Lung ventilation during treadmill locomotion in a terrestrial turtle, Terrapene carolina

Biophysics of morphogenesis in the vertebrate lung

Morphogenesis is a physical process that sculpts the final functional forms of tissues and organs. Remarkably, the lungs of terrestrial vertebrates vary dramatically in form across species, despite providing the same function of transporting oxygen and carbon dioxide. These divergent forms arise from distinct physical processes through which the epithelium of the embryonic lung responds to the mechanical properties of its surrounding mesenchymal microenvironment. Here we compare the physical processes that guide folding of the lung epithelium in mammals, birds, and reptiles, and suggest a conceptual framework that reconciles how conserved molecular signaling generates divergent mechanical forces across these species.

Turtle Shell Kinesis Underscores Constraints and Opportunities in the Evolution of the Vertebrate Musculoskeletal System

Species groups that feature traits with a low number of potentially variable (evolvable) character states are more likely to repeatedly evolve similar phenotypes, that is, convergence. To evaluate this phenomenon, this present paper addresses anatomical alterations in turtles that convergently evolved shell kinesis, for example, the movement of shell bones to better shield the head and extremities. Kinesis constitutes a major departure from the evolutionarily conserved shell of modern turtles, yet it has arisen independently at least 8 times. The hallmark signature of kinesis is the presence of shell bone articulations or "hinges," which arise via similar skeletal remodeling processes in species that do not share a recent common ancestor. Still, the internal biomechanical components that power kinesis may differ in such distantly related species. Complex diarthrodial joints and modified muscle connections expand the functional boundaries of the limb girdles and neck in a lineage-specific manner. Some lineages even exhibit mobility of thoracic and sacral vertebrae to facilitate shell closure. Depending on historical contingency and structural correlation, a myriad of anatomical alterations has yielded similar functional outcomes, that is, many-to-one mapping, during the convergent evolution of shell kinesis. The various iterations of this intricate phenotype illustrate the potential for the vertebrate musculoskeletal system to undergo evolutionary change, even when constraints are imposed by the development and structural complexity of a shelled body plan. Based on observations in turtles and comparisons to other vertebrates, a hypothetical framework that implicates functional interactions in the origination of novel musculoskeletal traits is presented.

Modular lung ventilation in Boa constrictor

The evolution of constriction and of large prey ingestion within snakes are key innovations that may explain the remarkable diversity, distribution and ecological scope of this clade, relative to other elongate vertebrates. However, these behaviors may have simultaneously hindered lung ventilation such that early snakes may have had to circumvent these mechanical constraints before those behaviors could evolve. Here, we demonstrate that Boa constrictor can modulate which specific segments of ribs are used to ventilate the lung in response to physically hindered body wall motions. We show that the modular actuation of specific segments of ribs likely results from active recruitment or quiescence of derived accessory musculature. We hypothesize that constriction and large prey ingestion were unlikely to have evolved without modular lung ventilation because of their interference with lung ventilation, high metabolic demands and reliance on sustained lung convection. This study provides a new perspective on snake evolution and suggests that modular lung ventilation evolved during or prior to constriction and large prey ingestion, facilitating snakes' remarkable radiation relative to other elongate vertebrates.

The metabolic cost of turning right side up in the Mediterranean spur-thighed tortoise (Testudo graeca)

Armoured, rigid bodied animals, such as Testudines, must self-right should they find themselves in an inverted position. The ability to self-right is an essential biomechanical and physiological process that influences survival and ultimately fitness. Traits that enhance righting ability may consequently offer an evolutionary advantage. However, the energetic requirements of self-righting are unknown. Using respirometry and kinematic video analysis, we examined the metabolic cost of self-righting in the terrestrial Mediterranean spur-thighed tortoise and compared this to the metabolic cost of locomotion at a moderate, easily sustainable speed. We found that self-righting is, relatively, metabolically expensive and costs around two times the mass-specific power required to walk. Rapid movements of the limbs and head facilitate successful righting however, combined with the constraints of breathing whilst upside down, contribute a significant metabolic cost. Consequently, in the wild, these animals should favour environments or behaviours where the risk of becoming inverted is reduced.

