Degree Of Habituation Research Articles

An increase in spontaneous activity mediates visual habituation.

SUMMARYThe cerebral cortex is spontaneously active, but the function of this ongoing activity remains unclear. To test whether spontaneous activity encodes learned experiences, we measured the response of neuronal populations in mouse primary visual cortex with chronic two-photon calcium imaging during visual habituation to a specific oriented stimulus. We find that, during habituation, spontaneous activity increases in neurons across the full range of orientation selectivity, eventually matching that of evoked levels. This increase in spontaneous activity robustly correlates with the degree of habituation. Moreover, boosting spontaneous activity with two-photon optogenetic stimulation to the levels of visually evoked activity accelerates habituation. Our study shows that cortical spontaneous activity is linked to habituation, and we propose that habituation unfolds by minimizing the difference between spontaneous and stimulus-evoked activity levels. We conclude that baseline spontaneous activity could gate incoming sensory information to the cortex based on the learned experience of the animal.

Not friends, just roommates: social organisation of two South American sea lion non-breeding colonies

ABSTRACT Groups of male South American sea lions (Otaria flavescens; SSLs) congregate in harbours on the northern coast of Argentina. These groups are very dynamic, with a high degree of habituation to human activities and the ability to colonise different types of artificial substrates, making them an interesting subject for understanding individual association patterns and spatio-temporal variations in this species. In the present study, we recorded the associations between individual bleach-marked SSLs in the harbours of Mar del Plata (PM) and Puerto Quequén (PQ) on four different substrate types during four non-breeding seasons. We found that the association pattern differed between the harbours, with a well-differentiated social structure being evident in PM but very little social differentiation occurring in PQ. The observed social structure in PM may have resulted from passive habitat preference rather than genuine social behaviour, as the association pattern disappeared when SSLs moved to sandy beaches within the harbour. Given that these colonies are must-see tourist attractions but may have negative interactions with human activities, we recommend considering the association between SSLs and artificial habitats to design effective management strategies and reduce potential conflicts.

Preliminary Behavioural Observations of Horseback Safaris: Initial Insights into the Welfare Implications for Horses and Herbivorous Plains Game Species.

Simple SummaryHorseback safari rides, where tourists are led by experienced guides on horseback to find and observe wildlife, are a popular activity in Africa. However, close encounters between horses and wildlife on safari rides may be stressful for both types of animals. In this study we looked at the behaviour of horses and wildlife during close encounters on horseback safari rides, focusing on their behaviour at the start and end of each encounter, and the most extreme behaviour seen. Encounters with seven wildlife species were observed, all large herbivores. The seven species differed in their behaviour towards the horses. The horses also differed in their behaviour towards the different wildlife species, being more wary of giraffe. Horses generally approached the wildlife species at walk and few flight behaviours were observed. Further studies, including those incorporating physiological measures of stress, are recommended.In Africa, wildlife-watching experiences create substantial revenue from tourists that can finance wildlife conservation. Horseback safaris, where an experienced guide takes guests through the bush on horseback to observe plains game species, are a popular activity. Close encounters between ridden horses and game species are unnatural and potentially stressful situations, and horseback safaris may have adverse impacts on both the horses and the wildlife they have come to observe. This study aims to provide a preliminary insight into the behavioural responses of horses and herbivorous plains game species, including giraffe, zebra and impala, as a proxy measure of the potential welfare implications of horseback safaris. Seventeen group safari rides were observed encompassing 72 encounters with plains game species. Game species differed in their response to encounters with the horseback safari ride. Equine response behaviour appeared to be influenced by the species of game encountered. Horses seemed more wary of giraffe than other species, with a higher percentage of horses showing stationary and retreat behaviour at the start of giraffe encounters. They were also most likely to shy at giraffe. The behavioural responses suggest that game encounters can elicit a stress response in both animal groups, although it is not usually extreme, potentially indicating that some degree of habituation has occurred. Balancing the welfare of both the horses and the plains game species along with tourist preferences may be challenging in this context.

Memristive Circuit Implementation of Biological Nonassociative Learning Mechanism and Its Applications.

