The function of pitching in Beetle's flight revealed by insect-wearable backpack

The study of insect flight orientation is important for investigating flapping-wing aerodynamics and designing bioinspired micro air vehicles (MAVs). Pitch orientation plays a vital role in flight control, which has been explored less than directional control. In this study, the role of pitching maneuvers in flight was revealed by mounting an insect-wearable backpack on a beetle, which transformed the live insect into a bioelectronic device. The flight status of the cyborg beetle in a large chamber was recorded wirelessly. Accordingly, the pitch angle and forward acceleration showed a strong linear relationship. The coupling of pitch angle and forward acceleration was due to a tilted net aerodynamic force and the induced air drag. Moreover, the left and right subalar muscles of the beetle, a pair of major flight muscles, were electrically stimulated in free flight on demand to pitch up the beetle's body. We demonstrated that the induced nose-up movements were effective for decelerating the beetle in air. The flight orientation findings from the flying cyborgs would inspire a new approach to the study of flapping-wing flight and control of flapping-wing MAVs.

Insect-Computer Hybrid Robot

An insect–computer hybrid robot, often referred to as a biological machine or an insect cyborg, is the fusion of a living insect platform and artificial microdevices, including stimulators, sensors, and computers. When compared with the artificial robots, a hybrid robot can be operated as an autonomous mobile machine with low energy consumption and hardware costs. A hybrid machine can verify various biological hypotheses, such as function determination, by stimulating a muscle or any other structure.

Oral dosing of chemical indicators for in vivo monitoring of Ca2+ dynamics in insect muscle

This paper proposes a remarkably facile staining protocol to visually investigate dynamic physiological events in insect tissues. We attempted to monitor Ca²⁺ dynamics during contraction of electrically stimulated living muscle. Advances in circuit miniaturization and insect neuromuscular physiology have enabled the hybridization of living insects and man-made electronic components, such as microcomputers, the result of which has been often referred as a Living Machine, Biohybrid, or Cyborg Insect. In order for Cyborg Insects to be of practical use, electrical stimulation parameters need to be optimized to induce desired muscle response (motor action) and minimize the damage in the muscle due to the electrical stimuli. Staining tissues and organs as well as measuring the dynamics of chemicals of interest in muscle should be conducted to quantitatively and systematically evaluate the effect of various stimulation parameters on the muscle response. However, existing staining processes require invasive surgery and/or arduous procedures using genetically encoded sensors. In this study, we developed a non-invasive and remarkably facile method for staining, in which chemical indicators can be orally administered (oral dosing). A chemical Ca²⁺ indicator was orally introduced into an insect of interest via food containing the chemical indicator and the indicator diffused from the insect digestion system to the target muscle tissue. We found that there was a positive relationship between the fluorescence intensity of the indicator and the frequency of electrical stimulation which indicates the orally dosed indicator successfully monitored Ca²⁺ dynamics in the muscle tissue. This oral dosing method has a potential to globally stain tissues including neurons, and investigating various physiological events in insects.

A wearable wireless platform for visually stimulating small flying insects

Linking neurons and muscles to their roles in behavior requires not only the ability to measure their response during unrestrained movement but also the ability to stimulate them and observe the behavioral results. Current wireless stimulation technologies can be carried by rodent-sized animals and very large insects. However, the mass and volume of these devices make them impractical for studying smaller animals like insects. Here we present a battery-powered electronics platform suitable to be carried on a flying locust (2.7 g). The device has an IR-based (infrared) receiver, can deliver optical or electrical stimulation, occupies a volume of 0.1 cm(3), and weighs ~280 mg. We show the device is capable of powering two white SMD light emitting diodes (LEDs) for ~4 min and can be recharged in ~20 min. We demonstrate that our system shows no crosstalk with an IR-based Vicon tracking system. The entire package is made from commercial off-the-shelf components and requires no microfabrication.

