Odor motion sensing enables complex plume navigation

ABSTRACTInsects can detect bilateral differences in odor concentration between their two antennae, enabling them to sense odor gradients. While gradients aid navigation in simple odor environments like static ribbons, their role in navigating complex plumes remains unknown. Here, we use a virtual reality paradigm to show that Drosophila use bilateral sensing for a distinct computation: detecting the motion of odor signals. Such odor direction sensing is computationally equivalent to motion detection algorithms underlying motion detection in vision. Simulations of natural plumes reveal that odor motion contains valuable directional information absent from the airflow, which Drosophila indeed exploit when navigating natural plumes. Olfactory studies dating back a century have stressed the critical role of wind sensing for insect navigation (Flügge, 1934; Kennedy and Marsh, 1974); we reveal an entirely orthogonal direction cue used by flies in natural environments, and give theoretical arguments suggesting that this cue may be of broad use across the animal kingdom.

The ACL can hypertrophy in response to mechanical loading: an MRI study in elite athletes (157)

Objectives: Several morphological risk factors for anterior cruciate ligament (ACL) injury have been identified,1,6,12,13 including the size of the ACL.5,8,12,15 A smaller ACL volume and diameter are associated with a greater risk of injury when comparing ACL-injured subjects to matched controls.5,8,12,15 Although morphological risk factors as a group have been largely characterized as non-modifiable,9,10 ACL surface and cross-sectional areas (CSA) have the potential for modifiability, especially during growth and development.7,11 These ACL area measures have increased and the mechanical properties of the ACL have improved following exercise through periods of growth in animal models.2,7,11,14 In humans, we are only aware of one study of ACL hypertrophy—a small study of elite weightlifters.7The main purpose of this study, therefore, was to determine whether the ACL can hypertrophy in response to mechanical loading by comparing bilateral differences in ACL CSA in athletes who habitually load one leg more than the other in training for their sport. Based on the work of Grzelak et al. in weightlifters,7 as well as animal evidence that the ACL responds to exercise,2,11,14 we hypothesized that these athletes would present with significantly greater ACL CSAs in the landing/drive leg, the knee that is loaded the most in comparison with the contralateral control knee. Demonstrating the potential for the ACL to hypertrophy via mechanical loading would provide a scientific basis for exploring ACL injury prevention strategies aimed at increasing ACL CSA and robustness given that a small ACL volume and diameter are known risk factors for injury. This is particularly important for all children and especially females since they are at a much higher risk for ACL injury, and thereafter the development of knee osteoarthritis. Methods: We recruited 50 figure skaters and springboard divers because they consistently and repeatedly use one leg more than the other, thereby ensuring that one knee was habitually loaded more than the other (Table 1). More specifically, figure skaters always land their jumps on the same leg, while springboard divers always drive the same leg (‘drive’ leg) into the board during their hurdle approach. Sport training for all participants began prior to puberty and continued through and after. Bilateral knee magnetic resonance images (MRIs) were acquired with a Philips Ingenia 3.0-T scanner using a dedicated knee coil. Each knee, resting in slight flexion in the coil, was scanned using three sequences, all in the plane of the ACL: (1) oblique-sagittal (repetition time (TR): 5100 ms; echo time (TE): 30 ms; slice thickness: 2.5 mm; pixel spacing: 0.19 x 0.19 mm); (2) oblique-coronal (TR: 4000 ms; TE: 30 ms; slice thickness: 2.5 mm; pixel spacing: 0.20 x 0.20 mm); (3) oblique-axial (TR: 5100 ms; TE: 30 ms; slice thickness: 2.5 mm; pixel spacing: 0.20 x 0.20 mm). Using the oblique-axial-plane scans, the ACL CSA was measured on the three slices that were closest to 50% of the ligament’s length, and then averaged (Figure 1). Using the oblique-sagittal-plane scans, which were reconstructed to run parallel to the patellar tendon, the anteroposterior diameter of the patellar tendon was measured perpendicular to the tendon’s longitudinal axis at a distance of 2 cm distal to the patella3,4 on the slice displaying the thickest part of the tendon at that height (Figure 2). In addition, isometric and isokinetic knee extensor and knee flexor peak torques were acquired using a dynamometer. Bilateral differences in ACL CSA, PT diameter, and knee muscle strength were evaluated via one-sample t-tests that compared the mean percent difference between limbs to a null hypothesis of a zero mean percent difference. Correlations between bilateral ACL CSA differences, age of training onset and years of training were also examined. Results: Athletes with repeated unilateral lower limb loading had significantly greater ACL CSAs in the dominant knee than the non-dominant knee (Table 1; ACL CSAs: dominant = 42.0 ± 8.8 mm2; non-dominant = 40.8 ± 9.1 mm2; % difference = 4.4 ± 13.8%; t = 2.236; p = 0.030). Also, these athletes had significantly greater AP patellar tendon diameters in the dominant knee than the non-dominant knee (Table 1; patellar tendon diameters: dominant = 4.1 ± 0.6 mm; non-dominant = 3.9 ± 0.5 mm; % difference = 4.5 ± 9.4%, t = 3.322; p = 0.002). The percent bilateral difference in ACL CSA, however, was not associated with training onset (r = 0.087, p = 0.553) or years of training (r = -0.068, p = 0.641). Lastly, isometric knee flexor peak torques were significantly greater in the landing/drive leg than the contralateral knee (Table 2). Peak torques from other contraction types or muscle group did not differ between limbs (Table 2). Conclusions: Athletes who habitually loaded one leg more than the other prior to, during and after puberty exhibited significant unilateral ACL hypertrophy in their landing/drive leg. These results support existing evidence that exercise, including resistance and endurance regimens, during periods of pubertal growth has the potential to increase ACL CSA and, therefore, its strength.2,7,14 This suggests that perhaps the ACL could be ‘trained’ to become larger, more robust, and thus at lower risk of injury given that a smaller ligament is associated with a greater risk of injury. The bilateral difference in patellar tendon morphology supports our assumption that the athletes participating in this study consistently loaded one knee more than the other during their sport training, and that increased loading led to the hypertrophy of two important structures in that knee. Many gaps in knowledge—ACL development during growth and how exercise may alter its morphology and mechanical properties—need to be addressed as injury prevention strategies that involve ‘training’ the ACL are explored.