Biological nonassociative learning is one of the simplest forms of unsupervised learning in animals and can be categorized into habituation and sensitization according to mechanism. This paper proposes a memristive circuit that is based on nonassociative learning and can adapt to repeated inputs, reduce power consumption (habituation), and be sensitive to harmful inputs (sensitization). The circuit includes 1) synapse module, 2) neuron module, 3) feedback module. The first module mainly consists of memristors representing synapse weights that vary with corresponding inputs. Memristance is automatically reduced when a harmful stimulus is input, and climbs at the input interval according to the feedback input when repeated stimuli are input. The second module produces spiking voltage when the total input is above the given threshold. The third module can provide feedback voltage according to the frequency and quantity of input stimuli. Simulation results show that the proposed circuit can generate output signals with biological nonassociative learning characteristics, with varying amplitudes depending on the characteristics of input signals. When the frequency and quantity of the input stimuli are high, the degree of habituation and sensitization intensifies. The proposed circuit has good robustness; can reduce the influence of noise, circuit parasitics and circuit aging during nonassociative learning; and simulate the afterimages caused by visual fatigue for application in automatic exposure compensation.

Effect of sleep deprivation on the electrophysiological signature of habituation to noxious laser stimuli.

Sleep deprivation induces hyperalgesia. However, this pro-nociceptive effect is not reflected at the electrophysiological level, since sleep restricted subjects show amplitude reduction of Laser-evoked Potentials (LEP). We aimed to explore the contribution of habituation to this paradoxical LEP amplitude decline. We compared LEP's of 12 healthy students (23.2 ± 1.1 years) after habitual sleep (HS) and a night of total sleep deprivation (TSD). Twelve repetitive laser stimulus blocks (each comprising twenty stimuli) were applied under three attention conditions ('focusing' - 'neutral' - 'distraction' condition). Stimulus blocks were split in part 1 (stimulus 1-10) and part 2 (stimulus 11-20). The contribution of habituation to the TSD-induced LEP amplitude decline was studied by calculating the percentage amplitude reduction of part 2 as compared to part 1. Individual sleepiness levels were correlated with (1) averaged LEP's and (2) the degree of habituation. TSD induced hyperalgesia to laser stimuli (p < 0.001). In contrast, depending on the attention condition, the P2 amplitude of the N2P2-complex was significantly reduced ('focusing': p = 0.004; 'neutral': p = 0.017; distraction: p = 0.71). Habituation of the P2 amplitude to radiant heat was increased after TSD ('focusing': p = 0.04; 'neutral': p < 0.001; distraction: p = 0.88). TSD had no significant effect on N1 amplitudes (p > 0.05). Individual sleepiness correlated negatively with averaged P2 amplitudes (p = 0.02), but not with the degree of habituation (p = 0.14). TSD induces hyperalgesia and results in attention-dependent enhanced habituation of the P2 component. Increased habituation may--to a substantial degree--explain the TSD-induced LEP-amplitude decline. For this article, a commentary is available at the Wiley Online Library.

Response of mule deer to habitat modification near natural gas development

Mule deer ( Odocoileus hemionus ) are known to shift habitat use in response to environmental modifications, including those associated with energy development. Their specific behavioral responses, however, and capacities to habituate to particular aspects of energy development have not been effectively studied. We examined mule deer response to habitat alteration near natural gas wells in Las Animas County, Colorado, USA in 2008—2010, an area experiencing development for extraction of natural gas. We created 10-1 ha openings in forests adjacent to 10 wells by removing standing trees in 2008, with concomitant establishment of 10 1-ha control sites adjacent to the same wells. On each site, we estimated deer use, indexed by pellet density, before and after tree removal. Concurrently, we measured plant production, cover, nutritional quality, species composition and biomass removed by deer and other large herbivores. Species richness and diversity and graminoid and forb cover and biomass increased on cut sites following tree removal. Use increased following tree removal on cut and control sites, but was greater on cut sites in 2010. Herbivores removed negligible quantities of vegetation on control sites in both years, suggesting that control sites may have been used primarily for concealment. Mule deer demonstrated the behavioral capacity to habituate to habitat modifications and other environmental changes associated with development for the extraction of energy. Managing forage and habitat availability appears to have the potential to affect the type of response and degree of habituation by mule deer to such development.

