Development and Reliability of a Visual-Cognitive Reactive Triple Hop Test

CONTEXT

Current lower-extremity return to sport testing primarily considers the physical status of an athlete; however, sport participation requires continuous cognitive dual-task engagement. Therefore, the purpose was to develop and evaluate the reliability of a visual-cognitive reactive (VCR) triple hop test that simulates the typical sport demand of combined online visual-cognitive processing and neuromuscular control to improve return to sport testing after lower-extremity injury.

DESIGN

Test-retest reliability.

METHODS

Twenty-one healthy college students (11 females, 23.5 [3.7] y, 1.73 [0.12] m, 73.0 [16.8] kg, Tegner Activity Scale 5.5 [1.1] points) participated. Participants performed a single-leg triple hop with and without a VCR dual task. The VCR task incorporated the FitLight system to challenge peripheral response inhibition and central working memory. Maximum hop distance, reaction time, cognitive errors, and physical errors were measured. Two identical testing visits were separated by 12 to 17 days (14 [1] d).

RESULTS

Traditional triple hop (intraclass correlation coefficients: ICC(3,1) = .96 [.91-.99]; standard error of the measurement = 16.99 cm) and the VCR triple hop (intraclass correlation coefficients(3,1) = .92 [.82-.97]; standard error of the measurement = 24.10 cm) both demonstrated excellent reliability for the maximum hop distance, and moderate reliability for the VCR triple hop reaction time (intraclass correlation coefficients(3,1) = .62 [.09-.84]; standard error of the measurement = 0.09 s). On average, the VCR triple hop resulted in a hop distance deficit of 8.17% (36.4 [5.1] cm; P < .05, d = 0.55) relative to the traditional triple hop.

CONCLUSIONS

Hop distance on the VCR triple hop had excellent test-retest reliability and induced a significant physical performance deficit when compared with the traditional triple hop assessment. The VCR triple hop reaction time also demonstrated moderate reliability.

Combining Neurocognitive and Functional Tests to Improve Return-to-Sport Decisions Following ACL Reconstruction

SYNOPSIS: Neuroplasticity after anterior cruciate ligament (ACL) injury alters how the nervous system generates movement and maintains dynamic joint stability. The postinjury neuroplasticity can cause neural compensations that increase reliance on neurocognition. Return-to-sport testing quantifies physical function but fails to detect important neural compensations. To assess for neural compensations in a clinical setting, we recommend evaluating athletes' neurocognitive reliance by augmenting return-to-sport testing with combined neurocognitive and motor dual-task challenges. In this Viewpoint, we (1) share the latest evidence related to ACL injury neuroplasticity and (2) share simple principles and new assessments with preliminary data to improve return-to-sport decisions following ACL reconstruction. J Orthop Sports Phys Ther 2023;53(8):1-5. Epub: 16 May 2023. doi:10.2519/jospt.2023.11489.

Cognitive Load Influences Drop Jump Landing Mechanics During Cognitive-Motor-Simulated Shooting

INTRODUCTION

Military duties require immense cognitive-motor multitasks that may predispose soldiers to musculoskeletal injury. Most cognitive challenges performed in the research laboratory are not tactical athlete specific, limiting generalizability and transferability to in-field scenarios. The purpose of this study was to determine the impact of a cognitive-motor multitask (forward drop jump landing while simultaneously performing simulated shooting) on knee kinetics and kinematics.

METHODS

Twenty-four healthy collegiate Reserve Officer's Training Corps members (18 males and 6 females, 20.42 ± 1.28 years, 174.54 ± 10.69 cm, 78.11 ± 14.96 kg) volunteered, and knee kinetics and kinematics were assessed between baseline and cognitive-loaded conditions. Repeated measures ANOVAs were conducted for each dependent variable with the within-subject factor of condition (baseline vs. cognitive load).

RESULTS

Univariate ANOVAs indicated that knee flexion angle at initial contact (IC) (decreased 6.07°; d = 3.14), knee flexion displacement (increased 6.78°; d = 1.30), knee abduction angle at IC (increased 2.3°; d = 1.46), peak knee abduction angle (increased 3.04°; d = 0.77), and peak vertical ground reaction force (increased 0.81 N/kg; d = 2.13) were significant between conditions (P < .001). Therefore, cognitive load resulted in decreased knee flexion and increased knee abduction angle at IC and greater peak vertical ground reaction force, all factors commonly associated with knee injury risk. Peak knee flexion angle and knee abduction displacement were not significant between conditions (P > .05).

