Processing of calling songs by an L-shaped neuron in the prothoracic ganglion of the female cricket, Acheta domesticus

ABSTRACT. An L-shaped auditory intemeuron (LI) has been recorded from extracellularly and intracellularly, and identified morphologically (by Lucifer yellow or cobalt injection) in the prothoracic ganglion of mature female Acheta domesticus. The morphology of the LI is very similar to ascending, prothoracic acoustic interneurons that are most sensitive to higher carrier frequencies in both A. domesticus and other gryllid species. Its terminations in the brain are similar to ascending acoustic interneurons found in other gryllids. The LI neuron is most sensitive to 4–5 kHz model calling songs (CSs), the main carrier frequency of the natural call. Thresholds to high frequencies (8–15 kHz) are 15–20 dB higher. Increasing CS intensities of up to 15 dB above threshold at 4–5 kHz result in increased firing rates by the LI. More than 15 dB increase in intensity causes saturation with little increase in spiking rate until the intensity surpasses 80 dB. In response to 70 dB or higher stimulus intensities, the LI responds to the second and third CS syllables with one or two spikes, pauses, and then produces a burst of nerve impulses with the same or greater latency than for lower intensity stimuli. In response to CS syllables of changing duration (10–30 ms) this neuron responds with a rather constant duration burst of impulses. Syllable periods of the CS stimuli were accurately encoded by the LI. Progressively stronger injection of hyperpolarizing current reduces, and ultimately stops spiking of the LI in response to CS stimuli. More intense stimulation with reduced hyperpolarization shows an initial spike, pause and burst of spikes. Intracellular recording from axonal regions of the neuron shows large spikes, small EPSPs and a developing hyperpolarization through the response to a CS chirp. Inhibitory input to the LI is demonstrated at 4.5, 8 and 16 kHz. This probably explains the specialized response characteristics of the LI which enhanced its encoding of CS syllable period.     

Patterned response to odor in single neurones of goldfish olfactory bulb: influence of odor quality and other stimulus parameters

Responses of 75 single units in the goldfish olfactory bulb were analyzed in detail for their relationship to the time-course of the change in odor concentration during each odor stimulus. Odor stimuli were controlled for rise time, duration, and peak concentration by an apparatus developed for the purpose. This apparatus enabled aqueous odor stimuli to be interposed into a constant water stream without changes in flow rate. The time-course of the concentration change within the olfactory sac was inferred from conductivity measurements at the incurrent and excurrent nostrils. Temporal patterns of firing rate elicited by stimuli with relatively slow rising and falling phases could be quite complex combinations of excitation and suppression. Different temporal patterns were produced by different substances at a single concentration in most units. Statistical measures of the temporal pattern of response for a small number of cells at a given concentration were more characteristic of the stimulus substance than any of three measures of magnitude of response. The temporal patterns change when the peak concentration, duration, and rise time of the stimuli are varied. The nature of these changes suggests that the different patterns are due primarily to the combined influence of two factors: (a) a stimulus whose concentration varies over time and (b) a relationship between concentration and impulse frequency which varies from unit to unit. Some units produce patterns suggestive of influence by neural events of long time constant. The importance of temporal patterns in odor quality and odor intensity coding is discussed.     

The influence of rate of temperature change and peak stimulus duration on pain intensity and quality

An important aspect of experimental pain research is that the assessment methods can investigate the different aspects of pain perception. The aim of the present study was to investigate the influence of rate of temperature change and peak stimulus duration on heat evoked pain intensity and quality. All stimuli were applied within the medial aspect of the anterior forearm. The rate of temperature change was varied from 1 to 16 C/s without any effect on the pain threshold. The pain threshold decreased with an increasing peak stimulus duration from 0.1 to 2 s, but not from 2 to 3 s. The pain intensity for suprathreshold stimuli (46 C, 48 C, 50 C) increased for decreasing rates and increasing duration. The pain intensity was highly correlated with the energy of the stimulus. When the rates of temperature change (1-16 C/s) are varied, no differences between pricking and burning pain were present at either low stimulus intensity (46 C) or high stimulus intensity (50 C). At low stimulus intensity (46 C), the pricking pain was not influenced by the duration (0.1-3 s), but the burning pain was intensified when the duration was increased from 1.5 to 3 s. At high intensity stimuli (50 C), the pricking pain intensified with an increased duration, whereas burning pain did not. The heat pain threshold is influenced by the peak stimulus duration, and not by the rate of temperature change. If suprathreshold stimuli are used, both the rate of temperature change and the peak stimulus duration can strongly affect the pain intensity and the pain quality. Therefore, the same stimulus modality can be used to assess the modulation of different pain intensities and of the pricking and burning pain qualities simply by varying the stimulus configuration.     