Benefit of social support for resilience-building is contingent on social context: examining cardiovascular adaptation to recurrent stress in women

Previous work on social support and stress tolerance using laboratory-based cardiovascular stress response paradigms has suggested that perceived social support may be effective in building resilience in recipients. However, such paradigms are often socially de-contextualized insofar as they fail to take account of the social aspects of stress itself. Using 90 healthy college women, the present study sought to examine the association between self-reported perceived social support and cardiovascular stress tolerance. Participants underwent two consecutive exposures to a mental arithmetic task. On second exposure to the stressor, participants completed the task under either social threat or control conditions. Social threat was manipulated using socially salient instructions, to create a high social context. Adaptation to stress was established in terms of comparisons between cardiovascular responses to successive exposures. Results showed that cardiovascular responses tended to habituate across time, with perceived social support associated with the degree of habituation, but only under certain contextual conditions; high perceived support was associated with effective habituation under control conditions only. This response pattern is consistent with the view that high perceived social support buffers against stress in healthful ways, but only in asocial contexts.

Stimulus-Specific Adaptation in the Gerbil Primary Auditory Thalamus Is the Result of a Fast Frequency-Specific Habituation and Is Regulated by the Corticofugal System

The detection of novel and therefore potentially behavioral relevant stimuli is of fundamental importance for animals. In the auditory system, stimulus-specific adaptation (SSA) resulting in stronger responses to rare compared with frequent stimuli was proposed as such a novelty detection mechanism. SSA is a now well established phenomenon found at different levels along the mammalian auditory pathway. It depends on various stimulus features, such as deviant probability, and may be an essential mechanism underlying perception of changes in sound statistics. We recorded neuronal responses from the ventral part of the medial geniculate body (vMGB) in Mongolian gerbils to determine details of the adaptation process that might indicate underlying neuronal mechanisms. Neurons in the vMGB exhibited a median spike rate change of 15.4% attributable to a fast habituation to the frequently presented standard stimulus. Accordingly, the main habituation effect could also be induced by the repetition of a few uniform tonal stimuli. The degree of habituation was frequency-specific, and comparison across simultaneously recorded units indicated that adaptation effects were apparently topographically organized. At the population level, stronger habituation effects were on average associated with the border regions of the frequency response areas. Finally, the pharmacological inactivation of the auditory cortex demonstrated that SSA in the vMGB is mainly regulated by the corticofugal system. Hence, these results indicate a more general function of SSA in the processing and analysis of auditory information than the term novelty detection suggests.

Startle responses in Parkinson patients during human gait

Falls frequently occur in patients with Parkinson's disease (Bloem et al. 2001). One potential source for such falls during walking might be caused by the reaction to loud noises. In normal subjects startle reactions are well integrated in the locomotor activity (Nieuwenhuijzen et al. 2000), but whether this is also achieved in Parkinson patients is unknown. Therefore, in the present study, the startle response during walking was studied in eight patients with Parkinson's disease and in eight healthy subjects. To examine how startle reactions are incorporated in an ongoing gait pattern of these patients, unexpected auditory stimuli were presented in six phases of the step cycle during walking on a treadmill. For both legs electromyographic activity was recorded from biceps femoris and tibialis anterior. In addition, we measured the stance and swing phases of both legs, along with the knee angles of both legs and the left ankle angle. In all subjects and all muscles, responses were detected. The pattern of the responses, latency, duration, and phase-dependent modulation was similar in both groups. However, the mean response amplitude was larger in patients due to a smaller habituation rate. No correlation was found between the degree of habituation and disease severity. Moreover, a decreased habituation was already observed in mildly affected patients, indicating that habituation of the startle response is a sensitive measure of Parkinson's disease. The results complement the earlier findings of reduced habituation of blink responses in Parkinson's disease. With respect to behavioral changes in healthy subjects we observed that startle stimuli induced a shortening of the step cycle and a decrease in range of motion. In the patient group, less shortening of the subsequent step cycle and no decrease in range of motion of the knee and ankle was seen. It is argued that the observed changes might contribute to the high incidence of falls in patients with Parkinson's disease.