CONCLUSIONS

Cognitive challenge induced knee landing biomechanics commonly associated with injury risk. Injury risk screening or return-to-training or duty assessments in military personnel might consider both baseline and cognitive conditions.

Development and reliability of a visual-cognitive medial side hop for return to sport testing

OBJECTIVES

To develop and evaluate the reliability of a new visual-cognitive medial side hop (VCMH) test that challenges physical and cognitive performance to potentially improve return to sport testing.

DESIGN

Test-retest experimental design.

SETTING

Laboratory.

PARTICIPANTS

Twenty-two healthy college students participated (11 females; 23.5 ± 3.64 years; 172.9 ± 11.58 cm; 74.1 ± 17.25 kg; Tegner Score 5.6 ± 1.1).

MAIN OUTCOME MEASURES

Subjects performed a medial side hop for distance with and without a visual-cognitive task (VCMH). Maximum hop distance and cognitive errors were measured.

RESULTS

There was strong reliability for the traditional medial side hop (ICC3,1 = 0.88[0.72, 0.95]; SEM = 7.16 cm) and VCMH distances (ICC3,1 = 0.86[0.66, 0.94]; SEM = 6.82 cm). Maximum hop distance was significantly lower during the VCMH (86.9 ± 18.2 cm) compared to the traditional medial side hop (96.3 ± 20.7 cm; p < 0.05; d = 0.74), with a performance deficit of 9.69%.

CONCLUSION

The VCMH has high test-retest reliability and resulted in a significant dual-task cost with a reduction in physical performance when compared to the traditional medial side hop.

Visual cognition associated with knee proprioception, time to stability, and sensory integration neural activity after ACL reconstruction

Visual cognitive ability has previously been associated with anterior cruciate ligament injury and injury risk biomechanics in healthy athletes. Neuroimaging reports have identified increased neural activity in regions corresponding to visual-spatial processing, sensory integration, and visual cognition in individuals after anterior cruciate ligament reconstruction (ACLR), indicating potential neural compensatory strategies for motor control. However, it remains unclear whether there is a relationship between visual cognition, neural activity, and metrics of neuromuscular ability after ACLR. The purpose of this study was to (1) evaluate the relationship between visual cognitive function and measurements of neuromuscular control (proprioception and time to stability [TTS]), isokinetic strength, and subjective function, and (2) examine the neural correlates of visual cognition between ACLR (n = 16; time since surgery 41.4 ± 33.0 months) and demographically similar controls (n = 15). Visual cognition was assessed by the ImPACT visual motor and visual memory subscales. Outcome variables of proprioception to target knee angle 20°, landing TTS, strength, and subjective function were compared between groups, and visual cognition was correlated within groups to determine the relationship between visual cognition and outcome variables controlled for time from surgery (ACLR group). The control group had better IKDC scores and strength. Visual memory and visual motor ability were negatively associated with proprioception error (r = -0.63) and TTS (r = -0.61), respectively, in the ACLR group but not controls. Visual cognition was associated with increased neural activity in the precuneus and posterior cingulate cortex in the ACLR group but not control participants. These data suggest the neural strategy in which ACLR participants maintain proprioception and stability varies, and may depend on visual cognition and sensory integration neural activity.

Cognitive Load Impairs Time to Initiate and Complete Shooting Tasks in ROTC Members

INTRODUCTION

Multitasking typically requires an individual to simultaneously process cognitive information while performing a motor task. Cognitive motor interference (CMi) is encountered when cognitive challenges negatively impact motor task performance. Military personnel encounter cognitively taxing situations, especially during combat or other tactical performance scenarios, which may lead to injury or motor performance deficits (i.e., shooting inaccuracy, delayed stimulus-response time, and slowed movement speed). The purpose of the current study was to develop four cognitive motor shooting paradigms to determine the effects of cognitive load on shooting performance in healthy Reserve Officers' Training Corps (ROTC) cadets.

