High-frequency oscillations within early and late phases of the phrenic neurogram

Spectral analyses were performed on phrenic neurogram recordings from 18 cats to identify high-frequency oscillations (HFOs) inherent in the signals at different phases of inspiratory activity. Gating the analysis for the entire inspiratory phase resulted in dual spectral HFOs (27 and 83 Hz), both of which persisted when the analysis was repeated on the later phase of phrenic inspiratory activity alone (29 and 82 Hz). A third pass at the same data, gating for just the early phase of phrenic discharge, however, resulted in single spectral HFOs at the higher frequency only (86 Hz). Because both early and late recruited phrenic motoneurons carry both higher and lower spectral frequencies, these results demonstrate that the lower frequency HFO is distinctly delayed in onset compared with the higher frequency HFO, the latter of which is believed to have a brain stem origin. This delayed onset may be important in identifying the source of the lower frequency HFO, which appears to be specific to various respiratory efferent systems.     

Frequency-dependent response of SI RA-class neurons to vibrotactile stimulation of the receptive field

Three types of experiment were carried out on anesthetized monkeys and cats. In the first, spike discharge activity of rapidly adapting (RA) SI neurons was recorded extracellularly during the application of different frequencies of vibrotactile stimulation to the receptive field (RF). The second used the same stimulus conditions to study the response of RA-I (RA) cutaneous mechanoreceptive afferents. The third used optical intrinsic signal (OIS) imaging and extracellular neurophysiological recording methods together, in the same sessions, to evaluate the relationship between the SI optical and RA neuron spike train responses to low- vs high-frequency stimulation of the same skin site. RA afferent entrainment was high at all frequencies of stimulation. In contrast, SI RA neuron entrainment was much lower on average, and was strongly frequency-dependent, declining in near-linear fashion from 6 to 200 Hz. Even at 200 Hz, however, unambiguous frequencyfollowing responses were present in the spike train activity of some SI RA neurons. These entrainment results support the "periodicity hypothesis" of Mountcastle et al. ( J Neurophysiol 32: 452-484, 1969) that the capacity to discriminate stimulus frequency over the range 5-50 Hz is attributable to the ability of SI RA pyramidal neurons to discharge action potentials in consistent temporal relationship to stimulus motion, and raise the possibility that perceptual frequency discriminative capacity at frequencies between 50 and 200 Hz might be accounted for in the same way. An increase in vibrotactile stimulus frequency within the range 6-200 Hz consistently resulted in an increase in RA afferent mean spike firing rate (M FR). SI RA neuron M FR also increased as frequency increased between 6 and 50 Hz, but declined as stimulus frequency was increased over the range 50-200 Hz. At stimulus frequencies > 100 Hz, and at positions in the RF other than the receptive field center (RF center ), SI RA neuron MFR declined sharply within 0.5-2s of stimulus onset and rebounded transiently upon stimulus termination. In contrast, when the stimulus was applied to the RF center, MFR increased with increasing frequency and tended to remain well maintained throughout the period of high-frequency stimulation. The evidence obtained in "combined" OIS imaging and extracellular microelectrode recording experiments suggests that SI RA neurons with an RF center that corresponds to the stimulated skin site occupy small foci within the much larger SI region activated by same-site cutaneous flutter stimulation, while for the RA neurons located elsewhere in the large SI region activated by a flutter stimulus, the stimulus site and RF center are different.     

Respiratory cycle timing and fast inspiratory discharge rhythms in the adult decerebrate rat

In supracollicular decerebrate paralyzed adult rats, neural respiration was monitored by bilateral phrenic recordings. In the study of respiratory cycle timing, the effects of vagal afferent input (lung inflation) on respiratory phase durations resembled those seen in decerebrate cats. 1) Withholding lung inflation during neural inspiration (I) produced lengthening of I phase duration by 46% (mean, n = 11). 2) Maintaining lung inflation during neural expiration (E) produced lengthening of E phase duration by 112% (mean, n = 4). In the study of fast rhythms in inspiratory discharges, phrenic nerve autospectra and bilateral (left-right) phrenic coherences in 16 rats revealed two types of fast rhythm: 1) high-frequency oscillation (HFO), which had significant coherence peaks (n = 9, range 106-160 Hz, mean 132 Hz); and 2) medium-frequency oscillation (MFO), which had autospectral peaks but no distinct coherence peaks (n = 11, range 46-96 Hz, mean 66 Hz). These rhythms resembled MFOs and HFOs in the decerebrate cat, but the modal frequency range was about twice as large. In addition, these frequency values differed markedly from the 20-40 Hz of the rhythms found in earlier studies in neonatal in vitro preparations; the difference may be due to developmental immaturity.     