Exhaustion is associated with reduced habituation of free cortisol responses to repeated acute psychosocial stress

We investigated the association between exhaustion and the habituation of free cortisol responses to repeated stress exposure. The study comprised 25 healthy male subjects (38–59 years) who were confronted three times with the Trier Social Stress Test. Mean cortisol responses showed the well-known general habituation effect. A two-way interaction day by exhaustion ( p < 0.05) indicated that mean cortisol responses vary across stress sessions depending on the extent of exhaustion. Linear regression revealed a negative dose–response relationship between exhaustion and the degree of habituation ( p < 0.02). We identified 19 individuals showing a response habituation (negative slope) and 6 individuals showing a response sensitization over the three sessions (positive slope) with the latter reporting higher exhaustion scores. It might be hypothesized that impaired habituation to repeated exposure to the same stressor could reflect a state of increased vulnerability for allostatic load. Absence of normal habituation might be one potential mechanism how exhaustion relates to increased disease vulnerability.

Effects of rotation on the P13 mid-latency auditory evoked potential in Rat

The P13 mid-latency auditory evoked potential in Rat is a sleep state-dependent response thought to be equivalent to the human P50 potential, a measure of the output of the reticular activating system. The amplitude of these potentials can be considered a measure of level of arousal, while, using a paired stimulus paradigm, the degree of habituation of the responses also can be assessed. Different durations of rotation were found to reduce the amplitude of the P13 potential, which recovered in a duration-dependent manner. Different durations of rotation led to decreases in habituation of the P13 potential again in a duration-dependent manner. These results suggest that rotation may affect the level of arousal as well as habituation to repetitive sensory inputs. Such effects could be interpreted to imply the presence, following rotation of sufficient duration, of a deficit in sensory gating, or distractibility, and are relevant for the study of the effects of space motion sickness.

Startle responses in hereditary hyperekplexia.

Patients with hereditary hyperekplexia have excessive startle responses that are accompanied by transient stiffness and also continuous stiffness in infancy. A point of mutation has been identified for the major form of hereditary hyperekplexia in the gene encoding the alpha 1 subunit of the glycine receptor. To measure startle reflexes and autonomic responses in the major form of hereditary hyperekplexia in the original Dutch pedigree. Startle reflexes and autonomic responses were examined by administering 3 series of 20 auditory stimuli at intervals of 10 seconds (90 and 113 dB) and 60 seconds (113 dB). The Department of Neurology and Clinical Neurophysiology at the Leiden University Hospital, Leiden, the Netherlands. Nine patients with the major form of hyperekplexia and 20 healthy controls. Of the 9 patients, 5 took medication. The patients are part of the Dutch hyperekplexia pedigree. Startle responses were quantified with latency periods and areas of electromyographic bursts of the orbicular muscle of the eye, sternocleidomastoid and biceps muscles, and the thenar muscles. Autonomic reactions were measured with psychogalvanic responses and beat to beat changes of blood pressure and heart rate. The electromyographic bursts of the 4 muscles occurred in similar order in both patients and controls. The onset of the latency periods in the patient group was significantly (P < .001) prolonged in patients who took medication. Without medication, patients had shorter latency periods of the sternocleidomastoid muscle (P = .003) than controls. The electromyographic burst occurred significantly more often in patients than in controls (P < .001). The areas of the bursts were significantly larger in patients than in controls (P < .001); the degree of habituation was significantly stronger in patients than in controls (P < .001). The amplitude of the psychogalvanic response was increased in hyperekplexia, and the degree of habituation was significantly weaker in patients than in controls. Blood pressure and heart rate did not clearly react in either group. Motor startle responses are stronger and show more habituation in patients with hereditary hyperekplexia than in controls. The excessive responses include the psychogalvanic response. Increased responses do not necessarily indicate decreased habituation in hyperekplexia.

