Interpulse Interval Research Articles

The Effect of Inter-pulse Interval on TMS Motor Evoked Potentials in Active Muscles.

ObjectiveThe time interval between transcranial magnetic stimulation (TMS) pulses affects evoked muscle responses when the targeted muscle is resting. This necessitates using sufficiently long inter-pulse intervals (IPIs). However, there is some evidence that the IPI has no effect on the responses evoked in active muscles. Thus, we tested whether voluntary contraction could remove the effect of the IPI on TMS motor evoked potentials (MEPs).MethodsIn our study, we delivered sets of 30 TMS pulses with three different IPIs (2, 5, and 10 s) to the left primary motor cortex. These measurements were performed with the resting and active right hand first dorsal interosseous muscle in healthy participants (N = 9 and N = 10). MEP amplitudes were recorded through electromyography.ResultsWe found that the IPI had no significant effect on the MEP amplitudes in the active muscle (p = 0.36), whereas in the resting muscle, the IPI significantly affected the MEP amplitudes (p < 0.001), decreasing the MEP amplitude of the 2 s IPI.ConclusionsThese results show that active muscle contraction removes the effect of the IPI on the MEP amplitude. Therefore, using active muscles in TMS motor mapping enables faster delivery of TMS pulses, reducing measurement time in novel TMS motor mapping studies.

Kisspeptin Overcomes GnRH Neuronal Suppression Secondary to Hyperprolactinemia in Humans.

ContextHyperprolactinemia suppresses gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) pulses. The hypothalamic neuropeptide kisspeptin potently stimulates the secretion of GnRH. The effects of exogenous kisspeptin administration on GnRH pulse generation in the setting of hyperprolactinemia have not previously been explored.ObjectiveThis work aimed to examine the effects of kisspeptin on GnRH secretion, as reflected by LH secretion, in women with hyperprolactinemia.MethodsWomen with hyperprolactinemia (n = 11) participated in two 12-hour visits. Before study visits, participants underwent washout of dopamine agonist and/or combined oral contraceptive. Frequent blood sampling was performed (1 sample was collected every 10 minutes). Visit 1 involved no intervention, to examine baseline LH pulsatility. During visit 2, kisspeptin 112–121 (0.24 nmol/kg) was administered every 1 hour, for 10 hours. At hour 11, one intravenous bolus of GnRH (75 ng/kg) was administered.ResultsRepetitive intravenous bolus kisspeptin administration increased the total number of LH pulses in the setting of hyperprolactinemia. The interpulse interval declined during the same time frames. LH pulse amplitude did not change, but the mean LH rose. In 6 participants with progesterone levels suggestive of an anovulatory state, mean LH and estradiol levels increased significantly at visit 2. In the entire cohort, follicle-stimulating hormone and prolactin levels did not change significantly across the 2 visits. A total of 73% of subjects exhibited an LH pulse within 30 minutes of first kisspeptin dose.ConclusionKisspeptin is capable of stimulating hypothalamic GnRH-induced LH pulses in the setting of hyperprolactinemia.

A resonant cavity system for exposing cell cultures to intense pulsed RF fields

The IEEE and ICNIRP had specified a maximum permissible exposure for instantaneous peak electric field of 100 kV/m. However, no rationale was given for this limit. A novel exposure system was designed through a detailed process of analytical analysis, numerical modelling and prototype testing. The system consists of a cylindrical re-entrant resonant cavity that can achieve an electric field strength of more than 100 kV/m with an input power of 200 W. The working of the system was evaluated in simulation and experiment in terms of scattering parameters, electric field distributions and specific absorption rate. The system was then used to carry out in-vitro exposures of a human lymphoid cell line (GG0257) to a 1195 MHz signal at 53 dBm peak power and a pulse width of 550 ns at a range of interpulse intervals to identify heating-induced changes in cell viability. The proposed system offers high Q value of 5920 in unloaded condition which was reduced to 57 when loaded with 12 ml of cell culture but still offering 67 kV/m of the field intensity. Using the system for the exposure of GG0257 cells lasting 18 min, interpulse intervals of 11 μs or less caused a reduction in the number of viable cells and a corresponding increase in necrotic cells. For a shorter exposure duration of 6 min, the reduction in cell viability was seen at interpulse intervals of 5.5 μs or less. The designed exposure system is well capable of handling high intensity electric fields. Temperature measurements with a fibre optic probe and temperature sensitive labels showed that changes in viability were associated with temperature increases above 46 °C. This novel exposure system is an efficient means to investigate the possible relationship between peak field intensity and biological effects to provide a rationale behind the maximum exposure limit of 100 kV/m.