Human Intracranial High Frequency Oscillations (HFOs) Detected by Automatic Time-Frequency Analysis

Objectives

High frequency oscillations (HFOs) have been proposed as a new biomarker for epileptogenic tissue. The exact characteristics of clinically relevant HFOs and their detection are still to be defined.

Methods

We propose a new method for HFO detection, which we have applied to six patient iEEGs. In a first stage, events of interest (EoIs) in the iEEG were defined by thresholds of energy and duration. To recognize HFOs among the EoIs, in a second stage the iEEG was Stockwell-transformed into the time-frequency domain, and the instantaneous power spectrum was parameterized. The parameters were optimized for HFO detection in patient 1 and tested in patients 2–5. Channels were ranked by HFO rate and those with rate above half maximum constituted the HFO area. The seizure onset zone (SOZ) served as gold standard.

Results

The detector distinguished HFOs from artifacts and other EEG activity such as interictal epileptiform spikes. Computation took few minutes. We found HFOs with relevant power at frequencies also below the 80–500 Hz band, which is conventionally associated with HFOs. The HFO area overlapped with the SOZ with good specificity > 90% for five patients and one patient was re-operated. The performance of the detector was compared to two well-known detectors.

Conclusions

Compared to methods detecting energy changes in filtered signals, our second stage - analysis in the time-frequency domain - discards spurious detections caused by artifacts or sharp epileptic activity and improves the detection of HFOs. The fast computation and reasonable accuracy hold promise for the diagnostic value of the detector.     

Contrast transfer function of the visual system]

Visually evoked potentials were used to determine the spatial contrast response function of the visual system and the visual acuity of the pigeon. The spatial contrast response describes the relationship between the contrast in a pattern of vertical stripes, whose luminance is a function of position, and the amplitude of the visually evoked response at various spatial frequencies for a given temporal frequency (pattern reversal frequency); it indicates how particular spatial frequencies are attenuated in the visual system. The visually evoked responses were recorded using monopolar stainless steel electrodes inserted into the stratum griseum superficiale of the optic tectum; the depth of penetration was determined on the basis of a stereotactic atlas. The stimulus patterns were generated on a video monitor placed 75 cm in front of the animal's eye perpendicular to the optic axis. The spatial contrast response function measured at 10% contrast and 0.5 Hz reversal frequency shows a peak at a spatial frequency of 0.5 c/deg, corresponding to 1 degree of visual angle, and decreases progressively at higher spatial frequencies. The high-frequency limit (cut-off frequency) for resolution of sinusoidal gratings, estimated from the contrast response function, is 15.5 c/deg, corresponding to a visual acuity of 1.9 min of arc.     

Motion detection in the presence and absence of background motion in anAnolis lizard

Anolis lizards respond to a moving object viewed in the periphery of their visual field by turning their eye to fixate the object with their central fovea. This paper describes the relative effectiveness of different patterns of motion of a small black lure in eliciting these eye movements and the way motion of a backdrop of vegetation affects the response. The stimulus was positioned 45 degrees from the animal's line of gaze and oscillated in the vertical axis at different frequencies between 0.5 and 10 Hz. At each frequency, the amplitude of the oscillation was increased until the lizard flicked its eye towards the stimulus. The minimum amplitude needed for response (0.22 degrees of visual angle) was independent of frequency and waveform. The probability of any response occurring was, however, lower at higher frequencies (7 and 10 Hz) and a 1.5 Hz square wave evoked the greatest proportion of responses. Sinusoidal oscillation of a background of vegetation at 1.6 Hz during or before motion of the stimulus lure reduced the probability of an eye flick but did not raise the minimum amplitude needed for a response. The suppressive effect was greatest when the lure was oscillated at frequencies close to that of the background. It is concluded that Anolis, which rely upon motion to detect objects in the periphery of the visual field, filter out irrelevant motion such as that of windblown vegetation by responding preferentially to particular patterns of motion and short term habituation to commonly present patterns of motion.     