Chelonian Sedation and Anesthesia

Anesthetic management of chelonians represents a unique challenge; the order Chelonia includes numerous species that display diverse anatomic features, habitats, body sizes, temperaments, and metabolic rates. Owing to their peculiar characteristics, safe and effective sedation and anesthesia may be more complicated than in other animals. For example, gas inductions are not indicated, and intravenous catheterization requires practice. The pharmacology of anesthetic drugs is severely impacted by body/environmental temperature, site of administration, and organ function. This review will summarize the current knowledge in terms of anatomy, physiology, and drug metabolism in chelonians, before discussing practical aspects of anesthesia.

Sedation and Anesthesia of Galapagos (Chelonoidis nigra), Aldabra (Aldabrachelys gigantea), and African Spurred Tortoises (Centrochelys sulcata): A Retrospective Review (2009-2019)

Simple Summary

Anesthesia is often required for the medical management of large tortoise species, but little has been published regarding effective anesthetic regimens for these species. The purpose of this study was to review anesthetic regimens that have been used safely and effectively in Galapagos (Chelonoidis nigra), Aldabra (Aldabrachelys gigantea), and African spurred (Centrochelys sulcata) tortoises, with the aim of improving medical management.

Abstract

Tortoises belong to the taxonomic family Testudinidae, which is considered one of the most imperiled families of the order Testudines. Anesthesia is often required for the medical and surgical management of large tortoises. The objectives of this retrospective study were to review drug regimens used to successfully anesthetize Galapagos (Chelonoidis nigra), Aldabra (Aldabrachelys gigantea) and African spurred (Centrochelys sulcata) tortoises, and to compare the times to effect and to extubation in tortoises administered different premedication protocols. Anesthetic records of giant tortoises admitted to the University of Florida College of Veterinary Medicine between January 2009 and December 2019 were reviewed. A total of 34 tortoises (six Aldabra, 23 Galapagos, and five African spurred) were included, resulting in 64 anesthetic events. Frequently used premedication protocols included an α₂-adrenergic agonist and ketamine combined with either midazolam (group α₂−adrenergic agonist, midazolam, ketamine, AMK; n = 34), a μ-opioid receptor agonist (group α₂−adrenergic agonist, μ-opioid receptor agonist, ketamine, AOK; n = 13), or a μ−opioid receptor agonist and midazolam (group α₂−adrenergic agonist, midazolam, μ-opioid receptor agonist, ketamine, AMOK; n = 10). Inhalant anesthetics (isoflurane, n = 21; sevoflurane, n = 23) were frequently used for maintenance of anesthesia following premedication. Out of the 34 total tortoises, 22 had only one anesthetic event, five had two anesthetic events, three had three anesthetic events, and four had four or more anesthetic events. Few adverse effects were observed and there was no mortality reported during the peri-anesthetic period. Sedation and general anesthesia of giant tortoises can be successfully performed with a combination of an α₂-adrenergic agonist and ketamine in combination with midazolam and/or a μ−opioid receptor agonist.

Shell and long-bone histology, skeletochronology, and lifestyle of Araripemys barretoi (Testudines: Pleurodira), a side-necked turtle of the Lower Cretaceous from Brazil

In this study we provide a comprehensive investigation of the microanatomical and microstructural aspects of the carapace and limb bones of the Early Cretaceous side-necked turtle, Araripemys barretoi, from the Araripe Basin, Brazil. Inter-elemental histovariability reveals different secondary remodelling of the skeletal elements within the same individual. The vascularisation is scarce and mainly longitudinal, also it ceases towards the bone surface, forming an avascular parallel-fibred bone with closely spaced LAGs. These traits indicate a late ontogenetic stage and a slow growth rate for one of the two A. barretoi specimens. The high cortical thickness of the costal plate suggests an increase of the shell stiffness. The elevated relative bone wall thickness of the ulna compared to other limb bones indicates a case of local pachyosteosclerosis, possibly to improve body stability in the aquatic environment.

Feasibility of a blind perineural injection technique for brachial plexus blockade in eastern box turtles (Terrapene carolina carolina): a cadaver study

OBJECTIVE

To describe the anatomy of the brachial plexus in eastern box turtles (Terrapene carolina carolina), develop a blind perineural injection technique for brachial plexus blockade and evaluate the distribution of three volumes of new methylene blue dye for injection in cadavers.

STUDY DESIGN

Prospective, randomized, blinded cadaveric study.