Adaptive temporal patterns of echolocation and flight behaviors used to fly through varied-sized windows by 2 species of high duty cycle bats.

As actively sensing animals guided by acoustic information, echolocating bats must adapt their vocal-motor behavior to various environments and behavioral tasks. Here, we investigated how the temporal patterns of echolocation and flight behavior were adjusted in 2 species of bats with a high duty cycle (HDC) call structure, Rhinolophus ferrumequinum and Hipposideros armiger, when they flew along a straight corridor and then passed through windows of 3 different sizes. We also tested whether divergence existed in the adaptations of the 2 species. Both H. armiger and R. ferrumequinum increased their call rates by shortening the pulse duration and inter-pulse interval for more rapid spatial sampling of the environment when flying through smaller windows. Bats produced more sonar sound groups (SSGs) while maintaining a stable proportion of calls that made up SSGs during approaches to smaller windows. The 2 species showed divergent adjustment in flight behavior across 3 different window sizes. Hipposideros armiger reduced its flight speed to pass through smaller windows while R. ferrumequinum increased its flight speed. Our results suggest that these 2 species of HDC bats adopt similar acoustic timing patterns for different tasks although they performed different flight behaviors.

Monophasic-Quadripulse Theta Burst Magnetic Stimulation for Motor Palsy Functional Evaluation After Intracerebral Hemorrhage.

Transcranial magnetic stimulation (TMS) is commonly employed for diagnostic and therapeutic purposes to enhance recovery following brain injury, such as stroke or intracerebral hemorrhage (ICH). Single-pulse TMS, most commonly used for diagnostic purposes and with motor evoked potential (MEP) recordings, is not suitable for clinical use in patients with severe motor paresis. To overcome this problem, we developed a quadripulse theta burst transcranial magnetic stimulation (QTS) device that combines the output from 16 stimulators to deliver a train of 16 monophasic magnetic pulses through a single coil. High-frequency theta rhythm magnetic bursts (bursts of four monophasic pulses, at 500 Hz, i.e., with a 2-ms interpulse interval, repeated at 5 Hz) were generated via a set of 16 separate magnetic stimulators connected to a specially designed combination module. No adverse effects or electroencephalogram (EEGs) abnormalities were identified during or after the recordings. MEP amplification in the QTS during four-burst theta rhythm stimulations produced four independent MEPs 20 ms after each burst onset maximizing the final third or fourth burst, which exhibited significantly greater amplitude than those resulting from a single burst or pulse. Motor functional palsy grades after ICH and QTS-MEP parameters and resting motor threshold (RMT) and amplitudes were significantly correlated (r = −0.83/−0.81 and 0.89/0.87; R2 = 0.69/0.66 and 0.79/0.76, p < 0.001; anterior/posterior-stimulus polarity, respectively). In conclusion, QTS-MEPs enabled a linear functional evaluation in patients with various degrees of motor paresis. However, the benefits, safety, and limitations of this device should be further explored in future studies.

Characterization of fin whale song off the Western Antarctic Peninsula.

Song is produced by a variety of terrestrial and marine animals and is particularly common among baleen whales. Fin whale (Balaenoptera physalus) song is comprised of relatively simple 20 Hz pulses produced at regular intervals. The timing of these intervals, in addition to the presence and frequency of overtones, appears to be unique to each population. The purpose of this study was to characterize Western Antarctic Peninsula fin whale song and describe temporal pattern variations in song type and occurrence. Recordings were collected in the area from 2001–2004 and again 2014–2016. One song type was identified with a primary inter-pulse interval (IPI) of approximately 14 s and secondary IPI of 12.5 s. This song occurred in three pattern variants: singlet, doublet, and long triplet. The interval between pulses increased by 1.5 s between recording periods while the frequency of the overtones decreased from 89 Hz to 86 Hz. Song was never recorded in August and while it was recorded at other times in some years, it was consistently present in recordings from April through June across all years. While multiple pattern variants were present each year, singlets were generally the most prevalent variant. Doublets and triplets occurred from February through June, with highest levels of variants in February. In later years the triplet variant presence increased and in 2016 it comprised 53% of recorded song bouts. Further research is needed to understand the reasons why song changes over time and to examine the feasibility of using song to delineate and identify populations.