Cone-beam computed tomographic assessment of the inclination of the articular eminence in patients with temporomandibular disorders and chewing side preference

Background Chewing side preference (CSP) has been proposed as one etiology of temporomandibular disorders (TMDs) as it can induce the structural changes of the temporomandibular joint. But its association with the inclination of the articular eminence (IAE) is unknown. This study aimed to compare IAE between patients with CSP and without CSP. Methods Cone-beam computed tomography images of 90 patients with TMD (mean age of 45.6 years, 69 with CSP, 21 without CSP) and 20 participants without TMD and CSP (mean age of 41.3 years) were measured to compare IAE and depth of the glenoid fossa (DGF) Results IAE and DGF showed a positive correlation among all the participants. Compared with the participants without TMD and CSP, the TMD patients without CSP presented a similar IAE but with a significantly higher value of DGF (p < 0.05); in contrast, the TMD patients with CSP presented a significantly greater IAE and DGF (p < 0.05). No bilateral differences in IAE and DGF were observed in all the participants. Except the male patients with CSP had a deeper fossa than did the female, no differences in IAE and DGF according to gender were observed. Conclusions TMD patients with CSP seem to have a deep glenoid fossa with steep eminence which might be considered one characteristic imaging feature.

A population of descending neurons that regulate the flight motor of Drosophila

Like many insect species, Drosophila melanogaster are capable of maintaining a stable flight trajectory for periods lasting up to several hours(1, 2). Because aerodynamic torque is roughly proportional to the fifth power of wing length(3), even small asymmetries in wing size require the maintenance of subtle bilateral differences in flapping motion to maintain a stable path. Flies can even fly straight after losing half of a wing, a feat they accomplish via very large, sustained kinematic changes to the both damaged and intact wings(4). Thus, the neural network responsible for stable flight must be capable of sustaining fine-scaled control over wing motion across a large dynamic range. In this paper, we describe an unusual type of descending neurons (DNg02) that project directly from visual output regions of the brain to the dorsal flight neuropil of the ventral nerve cord. Unlike most descending neurons, which exist as single bilateral pairs with unique morphology, there is a population of at least 15 DNg02 cell pairs with nearly identical shape. By optogenetically activating different numbers of DNg02 cells, we demonstrate that these neurons regulate wingbeat amplitude over a wide dynamic range via a population code. Using 2-photon functional imaging, we show that DNg02 cells are responsive to visual motion during flight in a manner that would make them well suited to continuously regulate bilateral changes in wing kinematics. Collectively, we have identified a critical set of DNs that provide the sensitivity and dynamic range required for flight control.

The Anterior Cruciate Ligament Can Become Hypertrophied in Response to Mechanical Loading: A Magnetic Resonance Imaging Study in Elite Athletes