ANIMALS

A total of 24 frozen-thawed box turtle cadavers; two turtles identified with shoulder injuries were subsequently excluded from the study. The remaining 22 turtles weighed 397 (190-581) g, median (range).

METHODS

The brachial plexus and regional anatomy were identified by dissection of seven cadavers to determine anatomic landmarks for a perineural injection technique. This technique was tested by randomizing 15 cadavers into one of three groups to be injected bilaterally with one of three volumes (0.1, 0.2 or 0.3 mL) of methylene blue dye 1% aqueous solution. Investigators blinded to the assigned group dissected cadavers 15 minutes after injection and used staining of the four cervical spinal nerves (C5-C8; 25% for each nerve) to record a staining score of the brachial plexus (0-100%).

RESULTS

Based on descriptions of the anatomy of the brachial plexus, an injection technique was designed. Injections of 0.1 mL methylene blue dye resulted in nine/10 injections with 100% nerve stained, and one/10 injection with 50% (two) nerves stained. All injections of 0.2 or 0.3 mL of methylene blue dye resulted in 100% nerves stained.

CONCLUSIONS AND CLINICAL RELEVANCE

Perineural injection of the brachial plexus with 0.1, 0.2 or 0.3 mL methylene blue dye was successful in 29/30 injections in box turtle cadavers weighing 190-581 g. Further studies are needed to determine the minimum volume of injectate that can be successfully used for this technique, and to evaluate its application and efficacy in live turtles.

BLOOD LACTATE CONCENTRATIONS IN EASTERN BOX TURTLES (TERRAPENE CAROLINA CAROLINA) FOLLOWING CAPTURE BY A CANINE SEARCH TEAM

Studies to assess wildlife health commonly evaluate clinical pathology changes, immune responses, pathogen presence, and contaminant exposure, but novel modalities are needed to characterize the unique physiologic responses of reptiles. Lactate is an indicator of hypoperfusion and/or anaerobic respiration and can be quickly and easily measured using a point-of-care analyzer. This study evaluated baseline blood lactate concentrations in free-living eastern box turtles (Terrapene carolina carolina, n = 116) using a point of care analyzer and then determined the effect of handling time, physical examination (PE) abnormalities, and quantitative polymerase chain reaction pathogen detection (Terrapene herpesvirus 1, Mycoplasma sp., Terrapene adenovirus) on lactate concentrations. Blood lactate concentrations were higher in turtles with Terrapene herpesvirus 1 (n = 11), quiet mentation, and increased packed cell volume (P < 0.05). Lactate concentrations increased between initial capture and PE, with peak values reaching 129 min after capture. Lactate at PE was positively associated with baseline lactate concentrations. Turtles with Terrapene herpesvirus 1 may have alterations in blood flow, oxygen delivery, or activity patterns, driving increases in baseline lactate. Increased handling time likely leads to more escape behaviors and/or breath holding, causing turtles to undergo anaerobic metabolism and raising lactate concentrations. Overall, lactate measured by a point of care analyzer shows variability caused by capture and health factors in eastern box turtles and may be a useful adjunctive diagnostic test in this species after full methodologic validation.

Vertebrate Evolution Conserves Hindbrain Circuits despite Diverse Feeding and Breathing Modes

Feeding and breathing are two functions vital to the survival of all vertebrate species. Throughout the evolution, vertebrates living in different environments have evolved drastically different modes of feeding and breathing through using diversified orofacial and pharyngeal (oropharyngeal) muscles. The oropharyngeal structures are controlled by hindbrain neural circuits. The developing hindbrain shares strikingly conserved organizations and gene expression patterns across vertebrates, thus begs the question of how a highly conserved hindbrain generates circuits subserving diverse feeding/breathing patterns. In this review, we summarize major modes of feeding and breathing and principles underlying their coordination in many vertebrate species. We provide a hypothesis for the existence of a common hindbrain circuit at the phylotypic embryonic stage controlling oropharyngeal movements that is shared across vertebrate species; and reconfiguration and repurposing of this conserved circuit give rise to more complex behaviors in adult higher vertebrates.