The effects of temperature on signalling in ocellar neurons of the desert locust, <Emphasis Type="Italic">Schistocerca gregaria</Emphasis>

In Schistocerca gregaria ocellar pathways, large second-order L-neurons use graded potentials to communicate signals from the ocellar retina to third-order neurons in the protocerebrum. A third-order neuron, DNI, converts graded potentials into axonal spikes that have been shown in experiments at room temperature to be sparse and precisely timed. I investigated effects of temperature changes that a locust normally experiences on these signals. With increased temperature, response latency decreases and frequency responses of the neurons increase. Both the graded potential responses in the two types of neuron and the spikes in DNI report greater detail about a fluctuating light stimulus. Over a rise from 22 to 35°C the power spectrum of the L-neuron response encompasses higher frequencies and its information capacity increases from about 600 to 1,700 bits/s. DNI generates spikes more often during a repeated stimulus but at all temperatures it reports rapid decreases in light rather than providing a continual measure of light intensity. Information rate carried by spike trains increases from about 50 to 185 bits/s. At warmer temperatures, increased performance by ocellar interneurons may contribute to improved aerobatic performance by delivering spikes earlier and in response to smaller, faster light stimuli.     

Testing excitability in human firing motoneurons during the interspike interval

Monosynaptic testing of excitability in firing triceps surae muscle motoneurons activated during volitional contraction was performed using a technique for recording potentials from single motor units and by producing H-reflex. Motoneuronal excitability was assessed according to level of firing index. Motoneuronal firing index decreased during transition from a low background rhythmic firing rate of less than 6 spikes/sec to one of 6–8 spikes/sec. It hardly changed with a further rise in rate to 12 spikes/sec. The dependence between firing index and spike rate are put down to changes occurring in motoneuronal excitability during the interspike interval. Findings indicate that in the low frequency range of motoneuronal firing characteristic of natural muscle contraction, discharge rate may be considered one of the factors determining excitability in the motoneuron and hence its transmission qualities.Institute of Problems in Information Transmission, Academy of Sciences of the USSR. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 210–216, March–April, 1987.     

Voltage-dependent burst-to-tonic switching of thalamic cell activity: an in vitro study

The electroresponsiveness of mammalian thalamic neurons was studied in a slice preparation of the guinea pig diencephalon. Although the morphology of the cells varied, their electroresponsive properties were the same. Stimulation of thalamic cells at a membrane potential more negative than--60 mV produced burst responses and stimulation of more depolarized levels produced tonic firing of fast spikes. The burst response is generated by an inactivating Ca++-conductance. It is seen as a slow Ca++-spike which in turn triggers fast Na+-spikes. The Ca++-conductance is deinactivated by hyperpolarization beyond--60 mV. The membranes of thalamic neurons contain a number of other conductances including a Ca++-dependent K+-conductance producing spike afterhyperpolarization and a non-inactivating Na+-conductance which plays an important role during tonic activity of the cells. The early part of a response to a long-lasting stimulus given at rest or at a hyperpolarized level is dominated by the burst and thus is is independent of the stimulus amplitude. During the late part of such a response the firing rate is highly dependent of the stimulus intensity. Current-frequency plots for the first inter-spike intervals after the burst during long stimuli are upward convex, but after "steady-state" is reached the plots are almost linear.     

Responses of central auditory neurons to frequency-modulated stimuli

Unit responses of the inferior colliculi of albino rats to frequency-modulated stimuli were investigated. The number of spikes, firing pattern, and duration of the discharge were determined. Parameters of unit responses obtained with different directions of frequency modulation were compared with the results of testing the effect of constant-frequency tones on the neurons. The distinguishing features of the unit responses to stimuli with different directions of frequency modulation were compared with the characteristics of the frequency-threshold curve and the lateral inhibitory zones, taken as indices of the unit responses to constant-frequency tones. With a change in stimulus frequency upward or downward from the initial level the unit responses to both directions could be similar as regards the number of spikes per discharge and the firing pattern or could differ sharply depending on the direction or, finally, they could arise only if the stimulus frequency changed in one direction. In some cases selectivity for the direction of the change in stimulus frequency was due to the width and position of the lateral inhibitory zones. However, for one-third of the neurons tested analysis of the spatial characteristics of the excitatory and inhibitory zones alone was insufficient to explain the high selectivity in the formation of a response to a stimulus with frequency modulation in one direction only.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol.6, No.3, pp.237–245, May–June, 1974.     