Time-dependence of SI RA neuron response to cutaneous flutter stimulation

Spike discharge activity of RA-type SI cortical neurons was recorded extracellularly in anesthetized monkeys and cats. Multiple applications (trials) of 10-50 Hz sinusoidal vertical skin displacement stimulation ("flutter") were delivered to the receptive field (RF). Analysis revealed large and systematic temporal trends not only in SI RA neuron responsivity (measured as spikes/s and as spikes/stimulus cycle), but also in entrainment, and in phase angle of the entrained responses. In contrast to SI RA neurons, the response of RA skin afferents to comparable conditions of skin flutter stimulation exhibited little or no dynamics. The occurrence and form of the SI RA neuron response dynamics that accompany skin flutter stimulation are shown to depend on factors such as stimulus frequency and the locus of the recording site in the global cortical response pattern. Comparison of recordings obtained in near-radial vs tangential microelectrode penetrations further reveals that the SI RA neuron response dynamics that occur during skin flutter stimulation are relatively consistent within, but heterogeneous across column-sized regions. The observed SI RA neuron response dynamics are suggested to account, in part, for the improved capacity to discriminate stimulus frequency after an exposure ("adaptation") to skin flutter stimulation (Goble and Hollins, J Acoust Soc Am 96: 771-780, 1994). Parallels with recent proposals about the contributions to visual perception of short-term primary sensory cortical neuron dynamics and synchrony in multineuron spike activity patterns are identified and discussed.     

Time-dependence of SI RA neuron response to cutaneous flutter stimulation

Spike discharge activity of RA-type SI cortical neurons was recorded extracellularly in anesthetized monkeys and cats. Multiple applications (trials) of 10-50 Hz sinusoidal vertical skin displacement stimulation ("flutter") were delivered to the receptive field (RF). Analysis revealed large and systematic temporal trends not only in SI RA neuron responsivity (measured as spikes/s and as spikes/stimulus cycle), but also in entrainment, and in phase angle of the entrained responses. In contrast to SI RA neurons, the response of RA skin afferents to comparable conditions of skin flutter stimulation exhibited little or no dynamics. The occurrence and form of the SI RA neuron response dynamics that accompany skin flutter stimulation are shown to depend on factors such as stimulus frequency and the locus of the recording site in the global cortical response pattern. Comparison of recordings obtained in near-radial vs tangential microelectrode penetrations further reveals that the SI RA neuron response dynamics that occur during skin flutter stimulation are relatively consistent within, but heterogeneous across column-sized regions. The observed SI RA neuron response dynamics are suggested to account, in part, for the improved capacity to discriminate stimulus frequency after an exposure ("adaptation") to skin flutter stimulation (Goble and Hollins, J Acoust Soc Am 96: 771-780, 1994). Parallels with recent proposals about the contributions to visual perception of short-term primary sensory cortical neuron dynamics and synchrony in multineuron spike activity patterns are identified and discussed.     

Comparison of plethysmographic methods for obtaining thoracic gas volume in anesthetized dogs

In dogs, respiratory system resistance (Rrs) is frequency independent, and during high-frequency oscillatory ventilation (HFO) the relationship between CO2 elimination (VCO2) and frequency is linear. In contrast, we found in rabbits a large frequency-dependent decrease in Rrs with increasing frequency along with a nonlinear relationship between frequency and VCO2 (J. Appl. Physiol. 57: 354-359, 1984). We proposed that frequency dependent mechanical properties of the lung account for inter-species differences in the frequency dependence of gas exchange during HFO. In the current study we tested this hypothesis further by measuring VCO2 and Rrs as a function of frequency in a species of monkey (Macaca radiata). In these monkeys, Rrs decreased minimally between 4 and 8 Hz and in general increased at higher frequencies, whereas VCO2 was linearly related to frequency. This is further evidence supporting the hypothesis that nonlinear frequency-VCO2 behavior during HFO is related to frequency-dependent behavior in Rrs.     

Intracellular responses of antennal chordotonal sensilla of the American cockroach

The responses of mechanoreceptor neurons in the antennal chordotonal organ have been examined in cockroaches by intracellular recording methods. The chordotonal organ was mechanically stimulated by sinusoidal movement of the flagellum. Stimulus frequencies were varied between 0.5 and 150 Hz. Receptor neurons responded with spike discharges to mechanical stimulation, and were classed into two groups from plots of their average spike frequencies against stimulus frequency. Neurons in one group responded to stimulation over a wide frequency range (from 0.5 to 150 Hz), whereas those in a second group were tuned to higher frequency stimuli. The peak stimulus frequency at which receptor neurons showed maximum responses differed from cell to cell. Some had a peak response at a stimulus frequency given in the present study (from 0.5 to 150 Hz), whereas others were assumed to have peak responses beyond the highest stimulus frequency examined. The timing for the initiation of spikes or of a burst of spikes plotted against each stimulus cycle revealed that spike generation was phase-locked in most cells. Some cells showed phase-independent discharges to stimulation at lower frequency, but increasing stimulus frequencies spike initiation began to assemble at a given phase of the stimulus cycle. The response patterns observed are discussed in relation to the primary process of mechanoreception of the chordotonal organ.     