METHODS

Thirty-two healthy collegiate ROTC members (24 male and 8 female; 20.47 ± 1.24 years, 174.95 ± 10.58 cm, and 77.99 ± 13.90 kg) were recruited to complete four simulated shooting tasks with additional "motor" challenge (180° turn, gait, weighted, and unweighted landing) and with and without a "cognitive" decision-making challenge requiring response selection and inhibition to both auditory and visual stimuli, totaling eight multi-task cognitive motor shooting conditions. The current study was approved by the university's Institutional Review Board. Task initiation (seconds), task completion (seconds), and number of misses were calculated to determine marksmanship efficiency and accuracy. For each task, a multivariate repeated-measures analysis of variance (ANOVA) was conducted for the combined dependent variables. If the overall multivariate repeated-measures ANOVA was significant, follow-up univariate ANOVAs were conducted for each dependent variable. Alpha was set at α = 0.05 for all analyses.

RESULTS

Task initiation increased for the cognitive condition for the 180° turn (4.29 ± 1.22 seconds baseline, 5.09 ± 1.39 seconds cognitive; P < .05), gait (2.76 ± .60 seconds baseline, 3.93 ± .62 seconds cognitive; P < .05), unweighted (1.27 ± .57 seconds baseline, 3.39 ± .63 seconds cognitive; P < .05), and weighted landing (1.46 ± .72 seconds baseline, 3.35 ± .60 seconds cognitive; P < .05). Task completion time increased for the cognitive condition for the 180° turn (3.48 ± 1.53 seconds baseline, 4.85 ± 1.24 seconds cognitive; P < .05), gait (7.84 ± 2.07 seconds baseline, 9.23 ± 1.76 seconds cognitive; P < .05), unweighted (5.98 ± 1.55 seconds baseline, 7.45 ± 1.51 seconds cognitive; P < .05), and weighted landing (6.09 ± 1.42 seconds baseline, 7.25 ± 1.79 seconds cognitive; P < .05). There were no statistically significant differences in the number of misses for any of the tasks between conditions (P > .05).

CONCLUSIONS

The addition of a cognitive load increased both task initiation and task completion times during cognitive motor simulated shooting. Adding cognitive loads to tactical performance tasks can result in CMi and negatively impact tactical performance. Thus, consideration for additional cognitive challenges into training may be warranted to reduce the potential CMi effect on tactical performance.

Quadriceps Strength Influences Patient Function More Than Single Leg Forward Hop During Late-Stage ACL Rehabilitation

BACKGROUND

A comprehensive battery of tests are used to inform return to play decisions following anterior cruciate ligament (ACL) reconstruction. Performance measures contribute to patient function, but it is not clear if achieving symmetrical performance on strength and hop tests is sufficient or if a patient also needs to meet minimum unilateral thresholds.

HYPOTHESIS/PURPOSE

To determine the association of quadriceps strength and single-leg forward hop performance with patient-reported function, as measured by the IKDC Subjective Knee Form (IKDC), during late-stage ACL rehabilitation. A secondary purpose was to determine which clinical tests were the most difficult for participants to pass.

STUDY DESIGN

Descriptive Laboratory Study.

METHODS

Forty-eight individuals with a history of ACL-R (32 female, 16 male; mean±SD age=18.0±2.7 y; height=172.4±7.6 cm; mass=69.6±11.4 kg; time since surgery=7.7±1.8 months; IKDC=86.8±10.6) completed the IKDC survey, quadriceps isometric strength, and single-leg forward hop performance. The relationship between IKDC scores and performance measures (LSI and involved limb) was determined using stepwise linear regression. Frequency counts were used to determine whether participants met clinical thresholds (IKDC ≥ 90%, quadriceps and single-leg forward hop LSI ≥ 90%, quadriceps peak torque ≥ 3.0 Nm/kg, and single-leg forward hop ≥ 80% height for females and ≥ 90% height for males).

RESULTS

Quadriceps LSI and involved limb peak torque explained 39% of the variance in IKDC scores while measures of single-leg forward hop performance did not add to the predictive model. Nearly 90% of participants could not meet established clinical thresholds on all five tests and quadriceps strength (LSI and peak torque) was the most common unmet criteria (71% of participants).

CONCLUSIONS

During late-stage ACL rehabilitation deficits in quadriceps strength contribute more to patient function and are greater in magnitude compared to hop test performance.

LEVEL OF EVIDENCE

Cross-Sectional Study, Level 3.