Biased competition through variations in amplitude of <Emphasis Type="Italic">γ</Emphasis>-oscillations

Experiments in visual cortex have shown that the firing rate of a neuron in response to the simultaneous presentation of a preferred and non-preferred stimulus within the receptive field is intermediate between that for the two stimuli alone (stimulus competition). Attention directed to one of the stimuli drives the response towards the response induced by the attended stimulus alone (selective attention). This study shows that a simple feedforward model with fixed synaptic conductance values can reproduce these two phenomena using synchronization in the gamma-frequency range to increase the effective synaptic gain for the responses to the attended stimulus. The performance of the model is robust to changes in the parameter values. The model predicts that the phase locking between presynaptic input and output spikes increases with attention.     

Medullary electrosensory processing in the little skate

1. Ampullary electroreceptors in elasmobranchs are innervated by fibers of the ALLN, which projects to the dorsal octavolateralis nucleus (DON). The purpose of this study is to examine the response characteristics of ALLN fibers and DON neurons to weak D.C. and sinusoidal electric field stimuli presented as local dipole fields. 2. ALLN fibers respond to presentation of D.C. fields with a phasic burst, followed by a more slowly adapting period of firing. Ascending efferent neurons (AENs) in the DON respond to stimuli with a similar initial burst, which adapts more quickly. 3. Type 1, 2, and 3 neurons are possible local interneurons or commissural DON neurons. Type 1 neurons demonstrate response properties similar to those of AENs. Type 2 cells demonstrated slowly adapting responses to excitatory stimuli, the duration of the response increased with the amplitude of the stimulus. Type 3 neurons demonstrated an increased rate of firing, but the response lacked any specific temporal characteristics. 4. ALLN fibers typically have receptive fields consisting of a single ampulla. The receptive field sizes of DON neurons exhibited varying degrees of convergence for different cell types. 5. Responses of ALLN fibers and DON neurons to weak sinusoidal stimuli demonstrated very similar frequency response characteristics for all cell types. The peak sensitivity of electrosensory neurons was between 5-10 Hz.     

Network interactions among sensory neurons in the leech

Interactions among mechanosensory neurons, sensitive to touch, pressure and nociceptive stimuli in the leech nervous system were studied in isolated ganglia and in body-wall preparations. Pairs of touch-pressure, touch-nociceptive and pressure-nociceptive neurons were tested by suprathreshold stimulation of one neuron while recording the response of the other, in both directions. Pressure and nociceptive stimulation evoked depolarizing and hyperpolarizing responses in touch cells, mediated by interneurons. The relative expression of these responses depended on the stimulus duration. One or two pressure cell spikes produced, predominantly, a depolarization of the touch cells, and increasing number of spikes evoked a hyperpolarization. Nociceptive cells produced primarily the hyperpolarization of touch cells at any stimulus duration. When touch cells were induced to fire by injection of positive current into the soma, stimulation of pressure cells inhibited touch cell activity. However, when touch cells were induced to fire by peripheral stimulation, pressure cell activation failed to inhibit touch cell firing. The results suggest that excitation of pressure and nociceptive cells would not limit the responses of touch cells to peripheral stimuli, but would inhibit the firing of touch cells evoked by their central connectivity network.     

Electrophysiological responses of the chemoreceptor neurones in the antennal taste sensilla to plant alkaloids and glucosides in a granivorous ground beetle

The electrophysiological response of chemoreceptor neurones from the antennal chaetoid taste sensilla of the omnivorous ground beetle Pterostichus oblongopunctatus to several plant alkaloids and glucosides is investigated. A quinine‐sensitive neurone responding to quinine and quinine hydrochloride is found, most probably related to the granivorous feeding habit of P. oblongopunctatus. The response to quinine hydrochloride is concentration‐dependent at 0.001–50 mm , with the response threshold at 0.01 mm and a maximum rate of firing of 67 spikes/s at 50 mm . The stimulatory effect of caffeine is very weak, where the firing rate increases by only 1.4 spikes/s at a concentration of 10 mm compared with that evoked by a control stimulus. In addition, both quinine and quinine hydrochloride strongly inhibit spike production by the salt‐ and pH‐sensitive neurones when presented in mixtures with 10 mm NaCl. Several tested plant secondary compounds (i.e. salicin, sinigrin, caffeine and nicotine), which have only little or no effect on the firing rate of the quinine‐sensitive neurone, greatly reduce the responses of the salt‐ and pH‐sensitive neurones. The results of the present study suggest that the antennal taste sensilla of P. oblongopunctatus may detect plant defensive compounds both through the activation of a quinine‐sensitive neurone and via peripheral inhibition of other chemoreceptor neurones of the taste sensillum.     