Feedback Inhibition and Throughput Properties of an Integrate-and-Fire-or-Burst Network Model of Retinogeniculate Transmission

Computational modeling has played an important role in the dissection of the biophysical basis of rhythmic oscillations in thalamus that are associated with sleep and certain forms of epilepsy. In contrast, the dynamic filter properties of thalamic relay nuclei during states of arousal are not well understood. Here we present a modeling and simulation study of the throughput properties of the visually driven dorsal lateral geniculate nucleus (dLGN) in the presence of feedback inhibition from the perigeniculate nucleus (PGN). We employ thalamocortical (TC) and thalamic reticular (RE) versions of a minimal integrate-and-fire-or-burst type model and a one-dimensional, two-layered network architecture. Potassium leakage conductances control the neuromodulatory state of the network and eliminate rhythmic bursting in the presence of spontaneous input (i.e., wake up the network). The aroused dLGN/PGN network model is subsequently stimulated by spatially homogeneous spontaneous retinal input or spatio-temporally patterned input consistent with the activity of X-type retinal ganglion cells during full-field or drifting grating visual stimulation. The throughput properties of this visually-driven dLGN/PGN network model are characterized and quantified as a function of stimulus parameters such as contrast, temporal frequency, and spatial frequency. During low-frequency oscillatory full-field stimulation, feedback inhibition from RE neurons often leads to TC neuron burst responses, while at high frequency tonic responses dominate. Depending on the average rate of stimulation, contrast level, and temporal frequency of modulation, the TC and RE cell bursts may or may not be phase-locked to the visual stimulus. During drifting-grating stimulation, phase-locked bursts often occur for sufficiently high contrast so long as the spatial period of the grating is not small compared to the synaptic footprint length, i.e., the spatial scale of the network connectivity.     

Temporal Features of Spike Trains in the Moth Antennal Lobe Revealed by a Comparative Time-Frequency Analysis

The discrimination of complex sensory stimuli in a noisy environment is an immense computational task. Sensory systems often encode stimulus features in a spatiotemporal fashion through the complex firing patterns of individual neurons. To identify these temporal features, we have developed an analysis that allows the comparison of statistically significant features of spike trains localized over multiple scales of time-frequency resolution. Our approach provides an original way to utilize the discrete wavelet transform to process instantaneous rate functions derived from spike trains, and select relevant wavelet coefficients through statistical analysis. Our method uncovered localized features within olfactory projection neuron (PN) responses in the moth antennal lobe coding for the presence of an odor mixture and the concentration of single component odorants, but not for compound identities. We found that odor mixtures evoked earlier responses in biphasic response type PNs compared to single components, which led to differences in the instantaneous firing rate functions with their signal power spread across multiple frequency bands (ranging from 0 to 45.71 Hz) during a time window immediately preceding behavioral response latencies observed in insects. Odor concentrations were coded in excited response type PNs both in low frequency band differences (2.86 to 5.71 Hz) during the stimulus and in the odor trace after stimulus offset in low (0 to 2.86 Hz) and high (22.86 to 45.71 Hz) frequency bands. These high frequency differences in both types of PNs could have particular relevance for recruiting cellular activity in higher brain centers such as mushroom body Kenyon cells. In contrast, neurons in the specialized pheromone-responsive area of the moth antennal lobe exhibited few stimulus-dependent differences in temporal response features. These results provide interesting insights on early insect olfactory processing and introduce a novel comparative approach for spike train analysis applicable to a variety of neuronal data sets.     