Knee Kinetics in Baseball Hitting and Return to Play after ACL Reconstruction

The purpose of this study was to describe the knee kinetics of baseball hitting, develop a tool to predict knee kinetics from easily obtainable measures, and to compare knee kinetics to other exercises along the rehabilitation continuum to determine a timeline for when hitting may resume after ACL reconstruction. Nineteen high school baseball athletes (16.3±0.8 yrs, 180.6±5.7 cm, 78.4±10.8 kg) participated. Participants took ten swings off a tee. Kinetic data were recorded using an electromagnetic tracking system. Data from swings with the top three exit velocities were averaged for analysis. Linear regressions were used to determine if predictors of height, mass, age and exit velocity could predict the following torques: bilateral knee net, extension, internal and external rotation, valgus and varus torque; and anterior force. Backwards regression models revealed independent variables could significantly predict front knee net, internal and external rotation, extension, and varus torque, and anterior force; and back knee net and valgus torque. Based on the kinetics of baseball hitting compared to those of rehabilitation exercises, if the involved knee is the front, we suggest tee hitting may be initiated at 13 weeks after ACL reconstruction. If the involved knee is the back, we suggest tee hitting may initiated at 17 weeks after ACL reconstruction.

Orexin A effects on the olfactory bulb spontaneous activity and odor responsiveness in freely breathing rats

The mitral cells (MCs) of the olfactory bulb (OB) are relay neurons between the periphery and the central nervous structures. MCs receive in turn a centrifugal control from several higher brain centers that depends on the nutritional state. In this study, we investigated the effects of orexin A (ORX), a novel molecule known to regulate food intake and whose receptors are present in the OB, on the electrophysiological activity of single MCs. Using icv-injections and direct applications on the OB, we determined the respective central and local effects of this molecule on the MCs' spontaneous firing activity and responsiveness to different odors. Icv-injections and local OB-applications were found to induce a significant decrease in spontaneous firing activity in 14% and 50% of the recorded MCs, respectively. In one case, ORX application on the OB caused a significant firing increase. Effects of OB-applications had shorter delays. The responsiveness of some MCs to food and non-food odors was also changed, but the proportion of changes was not statistically significant. Icv-injection effects likely resulted from a local action of ORX on the OB. Changes of spontaneous firing activity and odor responsiveness are discussed in terms of regulation of the functioning of the olfactory system.

Olfactory experience decreases responsiveness of the olfactory bulb in the adult rat

We recently reported the existence of dramatic modifications of the olfactory bulb reactivity following a very simple manipulation of the olfactory input as an exposure to an odorant. The present study aimed at testing the possibility that such effects could depend on the nature of the exposure odour. For this purpose, rats were exposed 20 min per day during six consecutive days to cineole, methyl-amyl ketone, isoamyl acetate or with no odour in the control group. On day 7, rats were anaesthetized and the spontaneous activity of mitral/tufted cells was recorded along with their responses to the familiar odour and to four novel odours. Results revealed that: (i) the firing frequencies were not significantly different in the four groups; (ii) the proportion of excitatory responses was considerably decreased in the exposed groups while the number of non-responses was significantly enhanced; (iii) excitatory responses were decreased not only to the familiar odour but also to four other novel odours; (iv) this lower responsiveness was long lasting at least for isoamyl acetate exposure; and (v) increasing concentration of test odours was not enough to allow mitral/tufted cells to recover control responsiveness. All of these effects have a differential importance according to the exposure odour. In particular, the more powerful an odour is in activating control cells, the more non-specific the decrease in mitral/tufted cell reactivity is. Hypotheses on the underlying mechanisms are advanced.

Repeating triplets of spikes and oscillations in the mitral cell discharges of freely breathing rats

The olfactory bulb responses to odours display evident temporal organization, both in the form of high-frequency oscillations and precisely replicating triplets of spikes. In this study, the frequency of replicating triplets in a sample of 118 individual responses from 45 cells was compared with that in simulations of non-homogeneous Poisson processes, constructed from the experimental post-stimulus time histograms (PSTHs). In a large majority of the records, replicating triplets (to a precision of 0.5 ms) are found to be more numerous in the physiological records; in some of them, they are approximately 10 times more abundant. An excess of precisely replicating triplets is also found in records where no oscillations are apparent in the autocorrelograms. Triplet replication thus seems a more robust phenomenon than transient oscillation. Not unlike fast oscillations observed in other preparations, replicating triplets produced by a given mitral cell are generally observed only during a restricted period of time of the respiratory cycle (at least in the case of the responses under olfactory stimulation). No relation was found, however, between the nature and strength of the olfactory stimulus and the frequency of replicating patterns. In the absence of olfactory stimulation, some mitral cell discharges also contain more replicating triplets than the non-homogeneous Poisson simulations. Thus, replicating triplets in single-cell discharges seem to play only an indirect role in the coding of olfactory information at the mitral cell output level.