Brightness discrimination in the day- and night-adapted wandering spider Cupiennius salei

Cupiennius salei is a nocturnal spider with eight eyes, which undergo a remarkable circadian cycle: the rhabdomeric membrane of the photoreceptor cells is dismantled during the day and rebuilt at the beginning of the night. Such drastic changes might influence the brightness discrimination ability. We tested this hypothesis by presenting square-shaped flickering stimuli with certain luminances on stationary backgrounds with other luminances to spiders with day- or night-adapted eyes. When the spider, through its three pairs of so-called secondary eyes, perceives a visible contrast between the stimulus and the background, its principal eye muscle activity should increase. We therefore recorded this activity in vivo to assess the brightness discrimination ability of Cupiennius salei. Our results show that this spider has good brightness discrimination ability, which is significantly better with dark-adapted eyes. A Michelson contrast of 0.1 to 0.2 at night, and of 0.2 to 0.3 for day-adapted eyes, is sufficient to elicit a significant response, except below a critical value of luminance (~16 cd m(-2)), where the minimal perceivable contrast needs to be higher. In the Discussion we compare these performances with those of other animals, in particular with jumping spiders.

Bilateral flight muscle activity predicts wing kinematics and 3-dimensional body orientation of locusts responding to looming objects

We placed locusts in a wind tunnel using a loose tether design that allowed for motion in all three rotational degrees of freedom during presentation of a computer-generated looming disc. High-speed video allowed us to extract wing kinematics, abdomen position and 3-dimensional body orientation. Concurrent electromyographic (EMG) recordings monitored bilateral activity from the first basalar depressor muscles (m97) of the forewings, which are implicated in flight steering. Behavioural responses to a looming disc included cessation of flight (wings folded over the body), glides and active steering during sustained flight in addition to a decrease and increase in wingbeat frequency prior to and during, respectively, an evasive turn. Active steering involved shifts in bilateral m97 timing, wing asymmetries and whole-body rotations in the yaw (ψ), pitch (χ) and roll (η) planes. Changes in abdomen position and hindwing asymmetries occurred after turns were initiated. Forewing asymmetry and changes in η were most highly correlated with m97 spike latency. Correlations also increased as the disc approached, peaking prior to collision. On the inside of a turn, m97 spikes occurred earlier relative to forewing stroke reversal and bilateral timing corresponded to forewing asymmetry as well as changes in whole-body rotation. Double spikes in each m97 occurred most frequently at or immediately prior to the time the locusts turned, suggesting a behavioural significance. These data provide information on mechanisms underlying 3-dimensional flight manoeuvres and will be used to drive a closed loop flight simulator to study responses of motion-sensitive visual neurons during production of realistic behaviours.

A battery-free multichannel digital neural/EMG telemetry system for flying insects

This paper presents a digital neural/EMG telemetry system small enough and lightweight enough to permit recording from insects in flight. It has a measured flight package mass of only 38 mg. This system includes a single-chip telemetry integrated circuit (IC) employing RF power harvesting for battery-free operation, with communication via modulated backscatter in the UHF (902-928 MHz) band. An on-chip 11-bit ADC digitizes 10 neural channels with a sampling rate of 26.1 kSps and 4 EMG channels at 1.63 kSps, and telemeters this data wirelessly to a base station. The companion base station transceiver includes an RF transmitter of +36 dBm (4 W) output power to wirelessly power the telemetry IC, and a digital receiver with a sensitivity of -70 dBm for 10⁻⁵ BER at 5.0 Mbps to receive the data stream from the telemetry IC. The telemetry chip was fabricated in a commercial 0.35 μ m 4M1P (4 metal, 1 poly) CMOS process. The die measures 2.36 × 1.88 mm, is 250 μm thick, and is wire bonded into a flex circuit assembly measuring 4.6 × 6.8 mm.

