Inhalation-modulated detection of olfactory BOLD responses in the human brain

Aino-Lotta I Alahäivälä; Divesh Thaploo; Simon Wein; Philipp Seidel; Marco Riebel; Thomas Hummel; Jens Volkmar Schwarzbach

doi:10.3389/fnimg.2023.1260893

Inhalation-modulated detection of olfactory BOLD responses in the human brain

Front Neuroimaging. 2023 Dec 1:2:1260893. doi: 10.3389/fnimg.2023.1260893. eCollection 2023.

Authors

Aino-Lotta I Alahäivälä¹, Divesh Thaploo², Simon Wein¹, Philipp Seidel¹, Marco Riebel¹, Thomas Hummel², Jens Volkmar Schwarzbach¹

Affiliations

¹ Biomedical Imaging Group, Department of Psychiatry and Psychotherapy, University of Regensburg, Regensburg, Germany.
² Interdisciplinary Center Smell and Taste, Department of Otorhinolaryngology, Technische Universität Dresden, Dresden, Germany.

Abstract

Introduction: In contrast to other sensory domains, detection of primary olfactory processes using functional magnetic resonance imaging has proven to be notably challenging with conventional block designs. This difficulty arises from significant habituation and hemodynamic responses in olfactory areas that do not appear to align with extended boxcar functions convolved with a generic hemodynamic response model. Consequently, some researchers have advocated for a transition to event-related designs, despite their known lower detection power compared to block designs.

Methods: Here, we conducted a block design experiment with 16s of continuous odorant stimulation alternating with 16s of continuous odorless air stimulation in 33 healthy participants. We compared four statistical analyses that relied either on standard block designs (SBD1-2) or on block designs that were modulated by the participants' individual breathing patterns (MBD1-2).

Results: We found that such modulated block designs were comparatively more powerful than standard block designs, despite having a substantially lower design efficiency. Using whole-brain effect size maps, we observed that the right insular and medial aspects of the left piriform cortex exhibited a preference for a breathing-modulated analysis approach.

Discussion: Research in olfaction that necessitates designs with longer-lasting blocks, such as those employed in the investigation of state-dependent processing, will benefit from the breathing-modulated analyses outlined in this study.

Keywords: block designs; breathing-modulated analysis; design efficiency; effect size maps; functional magnetic resonance imaging; habituation; olfaction.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. A-LA was supported by the Osk. Huttunen Foundation and a Doctoral Dissertation Fellowship from the University of Regensburg. JS and PS were supported by the German Research Foundation (GRK 2174: Neurobiology of Emotion Dysfunctions). TH received funding from the Volkswagenstiftung (Olfactorial Perceptronics).