Bio-Inspired Covert Active Sonar Detection Method Based on the Encoding of Sperm Whale Clicks

The covertness of an active sonar is a very important issue and the sonar signal waveform design was studied to improve covertness of the system. Click is one of the most common cetacean sounds, and has excellent detection performance. Meanwhile, existing interception systems normally classify cetacean sounds as ocean noise and filter them out. Based on this, a bio-inspired covert active sonar detection method is proposed by encoding the clicks produced by sperm whales. First, based on the frequency distribution characteristic of sperm whale clicks and frequency-hopping sequence, a set of bionic sub-pulses are constructed by encoding the centroid frequency of the real clicks. Based on the inter-click interval characteristic of the clicks and time-hopping sequence, the bionic sonar signal is constructed by combining the constructed bionic sub-pulses and encoding the inter-pulse interval between two adjacent pulses. Then, a single bionic sonar signal is utilized to estimate the speed and range of the target. Based on the characteristics of sperm whale click trains, a camouflage application method is designed to improve the camouflage ability of the bionic sonar signal. Finally, experiment results show that when the target speed is 5m/s and 10m/s and the signal to noise ratio varies from −20dB to 20dB, the root-mean-square error of estimated speed and range are lower than 0.1m/s and 0.1m, respectively. In addition, the constructed bionic sub-pulses have a 99% probability of being classified into sperm whale clicks. Experimental results demonstrate the effectiveness and covertness of the proposed method.

Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to One-Sixth-Octave Noise Bands Centered at 8 and 16 kHz: Effect of Duty Cycle and Testing the Equal-Energy Hypothesis

To determine the frequency-dependent susceptibility of California sea lions (Zalophus californianus) to noise-induced temporary hearing threshold shift (TTS), two subjects were exposed for 60 min to two fatiguing sounds: continuous one-sixth-octave noise bands (NBs) centered at 8 kHz (at sound exposure levels [SELs] of 166 to 190 dB re 1 µPa2s) and at 16 kHz (at SELs of 183 to 207 dB re 1 µPa2s). Using a psychoacoustic technique, TTSs were quantified at 8, 11.3, 16, 22.4, and 32 kHz (at the center frequency of each NB, half an octave higher, and one octave higher). For both NBs, higher SELs resulted in greater TTSs. In the SEL ranges that were tested, the largest TTSs occurred when the hearing test frequency was half an octave higher than the frequency of the fatiguing sound. When their hearing was tested at the same time after the fatiguing sounds stopped, initial TTSs and hearing recovery patterns were similar in both sea lions. The effect of fatiguing sound duty cycle on TTS was investigated with the 8 kHz NB, using 1,600 ms signals at a mean sound pressure level (SPL) of 154 dB re 1 µPa. Duty cycle reduction from 100 to 90% resulted in a large decrease in TTS; no TTS was observed at duty cycles ≤ 30%. The equal-energy hypothesis was tested with the 8 kHz NB and found to hold true: five combinations of SPL and exposure duration all resulting in a 182 dB SEL produced similar initial TTSs in both sea lions. These findings will contribute to the protection of otariid hearing from anthropogenic noise by facilitating the development of evidence-based underwater sound weighting functions. Our results also show that the introduction of short inter-pulse intervals to underwater sounds aids in the protection of otariid hearing by allowing recovery to take place.

How Fast Is Too Fast? Boundaries to the Perception of Electrical Stimulation of Peripheral Nerves.

Transcutaneous electrical stimulation is a promising technique for providing prosthetic hand users with information about sensory events. However, questions remain over how to design the stimulation paradigms to provide users the best opportunity to discriminate these events. Here, we investigate if the refractory period influences how the amplitude of the applied stimulus is perceived. Twenty participants completed a two-alternative forced choice experiment. We delivered two stimuli spaced between 250 ms to 450 ms apart (inter-stimulus-interval, isi). The participants reported which stimulus they perceived as strongest. Each stimulus consisted of either a single or paired pulse delivered transcutaneously. The inter-pulse interval (ipi) for the paired pulse stimuli varied between 6 and 10 ms. We found paired pulses with an ipi of 6 ms were perceived stronger than a single pulse less often than paired pulses with an ipi of 8 ms (p = 0.001) or 10 ms (p < 0.0001). Additionally, we found when the isi was 250 ms, participants were less likely to identify the paired pulse as strongest, than when the isi was 350 or 450 ms. This study emphasizes the importance of basing stimulation paradigms on the underlying neural physiology. The results indicate there is an upper limit to the commonly accepted notion that higher stimulation frequencies lead to stronger perception. If frequency is to be used to encode sensory events, then the results suggest stimulus paradigms should be designed using frequencies below 125 Hz.

