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Biomedical subjects

K G Pearson

Publications and source records attributed to K G Pearson.

At least 55 records · Page 3Linked to original sources
PubMed1993

Modification of reflexes in normal and abnormal movements.

The trajectories observed for the limb during human locomotion are determined by a mixture of influences, some arising from neural circuits entirely within the central nervous system and others arising from a variety of sensory receptors. Muscle reflexes are highly modulated during locomotion in an adaptive manner within each phase of the step cycle. Furthermore, the modulation can be modified quickly for different tasks such as standing, walking and running, probably by changes in presynaptic inhibition. This modulation is often lost or severely reduced in patients with spasticity after spinal cord or head injury. In normal subjects cutaneous reflexes can be completely reversed from exciting to inhibiting a muscle during each step cycle, particularly in muscles that normally show two bursts of activity per cycle (e.g., tibialis anterior). In some patients stimulation of a mixed nerve (e.g., common peroneal) can directly produce muscle contraction, generate a reflex response (flexor reflex) and transiently reduce spasticity in antagonist (extensor) muscles. Thus, simple systems employing stimulation can enhance gait to a certain extent in patients with incomplete injuries.

Electric Stimulation↗
PubMed1993

Reversal of the influence of group Ib afferents from plantaris on activity in medial gastrocnemius muscle during locomotor activity.

1. Rhythmic locomotor activity was evoked in clonidine-treated acute and chronic spinal cats, and the effect of stimulating group I afferents from the plantaris muscle on the timing and magnitude of bursts in medial gastrocnemius (MG) motoneurons was examined. 2. The locomotor rhythm was entrained when group I afferents in the plantaris nerve were electrically stimulated with trains of stimuli presented at rates above and below the intrinsic frequency of the rhythmic activity. During entrainment at rates higher than the intrinsic frequency, a burst of activity in ipsilateral MG motoneurons was initiated approximately 40 ms after the onset of each stimulus train. At lower rates of entrainment the onset of MG bursts preceded the onset of the stimulus trains, and each stimulus train had an excitatory effect on the MG burst with a latency in the range of 30-50 ms. A similar excitatory effect was observed when the stimulus trains were triggered at a preset delay after the endogenous generation of the MG bursts. 3. The excitatory action of plantaris group I afferents on the MG motoneurons was only seen during periods of locomotor activity. In the absence of rhythmic activity, the same stimulus trains reduced any ongoing tonic activity in MG motoneurons. 4. Vibration of the plantaris muscle to preferentially activate group Ia afferents neither entrained the locomotor rhythm nor increased the magnitude of the MG bursts. 5. We conclude that during locomotor activity, input from group Ib afferents of the plantaris muscle has an excitatory action on the system of interneurons generating the extensor bursts, i.e., on the extensor half-center of the central rhythm generator.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1993

Alteration of bursting properties in interneurons during locust flight.

1. The contribution of bursting properties to the generation of the flight motor pattern was examined for two identified interneurons (interneurons 566 and 567) in the flight system of the locust Locusta migratoria by means of intracellular recording and stimulation techniques. These interneurons are important elements in transmitting proprioceptive information from the hindwing tegula to wing elevator motoneurons. 2. Offset currents injected into these neurons revealed that bursts are triggered in the intact flying animal by synaptic input from tegula afferents (n = 10). These bursts lead to an amplification of proprioceptive input that is crucial for the generation of the intact flight motor pattern. In the absence of afferent input the activity of these neurons remained subthreshold for triggering a burst. This explains why these neurons exhibit only weak rhythmic oscillations in deafferented animals. 3. The property of interneuron 566 to burst was conditional, always being expressed during flight (n = 14) and occurring only occasionally in the quiescent animal. In the absence of flight, stimulation of tegula afferents never evoked bursts in interneuron 566 (n = 7) and depolarizing current pulses evoked weak bursts in only three of nine preparations. In 2 of 14 animals, bursting property of interneuron 566 was enhanced just after the termination of flight. 4. Variability in the bursting property was also found for interneuron 567. In the quiescent animal, tegula-evoked compound excitatory postsynaptic potentials were not sufficient to trigger bursts (n = 3) but depolarizing current pulses evoked always weak rhythmic bursting activity (n = 4). This bursting property was also variable and in one animal we found long-lasting plateau potentials that could be evoked by current injection after flight was elicited several times. 5. The data presented demonstrate that the capacity to burst is conditional in the interneurons 566 and 567. Bursting properties are always induced during flight and function to amplify proprioceptive pathways that are important for the generation of the intact flight motor pattern.

Afferent Pathways↗
PubMed1992

Reorganization of sensory regulation of locust flight after partial deafferentation.

