Hybrid III Manikin Lumbar Spine Loading Under Vertical Impact.

INTRODUCTION: Clinical investigations have attributed lumbar spine injuries in combat to the vertical vector. Injury prevention strategies include the determination of spine biomechanics under this vector and developing/evaluating physical devices for use in live fire and evaluation-type tests to enhance Warfighter safety. While biological models have replicated theater injuries in the laboratory, matched-pair tests with physical devices are needed for standardized tests. The objective of this investigation is to determine the responses of the widely used Hybrid III lumbar spine under the vertical impact-loading vector. MATERIALS AND METHODS: Our custom vertical accelerator device was used in the study. The manikin spinal column was mounted between the inferior and superior six-axis load cells, and the impact was delivered to the inferior end. The first group of tests consisted of matched-pair repeatability tests, second group consisted of adding matched-pair tests to this first group to determine the response characteristics, and the third group consisted of repeating the earlier two groups by changing the effective torso mass from 12 to 16 kg. Peak axial, shear, and resultant forces at the two ends of the spine were obtained. RESULTS: The first group of 12 repeatability tests showed that the mean difference in the axial force between two tests at the same velocity across the entire range of inputs was <3% at both ends. In the second group, at the inferior end, the axial and shear forces ranged from 4.9-25.2 kN to 0.7-3.0 kN. Shear forces accounted for a mean of 11 ± 6% and 12 ± 4% of axial forces at the two ends. In the third group of tests with increased torso mass, repeatability tests showed that the mean difference in the axial force between the two tests at the same velocity across the entire range of inputs was <2% at both ends. At the inferior end, the axial and shear forces ranged from 5.7-28.7 kN to 0.6-3.4 kN. Shear forces accounted for a mean of 11 ± 8% and 9 ± 3% of axial forces across all tests at the inferior and superior ends. Other data including plots of axial and shear forces at the superior and inferior ends across tested velocities of the spine are given in the paper. CONCLUSIONS: The Hybrid III lumbar spine when subjected to vertical impact simulating underbody blast levels showed that the impact is transmitted via the axial loading mechanism. This finding paralleled the results of axial force predominance over shear forces and axial loading injuries to human spines. Axial forces increased with increasing velocity suggesting the possibility of developing injury assessment risk curves, i.e., the manikin spine does not saturate, and its response is not a step function. It is possible to associate probability values for different force magnitudes. A similar conclusion was found to be true for both magnitudes of added effective torso mass at the superior end of the manikin spinal column. Additional matched-pair tests are needed to develop injury criteria for the Hybrid III male and female lumbar spines.

Purkinje Cell Activity in the Medial and Lateral Cerebellum During Suppression of Voluntary Eye Movements in Rhesus Macaques.

Volitional suppression of responses to distracting external stimuli enables us to achieve our goals. This volitional inhibition of a specific behavior is supposed to be mainly mediated by the cerebral cortex. However, recent evidence supports the involvement of the cerebellum in this process. It is currently not known whether different parts of the cerebellar cortex play differential or synergistic roles in the planning and execution of this behavior. Here, we measured Purkinje cell (PC) responses in the medial and lateral cerebellum in two rhesus macaques during pro- and anti-saccade tasks. During an antisaccade trial, non-human primates (NHPs) were instructed to make a saccadic eye movement away from a target, rather than toward it, as in prosaccade trials. Our data show that the cerebellum plays an important role not only during the execution of the saccades but also during the volitional inhibition of eye movements toward the target. Simple spike (SS) modulation during the instruction and execution periods of pro- and anti-saccades was prominent in PCs of both the medial and lateral cerebellum. However, only the SS activity in the lateral cerebellar cortex contained information about stimulus identity and showed a strong reciprocal interaction with complex spikes (CSs). Moreover, the SS activity of different PC groups modulated bidirectionally in both of regions, but the PCs that showed facilitating and suppressive activity were predominantly associated with instruction and execution, respectively. These findings show that different cerebellar regions and PC groups contribute to goal-directed behavior and volitional inhibition, but with different propensities, highlighting the rich repertoire of the cerebellar control in executive functions.

OptiFlex: Multi-Frame Animal Pose Estimation Combining Deep Learning With Optical Flow.