Venous blood gas in free-living eastern box turtles (Terrapene carolina carolina) and effects of physiologic, demographic and environmental factors

Sustainable wildlife populations depend on healthy individuals, and the approach to determine wellness of individuals is multifaceted. Blood gas analysis serves as a useful adjunctive diagnostic test for health assessment, but it is uncommonly applied to terrestrial reptiles. This study established reference intervals for venous blood gas panels in free-living eastern box turtles (Terrapene carolina carolina, N = 102) from Illinois and Tennessee, and modeled the effects of environmental and physiologic parameters on each blood gas analyte. Blood gas panels included pH, partial pressure of oxygen (pO₂), partial pressure of carbon dioxide (pCO₂), total carbon dioxide (TCO₂), bicarbonate (HCO₃^-), base excess (BE) and lactate. Candidate sets of general linear models were constructed for each blood gas analyte and ranked using an information-theoretic approach (AIC). Season, packed cell volume (PCV) and activity level were the most important predictors for all blood gas analytes (P < 0.05). Elevations in PCV were associated with increases in pCO₂ and lactate, and decreases in pH, pO₂, HCO₃^-, TCO₂ and BE. Turtles with quiet activity levels had lower pH and pO₂ and higher pCO₂ than bright individuals. pH, HCO₃^-, TCO₂ and BE were lowest in the summer, while pCO₂ and lactate were highest. Overall, blood pH was most acidic in quiet turtles with elevated PCVs during summer. Trends in the respiratory and metabolic components of the blood gas panel tended to be synergistic rather than antagonistic, demonstrating that either (1) mixed acid-base disturbances are common or (2) chelonian blood pH can reach extreme values prior to activation of compensatory mechanisms. This study shows that box turtle blood gas analytes depend on several physiologic and environmental parameters and the results serve as a baseline for future evaluation.

How important is the CO2 chemoreflex for the control of breathing? Environmental and evolutionary considerations

Haldane and Priestley (1905) discovered that the ventilatory control system is highly sensitive to CO₂. This "CO₂ chemoreflex" has been interpreted to dominate control of resting arterial PCO₂/pH (P_aCO₂/pH_a) by monitoring P_aCO₂/pH_a and altering ventilation through negative feedback. However, P_aCO₂/pH_a varies little in mammals as ventilation tightly couples to metabolic demands, which may minimize chemoreflex control of P_aCO₂. The purpose of this synthesis is to (1) interpret data from experimental models with meager CO₂ chemoreflexes to infer their role in ventilatory control of steady-state P_aCO₂, and (2) identify physiological causes of respiratory acidosis occurring normally across vertebrate classes. Interestingly, multiple rodent and amphibian models with minimal/absent CO₂ chemoreflexes exhibit normal ventilation, gas exchange, and P_aCO₂/pH_a. The chemoreflex, therefore, plays at most a minor role in ventilatory control at rest; however, the chemoreflex may be critical for recovering P_aCO₂ following acute respiratory acidosis induced by breath-holding and activity in many ectothermic vertebrates. An apparently small role for CO₂ feedback in the genesis of normal breathing contradicts the prevailing view that central CO₂/pH chemoreceptors increased in importance throughout vertebrate evolution. Since the CO₂ chemoreflex contributes minimally to resting ventilation, these CO₂ chemoreceptors may have instead decreased importance throughout tetrapod evolution, particularly with the onset and refinement of neural innovations that improved the matching of ventilation to tissue metabolic demands. This distinct and elusive "metabolic ventilatory drive" likely underlies steady-state P_aCO₂ in air-breathers. Uncovering the mechanisms and evolution of the metabolic ventilatory drive presents a challenge to clinically-oriented and comparative respiratory physiologists alike.

Shoulder girdle rotation, forelimb movement and the influence of carapace shape on locomotion in Testudo hermanni (Testudinidae)

Studies into the function of structures are crucial for making connections between morphology and behaviour of organisms, but are still rare for the terrestrial Testudinidae. We investigated the kinematics of shoulder girdle and forelimb motion in Hermann's tortoise Testudo hermanni using biplanar X-ray fluoroscopy with a twofold aim: firstly, to understand how the derived shapes of shoulder girdle and carapace together influence rotation of the girdle; and, secondly, to understand how girdle rotation affects forelimb excursion. The total degree of shoulder rotation in the horizontal plane is similar to a species with a less domed shell, but because of the long and nearly vertically oriented scapular prong, shoulder girdle rotation contributes more than 30% to the horizontal arc of the humerus and nearly 40% to the rotational component of step length. The antebrachium and manus, which act as a functional unit, contribute roughly 50% to this component of the step length because of their large excursion almost parallel to the mid-sagittal plane. This large excursion is the result of the complex interplay between humerus long-axis rotation, counter-rotation of the antebrachium, and elbow flexion and extension. A significant proportion of forelimb step length results from body translation that is due to the propulsive effect of the other limbs during their stance phases. Traits that are similar to other tortoises and terrestrial or semi-aquatic turtles are the overall slow walk because of a low stride frequency, and the lateral-sequence, diagonally coupled footfall pattern with high duty factors. Intraspecific variation of carapace shape and shoulder girdle dimensions has a corresponding effect on forelimb kinematics.