Previous investigations have shown that the flight motor pattern of the mature locust (Locusta migratoria L.) relies heavily on the input of the hindwing tegulae. Removal of the hindwing tegulae results in an immediate change in the motor pattern: the wingbeat frequency (WBF) decreases and the interval between the activity of depressor and elevator muscles (D-E interval) increases. In contrast, removal of the forewing tegulae has little effect on the motor pattern. Here we report adaptive modifications in the flight system that occur after the removal of the hindwing tegulae. Over a period of about 2 weeks following hindwing tegula removal, the flight motor pattern progressively returned towards normal, and in about 80% of the animals recovery of the flight motor pattern was complete. We describe the changes in the activity pattern of flight muscles and in the patterns of depolarizations in flight motoneurons and flight interneurons associated with this recovery. In contrast to the situation in the intact animal, the activity of the forewing tegulae is necessary in recovered animals for the generation of the motor pattern. Removal of the forewing tegulae in recovered animals resulted in similar changes in the flight motor pattern as were observed in intact animals after the removal of the hindwing tegulae. Furthermore, electrical stimulation of forewing tegula afferents in recovered animals produced similar resetting effects on the motor pattern as electrical stimulation of the hindwing tegulae afferents in intact animals. From these observations we conclude that recovery is due to the functional replacement of the removed hindwing tegulae by input from the forewing tegulae.

Animals↗
PubMed1992

Connections of the forewing tegulae in the locust flight system and their modification following partial deafferentation.

The flight motor pattern of the adult locust (Locusta migratoria L.) is able to recover from the loss of the hindwing tegulae. This recovery is due to a functional substitution of the hindwing tegulae by the forewing tegulae (Büschges, Ramirez, and Pearson, 1992). To assess changes in the pathways from the forewing tegulae in the flight system, we investigated the pathways of the forewing tegula in intact locusts and in animals 2 weeks after hindwing tegula removal. The following physiological alterations in these pathways were found to be associated with the recovery: (1) In the intact locusts, the connections of forewing tegula afferents to flight interneurons are variable but this variability did not occur in recovered animals, and (2) larger numbers of forewing tegula afferents connect to interneurons that excite elevator motoneurons (interneurons 566 and 567) and to an interneuron that inhibits depressor motoneurons (interneuron 511). The size of unitary excitatory postsynaptic potentials (EPSPs) evoked by signal forewing tegula afferents was found not to be altered in recovered animals. The changes in connectivity of forewing tegula afferents are correlated with morphological alterations in the structure of the terminal processes of the afferents and with sprouting of some branches of interneurons receiving input from these afferents.

Animals↗
PubMed1992

Entrainment of the locomotor rhythm by group Ib afferents from ankle extensor muscles in spinal cats.

1. Previous studies have concluded that the timing of the locomotor rhythm can be strongly influenced by input from group Ib afferents from leg extensor muscles (Duysens and Pearson 1980; Conway et al. 1987). The main objective of the present study was to obtain additional evidence for this conclusion by examining the characteristics of entrainment of the locomotor rhythm by rhythmic stimulation of group I afferents and by rhythmic force pulses in the ankle extensor muscles. 2. A reduced, non-immobilized preparation was developed in spinal cats that allowed isometric contractions of ankle extensor muscles to be elicited by ventral root stimulation during the expression of locomotor activity. The same preparation was used to examine the influence of electrically stimulating group I afferents from the ankle extensors and the effect of rhythmically stretching these muscles. The locomotor rhythm was initiated by sustained mechanical stimulation of the perineum following the administration of Clonidine and, in some preparations, Naloxone. 3. The timing of the onset of flexor burst activity was examined during entrainment with saw-tooth and ramp-and-hold stretches of the ankle extensor muscles. Flexor bursts were initiated about 200 ms following the release from the stretch, and this latency was independent of the entrainment frequency. 4. The locomotor rhythm was readily entrained by rhythmic contractions of the ankle extensor muscles produced by ventral root stimulation provided the magnitude of the contractions was greater than about 10N. Repetitive stimulation of group I muscle afferents from the ankle extensors also entrained the locomotor rhythm, with the timing of motor activity being similar to that during entrainment with rhythmic muscle contractions. Burst activity in the ipsilateral extensors was coincident with the stimulus trains in both cases. This similarity argues for entrainment being produced mainly by input from group Ib afferents. 5. The functional implication of the results of this and previous studies is that input from group Ib afferents during the stance phase of walking acts to inhibit generation of flexor burst activity and to promote extensor activity. The proposal that a decline in Ib activity near the end of the stance phase is involved in regulating the stance to swing transition is discussed.

Afferent Pathways↗
PubMed1992

The use of naloxone to facilitate the generation of the locomotor rhythm in spinal cats.

