Attention-dependent neural oscillations in the human olfactory system

he overall goal of the proposed research is to characterize the temporal evolution and frequency composition of olfactory attentional neural correlates in the human brain. Because olfactory processing is naturally bound by the respiratory rhythm (odors can only be encountered by inhaling through the nose), we began by characterizing rhythmic, respiratory-linked oscillations in the olfactory cortex during the K99 phase of this award. We found that slow respiratory oscillations were present in olfactory cortex, and that these slow respiratory oscillations entrained higher frequency spectral changes in other limbic brain regions. During the R00 phase, we will expand upon these findings, further characterizing limbic respiratory entrained spectral enhancement, and also continue to better characterize olfactory predictive coding mechanisms. Because olfactory brain structures are located deep within the limbic temporal portions of the brain, the electrical signals generated from these regions are severely attenuated at the scalp, limiting the value of surface EEG in measuring olfactory local field potentials. To overcome this problem, we have optimized an olfactory (ECoG) paradigm in which electrical signals are recorded directly from olfactory brain structures in patients who are undergoing brain surgery for intractable epilepsy. Using this technique, the precise timing and frequency of olfactory attentional oscillations will be investigated. Given the lack of a requisite pre-cortical thalamic relay in the olfactory system, the proposed research will test the hypothesis that olfactory respiratory oscillations spread to non-olfactory brain regions, affecting attentional mechanisms and cognition as well. The proposed research will use ECoG approaches to test two specific hypotheses regarding complex forms of olfactory attention. First, experiments are proposed to determine the spatiotemporal composition of neural oscillatory responses in relation to respiration and modality-specific olfactory attentional mechanisms. Second, experiments are proposed to determine the neural origins of olfactory predictive coding mechanisms. Further studies will make use of electrical stimulation techniques to establish the necessity of identified brain regions in the formation of predictive spectro-temporal odor templates.