Possibilities offered by implantable miniaturized cuff-electrodes for insect neurophysiology

Recent advances in microsystems technology led to a miniaturization of cuff-electrodes, which suggests these electrodes not just for long-term neuronal recordings in mammalians, but also in medium-sized insects. In this study we investigated the possibilities offered by cuff-electrodes for neuroethology using insects as a model organism. The implantation in the neck of a tropical bushcricket resulted in high quality extracellular nerve recordings of different units responding to various acoustic, vibratory, optical and mechanical stimuli. In addition, multi-unit nerve activity related to leg movements was recorded in insects walking on a trackball. A drawback of bi-polar nerve recordings obtained during tethered flight was overlay of nerve activity with large amplitude muscle potentials. Interestingly, cuff-electrode recordings were robust to withstand walking and flight activity so that good quality nerve recordings were possible even three days after electrode implantation. Recording multi-unit nerve activity in intact insects required an elaborate spike sorting algorithm in order to discriminate neuronal units responding to external stimuli from background activity. In future, a combination of miniaturized cuff-electrodes and light-weight amplifiers equipped with a wireless transmitter will allow the investigation of neuronal processes underlying natural behavior in freely moving insects. By this means cuff-electrodes may contribute to the development of realistic neuronal models simulating neuronal processes underlying natural insect behavior, such like mate choice and predator avoidance.

Flicker-induced eye movements and the behavioural temporal cut-off frequency in a nocturnal spider

We investigated changes in the eye muscle activity in the spider Cupiennius salei as a response to temporal intensity modulations. These spiders are known to enhance eye muscle activity in their principal eyes when moving stimuli are detected in the secondary eyes. We measured the activity of the dorsal eye muscle using a small telemetric unit attached to the spiders' prosoma and confronted the animals to flicker stimuli presented on a cathode ray tube monitor. We registered a significant increase in eye muscle activity as response to temporal light intensity modulations, which implies that no directed motion is required to trigger the spiders' response. This allowed the determination of the behavioural temporal cut-off frequency. None of the frequencies higher than 8.6 cycles s(-1) and all of the frequencies lower than 4.3 cycles s(-1) elicited a significant increase in eye muscle activity. A behavioural cut-off frequency of only a few cycles per second is well in line with the temporal properties of the photoreceptor cells determined using intracellular recordings. A relatively low temporal resolution and a relatively high spatial resolution suit well C. salei's lifestyle as a nocturnal sit-and-wait hunter.

Active sensing in a freely walking spider: look where to go

The Central American hunting spider Cupiennius salei, like most other spiders, has eight eyes, one pair of principal eyes and three pairs of secondary eyes. The principal eyes and one pair of the secondary eyes have almost completely overlapping visual fields, and presumably differ in function. The retinae of the principal eyes can be moved independently by two pairs of eye muscles each, whereas the secondary eyes do not have such eye muscles. The behavioural relevance of retinal movements of freely moving spiders was investigated by a novel dual-channel telemetric registration of the eye muscle activities. Walking spiders shifted the ipsilateral retina with respect to the walking direction before, during and after a turning movement. The change in the direction of vision in the ipsilateral anterior median eye was highly correlated with the walking direction, regardless of the actual light conditions. The contralateral retina remained in its resting position. This indicates that Cupiennius salei shifts it visual field in the walking direction not only during but sometimes previous to an intended turn, and therefore "peers" actively into the direction it wants to turn.

Wireless Neural/EMG Telemetry Systems for Small Freely Moving Animals

We have developed miniature telemetry systems that capture neural, EMG, and acceleration signals from a freely moving insect or other small animal and transmit the data wirelessly to a remote digital receiver. The systems are based on custom low-power integrated circuits (ICs) that amplify, filter, and digitize four biopotential signals using low-noise circuits. One of the chips also digitizes three acceleration signals from an off-chip microelectromechanical-system accelerometer. All information is transmitted over a wireless ~ 900-MHz telemetry link. The first unit, using a custom chip fabricated in a 0.6- μm BiCMOS process, weighs 0.79 g and runs for two hours on two small batteries. We have used this system to monitor neural and EMG signals in jumping and flying locusts as well as transdermal potentials in weakly swimming electric fish. The second unit, using a custom chip fabricated in a 0.35-μ m complementary metal-oxide semiconductor CMOS process, weighs 0.17 g and runs for five hours on a single 1.5-V battery. This system has been used to monitor neural potentials in untethered perching dragonflies.