Method for increasing the noise immunity of receiving UWB signals based on modulation of the duration of inter-pulse intervals in bit parcels

Method for increasing the noise immunity of receiving UWB signals based on modulation of the duration of inter-pulse intervals in bit parcels

Design and application of neural electrical stimulation system with time-varying parameters

Currently, commercial devices for electrical neural stimulations can only provide fixed stimulation paradigms with preset constant parameters, while the development of new stimulation paradigms with time-varying parameters has emerged as one of the important research directions for expanding clinical applications. To facilitate the performance of electrical stimulation paradigms with time-varying parameters in animal experiments, the present study developed a well-integrated stimulation system to output various pulse sequences by designing a LabVIEW software to control a general data acquisition card and an electrical stimulus isolator. The system was able to generate pulse sequences with inter-pulse-intervals (IPI) randomly varying in real time with specific distributions such as uniform distribution, normal distribution, gamma distribution and Poisson distribution. It was also able to generate pulse sequences with arbitrary time-varying IPIs. In addition, the pulse parameters, including pulse amplitude, pulse width, interphase delay of biphasic pulse and duration of pulse sequence, were adjustable. The results of performance tests of the stimulation system showed that the errors of the parameters of pulse sequences output by the system were all less than 1%. By utilizing the stimulation system, pulse sequences with IPI randomly varying in the range of 5~10 ms were generated and applied in rat hippocampal regions for animal experiments. The experimental results showed that, even with a same mean pulse frequency of ~130 Hz, for neuronal populations, the excitatory effect of stimulations with randomly varying IPIs was significantly greater than the effect of stimulations with fixed IPIs. In conclusion, the stimulation system designed here may provide a useful tool for the researches and the development of new paradigms of neural electrical stimulations.

ArTGen: An Arduino-based trigger generator to remotely handle pulse timing in TMS units

Abstract Introduction: Transcranial magnetic stimulation (TMS) protocols are associated with specific combinations of stimulation parameters, including the location of the targeted site, E-field intensity and orientation, pulse shape and duration, variable/fixed inter-pulse interval (IPI), and coil shape and dimension. Among these parameters, IPI may significantly affect the direction of induced neuroplasticity and the possible interference of habituation and expectation effects with TMS-evoked potentials. The TMS units are not always flexible enough to generate customized pulse sequences, thus external devices/software are commonly used. To remotely handle the randomization of IPI, we designed an effective and cheap device (ArTGen – Arduino Uno-based Trigger Generator) for generating arbitrary sequences of square-wave digital pulses. Materials and methods: Using an external foot-switch pedal the TMS experimenter is able to handle the ArTGen’s firmware to remotely drive a customized sequence of pulses in the TMS unit. We designed the firmware to switch among four conditions (single pulse, sequence of jittered pulses, pause and stop) based on a single and double foot-switch taping. We used two BNC sockets to manage respectively the foot-switch signal and the randomized TTLs in output to ArTGen. We tested ArTGen on Magstim Rapid2 with AirFilm® figure-8 coil in tasks with the following characteristics: (i) %Maximal Stimulation Output at 50%; (ii) 100 pulses and (iii) central pulse frequencies set to either 0.1, 5, 10, 15, or 20 Hz. Results: Our results show that all the TTLs released by ArTGen were correctly detected by Magstim Rapid2, and highlight a short delay (computed as the difference between the Arduino trigger and the Magstim Rapid2 output) of about 5μsec across all pulse frequencies. Conclusion: ArTGen is a stand-alone, portable, and not cumbersome opensource device used to randomize TMS pulses or to trigger/synchronize different devices in a closed-loop TMS system with microseconds of accuracy. Keywords: TMS unit, Arduino board, Inter Pulse Interval randomization, Closed Loop TMS System Synchronization

Forced mode locking in a semiconductor laser

A brief description of the theory of mode locking of a semiconductor laser when the modulating generator frequency is close to the intermode frequency is given. It is shown that during mode locking there is phase locking, due to which the dispersion of summed intensity in the interpulse interval tends to zero.