Effect of fast moving stimuli and saccadic eye movements on cell activity in visual areas V1 and V2 of behaving monkeys

Extracellular recordings were carried out in the visual cortex of behaving monkeys trained on a fixation/detection task, during which a target light was displayed stationary or suddenly moving on a tangent translucent screen. The responses of visual cortical cells to fast moving stimuli during steady fixation and those obtained during rapid eye movements (saccades) which moved their receptive field across a stationary stimulus, were studied. Areas V1 and V2 were explored. When tested with rapidly moving stimuli (500 deg/sec) during steady fixation, neurons in each area behaved in almost the same way. About one fourth of them were activated, the remainder showing either no response (little more than a half of them) or a reduction of the spontaneous firing rate. In both areas, some of the neurons activated during steady fixation did not respond or responded very weakly during eye motion at saccadic velocity (500 +/- 50 deg/sec). Neurons of this type, which we refer to as 'real motion' cells, could somehow contribute to the maintenance of visual stability during the execution of large eye movements.     

Posthyperpolarization rebound: Gradualness of intensity and duration effects

Rebound was recorded in the latent pacemaker neuron ofLimnaea stagnalis as an off-response to incoming pulses of constant duration (50 msec) and different strengths (0.17–16.1 nA) or of different duration (10 msec-360 sec) and constant strength (5 nA). To pulses of short duration and weak strength this response consists of a single depolarization wave. With an increase in these parameters the wave gradually grows and is followed by a hyperpolarization wave. At an intensity of 10–12 nA or duration of about 200 msec the rebound response becomes spike-shaped, but the spike is completely formed only at 15.2 nA or 4–5 sec. The last stage of its formation is characterized by "constriction" of the depolarization component. A further increase in pulse intensity of the same duration does not change the rebound response. On the other hand, with a further increase in pulse duration in the corresponding series of experiments fresh spikes were continually added to the first, and depending on the choice of durations, this process could be followed step by step. At a duration of about 190 sec the rebound response reached saturation when it consisted of 8 spikes with a total response duration of about 5 sec. These results are used as the basis for a hypothesis of the possible organization of excitation of the somatic membrane of mollusk pacemaker neurons. Some aspects of the possible mechanism of rebound formation are discussed.Institute of Physiology and Pathology of the Cardiovascular System, Kaunas Medical Institute, Kaunas, Lithuania. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 451–459, September–October, 1973.     

Functional features of electroreceptors (small pit organs) in the catfish

Characteristics of responses of the small pit organs of the catfishIctalurus nebulosus to the action of electrical stimuli of varied polarity, intensity, and duration were studied. Single fibers of the lateral nerve innervating these organs possessed regular spontaneous activity with a frequency of 35–45/sec or grouped activity, coinciding with the rhythm of the animal's swimming movements. Threshold current densities varied from 10⁻¹¹ to 10⁻¹⁰ A/mm². Electrical stimuli evoked a phasic-tonic response of the receptor. The latent period was 10–50 msec for on-responses and 10–200 msec for off-responses. In the presence of strong electric fields the receptor responded to a cathodal stimulus by excitation, whereas under ordinary experimental conditions an anodal stimulus is excitatory. The properties of small pit organs are compared with the characteristics of other electroreceptors.     

Unit responses of the inferior colliculi to changes in the intensity of an amplitude-modulated signal

Unit responses of the inferior colliculi of anesthetized rats to amplitude-modulated sounds during a change in the carrier intensity were investigated. The following unit response characteristics were assessed: the number of spikes in the response, the range of reproduction of the modulation frequency, the response duration, and the pattern of the spike response relative to the envelope of the amplitude-modulated stimulus. The following parameters of the stimulus were varied: carrier intensity (usually of optimal frequency or noise), frequency of modulation (from 2 to 100 Hz), and carrier frequency. With a decrease in the intensity of the carrier in the case of monotonic neurons, and also with an increase or decrease in the intensity of the carrier relative to its optimal level in nonmonotonic neurons, the following changes in the discharge were regularly observed: the number of spikes in the response and its duration were reduced down to the appearance of only one initial response, the range of reproduction of the rhythm of modulation was narrowed, and the response pattern was sharply modified.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR. I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 355–366, July–August, 1973.     

