and humans. In a recent study of olfactory effects on path integration in young homing pigeons, we showed that birds deprived of odors during displacement to nearby release sites were disoriented, while those exposed to natural odors, or to artificial/novel odors, were homeward oriented. These findings show that olfactory input activates non-olfactory path integration systems and, in the absence of olfactory stimulation, cues normally used by young pigeons for path integration, failed to produce homeward orientation.  Interestingly, in humans, olfactory dysfunction is frequently observed in patients in the early stages of Alzheimer’s disease. A large portion of those patients  also exhibit a specific failure of path integration ability, including  a deficit in perception of radial optic flow cues necessary for accurate heading determination (“motion blindness”). Here we suggest that loss of olfactory activation of path integrations systems could explain the navigational impairment in the early stages of Alzheimer's disease patients. Moreover, we propose that odor exposures, similar to experiments carried out with pigeons, provide a powerful non-invasive technique to determine whether deficits on olfactory activation play a significant role in this debilitating disease.

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