Short-lasting exposure to one odour decreases general reactivity in the olfactory bulb of adult rats

We investigated in adult rats whether a relatively short exposure to a novel odour can lead to changes in reactivity of olfactory bulb principal neurons. Naive rats were exposed to isoamyl acetate for 20 min per day either for 6 consecutive days or for a single 20-min exposure. Control group was non-exposed. Under anaesthesia, responsiveness of each recorded single mitral/tufted cell was tested towards isoamyl acetate and four other odours. Results show that the proportion of responding cells in the exposed groups decreased drastically when compared to controls. In the two experimental groups recorded 24 h following the last exposure, mitral/tufted cells show a significant decrease in the number of excitatory responses. In parallel, the number of non-responsive cells increased by at least a fourfold factor. This decrease in reactivity was not selective towards the odour used during the exposure but concerned any of the five test-odours presented during recordings. Finally, this lower responsiveness was long lasting as it was still observed 10 days after the end of the last exposure. This preliminary study points out the importance of even limited sensory experience in neural representation of odours.

GABAergic control of odor-induced activity in the frog olfactory bulb: electrophysiological study with picrotoxin and bicuculline

In the olfactory bulb, the first relay of the olfactory pathways, GABA, could be largely involved in the information processing since the two main populations of interneurons, periglomerular and granular cells, use it as neurotransmitter through reciprocal synapses with second-order neurons. This study planned to clarify the role of GABAergic inhibition in odor coding and, more precisely, the role of glomerular GABAergic inhibition. To do so, we attempted to specifically block in vivo GABAA receptors with either picrotoxin or bicuculline. The drug was applied at the level of the glomerular layer so that the antagonist could act primarily via periglomerular cells. The analysis of the effects of blocking GABAA on the coding was studied by recording the second-order neuron responses to odor stimuli delivered in a wide concentration range. Under drug treatment, the second-order neuron properties were deeply changed: response thresholds to odors were often lowered and spike bursts were more sustained in frequency and in duration. Thus, the GABAergic control on second-order neurons might be carried out by limiting the neuron excitability. GABAA antagonists applied in this manner could act to suppress the inhibitory effect of either the periglomerular cells or of the granule cells, both of which have been shown to contain enzymes for GABA production. The placement of the drug suggests to us that the action is primarily at the glomerulus. The results are consistent with periglomerular cells exerting a tonic inhibition on second-order neurons, an inhibition whose strength would be modulated by stimulus intensity. As a result, the amplifying role of glomerular convergence might be partly counterbalanced by input inhibition. Nevertheless, due to our procedure of drug application, one cannot rule out the possibility that the effects observed may partly reflect granular cell blocking. It can be concluded that the whole GABAergic inhibition, through GABAA receptors, permits a wide dynamic range of intensity coding.

The neurotrophic factor neuroleukin is 90% homologous with phosphohexose isomerase

Neuroleukin (NLK) is a protein of relative molecular mass (Mr) 56,000 (56K) secreted by denervated rat muscle and found in large amounts in muscle, brain, heart and kidneys. The protein is a neurotrophic factor for spinal and sensory neurons and a lymphokine product of lectin-stimulated T-cells. It also induces immunoglobulin secretion by human mononuclear cells. Molecular clones of NLK have been expressed in monkey COS cells and the product was shown to have the same biological and biochemical properties as the extracted protein. NLK is abundant in muscle, brain and kidney, but is active at concentrations of 10(-9) to 10(-11) M, similar to those for other polypeptide factors. We have cloned the gene for pig muscle phosphohexose isomerase (PHI) (EC 5.3.1.9) which catalyses the conversion of glucose-6-phosphate to fructose-6-phosphate, an obligatory step in glycolysis, and determined its amino-acid sequence. Surprisingly, it is 90% homologous to the sequence of mouse neuroleukin.

