A comparison of signal detection between an echolocating dolphin and an optimal receiver

Summary An electronic simulated target apparatus was used in a two-experiment study to compare the target detection performance of an echolocating bottlenose dolphin with an optimal receiver. Random Gaussian noise with a relatively flat spectrum from 20 to 160 kHz was used as a masking source. Experiment I was conducted to establish a technique for estimating the echo energy-to-noise ratio,E _e /N, at the dolphin's threshold of detection. Dolphins typically vary the amplitude of their emitted signal over a large range making it difficult to estimateE _e /N. In the first part of experiment I, the simulated echo was a double click, the pulses separated by 200 s, with each pulse being a replica of the dolphin's transmitted signal. A staircase psychophysical procedure was used to obtain the detection threshold, and the echo energy-to-noise ratio based on the highest amplitude click emitted per trial, (E _e /N)_max, was determined at each reversal point. The second echo type consisted of one of the animal's echolocation clicks, previously measured, digitized and stored in an erasable programmable read-only memory (EPROM). The electronic target simulator was modified so that every time the dolphin emitted an echolocation signal, the EPROM was triggered to produce two pulses separated by 200 s. On any trial, the EPROM signal was played back at a fixed amplitude, regardless of the amplitude of the dolphin's emitted signal. TheE _e /N obtained with the EPROM signal at threshold was found to be 2.9 dB lower than (E _e /N)_max obtained with the normal phantom target. Therefore an estimate ofE _e /N can be obtained by subtracting 2.9 dB from (E _e /N)_max.Experiment II was conducted to obtain isosensitivity data that could be plotted in an ROC (receiver operating characteristic) format. The response bias of the dolphin was manipulated by varying the food reinforcement payoff matrix. In terms of the ratio of correct detections to correct rejections, the payoff matrix was varied over four values: 11, 41, 81, and 14. A modified method of constants procedure was used to obtain the dolphin target detection performance data. Each session consisted of two 20-trial blocks in which a strong echo was used in the first block and a weak echo in the second block. The energy-to-noise ratio required by an optimal detector to approximate the dolphin's performance was obtained by determining the appropriate detection sensitivity,d, that best fitted the dolphin's data plotted in an ROC format. The results of experiment II indicated that the dolphin required approximately 7.4 dB higherE _e /N than an optimal detector to detect the phantom target.Abbreviations response bias - d detection sensitivity - E _e echo energy flux density - EPROM erasable programmable read-only memory - N noise spectral density - p(t) instantaneous acoustic pressure - P(Y/SN) probability of detection - P(Y/N) probability of false alarm - ROC receiver-operating-characteristics - SE source energy flux density     

Cochlear Responses to Condensation and Rarefaction Clicks

Auditory nerve responses to condensation and rarefaction clicks (CC and RC) have been recorded over a wide intensity range with gross electrodes. At low intensities the RC responses are nearly identical to CC responses. At high intensities RC and CC response waveforms are similar, but the latency of the N₁ peak in the RC response is 0.2 msec. shorter than that for the corresponding CC response. At intermediate intensities the RC and CC response waveforms are quite different. These results can be interpreted in terms of a model in which there are two excitatory mechanisms for the neural response, which are operative in different intensity ranges. The cochlear microphonic potential and a “slow” potential are suggested as possible excitatory mechanisms.     

Inhibitory control of sensory gating in a computer model of the CA3 region of the hippocampus