Configurational pattern discrimination responsible for dishabituation in common toads Bufo bufo (L.): Behavioral tests of the predictions of a neural model

Summary Recently, a neural model of visual pattern discrimination for stimulus-specific habituation was developed, based on previous behavioral studies which demonstrated that toads exhibit a dishabituation hierarchy for different worm-like stimuli. The model suggests that visual objects are represented by temporal coding and predicts that the dishabituation hierarchy changes when the stimulus/background contrast direction is reversed or the stimulus size is varied. The behavioral experiments reported in this paper were designed to test these predictions, (1) For a pair of stimuli from the contrast reversal prediction, the experimental results validated the theory. (2) For a pair of stimuli from the size reduction prediction, the experimental results failed to validate the theory. Further experiments concerning size effects suggest that configurai visual pattern discrimination in toads exhibits size invariance. (3) Inspired by the Groves-Thompson account of habituation, we found that dishabituation by a second stimulus has a separate process from habituation to a first stimulus. This paper serves as an example of a fruitful dialogue between experimentation and modeling, crucial for understanding brain functions.Abbreviations a-h worm-like stimulus patterns - AT anterior thalamus - ERF excitatory receptive field - IRF inhibitory receptive field - RF receptive field - R2 to R4 retinal ganglion cell types - vMP posterior ventromedial pallium     

Ventilatory effectiveness of high-frequency oscillation applied to the body surface

To determine the ventilatory effectiveness of high-frequency oscillation (HFO) at different sites on the body surface, we applied HFO separately to the abdomen, the rib cage, or the whole body in eight anesthetized and paralyzed dogs. Test frequencies were 5, 7, 9, and 11 Hz with tidal volume kept constant at 2.5 ml/kg. During HFO application to the abdomen, we observed significantly higher arterial O2 partial pressure (P less than 0.05) at 5, 7, and 9 Hz and lower arterial CO2 partial pressure (P less than 0.05) at 7, 9, and 11 Hz than with rib cage or whole-body HFO. There was no significant difference in blood gases between rib cage and whole-body HFO. Thus, using blood gases as an index of ventilatory effectiveness, the present study showed that HFO applied at the abdomen was the most effective of the three kinds of body surface HFO. In comparison to rib cage or whole-body application, abdominal HFO was accompanied by substantial paradoxical movement of the diaphragm and rib cage. The associated lung distortion may result in pendelluft, which in turn may be the mechanism for increased ventilatory effectiveness with abdominal application of HFO.     

A neural basis for gyroscopic force measurement in the halteres of <Emphasis Type="Italic">Holorusia</Emphasis>

Dipteran flight requires rapid acquisition of mechanosensory information provided by modified hindwings known as halteres. Halteres experience torques resulting from Coriolis forces that arise during body rotations. Although biomechanical and behavioral data indicate that halteres detect Coriolis forces, there are scant data regarding neural encoding of these or any other forces. Coriolis forces arise on the haltere as it oscillates in one plane while rotating in another, and occur at oscillation frequency and twice the oscillation frequency. Using single-fiber recordings of haltere primary afferent responses to mechanical stimuli, we show that spike rate increases linearly with stimulation frequency up to 150 Hz, much higher than twice the natural oscillation frequency of 40 Hz. Furthermore, spike-timing precision is extremely high throughout the frequency range tested. These characteristics indicate that afferents respond with high speed and high precision, neural features that are useful for detecting Coriolis forces. Additionally, we found that neurons respond preferentially to specific stimulus directions, with most responding more strongly to stimulation in the orthogonal plane. Directional sensitivity, coupled with precise, high-speed encoding, suggests that haltere afferents are capable of providing information about forces occurring at the haltere base, including Coriolis forces.     

Ventilation by external high-frequency oscillation in cats

Eight anesthetized tracheostomized cats were placed in an 8.2-liter airtight chamber with the trachea connected to the exterior. Thirty-two combinations of high-frequency oscillations (HFO) (0.5-30 Hz; 25-100 ml) were delivered for 10 min each in random order into the chamber. Arterial blood gas tensions during oscillation were compared with control measurements made after 10 min of spontaneous breathing without oscillation when the mean arterial PCO2 (PaCO2) was 30.1 Torr. Ventilation due to spontaneous breathing (Vs) and oscillation (Vo) were derived from the chamber pressure trace and a pneumotachograph, respectively. As the oscillation frequency increased, oscillated tidal volume (Vo) decreased from a mean of 39 (0.5 Hz) to 3.3 ml (30 Hz) when 100 ml was delivered to the chamber. From 6-25 Hz, apnea occurred with Vo less than estimated respiratory dead space (VD); the minimum effective Vo/VD ratio was 0.37 +/- 0.05. Although Vo was maximal at 10 Hz at each oscillation volume, the lowest PaCO2 occurred at 2-6 Hz, and arterial PO2 rose as expected during hypocapnia. Above 10 Hz, PaCO2 was determined by Vo and was independent of frequency, whereas at lower frequencies, PaCO2 was related to Vo; below 6 Hz, PaCO2 varied inversely with the calculated alveolar ventilation. As oscillations became more effective, both PaCO2 and Vs fell progressively and were highly correlated; apnea occurred when PaCO2 was reduced by a mean of 4.5 Torr. Mean chamber pressure remained near zero up to 15 Hz, indicating functional residual capacity did not change. We conclude that externally applied HFO can readily maintain gas exchange in vivo, with Vo less than VD at frequencies over 2 Hz.     

