For many organisms, searching for relevant targets such as food or mates entails active, strategic sampling of the environment. Finding odorous targets may be the most ancient search problem that motile organisms evolved to solve. While chemosensory navigation has been well characterized in micro-organisms and invertebrates, spatial olfaction in vertebrates is poorly understood. We have established an olfactory search assay in which freely-moving mice navigate noisy concentration gradients of airborne odor. Mice solve this task using concentration gradient cues and do not require stereo olfaction for performance. During task performance, respiration and nose movement are synchronized with tens of milliseconds precision. This synchrony is present during trials and largely absent during inter-trial intervals, suggesting that sniff-synchronized nose movement is a strategic behavioral state rather than simply a constant accompaniment to fast breathing. To reveal the spatiotemporal structure of these active sensing movements, we used machine learning methods to parse motion trajectories into elementary movement motifs. Motifs fall into two clusters, which correspond to investigation and approach states. Investigation motifs lock precisely to sniffing, such that the individual motifs preferentially occur at specific phases of the sniff cycle. The allocentric structure of investigation and approach indicate an advantage to sampling both sides of the sharpest part of the odor gradient, consistent with a serial sniff strategy for gradient sensing. This work clarifies sensorimotor strategies for mouse olfactory search and guides ongoing work into the underlying neural mechanisms.

For many organisms, searching for relevant targets such as food or mates entails active, strategic sampling of the environment. Finding odorous targets may be the most ancient search problem that motile organisms evolved to solve. While chemosensory navigation has been well characterized in micro-organisms and invertebrates, spatial olfaction in vertebrates is poorly understood. We have established an olfactory search assay in which freely-moving mice navigate noisy concentration gradients of airborne odor. Mice solve this task using concentration gradient cues and do not require stereo olfaction for performance. During task performance, respiration and nose movement are synchronized with tens of milliseconds precision. This synchrony is present during trials and largely absent during inter-trial intervals, suggesting that sniff-synchronized nose movement is a strategic behavioral state rather than simply a constant accompaniment to fast breathing. To investigate the spatiotemporal structure of these active sensing movements, we used machine learning methods to parse motion trajectories into elementary movement motifs. Motifs fall into two clusters, which correspond to investigation and approach states. Investigation motifs lock precisely to sniffing, such that the individual motifs preferentially occur at specific phases of the sniff cycle. This work clarifies sensorimotor strategies for mouse olfactory search and guides ongoing work into the underlying neural mechanisms. Bhattacharyya U, Singh Bhalla U. Robust and rapid air borne odor tracking without casting. eNeuro. 2015 11; 2(6):Eneuro.0102-15. doi: 10.1523/ENEURO.0102-15.2015. Bi S, Sourjik V. Stimulus sensing and signal processing in bacterial chemotaxis.

Background & Purpose: Our Dual Monitor Protocol with postural challenges in normotensives (n=15), hypertensives (n=14) and alcohol-dependents (n=11) revealed that an auscultatory ambulatory blood pressure monitor (ABPM) was inaccurate and unreliable, misclassifying 70% or more of hypertensives. Our goal was to apply the same procedures to determine the accuracy and reliability of oscillometric Oscar 2 and SpaceLabs 90207/90217 ABPMs. Methods: Two observers (O1, O2) using a mercury (Hg) column and ThinkLabs digital stethoscope assessed simultaneous, same arm BPs in 10 subjects (8 normotensives, 2 labile hypertensives) seated in the lab. ABPMs measured in triplicate simultaneous, opposite arm BPs on both arms alternating with Hg column BPs. Eight of 10 subjects were exposed to additional postural challenges in the lab, while four of 10 performed repeated 24-hr ABPM. Results: In the lab, the Oscar overestimated the observers’ systolic (SBP) by ~ 9 mm Hg (8.8, 95% CI: 6.9 - 10.1; 125.1 vs 116.3 mm Hg, P < 0.001), while the Spacelabs overestimated the observers’ SBP by ~ 5 mm Hg (5.4, 95% CI: 3.6 - 7.3, 121.7 vs 116.3 mm Hg, P < 0.001). Though there was a high degree of variability (both ABPMs, 15 mm Hg below to 23 mm Hg above O1O2), the average diastolic (DBP) difference was not statistically significant (Oscar vs O1O2: 69.7 vs 68.5 mm Hg, P = 0.27; Spacelabs vs O1O2: 69.9 vs 68.5 mm Hg, P = 0.23). For 24-hr ABPM in a normotensive, the Oscar had a similar average SBP (125.1 vs 125.6 mm Hg), but higher DBP (5.0 mm Hg, 67.6 vs 62.6 mm Hg, P < 0.001) and higher MAP (3.1 mm Hg, 86.7 vs 83.6 mm Hg, P < 0.001) vs observer-corrected values. For 24-hr ABPM in a hypertensive, the Spacelabs underestimated observer-corrected, 24-hr SBP, DBP and MAP by 5.2, 10.3 and 9.0 mm Hg (all P < 0.001). Both ABPMs were largely intolerant of motion, including stair climbing or walking and exhibited run-away inflations interpreted as not having exceeded SBP. Conclusions: While ABPMs may provide trends and predictions in population studies, we question ABPM accuracy and reliability in evaluating individual patients due to the high degree of variability. We find it unusual that approval protocols do not require postural testing. Further studies are needed to investigate the accuracy and reliability of oscillometric ABPMs.

Purpose: To compare the accuracy & level of agreement of Oscar 2 & Spacelabs 90207 ABPMs with 2 observers (O1O2) using an Hg column & ThinkLabs digital stethoscope. Methods: O1O2 measured simultaneous same arm Hg column BPs & ABPMs assessed simultaneous opposite arm BPs in triplicate in 17 seated subjects (7 ♀, 10 ♂). Supine, seated & standing BPs were measured using non-dominant relaxed arms in 12 subjects. Hypotheses: ABPM & O1O2 BPs would differ clinically & statistically with accuracy based on posture because ABPM proprietary equations are derived from seated BPs & use peak cuff pressure to estimate systolic (SBP) & diastolic (DBP) pressures. Results: For seated subjects, the Oscar overestimated O1O2 SBP by ~ 10 mm Hg (Δ = -9.8 ± 9.4 mm Hg, P < 0.001), but with extreme variability as 95% of Oscar SBPs were 9.0 mm Hg below to 28.7 mm Hg above O1O2. The Spacelabs overestimated O1O2 SBP by ~ 5 mm Hg (Δ = -5.2 ± 7.8 mm Hg, P < 0.001) with 95% of Spacelabs SBPs 10.5 mm Hg below to 20.9 mm Hg above O1O2. There was a stepwise increase in the Oscars’ SBP overestimation of Hg column BPs from supine (-3.1 mm Hg, P < 0.01), to seated (-5.3 mm Hg, P < 0.001) to standing (-6.6 mm Hg, P < 0.01). The Oscar overestimated supine (-7.0 mm Hg, P < 0.001), but underestimated standing (3.9 mm Hg, P < 0.05) DBPs. The Spacelabs also overestimated supine (-6.5 mm Hg, P < 0.001), but underestimated standing (4.8 mm Hg, P < 0.01) DBPs. Conclusions: Our results confirm that leading oscillometric ABPMs are prone to clinically & statistically significant errors even in a controlled lab setting. Given that ABPMs are motion intolerant & unable to assess & adjust for a patient’s posture, errors will be compounded during 24-hr field testing. Results will vary based on the ABPM & postural %s assumed by each patient. International & national ABPM testing protocols must be strengthened & require postural testing as an essential component of validation.

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