 A model of the CA3 region of the hippocampus was used to simulate the P50 auditory-evoked potential response to repeated stimuli in order to study the neuronal circuits involved in a sensory-processing deficit associated with schizophrenia. Normal subjects have a reduced P50 auditory-evoked potential amplitude in response to the second of two paired auditory click stimuli spaced 0.5 s apart. However, schizophrenic patients do not gate or reduce their response to the second click. They have equal auditory-evoked response amplitudes to both clicks. When schizophrenic patients were medicated with traditional neuroleptics, the evoked potential amplitude to both clicks increased, but gating of the second response was not restored or improved. Animal studies suggest a role for septohippocampal cholinergic activity in sensory gating. We used a computational model of this system in order to study the relative contributions of local processing and afferent activity in sensory gating. We first compared the effect of information representation as average firing rate to information representation as cell assemblies in order to evaluate the best method to represent the response of hippocampal neurons to the auditory click. We then studied the effects of nicotinic cholinergic input on the response of the network and the effect of GABA_B receptor activation on the ability of the local network to suppress the test response. The results of our model showed that nicotinic cholinergic input from the septum to the hippocampus can control the flow of sensory information from the cortex into the hippocampus. In addition, postsynaptic GABA_B receptor activation was not sufficient to suppress the test response when the interstimulus interval was 500 ms. However, presynaptic GABA_B receptor activity may be responsible for the suppression of the test response at this interstimulus interval. Received: 3 December 2001 / Accepted: 23 October 2002 / Published online: 28 February 2003 Correspondence to: K. A. Moxon (e-mail: karen.moxon@drexel.edu, Tel.:+1-215-8951959, Fax: +1-215-8954983) Supported by USPHS, MH01245, MH58414, MH-50787, MH-01121, and research grants from the Department of Veterans Affairs and the National Alliance for Research on Schizophrenia and Depression.     

CONFERENCE REPORT

ABSTRACT

Sperm whale Physeter macrocephalus L. clicks have been studied for nearly fifty years, during which time great efforts have been made to understand the functions and production mechanisms of this sound. Other than clicks, sperm whales may also produce low intensity sounds arranged in short sequences, named trumpets, which have been recorded occasionally in the past by few groups of researchers. Sperm whale recordings collected in the Mediterranean Sea with a towed array and digital tags were used to describe the temporal and spectral characteristics of trumpets. This sound is made of a series of repeated units, around 0.2 s long, arranged in short sequences lasting between 0.6 s to 3.5 s. Each of these units comprises an amplitude modulated tonal waveform with a complex harmonic structure, and a spectrum composed of a low frequency component at 500 Hz and a mid-frequency component at 3 kHz. The apparent source level could be estimated for one of the trumpets and was estimated to be 172 dB_pp re: 1μPa at lm with energy flux density of 147 dB re: 1μ Pa²s.     

Investigation of electrical responses recorded from the fenestra cochleae in cats

Electrical responses of the fenestra cochleae to stimulation by clicks of different intensity, polarity, and frequency, were studied in anesthetized cats. The absolute values of amplitude and latent period of the neural component of the response reflect the physiological state of the auditory nerve. Besides ordinary potentials characterized by peaks N1 and N2, specific responses were observed when clicks with an intensity of 85 dB or "rarefaction" clicks were used. Dependence of the amplitude of these responses on the intensity of acoustic stimuli of different polarity was investigated during a change in the rhythm of the stimulation; the effect of different rhythms of stimulation on the gradient of the curve reflecting this relationship was examined. The possible mechanisms of the effect of stimulus frequency are discussed.Scientific-Research Institute of Otolaryngology, Ministry of Health of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 151–157, March–April, 1979.     

An acoustic valve within the nose of sperm whales Physeter macrocephalus

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Primary Sensory and Motor Cortex Excitability Are Co-Modulated in Response to Peripheral Electrical Nerve Stimulation

Peripheral electrical stimulation (PES) is a common clinical technique known to induce changes in corticomotor excitability; PES applied to induce a tetanic motor contraction increases, and PES at sub-motor threshold (sensory) intensities decreases, corticomotor excitability. Understanding of the mechanisms underlying these opposite changes in corticomotor excitability remains elusive. Modulation of primary sensory cortex (S1) excitability could underlie altered corticomotor excitability with PES. Here we examined whether changes in primary sensory (S1) and motor (M1) cortex excitability follow the same time-course when PES is applied using identical stimulus parameters. Corticomotor excitability was measured using transcranial magnetic stimulation (TMS) and sensory cortex excitability using somatosensory evoked potentials (SEPs) before and after 30 min of PES to right abductor pollicis brevis (APB). Two PES paradigms were tested in separate sessions; PES sufficient to induce a tetanic motor contraction (30–50 Hz; strong motor intensity) and PES at sub motor-threshold intensity (100 Hz). PES applied to induce strong activation of APB increased the size of the N₂₀-P₂₅ component, thought to reflect sensory processing at cortical level, and increased corticomotor excitability. PES at sensory intensity decreased the size of the P25-N33 component and reduced corticomotor excitability. A positive correlation was observed between the changes in amplitude of the cortical SEP components and corticomotor excitability following sensory and motor PES. Sensory PES also increased the sub-cortical P₁₄-N₂₀ SEP component. These findings provide evidence that PES results in co-modulation of S1 and M1 excitability, possibly due to cortico-cortical projections between S1 and M1. This mechanism may underpin changes in corticomotor excitability in response to afferent input generated by PES.     