Predation on mammals by the chimpanzee (Pan troglodytes)

With respect to prey selectivity and predation frequency, chimpanzees (Pan troglodytes) show local differences as well as diachronic variability within the same population. When data on predation from three long-term studies at Mahale, Gombe, and Tai are compared, some differences and similarities emerge; Mahale is more like Gombe than Tai in regard of prey selection but features of hunting at Tai with respect to predation frequency are not conspicuous. The most responsible factor for diversity in prey selectivity is a distinct “prey image” maintained by chimpanzees of different populations, although it is necessary to clarify in future studies why and how such tradition develops. Relative body size of chimpanzees to prey species and/or the degree of cooperation among members of a hunting party may explain the variability in prey size selected at each site, the latter influencing the frequency of successful hunts at the same time. Although various degrees of habituation and different sampling methods including artificial feeding might have obscured the real differences, recent data from the three populations do not seem to be biased greatly by such factors. Nevertheless, it is still difficult to make strict comparisons due to the lack of sufficient standardized data across the three populations on the frequency of hunting and predation. It is suggested that the size or demographic trend of a chimpanzee unit-group, especially the number of adult males included, necessarily influences its hunting frequency as well as its prey profile. It is also suggested that factors which bring these males together into a party (e.g. fruit abundance, swollen females, conflict between unit-groups etc.) strongly affect theactual hunting and kill rates. Other possible factors responsible for the local differences are forest structure (e.g. tree height), skilful “hero” chimpanzees, and competition with sympatric carnivorous animals. A total of at least 32 species have been recorded as prey mammals of chimpanzees from 12 study sites and the most common prey mammals are primates (18 species), of which 13 species are forest monkeys. Forest monkeys, colobine species in particular, are often the most common victims of the predation by chimpanzees at each site. We may point out a tendency toward selective hunting for the forest monkeys in terms of the selectivity of prey fauna among all three subspecies of chimpanzees, including populations living in drier environment. The mode of chimpanzee hunting seems to correspond to the highest available biomass of gregarious, arboreal monkeys in the forest, colobine species in particular. In contrast, bonobos (P. paniscus) are less carnivorous than chimpanzees, only rarely preying on a few species of small mammals. The sharp contrast of the two allied species in their predatory tendencies appears to have something to do with the differences in the structure of primary production between their habitats.

Habituation and dishabituation to speech and office noise.

The authors examined whether background noise can be habituated to in the laboratory by using memory for prose tasks in 3 experiments. Experiment 1 showed that background speech can be habituated to after 20 min exposure and that meaning and repetition had no effect on the degree of habituation seen. Experiment 2 showed that office noise without speech can also be habituated to. Finally, Experiment 3 showed that a 5-min period of quiet, but not a change in voice, was sufficient to partially restore the disruptive effects of the background noise previously habituated to. These results are interpreted in light of current theories regarding the effects of background noise and habituation; practical implications for office planning are discussed.

The startle pattern in the minor form of hyperekplexia.