Sensitivity of yeast cells to reactive oxygen species generated in the extracellular space

Even when cytoplasmic scavenging activities are plentiful, yeast cells (S. cerevisiae) remain particularly sensitive towards reactive oxygen species generated in the extracellular space (either by the xanthine/xanthine oxidase reaction or by the redox cycling of menadione). A sharp reduction of the extent of cellular alterations when SOD and/or catalase were supplemented in the incubation buffer, points to a contribution of both O-.2 and H2O2 in the toxic process. Although oxygen metabolites as well as t-butylhydroperoxide (tBH), a highly toxic organic peroxide, may be directly responsible for cellular damage, their toxicity is largely reduced in the presence of Desferal. A role of metal ions in potentiating the toxicity points to the involvement of OH. radicals, actually produced in the medium. With tBH, metal cations would be rather active in promoting peroxidative chain reactions. In the case of an extracellular oxidative attack, it may be foreseen that the plasma membrane will form a preferential target. An increased permeability of the plasma membrane towards ionized molecules and uncharged polycarboxylic acids is indeed observed after an oxidative treatment. The loss of selective permeability is, as a rule, correlated with a drop in viability. Early alterations, disrupting the functional organization of the plasma membrane have been sought. The permease involved in the active transport of purine(s) has appeared to be an appropriate marker for checking its functional integrity. This transport function appears to be very sensitive to damage induced by O-.2 generators, particularly under conditions in which the resulting lethality is still kept low and in which the energization of active transport processes remains unimpaired.

Potentiation of oxygen toxicity by menadione in Saccharomyces cerevisiae

The cytotoxicity of molecular oxygen can be sharply increased in the yeast Saccharomyces cerevisiae by the use of redox compounds capable of shunting electrons in vivo and of spontaneous reoxidation under aerobic conditions. Among these redox compounds, menadione (Vitamin K3) is particularly able to stimulate the cyanide-resistant respiration of the yeast cells. Under steady-state conditions, the efficiency of menadione is modulated by the physiological state of the yeast cells and also depends on the availability of reducing agents within the cell. Menadione shows lethal effects towards yeast cells in the presence of O2 only, as a result of the production of toxic metabolites like O2-. and H2O2 which are actually detected in the extracellular fluid. Inhibitors of the enzymes scavenging O2-. and H2O2 generally potentiate the lethal effects of this redox compound. On the other hand, superoxide dismutase and/or catalase supplemented into the incubation buffer have been found to protect the cells to various extents from the cytotoxic effects of menadione. Our data support the following conclusions: When the cellular enzymatic defences are functional, the moderate lethality induced by menadione is principally mediated by O2-. ions acting on the outer side of the cell (peripheral region). In the presence of cyanide, but not of azide, the loss of viability also results from additional damage occurring within the inner cell region. In this case, intracellular injury can be caused by H2O2 alone but our data also suggest that during redox cycling more reactive species--O2-. and probably OH.--are generally intracellularly and are involved in the cytotoxic process.

Chemical Test for Mammalian Feces: Collaborative Study

A chemical method was developed to determine the presence of mammalian feces in food. The method consisted of the colorimetric determination of alkaline phosphatase and involved the splitting of the phosphate radical from phenolphthalein diphosphate and the resultant color development of phenolphthalein in a basic medium. A collaborative study testing the feces of 22 animals resulted in a 95% correct identification of samples as mammalian feces. The method has been adopted official first action.

Single unit responses of olfactory bulb neurones to odour presentation in awake rabbits

The changes in single unit activity induced by short odour presentations were studied in the olfactory bulbs of awake rabbits. 1. It was found that an accurate evaluation of the cell responses required the separate processing of the inspiration- and expiration-related activity. 2. Three main types of response were observed during odour presentation. One was characterized by an increase in firing over several successive inspirations, with a decrease in the corresponding expiratory phases. The other two were characterized by an inspiration-related increase or decrease in activity without any modifications during expiration. 3. The end of odour presentation led to inconsistent "off-effects" in the cells affected by the stimulation. The most conspicuous were: a complete cessation of the firing for several respiratory cycles following an excitation, an excitatory rebound following inhibition, a reversal of the respiratory phase-related discharge, i.e., activity decrease during inspiration and the increase during expiration. 4. The findings are discussed with reference to previous studies on anaesthetized animals, together with their relevance to sensory coding in the olfactory bulb.

SOME REACTIONS OF ETHYL 2-PYRIDINEACETATE: 1,2-DICARBETHOXY-3-OXO-OCTAHYDROPYRROCOLINE

Ethyl α-acetoxy-2-pyridineacetate and ethyl α-bromo-2-pyridineacetate have been prepared, and the latter converted in three steps to 1,2-dicarbethoxy-3-oxooctahydropyrrocoline. The main carbonyl band of simple saturated five membered lactams in the infrared is observed to lie close to 1700 cm−1