Sniffing behaviour, or recognizing a lily by smell, but not recognizing a sock on sight.

We report a 65-year-old man with a post-anoxic encephalopathy who showed compulsive sniffing at available objects. This stereotyped environment-driven behaviour has not been previously described. Other compulsive environment-driven responses, such as manipulation and utilization of tools and hyperlexia, were also present. The disorder shared several features with the Klüver-Bucy syndrome where mouthing of objects, rather than smelling them, is common. The patient had a severe dementia, with amnesia, anomia, apraxia, and visual agnosia. Whereas he could not recognize very familiar objects on sight, he could in contrast correctly identify several familiar odours. Although sniffing was a compulsive and purposeless environment-driven behaviour, the question may be asked whether a relatively preserved olfactory recognition, in the presence of a severe disorder of visual recognition and knowledge, could have favoured a stereotyped exploration of objects by smelling.