Colour blindness of the movement-detecting system of the spider Cupiennius salei

The nocturnal wandering spider Cupiennius salei has one pair of principal eyes and three pairs of secondary eyes located on the prosoma, which differ in both morphology and function. Their spectral sensitivity, measured with intracellular recordings, is due to three different types of photoreceptors with absorbance maxima in the mid-range of the spectrum, at 480 nm and 520 nm and in the UV at 360 nm. Based on these physiological data colour vision might be possible. In the present study, the ability to discriminate coloured moving stimuli from grey backgrounds was tested. The perception of moving coloured stripes in front of backgrounds with 29 different grey levels was measured by using extracellular recordings from the anterior median eye muscles as a monitoring system. Each of these eyes has two muscles, which increase their activity when moving stimuli are presented in front of a secondary eye. This variation in eye muscle activity can be recorded extracellulary in a living spider using a single channel telemetry device. If colour perception exists, the animal should be able to detect a moving coloured stripe in front of any grey level. Blue, green and red stripes were used as moving stimuli, in front of all 29 grey backgrounds. The results indicate that C. salei is not able to discriminate the coloured stimuli from distinct shades of grey. It is therefore evident that the movement-detecting system in this spider appears to be colour blind.

The orientation-dependent visual spatial cut-off frequency in a spider

Cupiennius salei (Araneae, Ctenidae) has, like most spiders, eight camera-type eyes. The anterior median eyes are called principal eyes and have a movable retina; all of the other eyes are referred to as secondary eyes and are equipped with a reflecting tapetum. The photoreceptors in the secondary eyes are arranged in rows on the tapetum and the inter-receptor angle along such a row is smaller than normal to it. In this study, the vertical and horizontal spatial cut-off frequencies of moving gratings were measured for the posterior median (PM) eyes, and the data were then compared with the anatomical data reported in the literature. Detection of moving objects in the secondary eyes enhances the eye muscle potential frequency in the principal eyes. We thus recorded the eye muscle activity with a telemetric unit as a monitor for motion detection while moving stimuli – sinusoidally modulated bright and dark stripes – were presented to the PM eyes on a computer screen. A significant increase in the eye muscle activity was measured for gratings at an angular wavelength of 2.0 deg in the vertical orientation and of 2.7 deg in the horizontal direction. In the vertical orientation the critical wavelength is twice the inter-receptor angle; in the horizontal orientation the spiders responded to wavelengths that are smaller than twice the corresponding inter-receptor angle. The cut-off frequency seems thus to be limited by the visual field of the photoreceptors rather than the inter-receptor angle. The relative intensity modulations modelled for the two different grating orientations in single photoreceptor cells were in line with our data.

Activity Patterns and Timing of Muscle Activity in the Forward Walking and Backward Walking Stick Insect Carausius morosus

Understanding how animals control locomotion in different behaviors requires understanding both the kinematics of leg movements and the neural activity underlying these movements. Stick insect leg kinematics differ in forward and backward walking. Describing leg muscle activity in these behaviors is a first step toward understanding the neuronal basis for these differences. We report here the phasing of EMG activities and latencies of first spikes relative to precise electrical measurements of middle leg tarsus touchdown and liftoff of three pairs ( protractor/retractor coxae, levator/depressor trochanteris, extensor/flexor tibiae) of stick insect middle leg antagonistic muscles that play central roles in generating leg movements during forward and backward straight walking. Forward walking stance phase muscle (depressor, flexor, and retractor) activities were tightly coupled to touchdown, beginning on average 93 ms prior to and 9 and 35 ms after touchdown, respectively. Forward walking swing phase muscle (levator, extensor, and protractor) activities were less tightly coupled to liftoff, beginning on average 100, 67, and 37 ms before liftoff, respectively. In backward walking the protractor/retractor muscles reversed their phasing compared with forward walking, with the retractor being active during swing and the protractor during stance. Comparison of intact animal and reduced two- and one-middle-leg preparations during forward straight walking showed only small alterations in overall EMG activity but changes in first spike latencies in most muscles. Changing body height, most likely due to changes in leg joint loading, altered the intensity, but not the timing, of depressor muscle activity.

