Sound production biomechanics in three-spined toadfish and potential functional consequences of swim bladder morphology in the Batrachoididaea).

The relationship between sound complexity and the underlying morphology and physiology of the vocal organ anatomy is a fundamental component in the evolution of acoustic communication, particularly for fishes. Among vertebrates, the mammalian larynx and avian syrinx are the best-studied vocal organs, and their ability to produce complex vocalizations has been modeled. The range and complexity of the sounds in mammalian lineages have been attributed, in part, to the bilateral nature of the vocal anatomy. Similarly, we hypothesize that the bipartite swim bladder of some species of toadfish (family Batrachoididae) is responsible for complex nonlinear characters of the multiple call types that they can produce, supported by nerve transection experiments. Here, we develop a low-dimensional coupled-oscillator model of the mechanics underlying sound production by the two halves of the swim bladder of the three-spined toadfish, Batrachomoeus trispinosus. Our model was able to replicate the nonlinear structure of both courtship and agonistic sounds. The results provide essential support for the hypothesis that fishes and tetrapods have converged in an evolutionary innovation for complex acoustic signaling, namely, a relatively simple bipartite mechanism dependent on sonic muscles contracting around a gas filled structure.

A bio-inspired spatial patterning circuit.

Lateral Inhibition (LI) is a widely conserved patterning mechanism in biological systems across species. Distinct from better-known Turing patterns, LI depend on cell-cell contact rather than diffusion. We built an in silico genetic circuit model to analyze the dynamic properties of LI. The model revealed that LI amplifies differences between neighboring cells to push them into opposite states, hence forming stable 2-D patterns. Inspired by this insight, we designed and implemented an electronic circuit that recapitulates LI patterning dynamics. This biomimetic system serve as a physical model to elucidate the design principle of generating robust patterning through spatial feedback, regardless of the underlying devices being biological or electrical.

A cost-effective and field-ready potentiostat that poises subsurface electrodes to monitor bacterial respiration.

Here, we present the proof-of-concept for a subsurface bioelectrochemical system (BES)-based biosensor capable of monitoring microbial respiration that occurs through exocellular electron transfer. This system includes our open-source design of a three-channel microcontroller-unit (MCU)-based potentiostat that is capable of chronoamperometry, which laboratory tests showed to be accurate within 0.95 ± 0.58% (95% Confidence Limit) of a commercial potentiostat. The potentiostat design is freely available online: http://angenent.bee.cornell.edu/potentiostat.html. This robust and field-ready potentiostat, which can withstand temperatures of -30°C, can be manufactured at relatively low cost ($600), thus, allowing for en-masse deployment at field sites. The MCU-based potentiostat was integrated with electrodes and a solar panel-based power system, and deployed as a biosensor to monitor microbial respiration in drained thaw lake basins outside Barrow, AK. At three different depths, the working electrode of a microbial three-electrode system (M3C) was maintained at potentials corresponding to the microbial reduction of iron(III) compounds and humic acids. Thereby, the working electrode mimics these compounds and is used by certain microbes as an electron acceptor. The sensors revealed daily cycles in microbial respiration. In the medium- and deep-depth electrodes the onset of these cycles followed a considerable increase in overall activity that corresponded to those soils reaching temperatures conducive to microbial activity as the summer thaw progressed. The BES biosensor is a valuable tool for studying microbial activity in situ in remote environments, and the cost-efficient design of the potentiostat allows for wide-scale use in remote areas.

Nonlinear acoustic complexity in a fish 'two-voice' system.

Acoustic signals play essential roles in social communication and show a strong selection for novel morphologies leading to increased call complexity in many taxa. Among vertebrates, repeated innovations in the larynges of frogs and mammals and the syrinx of songbirds have enhanced the spectro-temporal content, and hence the diversity of vocalizations. This acoustic diversification includes nonlinear characteristics that expand frequency profiles beyond the traditional categorization of harmonic and broadband calls. Fishes have remained a notable exception to evidence for such acoustic innovations among vertebrates, despite their being the largest group of living vertebrates that also exhibit widespread evolution of sound production. Here, we combine rigorous acoustic and mathematical analyses with experimental silencing of the vocal motor system to show how a novel swim bladder mechanism in a toadfish enables it to generate calls exhibiting nonlinearities like those found among frogs, birds and mammals, including primates. By showing that fishes have evolved nonlinear acoustic signalling like all other major lineages of vocal vertebrates, these results suggest strong selection pressure favouring this mechanism to enrich the spectro-temporal content and complexity of vocal signals.