Origin of the unique ventilatory apparatus of turtles

The turtle body plan differs markedly from that of other vertebrates and serves as a model system for studying structural and developmental evolution. Incorporation of the ribs into the turtle shell negates the costal movements that effect lung ventilation in other air-breathing amniotes. Instead, turtles have a unique abdominal-muscle-based ventilatory apparatus whose evolutionary origins have remained mysterious. Here we show through broadly comparative anatomical and histological analyses that an early member of the turtle stem lineage has several turtle-specific ventilation characters: rigid ribcage, inferred loss of intercostal muscles and osteological correlates of the primary expiratory muscle. Our results suggest that the ventilation mechanism of turtles evolved through a division of labour between the ribs and muscles of the trunk in which the abdominal muscles took on the primary ventilatory function, whereas the broadened ribs became the primary means of stabilizing the trunk. These changes occurred approximately 50 million years before the evolution of the fully ossified shell.

The evolutionary origin of the turtle shell and its dependence on the axial arrest of the embryonic rib cage

Turtles are characterized by their possession of a shell with dorsal and ventral moieties: the carapace and the plastron, respectively. In this review, we try to provide answers to the question of the evolutionary origin of the carapace, by revising morphological, developmental, and paleontological comparative analyses. The turtle carapace is formed through modification of the thoracic ribs and vertebrae, which undergo extensive ossification to form a solid bony structure. Except for peripheral dermal elements, there are no signs of exoskeletal components ontogenetically added to the costal and neural bones, and thus the carapace is predominantly of endoskeletal nature. Due to the axial arrest of turtle rib growth, the axial part of the embryo expands laterally and the shoulder girdle becomes encapsulated in the rib cage, together with the inward folding of the lateral body wall in the late phase of embryogenesis. Along the line of this folding develops a ridge called the carapacial ridge (CR), a turtle-specific embryonic structure. The CR functions in the marginal growth of the carapacial primordium, in which Wnt signaling pathway might play a crucial role. Both paleontological and genomic evidence suggest that the axial arrest is the first step toward acquisition of the turtle body plan, which is estimated to have taken place after the divergence of a clade including turtles from archosaurs. The developmental relationship between the CR and the axial arrest remains a central issue to be solved in future.

Evolution of air breathing: oxygen homeostasis and the transitions from water to land and sky

Life originated in anoxia, but many organisms came to depend upon oxygen for survival, independently evolving diverse respiratory systems for acquiring oxygen from the environment. Ambient oxygen tension (PO2) fluctuated through the ages in correlation with biodiversity and body size, enabling organisms to migrate from water to land and air and sometimes in the opposite direction. Habitat expansion compels the use of different gas exchangers, for example, skin, gills, tracheae, lungs, and their intermediate stages, that may coexist within the same species; coexistence may be temporally disjunct (e.g., larval gills vs. adult lungs) or simultaneous (e.g., skin, gills, and lungs in some salamanders). Disparate systems exhibit similar directions of adaptation: toward larger diffusion interfaces, thinner barriers, finer dynamic regulation, and reduced cost of breathing. Efficient respiratory gas exchange, coupled to downstream convective and diffusive resistances, comprise the "oxygen cascade"-step-down of PO2 that balances supply against toxicity. Here, we review the origin of oxygen homeostasis, a primal selection factor for all respiratory systems, which in turn function as gatekeepers of the cascade. Within an organism's lifespan, the respiratory apparatus adapts in various ways to upregulate oxygen uptake in hypoxia and restrict uptake in hyperoxia. In an evolutionary context, certain species also become adapted to environmental conditions or habitual organismic demands. We, therefore, survey the comparative anatomy and physiology of respiratory systems from invertebrates to vertebrates, water to air breathers, and terrestrial to aerial inhabitants. Through the evolutionary directions and variety of gas exchangers, their shared features and individual compromises may be appreciated.