Double orientation tuning of cat visual cortical neurons

Orientation tuning of 148 primary visual cortical neurons was studied in acute experiments on unanesthetized, curarized cats by analysis of their spike responses to flashes in a receptive field of a bar of light of optimal size. Orientation tuning of 88 neurons (59%) was found to be bimodal: Besides the principal preferred orientation there was a second, making an angle with the first. The second tuning maximum in some cases (64%) was exhibited only with a change in stimulus intensity or background brightness. Analysis of orientation tuning by the time-slice method, i.e., on the basis of individual cuts of the spike trace, showed double tuning to be present in 69% of cases only at certain moments after the beginning of stimulation. The results of analysis of the model showed that the double orientation tuning effect may be the result of the specific configuration of the receptive field, the use of a stimulus longer than the receptive field, the presence of a series of alternating excitatory and inhibitory zones in the receptive field, and also of end inhibitory zones on the narrow ends of the field. The unequal change in zones of the receptive fields in time explains the appearance of double orientation tuning in individual fragments of the spike trace. The functional role of double, "cross-wise" tuning in some primary visual cortical neurons and their role in the detection of the features of visual patterns are discussed.     

A system of insect neurons sensitive to horizontal and vertical image motion connects the medulla and midbrain

Summary The response properties and gross morphologies of neurons that connect the medulla and midbrain in the butterfly Papilio aegeus are described. The neurons presented give direction-selective responses, i.e. they are excited by motion in the preferred direction and the background activity of the cells is inhibited by motion in the opposite, null, direction. The neurons are either maximally sensitive to horizontal motion or to slightly off-axis vertical upward or vertical downward motion, when tested in the frontal visual field. The responses of the cells are dependent on the contrast frequency of the stimulus with peak values at 5–10 Hz. The receptive fields of the medulla neurons are large and are most sensitive in the frontal visual field. Examination of the local and global properties of the receptive fields of the medulla neurons indicates that (1) they are fed by local elementary motion-detectors consistent with the correlation model and (2) there is a non-linear spatial integration mechanism in operation.     

CO2 elimination as a function of frequency and tidal volume in rabbits during HFO

CO2 elimination (VCO2) was monitored during high-frequency oscillation (HFO) over a frequency (f) range of 2-30 Hz in anesthetized and paralyzed rabbits to determine whether effective gas exchange could be achieved in this species, to determine the f and tidal volume (VT) dependence of gas exchange in this species, and to compare these results with those from dog and human studies. We were able to produce VCO2 levels during HFO that exceeded normal steady-state levels of CO2 production with VT's less than the total dead space volume. VCO2 was related to f in a curvilinear fashion, whereas in some rabbits VCO2 became independent of f at higher frequencies. This curvilinear relationship between f and VCO2 is similar to data from humans but contrasts with the linear relationship found in dogs. Evidence is presented indicating frequency-dependent behavior of gas exchange is correlated with a frequency-dependent decrease in respiratory system resistance. We propose that the frequency-dependent mechanical properties of the rabbit lung may also account for the species differences in HFO gas exchange.     

Dynamic properties of two control systems underlying visually guided turning in house-flies

Summary The compensatory optomotor turning reaction as well as the turning response towards objects play an important role in visual orientation. On the basis of behavioural experiments under precisely defined stimulus conditions it is concluded that in female house-flies these motion-dependent responses are mediated by two parallel control systems with different dynamic and spatial integration properties. One of them (large-field system) is most sensitive to the motion of large textured patterns and controls the yaw torque mainly at low oscillation frequencies (below 0.1 Hz) of the stimulus panorama. In contrast, the other control system (small-field system) is tuned to the detection of relatively small moving patterns and shows its strongest responses at high oscillation frequencies (between 1 and 4 Hz), i.e. in a frequency range where the large-field system contributes to the turning response with only a relatively small gain.In free flight, house-flies do not curve smoothly but in sequences of rapid turns which induce retinal large-field motion of continually changing sign (Wagner 1986b). The dynamic properties of the large-field system might thus be interpreted as a simple strategy to almost eliminate the unwanted optomotor yaw torque induced by active self-motion. In contrast, the small-field system might still be operational under these conditions.