Parameters of the Spinal Dorsal Surface Potential under Conditions of Experimental Hyperthyroidism

On Wistar rats with experimental hyperthyroidism (HTh) and a control group of the rats, we measured the parameters of the components of the spinal dorsal surface potentials (DSP) evoked by stimulation of the corresponding lumbar dorsal roots; the afferent spike (AS), N ₁-N ₃ components, and P wave were examined. After development of HTh, the amplitudes of all DSP components dramatically increased (by a factor from 1.8 to 3.1) with a simultaneous noticeable increase in the thresholds of the AS and N ₁-N ₃ DSP components and a drop in their chronaxia. Under the above conditions, there were no significant changes in the intensity of occlusion and characteristics of the heterosynaptic intersegmental interaction, while the intensity of presynaptic inhibition of the N ₁ DSP component decreased. Possible mechanisms of the observed modifications of the DSP parameters are discussed.     

Auditory brain stem responses in characterization of dolphin hearing

Summary Auditory brain stem responses (ABR) were recorded from the head surface of non-anesthetized and non-relaxed bottle-nosed dolphins, Tursiops truncatus. The region of best ABR recording was shown to be located 6–9 cm caudal to the blowhole. The threshold values were about 1 mPa for noise bursts and –3 dB re 1 mPa for tone bursts of the optimal frequency (80 kHz). The maximum frequency at which ABR could be evoked was 140 kHz. The duration of temporal summation reached 0.5 ms at intensities near the threshold and decreased with an increase in intensity. When the stimuli were paired clicks of the same intensity, the time to complete recovery from the second response was about 5 ms, while that to its 50% recovery was 0.7 ms. When the conditioning click exceeded the testing one in intensity, prolongation of the recovery period was observed. A 40-dB intensity difference led to an approximately 10-fold prolongation of this period.Abbreviations ABR auditory brain stem response - EP evoked potential     

Effect of static magnetic fields on bioelectric properties of the Br and N1 neurons of snail Helix pomatia

The effects of 2.7 mT and 10 mT static magnetic fields were investigated on two identified neurons with different bioelectric properties of the snail Helix pomatia. Membrane resting potential, amplitude, spiking frequency, and duration of action potential were measured. The two neurons of H. pomatia, parabolic burster Br and silent N₁, showed different responses to a static magnetic field. The magnetic field of 2.7 mT intensity caused changes in the amplitude and duration of action potential of the Br neuron, whereas the 10 mT magnetic field changed the resting potential, amplitude spike, firing frequency, and duration of action potential of the Br neuron. Bioelectric parameters measured on the N₁ neuron did not change significantly in these magnetic fields.     

Dopaminergic modulation of the P50 auditory-evoked potential in a computer model of the CA3 region of the hippocampus: its relationship to sensory gating in schizophrenia

