P 379. Objective Assessment of Central Nervous Odor Processing in Infancy

Background: The sense of smell is of elementary importance for infants. Various studies have shown that infants already have a fully developed sense of smell at birth. Infants can perceive and distinguish odors. Among other things, they can distinguish the smell of their own mother from others. Up to now, the investigation of the sense of smell in infants was mainly based on observation of behavior, grimacing, and autonomous reactions. The interpretation of stimulus responses to olfactory stimulation was therefore subjective to a certain extent. Olfactory evoked potentials and changes in EEG power can be used to objectively investigate olfactory function and central nervous odor processing. These methods have not been used systematically in infancy.

Aim: The aim of this study was to evaluate a method for the objective assessment of central nervous olfactory processing in infancy.

Question: To investigate differences in the olfactory-induced EEG power change between food-associated and nonfood-associated odors time–frequency analysis is used.

Methods: Term-born healthy infants fed on formula or breast milk were included in the study. The odor was delivered by an olfactometer. Breast milk and formula were used as food-associated odors and farnesol was used as a nonfood-associated odor. The EEG was derived from 11 electrodes, according to the international 10 to 20 system (Fp1, Fp2, F3, Fz, F4, C3, Cz, C4, P3, Pz, P4). The EEG data were analyzed and statistically evaluated using “Letswave 6” in Matlab.

Results: Twenty-three term-born infants aged between 2 and 9 months (11 boys, 12 girls) took part in the study. All children went through the entire examination, no child had to be excluded. An EEG power change could be detected both after the presentation of farnesol and after milk odor. The power change occurred between 500 and 1,500 milliseconds after the odor presentation in a frequency band of 3 to 8 Hz. The t-test showed that the percentage power change between farnesol and milk differed significantly (farnesol 4.9 ± 14.1%; milk −6.2 ± 14.5%, t = 2.41, p = 0.025). After odor stimulation with milk, event-related desynchronization was observed in the EEG.

Conclusion: It could be shown that the central nervous processing of milk odor leads to significant event-related desynchronization. Event-related desynchronizations can be interpreted as directed attention in the current study to the smell of milk relevant to infants. The results of this study open up possibilities for further objective investigations of central nervous olfactory processing in infancy.