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R M Hennig

Publications and source records attributed to R M Hennig.

8 recordsLinked to original sources
PubMed2005

Increase of neuronal response variability at higher processing levels as revealed by simultaneous recordings.

A key problem for neuronal information processing is the variability of spike trains, something that is likely to constrain the encoding of sensory signals. We measured interspike-interval variability (coefficient of variation) as well as spike-count variability (Fano factor) in the metathoracic auditory system of locusts. We performed simultaneous intracellular recordings at the first three processing levels to establish identical physiological conditions. This allows us to assess whether variability is generated anew or is reduced during synaptic transmission and processing. Both the interspike-interval variability as well as the spike-count variability revealed similar trends and showed an increase from the periphery to higher processing levels. This result was confirmed by single-cell recordings. A comparison of ascending interneurons coding for sound direction and those encoding sound patterns showed that the latter respond more reliably to repeated stimulus presentations. In general, the variability of spiking responses was much lower than expected from a Poisson process. Furthermore, we observed a strong dependence of variability on the spike rate, which differed at the three levels investigated. The differences in spike rates account for most of the differences in variability observed between processing levels. For auditory receptors, we found a good agreement between the Fano factor and the squared coefficient of variation, suggesting similarities to a renewal process of spike generation at the periphery. At the level of interneurons, the Fano factor was lower than the squared coefficient of variation; this indicates a higher reliability than expected from the interspike-interval distribution.

Acoustic Stimulation↗
PubMed2004

Processing of auditory information in insects.

Insects exhibit an astonishing diversity in the design of their ears and the subsequent processing of information within their auditory pathways. The aim of this review is to summarize and compare the present concepts of auditory processing by relating behavioral performance to known neuronal mechanisms. We focus on three general aspects, that is frequency, directional, and temporal processing. The first part compares the capacity (in some insects high) for frequency analysis in the ear with the rather low specificity of tuning in interneurons by looking at Q10dB values and frequency dependent inhibition of interneurons. Since sharpening of frequency does not seem to be the prime task of a set of differently tuned receptors, alternative hypotheses are discussed. Moreover, the physiological correspondence between tonotopic projections of receptors and dendritic organization of interneurons is not in all cases strong. The second part is concerned with directional hearing and thus with the ability for angular resolution of insects. The present concepts, as derived from behavioral performances, for angular resolution versus lateralization and serial versus parallel processing of directional and pattern information can be traced to the thoracic level of neuronal processing. Contralateral inhibition, a mechanism for enhancing directional tuning, appears to be most effective in parallel pathways, whereas in serial processing it may have detrimental effects on pattern processing. The third part, after some considerations of signal analysis in the temporal domain, demonstrates that closely related species often use different combinations of temporal parameters in their recognition systems. On the thoracic level, analysis of temporal modulation functions and effects of inhibition on spiking patterns reveals relatively simple processing, whereas brain neurons may exhibit more complex properties.

Acoustic Stimulation↗
PubMed2004

Variability of spike trains and the processing of temporal patterns of acoustic signals-problems, constraints, and solutions.

Object recognition and classification by sensory pathways is rooted in spike trains provided by sensory neurons. Nervous systems had to evolve mechanisms to extract information about relevant object properties, and to separate these from spurious features. In this review, problems caused by spike train variability and counterstrategies are exemplified for the processing of acoustic signals in orthopteran insects. Due to size limitations of their nervous system we expect to find solutions that are stripped to the computational basics. A key feature of auditory systems is temporal resolution, which is likely limited by spike train variability. Basic strategies to reduce such variability are to integrate over time, or to average across several neurons. The first strategy is constrained by its possible interference with temporal resolution. Grasshoppers do not seem to explore temporal integration much, in spite of the repetitive structure of their songs, which invites for 'multiple looks' at the signal. The benefits of averaging across neurons depend on uncorrelated responses, a factor that may be crucial for the performance and evolution of small nervous systems. In spite of spike train variability the temporal information necessary for the recognition of conspecifics is preserved to a remarkable degree in the auditory pathway.

Acoustic Stimulation↗
PubMed2004

Neuronal adaptation improves the recognition of temporal patterns in a grasshopper.