Visual perception of motion in a hunting spider

Like most other spiders Cupiennius salei (Keyserling 1877) has two different eye types, one pair of principal eyes and three pairs of secondary eyes. The principal eyes have two eye muscles each, which allow movement of the retina and are mainly used for the discrimination of stationary objects. The secondary eyes without such eye muscles are supposed to detect moving objects. Masking experiments were used to analyse the role of these two eye types in motion detection. In a white arena the animals were stimulated with short sequences of moving black bars. The principal eyes move involuntarily when objects are moving within the visual field of an ipsilateral secondary eye. The eye muscle activity of the principal eyes was recorded using single channel telemetry, and activity changes were taken as an indicator for the perception of motion. Masking the principal eyes with black paint and presenting a moving visual stimulus did not modify the induced muscle activity, whereas masking the secondary eyes eliminated the increase in eye muscle activity. This suggests that the secondary eyes are responsible for movement detection. We conclude that the animals are able to detect moving targets visually only with the secondary eyes. The principal eyes, by contrast, do not seem to be involved in the detection of moving targets.

A Multitransducer Microsystem for Insect Monitoring and Control

This paper reports the development and in-vivo testing of a compact multitransducer microsystem intended for neuroethology experiments, including studies of gait dynamics in free-running insects. The system incorporates a combination of custom and off-the-shelf components. Its suite of measurement devices comprises leg-mounted strain gauges, electromyogram (EMG) and extracellular electrodes for the central nervous system, and a two-axis accelerometer. For signal conditioning and selection, the microsystem implements off-the-shelf electronics in a custom chip-on-board configuration. The microsystem measures 16 mm x 19 mm, supports 40 components and 56 I/O leads, and is assembled on a four-layer printed-circuit board. The entire system occupies only 0.65 cm3 and weighs less than 5 g. It has been successfully used to monitor leg-strain and EMG signals on walking cockroaches and for stimulation in the insect central nervous and muscular systems.

Turning manoeuvres in free-flying locusts: two-channel radio-telemetric transmission of muscle activity

A device has been constructed allowing the simultaneous transmission of two separate electrical signals in unrestrained small animals. We employed this device to investigate the motor output in free-flying locusts. The activation pattern of several combinations of different muscles was recorded, including bilateral symmetric muscles and pairs of antagonists. Particular attention was paid to the recruitment of a specific set of flight muscles in both winged segments during rolling manoeuvres. The relationship of the muscle activation with wing movement was analysed in combination with a high-speed video-monitoring. The muscles are activated in advance of the relevant stroke directions, in opposition to previous studies of tethered flying locusts. During turning manoeuvres a statistically significant difference in timing of the bilateral symmetric muscles is not apparent; this contrasts with the distinct difference revealed for the bilateral wing movement. It is discussed that rolling might rely on the fine tuned interaction of several major flight muscles or on the precise activation of a specific wing hinge muscle. Correspondence with investigations of bird flight is discussed.

An implantable electrode design for both chronic in vivo nerve recording and axon stimulation in freely behaving crayfish

A chronically implantable electrode design permitting alternate extracellular nerve recording and axon stimulation in freely behaving crayfish was developed. The electrode consists of a double hook made from 20 microm thin platinum wire that can be fitted to various nerve diameters, and is easily implantable. A fast curing, flexible two-component silicone was used for insulation. The double hook was connected to plugs and fixed on the carapace of a crayfish allowing the animals to roam freely. The setup also allows for repeated dis- and re-connection of the crayfish for alternating recording and stimulation. Two channel recordings were used to determine directionality and to discriminate between afferent activity of the two stretch receptor neurons and efferent activity of several motor neurons. In addition, they were also used to determine the conduction velocity of the recorded efferent activity. Stable two-channel recordings could be obtained for up to 5 months and 15 days without apparent effects on the animal. In vivo stimulation could be performed for at least 3 1/2 weeks. The implantable double hook is suitable for widespread use in invertebrate neurobiology.