The major and minor forms of hereditary hyperekplexia (HE) are characterized by excessive startle responses, which are accompanied by transient stiffness only in major HE; patients with major HE also have continuous stiffness during infancy. A point mutation has been identified for major HE in the gene encoding the alpha 1 subunit of the glycine receptor but not for minor HE. To measure startle reflexes and autonomic responses in the major and minor forms of HE in the original Dutch HE pedigree. Startle reflexes and autonomic responses were studied with 3 series of 20 auditory stimuli with intervals of 10 seconds (at 90 and 113 dB) and 60 seconds (at 113 dB). A university hospital neurologic department. Four patients with minor and 9 patients with major HE (patient groups) (a part of the Dutch HE family pedigree) and 20 healthy controls (control group). Startle movements were quantified with latencies and areas of electromyographic bursts of the following 4 muscles: the orbicular muscle of the eye, the sternocleidomastoid muscle, the biceps muscle of the arm, and thenar muscles. Autonomic reactions were measured with psychogalvanic responses. RESULTS. The 4 muscles contracted in similar order in the groups. The onset latencies of the orbicular muscle of the eye, the sternocleidomastoid muscle, and the biceps muscle of the arm were significantly prolonged in patients with minor HE (P < .006). The frequencies of occurrence of the electromyographic bursts were not different in the minor HE and major HE groups, but they were significantly higher in both patient groups compared with those in the control group (P < .001). The magnitude of the startle responses did not differ between the 2 patient groups (P = .4), but it was larger in both patient groups than in the control group (P < .001). Startle habituation in the minor HE group was much weaker than in the major HE group (P < .001) or in the control group (P < .001). The size of psychogalvanic responses (P = .1) and the degree of habituation (P = .24) in the minor HE group did not differ from those in the major HE group. Compared with that in the control group, the size of psychogalvanic responses in the minor HE group was larger (P < .001) and they habituated stronger (P < .001). The differences in the startle pattern between major HE and minor HE agree with the clinical and genetic findings: only major HE constitutes part of the HE phenotype. The cause of the minor HE is, as yet, unknown.

Physiological responses of farmed red deer to management practices and their modulation by long-acting neuroleptics

SUMMARYTwelve red deer (Cervus elaphus) hinds from a research facility in Eastern Scotland were randomly divided into two groups between June and September to study the physiological response to three management practices, given sequentially, which were expected to cause increasing levels of stress (herding; herding and handling; and herding, handling and a veterinary procedure). One group of animals received a long-acting neuroleptic (LAN; perphenazine enanthate and zuclopenthixol acetate) on three occasions at 4-week intervals. Automatic blood sampling equipment (ABSE) was used to obtain blood samples remotely before, during and after the application of each of the stressors. The plasma concentrations of cortisol, creatine phosphokinase (CPK), aspartate aminotransferase (AST), total protein (TP), 3,5,3'-triiodothyronine (T3), thyroxine (T4) and testosterone (T) were measured and heart rates recorded. The ABSE provided a useful means of collecting blood samples without the superimposition of stress factors associated with conventional sampling. Increases in plasma concentrations of cortisol (P&lt;0·01), CPK (P&lt;0·01) and AST (P&lt;0·05) were observed in all animals in response to all three management practices. There were smaller increases in plasma cortisol concentration (P&lt;0·05) in those animals treated with LAN. The results suggested a degree of habituation of the hinds to some procedures common to all treatments, in agreement with previous analysis of the behavioual response of these animals. Peaks of heart rate were recorded over the 30-min period stressors were applied. Higher heart rates and T3 and T4 concentrations were observed in LAN-treated animals. Heart rates returned to baseline more rapidly in the LAN-treated animals. Higher plasma concentrations of testosterone were recorded in the first week of the study (P&lt;0·001). Physiological and behavioural evidence supports the view that LANs are effective long-term tranquillizers in red deer.

Factors affecting habituation and recovery from habituation in the nematode Caenorhabditis elegans.

In four experiments, the factors that affect the rate of habituation, the degree of habituation, and the rate of recovery from habituation in a simple reflex circuit in Caenorhabditis elegans were investigated. The results showed that habituation was more pronounced and faster, and that recovery from habituation was more rapid, with short interstimulus intervals (ISIs) than with longer ISIs. Rate of recovery differed in animals that had reached asymptotic response levels when compared with animals still in the descending portion of the habituation curve. Once animals reached asymptotic response levels, rate of recovery appeared to be determined by ISI and not by additional stimuli.