Phase entrainment by periodic stimuli in silico: A quantitative study

We present a quantitative study of phase entrainment by periodic visual stimuli in a biologically inspired neural network. The objective is to understand the neuronal population dynamics that underlie phase entrainment of brain oscillations by external stimuli, which is used for therapeutic treatment in neurological disorders, for example in Parkinsonian tremor. Yet, the neuronal dynamics underpinning such entrainment is not fully understood. Rhythmic sensory stimulation is one way of studying phase synchronisation in the brain. A recent experimental study has reported phase entrainment of brain oscillations during steady state visually evoked potentials (SSVEP), which are scalp electroencephalogram corresponding to periodic stimuli. We have simulated SSVEP-like signals corresponding to periodic pulse input to our in silico model. We have used phase locking values, normalised Shannon entropy and conditional probability as synchronisation indices to show phase synchrony in the neuronal populations. Our experiment demonstrates that the phase synchronisation disappears with jitter in the input inter-pulse intervals, and this would not be the case if the output signal were to be the superposition of the responses to the different input signals. Thus, the phase synchronisation implies entrainment of the network response by the periodic input. Overall, our study shows the plausibility of using biologically inspired in silico models, validated by experimental works, to understand and make testable predictions on brain entrainment as a therapeutic treatment in specific neurological disorders.

Clustering of sperm whales recorded by a single hydrophone

Sperm whales (Physter macrocephalus) produce echolocation clicks composed of several pulses while searching for food when diving. The clicks are composed of segments three of which are: the p0 pulse (3 kHz to 15 kHz), the p1 pulse (3 kHz to 15 kHz), and the Low Frequency (LF) signal (<3 kHz) (Zimmer, 2005). The LF signal is omnidirectional in nature unlike the p1 pulse which is very directional. The power in the LF signal recorded by a single hydrophone is a function of the distance of the whale from the hydrophone and the source level of the whale. The power contained in the LF portion of the clicks can be used to assign clicking whales to groups with each group consisting of a least one individual. The inter-pulse interval (IPI) can then be used to determine the lengths of the whales in each cluster adding confidence to the estimated number of whales producing the clicks. Continuous Wavelet Transforms are used with underwater acoustic data recorded in the Gulf of Mexico in 2015 to determine the power of the LF signal, the length of the clicking whale and the alignment of the acoustical axis of the whale with the hydrophone.

Fin whale localization and environmental inversion using modal arrivals of the 20-Hz pulse

Fin whale doublet calls, described as two 20-Hz pulses recorded at different interpulse intervals, have been attributed to the whale's calling behavior, however they could also result from acoustic mode propagation effects. Modes travel with their own frequency-dependent group velocities. The dispersion of these modes results in the sound being recorded as multiple arrivals on a receiver. Multiple modal arrivals of 20-Hz fin whale calls were recorded, with mode one arriving after mode two. The time delay between modal arrivals varied throughout the recording and is range dependent. The range dependency of this time delay was used to estimate the range of the whale from individual hydrophones by determining the modal group velocities that resulted in the observed delays. A pair of hydrophones was used to localize the whale for the duration of time when two modes were detected. The KRAKEN normal mode model was utilized in an inversion scheme to determine the compressional wave speed and depth-to-bedrock in the study area that supported the estimated modal group velocities. The inversion resulted in a depth-to-bedrock of 200 m and compressional wave speed of 1735 m/s, which were supported by measurements reported in literature for nearby regions. [Work supported by BOEM.]

A Model-Based Framework for Assessing the Physiologic Structure of Electrodermal Activity.

Objective:We present a statistical model for extracting physiologic characteristics from electrodermal activity (EDA) data in observational settings.Methods:We based our model on the integrate-and-fire physiology of sweat gland bursts, which predicts inverse Gaussian (IG) inter-pulse interval structure. At the core of our model-based paradigm is a subject-specific amplitude threshold selection process for EDA pulses based on the statistical properties of four right-skewed models including the IG. By performing a sensitivity analysis across thresholds and fitting all four models, we selected for IG-like structure and verified the pulse selection with a goodness-of-fit analysis, maximizing capture of physiology at the time scale of EDA responses.Results:We tested the model-based paradigm on simulated EDA time series and data from two different experimental cohorts recorded during different experimental conditions, using different equipment. In both the simulated and experimental data, our model-based method robustly recovered pulses that captured the IG-like structure predicted by physiology, despite large differences in noise level. In contrast, established EDA analysis tools, which attempted to estimate neural activity from slower EDA responses, did not provide physiological validation and were susceptible to noise.Conclusion:We present a computationally efficient, statistically rigorous, and physiology-informed paradigm for pulse selection from EDA data that is robust across individuals and experimental conditions, yet adaptable to varying noise level.Significance:The robustness of the model-based paradigm and its physiological basis provide empirical support for the use of EDA as a clinical marker for sympathetic activity in conditions such as pain, anxiety, depression, and sleep states.