Encoding of sound duration by neurons in the auditory cortex of the little brown bat, Myotis lucifugus

Responses of 117 single- or multi-units in the auditory cortex (AC) of bats (Myotis lucifugus) to tone bursts of different stimulus durations (1– 400 ms) were studied over a wide range of stimulus intensities to determine how stimulus duration is represented in the AC. 36% of AC neurons responded more strongly to short stimulus durations showing short-pass duration response functions, 31% responded equally to all pulse durations (i.e., all-pass), 18% responded preferentially to stimuli having longer durations (i.e., long-pass), and 15% responded to a narrow range of stimulus durations (i.e., band-pass). Neurons showing long-pass and short-pass duration response functions were narrowly distributed within two horizontal slabs of the cortex, over the rostrocaudal extent of the AC. The effects of stimulus level on duration selectivity were evaluated for 17 AC neurons. For 65% of these units, an increase in stimulus intensity resulted in a progressive decrease in the best duration. In light of the unusual intensity-dependent duration responses of AC neurons, we hypothesized that the response selectivities of AC neurons is different from that in the brainstem. This hypothesis was validated by results of study of the duration response characteristics of single neurons in the inferior colliculus. Accepted: 8 November 1996     

Response characteristics of the BVP neuron model to periodic pulse inputs.

The characteristics of the BVP neuron model response to periodic pulse stimuli are investigated. Temporal patterns of the output of the model are analyzed as a function of the stimulus intensity and period. The BVP model exhibits the same chaotic behavior, and a Cantor function-like graph of the response frequency (mean firing rate) as in electrophysiological experiments. This shows that the BVP model describes the complicated response characteristics of the neuron at least qualitatively.     

Characteristics of unit responses of the cat cerebellar cortex to acoustic stimuli

Investigation of unit responses of the cerebellar cortex (lobules VI–VII of the vermis) to acoustic stimulation showed that the great majority of neurons responded by a discharge of one spike or a group of spikes with a latent period of 10–40 msec and with a low fluctuation value. Neurons identified as Purkinje cells responded to sound either by inhibition of spontaneous activity or by a "climbing fiber response" with a latent period of 40–60 msec and with a high fluctuation value. In 4 of 80 neurons a prolonged (lasting about 1 sec or more), variable response with a latent period of 225–580 msec was observed. The minimal thresholds of unit responses to acoustic stimuli were distributed within the range from –7 to 77 dB, with a mode from 20 to 50 dB. All the characteristics of the cerebellar unit responses studied were independent of the intensity, duration, and frequency of the sound, like neurons of short-latency type in the inferior colliculi. In certain properties — firing pattern, latent period, and threshold of response — the cerebellar neurons resemble neurons of higher levels of the auditory system: the medial geniculate body and auditory cortex.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 3–12, January–February, 1973.     

Coding of deflection velocity and amplitude by whisker primary afferent neurons: implications for higher level processing

Within the rat whisker-to-barrel pathway, local circuits in cortical layer IV are more sensitive to the initial timing of deflection-evoked thalamic responses than to the total number of spikes comprising them. Because thalamic response timing better reflects whisker deflection velocity than amplitude, cortical neurons are more responsive to the former than the latter. The aim of this study is to determine how deflection velocity and amplitude may be encoded by the primary afferent neurons innervating the vibrissae. Responses of 81 extracellularly recorded trigeminal ganglion neurons (60 slowly and 21 rapidly adapting) were studied using controlled whisker stimuli identical to those used previously to investigate the velocity and amplitude sensitivities of thalamic and cortical neurons. For either slowly (SA) or rapidly adapting (RA) neurons, velocity is reflected by both response magnitude, measured as the total number of evoked spikes/stimulus, and initial firing rate, measured as the number of spikes discharged during the first 2 ms of the response. Deflection amplitude, on the other hand, is represented only by the SA population in their response magnitudes. Thus, in both populations initial firing rates unambiguously reflect deflection velocity. Together with previous findings, results demonstrate that information about deflection velocity is preserved throughout the whisker-to-barrel pathway by central circuits sensitive to initial response timing.