Real-time development of data acquisition and analysis software for hands-on physiology education in neuroscience: G-PRIME.

We report on the real-time creation of an application for hands-on neurophysiology in an advanced undergraduate teaching laboratory. Enabled by the rapid software development tools included in the Matlab technical computing environment (The Mathworks, Natick, MA), a team, consisting of a neurophysiology educator and a biophysicist trained as an electrical engineer, interfaced to a course of approximately 15 students from engineering and biology backgrounds. The result is the powerful freeware data acquisition and analysis environment, "g-PRIME." The software was developed from week to week in response to curriculum demands, and student feedback. The program evolved from a simple software oscilloscope, enabling RC circuit analysis, to a suite of tools supporting analysis of neuronal excitability and synaptic transmission analysis in invertebrate model systems. The program has subsequently expanded in application to university courses, research, and high school projects in the US and abroad as free courseware.

Low-cost, high-fidelity, adaptive cancellation of periodic 60 Hz noise.

A common method to eliminate unwanted power line interference in neurobiology laboratories where sensitive electronic signals are measured is with a notch filter. However a fixed-frequency notch filter cannot remove all power line noise contamination since inherent frequency and phase variations exist in the contaminating signal. One way to overcome the limitations of a fixed-frequency notch filter is with adaptive noise cancellation. Adaptive noise cancellation is an active approach that uses feedback to create a signal that when summed with the contaminated signal destructively interferes with the noise component leaving only the desired signal. We have implemented an optimized least mean square adaptive noise cancellation algorithm on a low-cost 16 MHz, 8-bit microcontroller to adaptively cancel periodic 60 Hz noise. In our implementation, we achieve between 20 and 25 dB of cancellation of the fundamental 60 Hz noise component.

g-PRIME: A Free, Windows Based Data Acquisition and Event Analysis Software Package for Physiology in Classrooms and Research Labs.

We present g-PRIME, a software based tool for physiology data acquisition, analysis, and stimulus generation in education and research. This software was developed in an undergraduate neurophysiology course and strongly influenced by instructor and student feedback. g-PRIME is a free, stand-alone, windows application coded and "compiled" in Matlab (does not require a Matlab license). g-PRIME supports many data acquisition interfaces from the PC sound card to expensive high throughput calibrated equipment. The program is designed as a software oscilloscope with standard trigger modes, multi-channel visualization controls, and data logging features. Extensive analysis options allow real time and offline filtering of signals, multi-parameter threshold-and-window based event detection, and two-dimensional display of a variety of parameters including event time, energy density, maximum FFT frequency component, max/min amplitudes, and inter-event rate and intervals. The software also correlates detected events with another simultaneously acquired source (event triggered average) in real time or offline. g-PRIME supports parameter histogram production and a variety of elegant publication quality graphics outputs. A major goal of this software is to merge powerful engineering acquisition and analysis tools with a biological approach to studies of nervous system function.

Flexible multielectrodes can resolve multiple muscles in an insect appendage.

Research into the neuromechanical basis of behavior, either in biomechanics, neuroethology, or neuroscience, is frequently limited by methods of data collection. Two of the most pressing needs are for methods with which to (1) record from multiple neurons or muscles simultaneously and (2) perform this recording in intact, behaving animals. In this paper we present the fabrication and testing of flexible multielectrode arrays (fMEAs) that move us significantly towards these goals. The fMEAs were used to record the activity of several distinct units in the coxa of the cockroach Blaberus discoidalis. The devices fabricated here address the first goal in two ways: (1) their flexibility allows them to be inserted into an animal and guided through internal tissues in order to access distinct groups of neurons and muscles and (2) their recording site geometry has been tuned to suit the anatomy under study, yielding multichannel spike waveforms that are easily separable under conditions of spike overlap. The flexible nature of the devices simultaneously addresses the second goal, in that it is less likely to interfere with the natural movement of the animal.

Midbrain periaqueductal gray and vocal patterning in a teleost fish.