Establishing the Minimum Intensity of Transcranial Magnetic Stimulation Superconditioning Pulses to Effect Inhibition and Facilitation of Motor Evoked Potentials.

Previously, we showed that a three-pulse train of weak transcranial magnetic stimulation (TMS) pulses-a superconditioning (SC) train-when followed by a stronger TMS pulse could enhance the inhibition or facilitation of the resultant motor evoked potential (MEP) compared with that seen with traditional dual-pulse inputs. The purpose of the present study was to establish the relative minimum intensity of SC pulses needed to influence MEP output and whether this differed for upper- versus lower-limb muscles. We examined 33 older adult subjects, targeting abductor pollicis brevis and tibialis anterior muscles. Older subjects were included in the anticipation of using findings from this study to guide further studies in persons with amyotrophic lateral sclerosis. Three-pulse trains of SC inputs of different intensities were delivered either 1 millisecond before (for inhibition) or 10 millisecond before (for facilitation) a stronger TMS test pulse. Motor evoked potential magnitudes for SC +test sets were normalized to test input responses and were compared within and between subjects. For inhibition, the minimum intensity of SC pulses needed to influence the follow-on MEP was found to be 60% of the target muscle's resting three-pulse MEP threshold for most abductor pollicis brevis and tibialis anterior muscles (2-millisecond interpulse intervals). For facilitation, somewhat higher intensities (70%) were typically needed to cause facilitation. Both values of SC pulses for inhibition/facilitation are considerably lower than the intensity of the conditioning pulse-often reported as 80% of the single-pulse threshold-typically used in dual-pulse TMS paradigms. This approach may allow testing of upper motor neuron function using weaker stimulus pulse intensities than are typically employed, improving testing compliance in persons whose thresholds are elevated because of injury or disease.

Corticosterone pattern-dependent glucocorticoid receptor binding and transcriptional regulation within the liver.

Ultradian glucocorticoid rhythms are highly conserved across mammalian species, however, their functional significance is not yet fully understood. Here we demonstrate that pulsatile corticosterone replacement in adrenalectomised rats induces a dynamic pattern of glucocorticoid receptor (GR) binding at ~3,000 genomic sites in liver at the pulse peak, subsequently not found during the pulse nadir. In contrast, constant corticosterone replacement induced prolonged binding at the majority of these sites. Additionally, each pattern further induced markedly different transcriptional responses. During pulsatile treatment, intragenic occupancy by active RNA polymerase II exhibited pulsatile dynamics with transient changes in enrichment, either decreased or increased depending on the gene, which mostly returned to baseline during the inter-pulse interval. In contrast, constant corticosterone exposure induced prolonged effects on RNA polymerase II occupancy at the majority of gene targets, thus acting as a sustained regulatory signal for both transactivation and repression of glucocorticoid target genes. The nett effect of these differences were consequently seen in the liver transcriptome as RNA-seq analysis indicated that despite the same overall amount of corticosterone infused, twice the number of transcripts were regulated by constant corticosterone infusion, when compared to pulsatile. Target genes that were found to be differentially regulated in a pattern-dependent manner were enriched in functional pathways including carbohydrate, cholesterol, glucose and fat metabolism as well as inflammation, suggesting a functional role for dysregulated glucocorticoid rhythms in the development of metabolic dysfunction.

Multi-decadal observations of the size structure of sperm whales at Kaikōura, New Zealand

ABSTRACT Measurements of body length play an important role in the assessment of size and population structure of whales, allowing estimation of population parameters such as age at sexual and physical maturity. Uniquely, sperm whales can be measured from the interpulse interval (IPI) of their echolocation clicks, which contain information on the length of the head, which is allometrically related to body length. Measurements of IPI were taken from 424 acoustic recordings made between 1996 and 2019 at Kaikōura, New Zealand. Extrapolation to total length, using a new regression equation calculated from this population, revealed a significant increase in the mean length of whales visiting Kaikōura during summer in recent years (2014–2019), with no trend in the mean length for those visiting in winter. Increasing size during summer months appears to be driven by the growth of the same individuals returning summer after summer, combined with declining recruitment of new, smaller individuals. Thus, we hypothesise that the whales that visit in summer may represent an aging population. This is significant as sperm whales are a taonga [Of special significance to NZ Māori] species, top predators in the Kaikōura ecosystem, and the primary focus of the tourism industry at Kaikōura.