A dual-channel FM transmitter for acquisition of flight muscle activities from the freely flying hawkmoth, Agrius convolvuli

Moths can perform various flight maneuvers by the contraction of some direct and indirect flight muscles. Multi-channel recording from these flight muscles and analysis of their interaction is very important for understanding insect flight motor system. In this study, we developed a dual-channel FM transmitter for acquisition of muscle potentials, with which a male hawkmoth (Agrius convolvuli) could fly freely and perform pheromone triggered zigzag flight in a wind tunnel. The transmitter weighs only 0.25 g including single battery, has a 5 m receivable range and works for more than 30 min. Doubling channels was achieved by providing two oscillators (the carrier frequencies were 82 and 85 MHz), and interference between them was overcome by buffer amplifiers and independent reference electrodes for each channel. With this transmitter, we could acquire muscle potentials from some direct and indirect muscles during free flight. Combined with simultaneous high-speed video analysis, we observed distinct changes of motor patterns during takeoff. Our radio-telemetric system allows acquisition of actual information from freely flying moths; such information will lead to further progress in the study of insect flight.

An ultralight biotelemetry backpack for recording EMG signals in moths

A two-channel FM biopotential recording system fabricated on a foldable, lightweight, polyimide substrate is presented. Each channel consists of a biopotential amplifier followed by a Colpitts oscillator with operating frequency tunable in the 88-108 MHz commercial FM band. The overall system measures 10 mm X 10 mm X 3 mm, weighs 0.74 g, uses two 1.5-V batteries, dissipates about 2 mW, and has a transmission range of 2 m. Using this system, electromyogram signals have been recorded from the dorsal ventral muscle and the dorsal longitudinal muscle of a giant sphinx moth (manduca sexta).

Tegula function during free locust flight in relation to motor pattern, flight speed and aerodynamic output

Tegulae are complex proprioceptors at the wing base of locusts. Deafferentation of the tegulae causes a lack of specific phasic information related to the wing downstroke and the timing of the upstroke. Employing telemetry during free flight of the locust Schistocerca gregaria, we investigated the consequences of tegula ablation on free flight parameters including motor patterns (wingbeat frequency and the relationship between the activation of flight muscle antagonists), free flight speed and aerodynamic output. We investigated the role of the tegula pairs of both wings on the motor pattern generated in free-flying locusts. We show that the tegula organs are not essential for generating the motor patterns necessary for free flight. However, they are required for increasing the motor output to give additional effective lifting power during adaptive behaviour. We also investigated long-term changes in the free flight parameters after tegula ablation. The recovery of the adult flight system revealed in the present study suggests that there is adaptation to the loss of proprioceptive information; this argues for a full functional and behavioural recovery of the flight system of the locust under closed-loop conditions.

A radiotelemetric 2-channel unit for transmission of muscle potentials during free flight of the desert locust, Schistocerca gregaria

A new radio-telemetric technique for neuroethological investigation of the natural behaviour of insects is presented. The 2-channel miniature transmitter device allows the transmission of electromyograms of 2 muscles during free flight of a locust. The mass of this transmitter and power supply is 0.55 g and can be carried by a mature female without marked impairment of the free-flight behaviour. The radiated power of the transmitter is approximately 20 nW and is sufficient to cover a range of more than 20 m. The carrier-frequency (145 MHz) of the system is frequency-modulated by the inputs of the 2 different channels. Channel separation is achieved by a multivibrator circuit. The chopping frequency (2 kHz) allows a convenient resolution of both signal channels. The design of the 2-channel transmitter device is presented and tested. Its relevance for the studies of natural flight of locusts is given, however, other applications are also feasible.

Neural mechanisms of behavior

Work during the past year has revealed increasing diversity and complexity of sensory inputs that trigger behavior, and correspondingly wide-ranging adaptations of sensory receptors and receptor organs. Many of these have been discovered by taking careful account of the animal in its natural habitat. Studies on central processing have made major strides in the understanding of neural maps and assembly codes. Studies that are primarily experimental, as opposed to theoretical, continue to produce most of the significant advances in this field. Perhaps the single most dominant theme has been the continuing erasure of the line separating invertebrate and vertebrate neurobehavioral systems.