Midbrain structures, including the periaqueductal gray (PAG), are essential nodes in vertebrate motor circuits controlling a broad range of behaviors, from locomotion to complex social behaviors such as vocalization. Few single-unit recording studies, so far all in mammals, have investigated the PAG's role in the temporal patterning of these behaviors. Midshipman fish use vocalization to signal social intent in territorial and courtship interactions. Evidence has implicated a region of their midbrain, located in a similar position as the mammalian PAG, in call production. Here, extracellular single-unit recordings of PAG neuronal activity were made during forebrain-evoked fictive vocalizations that mimic natural call types and reflect the rhythmic output of a known hindbrain-spinal pattern generator. The activity patterns of vocally active PAG neurons were mostly correlated with features related to fictive call initiation. However, spike trains in a subset of neurons predicted the duration of vocal output. Duration is the primary feature distinguishing call types used in different social contexts and these cells may play a role in directly establishing this temporal dimension of vocalization. Reversible, lidocaine inactivation experiments demonstrated the necessity of the midshipman PAG for fictive vocalization, whereas tract-tracing studies revealed the PAG's connectivity to vocal motor centers in the fore- and hindbrain comparable to that in mammals. Together, these data support the hypotheses that the midbrain PAG of teleosts plays an essential role in vocalization and is convergent in both its functional and structural organization to the PAG of mammals.

Measuring and quantifying dynamic visual signals in jumping spiders.

Animals emit visual signals that involve simultaneous, sequential movements of appendages that unfold with varying dynamics in time and space. Algorithms have been recently reported (e.g. Peters et al. in Anim Behav 64:131-146, 2002) that enable quantitative characterization of movements as optical flow patterns. For decades, acoustical signals have been rendered by techniques that decompose sound into amplitude, time, and spectral components. Using an optic-flow algorithm we examined visual courtship behaviours of jumping spiders and depict their complex visual signals as "speed waveform", "speed surface", and "speed waterfall" plots analogous to acoustic waveforms, spectrograms, and waterfall plots, respectively. In addition, these "speed profiles" are compatible with analytical techniques developed for auditory analysis. Using examples from the jumping spider Habronattus pugillis we show that we can statistically differentiate displays of different "sky island" populations supporting previous work on diversification. We also examined visual displays from the jumping spider Habronattus dossenus and show that distinct seismic components of vibratory displays are produced concurrently with statistically distinct motion signals. Given that dynamic visual signals are common, from insects to birds to mammals, we propose that optical-flow algorithms and the analyses described here will be useful for many researchers.

Vocal pathways modulate efferent neurons to the inner ear and lateral line.

All sonic vertebrates face the problem of sound production interfering with their ability to detect and process external acoustic signals, including conspecific vocalizations. Direct efferent inputs to the inner ear of all vertebrates, and the lateral line system of some aquatic vertebrates, represent a potential mechanism to adjust peripheral sensitivity during sound production. We recorded from single efferent neurons that innervate the inner ear and lateral line in a sound-producing teleost fish while evoking fictive vocalizations predictive of the temporal features of natural vocalizations. The majority of efferent neurons showed an increase in activity that occurred in-phase with modulations in the fine temporal structure of the fictive vocalizations. Many of these neurons also showed a decrease in activity at fictive vocal offset. Efferents to the sacculus, the main auditory end organ, showed features especially well adapted for maintaining sensitivity to external acoustic signals during sound production. These included robust phase locking of efferent activity to each cycle of a fictive vocalization and a long-duration rebound suppression after each fictive vocalization that could provide a rapid, long-lasting period of sensitization to external acoustic stimuli such as the call of a conspecific. These results suggest that efferent activation by the vocal motor system can directly modulate auditory sensitivity to self-generated sounds and maintain sensitivity to ongoing external sounds. Given the conserved organization of the auditory efferent system across vertebrates, such mechanisms may be operative among all sonic vertebrates.

Tools for physiology labs: inexpensive equipment for physiological stimulation.

We describe the design of inexpensive equipment and software for physiological stimulation in the neurobiology teaching laboratory. The core component is a stimulus isolation unit (SIU) that uses DC-DC converters, rather than expensive high-voltage batteries, to generate isolated power at high voltage. The SIU has no offset when inactive and produces pulses up to 100 V with moderately fast (50 µs) rise times. We also describe two methods of stimulus timing control. The first is a simplified conventional, stand-alone analog pulse generator. The second uses a digital microcontroller interfaced with a personal computer. The SIU has performed well and withstood intensive use in our undergraduate physiology laboratory. This project is part of our ongoing effort to make reliable low-cost physiology equipment available for both student teaching and faculty research laboratories.