Just noticeable difference in olfaction: a discriminative tool between healthy elderly and patients with cognitive disorders associated with dementia.

Olfactory dysfunction appears to be one of the earliest signs of several age-related neurodegenerative disorders, including Alzheimer`s disease (AD) or Parkinson`s disease (PD). To rate performance and olfactory deficits in patients with cognitive disorders, various olfactory tasks have been used such as odor detection, discrimination, recognition memory, identification and naming but no study has been focused on just noticeable difference (JND), a sensitive tool of detection. The aim of this study was to investigate and compare variations in JNDs in healthy elderly and in patients with cognitive disorders associated with dementia. The results showed significantly higher olfactory JNDs in a population with cognitive disorders associated with dementia - i.e. a lower olfactory detection performance - compared to a control population paired in age, gender and education level. Additionally, the findings of the present study showed strong correlations between cognitive performances and JND scores in the control population contrary to the patient population. These findings are discussed in relation to the relevance of using olfactory JNDs in the diagnosis of dementias.