The postpulmonary septum of Varanus salvator and its implication for Mosasaurian ventilation and physiology

The postpulmonary septum (PPS) is a relatively thick sheet of connective tissue covering the inferior surface of the lungs in varanid lizards. The primary connection of the PPS is to the medial surface of the ribs; additional connections occur to the inferior midline of the dorsal vertebrae, the pericardium, and a direct (through loose connective tissue) link to the surface of the lung. The PPS effectively partitions the coelomic cavity into peritoneal and pleural cavities. Investigation demonstrates that the PPS is not capable of preventing displacement of the more caudal (peritoneal) viscera, which is displaced cranially during terrestrial locomotion; this cranial displacement could impinge on the tidal volume of the lungs. Kinematic analyses of terrestrial and aquatic locomotion in Varanus salvator document the different propulsive mechanics used during movement through these two media, and, most importantly, the marked reduction in lateral displacement of the trunk during swimming. These findings, when combined with previous studies of the cardiovascular and respiratory system of varanids performing terrestrial locomotion, suggest that mosasaurs had a versatile, effective respiratory system and were likely capable of both sustained swimming and prolonged submersion, such as during ambush foraging.

Functional morphology and evolution of aspiration breathing in tetrapods

In the evolution of aspiration breathing, the responsibility for lung ventilation gradually shifted from the hyobranchial to the axial musculoskeletal system, with axial muscles taking over exhalation first, at the base of Tetrapoda, and then inhalation as well at the base of Amniota. This shift from hyobranchial to axial breathing freed the tongue and head to adapt to more diverse feeding styles, but generated a mechanical conflict between costal ventilation and high-speed locomotion. Some "lizards" (non-serpentine squamates) have been shown to circumvent this speed-dependent axial constraint with accessory gular pumping during locomotion, and here we present a new survey of gular pumping behavior in the tuatara and 40 lizard species. We observed gular pumping behavior in 32 of the 40 lizards and in the tuatara, indicating that the ability to inflate the lungs by gular pumping is a shared-derived character for Lepidosauria. Gular pump breathing in lepidosaurs may be homologous with buccal pumping in amphibians, but non-ventilatory buccal oscillation and gular flutter have persisted throughout amniote evolution and gular pumping may have evolved independently by modification of buccal oscillation. In addition to gular pumping in some lizards, three other innovations have evolved repeatedly in the major amniote clades to circumvent the speed-dependent axial constraint: accessory inspiratory muscles (mammals, crocodylians and turtles), changing locomotor posture (mammals and birds) and respiratory-locomotor phase coupling to reduce the mechanical conflict between aspiration breathing and locomotion (mammals and birds).

The Coupled Evolution of Breathing and Locomotion as a Game of Leapfrog

Because the increase in metabolic rate related to locomotor activity places demands on the cardiorespiratory apparatus, it is not surprising that the evolution of breathing and of locomotion are coupled. As the respiratory faculty becomes more refined, increasingly aerobic life strategies can be explored, and this activity is in turn expedited by a higher-performance respiratory apparatus. This apparent leapfrogging of respiratory and locomotor faculties begins in noncraniate chordates and continues in water-breathing and air-breathing vertebrates. Because both locomotor and cardiorespiratory activities are coordinated in the brain, neurological as well as biochemical coupling is evident. In spite of very different breathing mechanisms in various vertebrate groups, the basic respiratory control mechanisms appear to have been conserved, and respiratory-locomotor coupling is evident in all classes of vertebrates. Hypaxial body wall muscles that were strictly locomotor in fish have respiratory function in amniotes, but some locomotor function remains in all groups.

Oscillations in the Olfactory Bulb Carry Information About Odorant History

While odorant-evoked oscillations in the vertebrate olfactory bulb have been studied extensively, information about their possible cognitive role has been missing. Using voltage-sensitive dye imaging, we show that repeated odorant presentations with interstimulus intervals of 2–12 s had dramatic and diverse effects on the three oscillations that occur in the turtle olfactory bulb. Two of the oscillations are strikingly depressed in response to the second stimulation even of a new odorant was presented. The third oscillation is enhanced if the odorant is the same but suppressed if the odorant is new. The effects suggest that the oscillations carry information about odorant novelty and consistency.