Anemotaxis is the term for the ability of animals to react to airflow stimuli. Insects exhibit these characteristics in some of the most well-studied cases. Mammals’ anemotactic abilities were little understood until recently, but a new study showed that rats can perceive airflow in a conditioning paradigm.
Mystacial whiskers and rat trigeminal ganglion cells were studied for their mechanical reactions to airflow stimulation. Scientists examined the function of all facial hairs in anemotaxis rather than just the five rows of mystacial whiskers depicted in the well-known posteromedial-barrel-subfield.
Scientists chose to examine several whisker subfields because the functional properties of these subfields vary. These whiskers appear to have biomechanical adaptations for ground sensing and could give the animal information about its motion, such as speed and heading.
Due to their exposed anatomical placement, the so-called supra-orbital whiskers above the eye are of obvious relevance in wind sensing. The DeepLabCut toolset, which has recently shown advancements in automated animal tracking, was used for this research on whisker variety in wind sensing.
Scientists asked questions such as:
- Which whiskers react maximally to airflow stimuli?
- Are whisker airflow responses dependent on whisker biomechanics and substructure?
- How do mechanical whisker airflow responses relate to the cortical barrel map?
- How do whiskers contribute differentially to airflow sensitivity?
Scientists discovered that the responses of various whiskers to airflow vary significantly. The supra-orbital whiskers respond differently to low airflow stimuli in particular, and these responses to airflow reflect the specific biomechanics of the supra-orbital whiskers. Micro-computed tomography (micro-CT) has revealed distinct follicular structures in the supra-orbital and pad whiskers.
In recordings made with Neuropixels probes, the supra-orbital vs. pad barrel field shows a larger wind response. Rats can also locate and identify low-level airflow stimuli. These abilities are impaired by obstructing supra-orbital whiskers or focusing on wind-sensitive hairs.
In rats, scientists observed whisker-based anemotaxis. Scientists observed the tips of anesthetized rats’ hairs in low and high airflow conditions to better understand how whiskers detect airflow. Low airflow circumstances, which are the ones most akin to the wind stimuli that occur normally, differentially engaged whisker tips. In contrast, high airflow conditions caused all the whisker tips to move.
Most whiskers barely moved, but the long supra-orbital (lSO) whisker, followed by the A1 whiskers, displayed the most displacement. The lSO whisker varies from other whiskers in that it is narrow in diameter, long, and exposed dorsally. Ex vivo removed lSO whiskers displayed remarkable airflow displacement as well, indicating that whisker-intrinsic biomechanics is likely the mechanism behind the unusual airflow sensitivity.
Micro-computed tomography (micro-CT) revealed that the ring-just was more complete/closed in the lSO, and other wind-sensitive whiskers, than in non-wind-sensitive whiskers, suggesting specialization of the supra-orbital for omnidirectional sensing.
Scientists noted, “We localized and targeted the cortical supra-orbital whisker representation in simultaneous Neuropixels recordings with D/E-row whisker barrels. The supra-orbital whisker representation responded to wind stimuli better than the D/E-row barrel cortex. We assessed the behavioral significance of whiskers in an airflow-sensing paradigm. We observed that rats spontaneously turn towards airflow stimuli in complete darkness.”
“We observed that rats spontaneously turn towards airflow stimuli in complete darkness. Selective trimming of wind-responsive whiskers diminished airflow-turning responses more than trimming of non-wind-responsive whiskers. Lidocaine injections targeted to supra-orbital whisker follicles also diminished airflow-turning responses compared to control injections. We conclude that supra-orbital whiskers act as wind antennae.”
Journal Reference:
- Matias Mugnaini, Dhruv Mehrotra et al. Supra-orbital whiskers act as wind-sensing antennae in rats. PLoS Biology. DOI: 10.1371/journal.pbio.3002168