 We modeled the neuronal circuits that may underlie a sensory-processing deficit associated with schizophrenia. Schizophrenic patients have small P50 auditory-evoked responses to click stimuli compared to normal subjects. The P50 auditory-evoked response is a positive waveform recorded in the EEG approximately 50 ms after the auditory click stimulus. In addition to relatively small amplitudes, schizophrenic patients do not gate or suppress the P50 auditory-evoked response to the second of two paired-click stimuli spaced 0.5 s apart. Neuropleptic medication, which decreases dopaminergic neuronal transmission, increases the amplitude of the P50 auditory-evoked response but does not improve gating. Normal subjects have large P50 auditory-evoked responses to click stimuli when compared to unmedicated schizophrenic patients, and they gate their response to paired click stimuli or have smaller P50 auditory-evoked response amplitudes to the second of two click stimuli spaced 0.5 s apart. Schizophrenic patients do not gate and have similar response amplitudes to both clicks. We hypothesized that the small amplitudes of unmedicated schizophrenic subjects were due to a state of occlusion whereby excessive background noise in local circuits reduced the ability of cells to respond synchronously to sensory input, thereby reducing the amplitude of the P50 waveform in the EEG. Because the P50 auditory-evoked potential amplitudes increased with neuroleptic medication, which reduces dopaminergic neuronal transmission, we hypothesized a role for dopamine in modulating the signal-to-noise (S/N) in the local circuits responsible for sensory gating. To test the hypothesis that modulation of the S/N ratio reduces sensory gating, we developed a model of the effects of dopaminergic neuronal transmission that modulates the S/N in neuronal circuits. The model uses the biologically relevant computer model of the CA3 region of the hippocampus developed in the companion paper [Moxon et al. (2003) Biol Cybern, this volume]. Modified Hebb cell assemblies represented the response of the network to the click stimulus. The results of our model showed that excessive dopaminergic input impaired the ability of cells to respond synchronously to sensory input, which reduced the amplitudes of the P50 evoked responses. Received: 3 December 2001 / Accepted: 23 October 2002 / Published online: 28 February 2003 Correspondence to: K.A. Moxon (e-mail: karen.moxon@drexel.edu, Tel.: +1-215-8951959, Fax: +1-215-8954983) Supported by USPHS, MH01245 & MH58414, MH-01121, and research grants from the Department of Veterans Affairs and the National Alliance for Research on Schizophrenia and Depression.     

Abnormal Pre-Attentive Arousal in Young Children with Autism Spectrum Disorder Contributes to Their Atypical Auditory Behavior: An ERP Study

Auditory sensory modulation difficulties and problems with automatic re-orienting to sound are well documented in autism spectrum disorders (ASD). Abnormal preattentive arousal processes may contribute to these deficits. In this study, we investigated components of the cortical auditory evoked potential (CAEP) reflecting preattentive arousal in children with ASD and typically developing (TD) children aged 3-8 years. Pairs of clicks (‘S1’ and ‘S2’) separated by a 1 sec S1-S2 interstimulus interval (ISI) and much longer (8-10 sec) S1-S1 ISIs were presented monaurally to either the left or right ear. In TD children, the P50, P100 and N1c CAEP components were strongly influenced by temporal novelty of clicks and were much greater in response to the S1 than the S2 click. Irrespective of the stimulation side, the ‘tangential’ P100 component was rightward lateralized in TD children, whereas the ‘radial’ N1c component had higher amplitude contralaterally to the stimulated ear. Compared to the TD children, children with ASD demonstrated 1) reduced amplitude of the P100 component under the condition of temporal novelty (S1) and 2) an attenuated P100 repetition suppression effect. The abnormalities were lateralized and depended on the presentation side. They were evident in the case of the left but not the right ear stimulation. The P100 abnormalities in ASD correlated with the degree of developmental delay and with the severity of auditory sensory modulation difficulties observed in early life. The results suggest that some rightward-lateralized brain networks that are crucially important for arousal and attention re-orienting are compromised in children with ASD and that this deficit contributes to sensory modulation difficulties and possibly even other behavioral deficits in ASD.     

Call recognition and female choice in a treefrog with a multicomponent call

Acoustic mating signals are typically species‐specific, and often additionally are subject to directional female preferences. Male executioner treefrogs, Dendropsophus carnifex, produce a multicomponent advertisement call composed of an introductory screech note followed by two or more click notes. Here, we tested (i) call recognition by comparing female directed phonotaxis towards individual and combined call components: screech vs. clicks vs. screech + clicks, (ii) female preferences for greater numbers of click notes and (iii) female preferences for faster call rates. The results demonstrated that screeches and clicks, presented either separately or together as a complete call, evoke similar female responses, suggesting that either note was sufficient to elicit a mate‐recognition response. Additionally, females preferred calls with greater numbers of click notes and with faster call rates. We interpret these results within the context of female mate selection in natural choruses.     