Animal pose estimation tools based on deep learning have greatly improved animal behaviour quantification. These tools perform pose estimation on individual video frames, but do not account for variability of animal body shape in their prediction and evaluation. Here, we introduce a novel multi-frame animal pose estimation framework, referred to as OptiFlex. This framework integrates a flexible base model (i.e., FlexibleBaseline), which accounts for variability in animal body shape, with an OpticalFlow model that incorporates temporal context from nearby video frames. Pose estimation can be optimised using multi-view information to leverage all four dimensions (3D space and time). We evaluate FlexibleBaseline using datasets of four different lab animal species (mouse, fruit fly, zebrafish, and monkey) and introduce an intuitive evaluation metric-adjusted percentage of correct key points (aPCK). Our analyses show that OptiFlex provides prediction accuracy that outperforms current deep learning based tools, highlighting its potential for studying a wide range of behaviours across different animal species.

Glissades Are Altered by Lesions to the Oculomotor Vermis but Not by Saccadic Adaptation.

Saccadic eye movements enable fast and precise scanning of the visual field, which is partially controlled by the posterior cerebellar vermis. Textbook saccades have a straight trajectory and a unimodal velocity profile, and hence have well-defined epochs of start and end. However, in practice only a fraction of saccades matches this description. One way in which a saccade can deviate from its trajectory is the presence of an overshoot or undershoot at the end of a saccadic eye movement just before fixation. This additional movement, known as a glissade, is regarded as a motor command error and was characterized decades ago but was almost never studied. Using rhesus macaques, we investigated the properties of glissades and changes to glissade kinematics following cerebellar lesions. Additionally, in monkeys with an intact cerebellum, we investigated whether the glissade amplitude can be modulated using multiple adaptation paradigms. Our results show that saccade kinematics are altered by the presence of a glissade, and that glissades do not appear to have any adaptive function as they do not bring the eye closer to the target. Quantification of these results establishes a detailed description of glissades. Further, we show that lesions to the posterior cerebellum have a deleterious effect on both saccade and glissade properties, which recovers over time. Finally, the saccadic adaptation experiments reveal that glissades cannot be modulated by this training paradigm. Together our work offers a functional study of glissades and provides new insight into the cerebellar involvement in this type of motor error.

Neurochemical fingerprinting of amygdalostriatal and intra-amygdaloid projections: a tracing-immunofluorescence study in the rat.

Amygdalostriatal and intra-amygdaloid fiber connectivity was studied in rats via injections of one of the tracers Phaseolus vulgaris leucoagglutinin (PHA-L) or biotinylated dextran amine (BDA) into various amygdaloid nuclei. To determine the neurotransmitter identity of labeled fibers we combined tracer detection with immunofluorescence staining, using antibodies against vesicular transporters (VTs) associated with glutamatergic (VGluT1, VGluT2) or GABAergic (VGAT) neurotransmission. High-magnification confocal laser scanning images were screened for overlap: occurrence inside tracer labeled fibers or axon terminals of immunofluorescence signal associated with one of the VTs. Labeled amygdalostriatal fibers were seen when tracer had been injected into the magnocellular and parvicellular portions of the basal amygdaloid nucleus and the lateral amygdaloid nucleus (nuclei belonging to 'cortical type' amygdaloid nuclei). Intra-amygdaloidal projection fibers were mostly found after tracer injections in the central and medial amygdaloid nuclei ('striatal type' amygdaloid nuclei). Terminals of tracer-labeled amygdalostriatal fibers contained immunofluorescence signal associated mostly with VGluT1 and to a lesser degree with VGluT2 or VGAT. Intra-amygdaloid labeled fibers showed colocalization mostly of VGluT1, followed by VGAT. VGluT2 co-occurred in a minority of intra-amygdaloid tracer-containing fiber terminals. We conclude from our observations that both amygdalostriatal and intra-amygdaloid projections, arising from, respectively, 'cortical type' and 'striatal type' amygdaloid nuclei contain strong glutamatergic and modest GABAergic components. The glutamatergic fibers express either VGluT1 or VGluT2. The absence in large numbers of tracer labeled fibers of expression of one of the selected VTs leads us to suspect that amygdalostriatal projection fibers may contain hitherto neglected neurotransmitters in these connections, e.g., aspartate.