Temporal Encoding During Unimodal and Bimodal Odor Processing in the Human Brain

In daily life, people encounter a wide range of odors, most of which contain multiple chemical substances. So-called bimodal odors stimulate both the olfactory and trigeminal nerve, and the interaction between these two systems shapes the perception of the odor. However, temporal encoding of these sensory systems during bimodal odor processing has received limited scientific attention.

To investigate this, we recorded the electrophysiological response in 17 participants to relatively unimodal olfactory (strawberry), trigeminal (l-isopulegol) and strongly bimodal (strawberry and l-isopulegol) stimuli.

ERP amplitudes and intensity ratings were significantly bigger for bimodal stimulation, as compared to unimodal stimulations. No significant difference was observed between N1 and P2 response latencies to olfactory and bimodal stimuli while responses to both stimuli showed longer latencies compared to the response of the trigeminal stimulus.

Results provide further evidence of interaction between olfactory and trigeminal systems; additional activation of the olfactory system results in more vigorous electrophysiological responses and the experience of higher intensity. In addition, results indicate that the trigeminal system is faster to react to stimulation.

The current study offers a view on the temporal processing of bimodal odorants that are most likely to be encountered in the environment. We link the more vigorous electrophysiological response to a more complex odorant with activation of different neural structures.