Arctiid moths and bat echolocation: broad-band clicks interfere with neural responses to auditory stimuli in the nuclei of the lateral lemniscus of the big brown bat

Clicks emitted by arctiid moths interfere with the ranging ability of echolocating bats. To identify possible neural correlates of this interference, we recorded responses of single units in the nuclei of the lateral lemniscus to combinations of a broad-band click and a test signal (pure tones or frequency-modulated sweeps). In 77% of 87 units tested, clicks interfered with neural responses to the test stimuli. The interference fell into two categories: latency ambiguity and suppression. Units showing latency ambiguity responded to both the click and the test signal. However, when the click occurred within a window of approximately 3 ms before the onset of the test signal, the latency of the response to the test signal was affected. Units that were suppressed did not respond to clicks. Nevertheless, when a click was presented immediately before or simultaneously with a test signal, the response to the test signal was eliminated. Both types of units were found throughout the lateral lemniscus except for the columnar division of the ventral nucleus, where all units tested exhibited latency ambiguity. There is a close match between the single unit data and previous studies of range difference discrimination in the presence of clicks. Accepted: 10 March 1997     

短声特性对豚鼠圆窗记录的N_1N_2反应的影响

研究了不同刺激声强情况下短声特性(极性、波形及相应频谱)改变对豚鼠圆窗记录的N_1N_2反应的影响。发现:①在低声强时,若维持刺激声强不变而使短声波形改变对N_1无影响,但是对N_2有轻微的影响。而高声强时,若维持刺激声强不变而使短声波形改变将引起N_N_2反应较为显著的变化。②不仅是短声的疏相,而且其密相对N_1N_2的形成有贡献。③N_1N_2反应不仅与短声刺激强度有关,而且还与短声的其它参数(如波宽等)有关。并就各项结果进行了讨论。     

A model for control of breathing in mammals: coupling neural dynamics to peripheral gas exchange and transport

A new model for aspects of the control of respiration in mammals has been developed. The model integrates a reduced representation of the brainstem respiratory neural controller together with peripheral gas exchange and transport mechanisms. The neural controller consists of two components. One component represents the inspiratory oscillator in the pre-Bötzinger complex (pre-BötC) incorporating biophysical mechanisms for rhythm generation. The other component represents the ventral respiratory group (VRG), which is driven by the pre-BötC for generation of inspiratory (pre)motor output. The neural model was coupled to simplified models of the lungs incorporating oxygen and carbon dioxide transport. The simplified representation of the brainstem neural circuitry has regulation of both frequency and amplitude of respiration and is done in response to partial pressures of oxygen and carbon dioxide in the blood using proportional (P) and proportional plus integral (PI) controllers. We have studied the coupled system under open and closed loop control. We show that two breathing regimes can exist in the model. In one regime an increase in the inspiratory frequency is accompanied by an increase in amplitude. In the second regime an increase in frequency is accompanied by a decrease in amplitude. The dynamic response of the model to changes in the concentration of inspired O₂ or inspired CO₂ was compared qualitatively with experimental data reported in the physiological literature. We show that the dynamic response with a PI-controller fits the experimental data better but suggests that when high levels of CO₂ are inspired the respiratory system cannot reach steady state. Our model also predicts that there could be two possible mechanisms for apnea appearance when 100% O₂ is inspired following a period of 5% inspired O₂. This paper represents a novel attempt to link neural control and gas transport mechanisms, highlights important issues in amplitude and frequency control and sets the stage for more complete neurophysiological control models.     

Denitrification of nitrate to nitrogen gas by washed cells ofRhizobium japonicum and by bacteroids fromGlycine max

Nitrate, nitrite and nitrous oxide were denitrified to N₂ gas by washed cells ofRhizobium japonicum CC706 as well as by bacteroids prepared from root nodules ofGlycine max (L.) Merr. (CV. Clark 63). Radiolabelled N₂ was produced from either K¹⁵NO₃ or Na¹⁵NO₂ by washed cells ofRh. japonicum CC705 grown with either nitrate only (5 mM) or nitrate (5 mM) plus glutamate (10 mM). Nitrogen gas was also produced from N₂O. Similar results were obtained with bacteroids ofG. max. The stoichiometry for the utilization of¹⁵NO ₃ ^- or¹⁵NO ₂ ^- and the produciton of¹⁵N₂ was 2:1 and for N₂O utilization and N₂ production it was 1:1. Some of the¹⁵N₂ gas produced by denitrification of¹⁵NO ₃ ^- in bacteroids was recycled via nitrogenase into cell nitrogen.     