The recognition of the temporal structure of sound patterns by grasshopper males was investigated in behavioural experiments. Males were tested with short (165-335 ms) song models in which the characteristic subunit pattern of syllables and pauses was modified either at the beginning or at the end of the stimuli. The highly specific responses of the animals indicate that neuronal adaptation has a substantial influence on the detection of the pauses which are essential cues for the subunit structure: pauses were less likely detected shortly after the beginning of a song model than at later positions. Even adaptation in auditory neurons that was induced by unspecific stimulation (with unmodulated noise) facilitated the processing of sound envelopes. The effects of stimulus prolongation and introduction of pauses appeared to combine linearly, similar to the effects of introducing two pauses instead of a single one. In the responses to some song models large interindividual differences were observed. Comparison across stimuli and repeated testing of a smaller number of individuals indicated a considerable consistency of behavioural preferences. However, the data yielded no clear evidence for the existence of individually distinct processing types among males, that conceivably would focus on different features of the stimuli.

Acoustic Stimulation↗
PubMed2003

Acoustic feature extraction by cross-correlation in crickets?

Common concepts of acoustic feature extraction within the auditory pathway of vertebrates and insects assume temporal filters tuned to particular periodicities. Crickets respond selectively to the conspecific song pattern and reveal a bandpass characteristic, which is thought to arise from a matched filter for a restricted range of periods. Unexpectedly, females of the two sibling species Teleogryllus oceanicus and T. commodus differed in fundamental filter properties. While T. oceanicus revealed a period filter, T. commodus exhibited a pulse duration filter. This finding raises the question of how so distinct properties of homologous neuronal circuits for pattern analysis have evolved during speciation. Evidence is presented that signal analysis by cross-correlation offers a simple explanation for differences in pattern selectivity as well as for the evolutionary transition. By cross-correlation the similarity of an external pattern with an internal template is determined over a certain time window. A comparison of behavioural data and cross-correlation values suggested that both species have similar templates. However, time windows were significantly different between species (T. oceanicus: 180-400 ms, T. commodus: 90-160 ms). Consequently, solely a change in the evaluation time window is required to account for the observed differences in feature extraction that serve to maintain species isolation.

Acoustic Stimulation↗
PubMed2000

Effects of signal duration on the recognition of masked communication signals by the grasshopper Chorthippus biguttulus.

The detection and recognition of acoustic communication signals masked by noise was investigated in a grasshopper (Chorthippus biguttulus) whose auditory system exhibits only poor spectral resolution and therefore has to operate in the time domain. The signals of this species consist of numerous identical subunits that enable the receiver, in principle, to make repetitive measurements. We aimed at determining the maximum integration time in this species by using stimuli of different durations under increasing noise levels. As a criterion for recognition the typical phonotactic turning response of the males was evaluated, which is reliably triggered by a female song, and thus is a sensitive indicator for recognition of conspecific signals. When confronted with a long signal (1000 ms) males tolerated a 2.4 dB higher noise level as compared to a short signal (250 ms). Noise tolerance improved with increasing signal duration from 250 ms to 450 ms. Beyond this signal duration, however, no further improvement was observed, indicating an upper limit for temporal integration that corresponds to only five song subunits. The gain in noise tolerance had a slope of 2.7 dB per doubling duration, which corresponds to the expectation derived from an energy detector model (3 dB per doubling duration) rather than to the value expected from signal detection theory (1.5 dB per doubling duration).

Animal Communication↗
PubMed1988

Ascending auditory interneurons in the cricket Teleogryllus commodus (Walker): comparative physiology and direct connections with afferents.

Ascending auditory interneurons of the cricket, Teleogryllus commodus (Walker), were investigated using simultaneous intracellular and extracellular recording in order to identify units which had previously been characterized only by extracellular recording. The morphology and physiology of the large adapting unit (LAU: Fig. 1) and of the small tonic unit (STU: Fig. 2) of Teleogryllus correspond well to those of the ascending neuron 2 (AN2) and the ascending neuron 1 (AN1) of Gryllus (Figs. 1, 2), respectively. A summary of the ascending auditory interneurons described by various authors in 5 species of crickets is presented in order to establish common identities. Physiological evidence for direct connections between auditory afferents and the ascending auditory interneurons AN1 (STU) and AN2 (LAU) is presented. Simultaneous intracellular recordings from receptors and interneurons in response to sound as well as the activity of auditory interneurons upon electrical stimulation of the tympanal nerve reveal short and constant latencies of receptor-evoked synaptic activity in AN1 (STU) and AN2 (LAU).

Animals↗