Background: Evidence, mainly from animal models, suggests that exercise during periods of pubertal growth can produce a hypertrophied anterior cruciate ligament (ACL) and improve its mechanical properties. In humans, the only evidence of ACL hypertrophy comes from a small cross-sectional study of elite weight lifters and control participants; that study had methodological weaknesses and, thus, more evidence is needed. Purpose: To investigate bilateral differences in the ACL cross-sectional area (CSA) for evidence of unilateral hypertrophy in athletes who have habitually loaded 1 leg more than the other. Study Design: Cross-sectional study; Level of evidence, 3. Methods: We recruited 52 figure skaters and springboard divers (46 female and 6 male; mean age, 20.2 ± 2.7 years) because the former always land/jump on the same leg while the latter always drive the same leg into the board during their hurdle approach. Sport training for all participants began before puberty and continued throughout as well as after. Using oblique axial– and oblique sagittal–plane magnetic resonance imaging, we measured the ACL CSA and the anteroposterior diameter of the patellar tendon, respectively. In addition, isometric and isokinetic knee extensor and flexor peak torques were acquired using a dynamometer. Bilateral differences in the ACL CSA, patellar tendon diameter, and knee muscle strength were evaluated via 2-sided paired-samples t tests. Correlations between the bilateral difference in the ACL CSA and age of training onset as well as between the bilateral difference in the ACL CSA and years of training were also examined. Results: A significantly larger ACL CSA (mean difference, 4.9% ± 14.0%; P = .041), as well as patellar tendon diameter (mean difference, 4.7% ± 9.4%; P = .002), was found in the landing/drive leg than in the contralateral leg. The bilateral difference in the ACL CSA, however, was not associated with the age of training onset or years of training. Last, the isometric knee flexor peak torque was significantly greater in the landing/drive leg than the contralateral leg (mean difference, 14.5% ± 33.8%; P = .019). Conclusion: Athletes who habitually loaded 1 leg more than the other before, during, and after puberty exhibited significant unilateral ACL hypertrophy. This study suggests that the ACL may be able to be “trained” in athletes. If done correctly, it could help lower the risk for ACL injuries.

Analysis of hard tissue facial symmetry after unilateral mandibular reconstruction

Background This study aimed to determine how successful reconstruction of the mandible can recover the symmetry. Materials and methods All patients who underwent surgical treatment for unilateral mandibular reconstruction in 4 years were retrospectively examined. Bilateral differences of gonion (GO) positions were measured in 3 dimensions based on immediate postoperative computed tomography. The data collected was analyzed in 3 ways: First, the comparison of bilateral differences of GO in 3 dimensions. Second, the mean Asymmetry Index in control subjects was used to divide all cases into three groups: “Symmetry,” “Asymmetry,” and “Marked asymmetry.” Third, “maximum normal asymmetry” was calculated, and all cases were categorized as below and above maximum normal asymmetry. The difference between two gonial angles was used to determine the amount of asymmetry. Results Forty-seven patients and 47 normal adults were enrolled. The mean bilateral GO difference in the control group was higher than in the study group patients, but it was not statistically significant. The mean Asymmetry Index for the control group was not also significantly higher than the study cases. The study group was “Symmetric” in 78.7% of the cases whereas the control group in 91.4%, 19.1% of the study group and 8.5% of controls were “Asymmetric,” and 2.1% of study cases and 0% of controls were “Markedly Asymmetric.” Maximum normal asymmetry was 82.9% in the study group and 97.8% in the control group. The mean differences between the right and left gonial angles were higher in the study group, but it was not significant (P = 0.1). Conclusions Our study’s results showed that bilateral symmetry in mandibular reconstruction patients was satisfactory and similar to the normal individuals.

Morphometric Evaluation of Detailed Asymmetry for the Proximal Humerus in Korean Population

Computer-assisted orthopedic surgery and patient-specific instruments are widely used in orthopedic fields that utilize contralateral side bone data as a template to restore the affected side bone. The essential precondition for these techniques is that the left and right bone features are similar. Although proximal humerus fracture accounts for 4% to 8% of all fractures, the bilateral asymmetry of the proximal humerus is not fully understood. The aim of this study is to investigate anthropometric differences of the bilateral proximal humerus. One hundred one pairs of Korean humerus CT data from 51 females and 50 males were selected for this research. To investigate bilateral shape differences, we divided the proximal humerus into three regions and the proximal humerus further into five sections in each region. The distance from the centroid to the cortical outline at every 10 degrees was measured in each section. Differences were detected in all regions of the left and right proximal humerus; however, males had a larger number of significant differences than females. Large bilateral differences were measured in the greater tubercle. Nevertheless, using contralateral data as a template for repairing an affected proximal humerus might be possible.

Track distance runners exhibit bilateral differences in the plantar fascia stiffness

Human steady-state locomotion modes are symmetrical, leading to symmetric mechanical function of human feet in general; however, track distance running in a counterclockwise direction exposes the runner’s feet to asymmetrical stress. This may induce asymmetrical adaptation in the runners’ foot arch functions, but this has not been experimentally tested. Here, we show that the plantar fascia (PF), a primary structure of the foot arch elasticity, is stiffer for the left than the right foot as a characteristic of runners, via a cross-sectional study on 10 track distance runners and 10 untrained individuals. Shear wave velocity (index of tissue stiffness: SWV) and thickness of PF and foot dimensions were compared between sides and groups. Runners showed higher PF SWV in their left (9.4 ± 1.0 m/s) than right (8.9 ± 0.9 m/s) feet, whereas untrained individuals showed no bilateral differences (8.5 ± 1.5 m/s and 8.6 ± 1.7 m/s, respectively). Additionally, runners showed higher left to right (L/R) ratio of PF SWV than untrained men (105.1% and 97.7%, respectively). PF thickness and foot dimensions were not significantly different between sides or groups. These results demonstrate stiffer PF in the left feet of runners, which may reflect adaptation to their running-specific training that involves asymmetrical mechanical loading.