Amplification of small signals by voltage-gated sodium channels in drone photoreceptors

Summary Photoreceptor cells of the drone,Apismellifera , have a voltage-gated Na⁺ membrane conductance that can be blocked by tetrodotoxin (TTX) and generates an action potential on abrupt depolarization: an action potential is triggered by the rising phase of a receptor potential evoked by an intense light flash (Autrum and von Zwehl 1964; Baumann 1968). We measured the intracellular voltage response to a small (9%), brief (30 ms) decrease in light intensity from a background, and found that its amplitude was decreased by 1M TTX. The response amplitude was maximal when the background intensity depolarized the cell to –38 mV. With intensities depolarizing the cell membrane to –45 to –33 mV the average response amplitude was decreased by TTX from 1.2mV to 0.5mV. TTX is also known to decrease the voltage noise during steady illumination (Ferraro et al. 1983) but, despite this, the ratio of peak-to-peak signal to noise was, on average, decreased by TTX. The results suggest that drone photoreceptors use voltage-gated Na⁺ channels for graded amplification of responses to small, rapid changes in light intensity.Abbreviations TTX tetrodotoxin - V _i intracellular potential with respect to the bath - V _o extracellular potential - V _m,V _i-V _o approximate transmembrane potential - S amplitude of the voltage response to an 8.9% decrease in light intensity - N voltage noise, usually measured as root mean square voltage deviation as described in Methods     

N5-(l-1-Carboxyethyl)-l-ornithine: NADP+ oxidoreductase inStreptococcus lactis: Distribution,constitutivity, and regulation

N⁵-(l-1-Carboxyethyl)-l-ornithine: NADP⁺ oxidoreductase [N⁵-(CE)ornithine synthase] catalyzes the NADPH-dependent reductive condensation between pyruvic acid and the terminal amino group ofl-ornithine andl-lysine to yield N⁵-(l-1-carboxyethyl)-l-ornithine and N⁶-(l-1-carboxyethyl)-l-lysine respectively. Polyclonal antibodies against N⁵-(CE)ornithine synthase purified fromStreptococcus lactis K1 have been used for the immunochemical (Western blot) detection and sizing of this enzyme in various lactic acid bacteria. The enzyme was confined to about one-half of the strains ofS. lactis examined. N⁵-(CE)ornithine synthase is constitutive, and in strains K1, 6F3, and (plasmid-free)H₁-4125 the native enzyme is a tetramer composed of identical subunits of M_r=38,000. However, in other strains, including 133 (ATCC 11454), C₁₀, and ML₈, the molecular weight of the native enzyme is approximately 130,000 and the corresponding subunit M_r=35,000. Analyses of the amino acid pool components maintained byS. lactis K1 during growth in medium containing [¹⁴C] labeled and unlabeled arginine have revealed that (i) exogenous arginine is the precursor of intracellular ornithine, citrulline, and N⁵-(CE)ornithine, and (ii) the rates of turnover of ornithine and citrulline were considerably faster than that of N⁵-(CE)ornithine. These data account for the biosynthesis and accumulation of N⁵-(CE)ornithine byS. lactis.     

有关猫听觉脑干电反应（ABR）两耳干涉作用的研究

用不同声强稳态白噪声和短声同时分别刺激两耳,观察白噪声负荷侧耳蜗破坏前后另一侧ＡＢＲ的改变,探讨两耳干涉作用及其可能的机制。结果显示,对侧耳蜗破坏前,４０ｄＢ和７５ｄＢ白噪声对０ｄＢ、４５ｄＢ、７０ｄＢ和７５ｄＢＳＰＬ的短声诱发的ＡＢＲ各波振幅均有明显影响（Ｐ＜０．０５０．０１）。耳蜗破坏后,同样条件下记录的ＡＢＲ振幅基本无明显变化（Ｐ＞０．０５）。提示白噪声对短声有一定的干涉作用。短声为７０ｄＢＳＰＬ时ＡＢＲＰ１波振幅的减小可能与中枢离中控制相关。