When plant teratomas turn into cancers in the absence of pathogens

Habituated calli have long been classified as neoplasms together with tumors from different origins. The general opinion is that habituation is a reversible process with an epigenetic basis. This is probably true in most cases examined. However, we show here that there might be several degrees of habituation, which can be considered as steps of a neoplastic progression leading to cancerisation in the absence of an introduced oncogenic pathogen. Cell rejuvenation, loss of the capacity to organize meristematic centers, and loss of totipotency are proposed to define plant cancer through this neoplastic progression of a callus.Habituated tissues share many morphological and biochemical similarities with so‐called vitreous shoots from micropropagation. Vitrification and hyperhydric malformations of shoots raised in vitro may be considered as steps of another neoplastic progression, which leads to cancerisation also in the absence of introduced oncogenic pathogens. In this case death of the whole organism occurs either through direct apex necrosis or indirectly, from the loss of the capacity for the primary meristems to function normally, which gives rise to completely anarchic structures. As in the animal kingdom, carcinogenesis in plants is the final result of a multistep process involving the irreversible conversion of a stem cell to a terminal‐differentiation‐resistant cell.

The effects of repeated doses of ethanol on exploration and its habituation.

The effects of ethanol (0.8-2.4 g/kg) on exploratory behavior and its habituation were investigated by testing DBA/2 mice in a holeboard apparatus. Mice familiar with the holeboard had lower levels of exploration than animals with no previous experience in the apparatus. If the animals received ethanol during their first exposure to the holeboard they did not show the same degree of habituation. Ethanol (0.8 g/kg) increased the exploration of animals naive to the holeboard, but failed significantly to increase the exploration of animals familiar with the apparatus. An increase in locomotor activity was observed following treatment with ethanol (2.4 g/kg). This was potentiated if animals received a single treatment with ethanol 3 days earlier, but only if they were tested in the apparatus following the initial treatment. These results have important implications for the design of experiments investigating tolerance and sensitization to ethanol's effects on locomotor activity and exploration.

Responses to pure tone stimuli and model songs of ventral cord neurones of Corixa punctata Ill. (Heteroptera: Corixidae)

The hearing organs of Corixa punctata males were stimulated with pure tones and model songs. Carrier frequencies of the stimuli ranged from 1 to 3 kHz, thus covering the peak frequencies of the conspecific song spectra. The spike responses of ventral cord neurones were recorded extracellularly. Four different neurone types were found on the right (R) side of the prothoracic ganglion and were characterized as follows: (1) Threshold curves of the 1.2−2.4 1 R neurones showed a double peak of best frequency sensitivity (Fig. 1). According to stimulus carrier frequency their response saturated or reached a maximum between 10 and 25 dB above threshold (Fig. 2A). Neurones copied different stimulus durations in a phasic-tonic way (Fig. 3A). Time structure of a model song, simulating the conspecific sound emission, was faithfully copied in the frequency range between 1.6 and 2.8 kHz (Fig. 3E). Neurone's responses habituated at the repetition rate of pulse trains typical for the conspecific song; the degree of habituation was determined by the carrier frequency and sound intensity of the pulses (Fig. 6). (2) Threshold curves of the 1.6−2.4 2 R neurones showed two peaks of best sensitivity but were 7–14 dB less sensitive than the 1.6−2.4 1 R neurones (Fig. 1). They responded only with an “on”-burst of spikes irrespective of stimulus carrier frequency and stimulus duration; the response magnitude was mainly determined by stimulus intensity (Figs 2B, 3B, 4A and B). Because of fast habituation they responded only to the first pulse train in a sequence with natural repetition rate (Fig. 3F). (3) Neurones of the 2.4 1 R type responded best at frequencies between 2.0 and 2.8 kHz (Fig. 1). Their intensity/response curves were bell shaped (Fig. 2C). Prolonged responses were typical for stimuli shorter than 20 ms (Fig. 3C). Pure tone stimuli of longer duration or high pulse repetition rates, as they occur in the natural songs, inhibited responses in these neurones (Figs 3C, 4C and D, 5). A pulse locked response pattern was well expressed only to the first two pulses in a pulse train (Fig. 3G). Carrier frequency and sound intensity determined the degree of response habituation to the natural repetition rate of pulse trains (Fig. 6). (4) Neurones of the 1.0 1 R type did not exhibit special tuning to the song spectra of Corixa. They responded best to acoustic stimuli with carrier frequencies below 1.6 kHz (Fig. 1). At higher frequencies they were about 20 dB less sensitive than the three other neurones. Pure tone stimuli were copied in a phasic-tonic way (Fig. 3D).