The locomotor rhythm evoked by perineal stimulation in clonidine-treated acute and chronic spinal cats can be produced more easily when the opioid receptor antagonist naloxone is also administered. Naloxone increases the frequency of the locomotor rhythm and decreases the intensity of skin stimulation required for evoking the rhythm. A useful property of naloxone is that it can restore the locomotor rhythm when the rhythm wanes, thus prolonging the time period over which locomotor activity can be generated. Administration of naloxone without clonidine does not enable the locomotor rhythm to be generated by skin stimulation, but it does reduce the concentration of clonidine required for the expression of a robust rhythm and may increase the chance of a successful preparation. We conclude that naloxone is a useful pharmacological tool for studies on the locomotor pattern generator.

Animals↗
PubMed1991

Octopamine induces bursting and plateau potentials in insect neurones.

The membrane properties of some inter- and motoneurones in the respiratory and flight systems of the locust Locusta migratoria were characterized during octopamine perfusion by means of intracellular recording techniques. Octopamine induced active membrane properties in these neurones. Plateau-potentials were evoked by brief current pulses or synaptic input in 3 of the identified neurones and endogenous bursting was evoked by prolonged current pulses in one identified interneurone. Hyperpolarizing pulses injected into these neurones either prematurely terminated or suppressed these responses, indicating that these potentials are due to active membrane properties intrinsic to these neurones. Such intrinsic membrane properties have not been described in insects before. Further investigations are necessary to examine whether these properties may play an important role in the generation of rhythmic motor patterns as has previously been demonstrated in many other vertebrate and invertebrate motor systems.

Animals↗
PubMed1991

Octopaminergic modulation of interneurons in the flight system of the locust.

1. Modulatory effects of octopamine perfusion on identified central neurons in the flight system of the locust Locusta migratoria were examined by means of intracellular recordings from the isolated metathoracic ganglion. 2. Octopamine increased the excitatory response of elevator motoneurons to electrical stimulation of the hindwing tegula and increased the probability of triggering rhythmic activity in the flight system by current injection into single interneurons. 3. These effects of octopamine on the flight system are due in part to octopamine inducing intrinsic bursting properties in flight interneurons. Plateau potentials were evoked in these interneurons by synaptic input from tegula or by the injection of depolarizing current pulses. These potentials were prematurely terminated by hyperpolarizing currents, and their generation was voltage sensitive in that they were suppressed with hyperpolarizing offset currents. 4. Longer depolarizing current pulses evoked endogenous bursting in a number of flight interneurons. This rhythmic bursting was reset by the injection of pulses of hyperpolarizing currents. The frequency of bursting was dependent on the injected current strength. 5. The injection of hyperpolarizing current into flight interneurons during octopamine-induced rhythmic activity lead to sudden decreases in the amplitude of the depolarizations thus indicating that plateau potentials contribute to the generation of the rhythmic depolarizations. 6. The shape of the depolarizations, the duration of the bursts (50-75 ms), and the frequency range of endogenous bursting (4-16 Hz) as seen in individual interneurons during octopamine perfusion were similar to the corresponding characteristics in the same neurons during wind-induced flight activity in deafferented locusts. This correspondence suggests that intrinsic bursting properties may play an important role in generating the normal motor pattern for flight.

Animals↗
PubMed1991

Fictive motor patterns in chronic spinal cats.

1. Fictive motor patterns were recorded in hind leg nerves of 10 adult chronic spinal cats (spinalized at T13). Four of these animals had been trained to step with their hind legs on a treadmill (late-spinal animals), whereas the remainder received no training and were examined a short time after spinalization (early-spinal animals). 2. A fictive pattern resembling the locomotor pattern for stepping was evoked in all animals in response to stimulation of the skin of the perineal region. (2-[2,6-Dichloroaniline]-2-imidazoline) hydrochloride (Clonidine) at doses ranging from 100 to 500 micrograms/kg iv facilitated the production of this pattern, particularly in early-spinal animals. 3. The fictive locomotor pattern in late-spinal animals was more complex than that occurring in early-spinal animals. In the latter the pattern consisted of an alternation of activity in flexor and extensor nerves, and changing leg position did not qualitatively alter the pattern, whereas in late-spinal animals the relative durations of the bursts in different flexors were usually not the same, and the pattern of flexor activity was dependent on leg position. 4. Moving the legs from extension to flexion progressively decreased the duration of flexor bursts, increased the cycle period, and decreased the ease with which the pattern could be evoked in both early- and late-spinal animals. 5. 1-beta-3,4-Dihydroxyphenylalanine (DOPA)/Isonocotinic acid 2-[(2-benzylcarbamoyl)ethyl]hydrazide (Nialamide) treatment following Clonidine in early-spinal animals increased the complexity of flexor burst activity. This, and other observations, indicates that DOPA and Clonidine do not have strictly identical actions on the locomotor pattern generator. 6. Stimulation of the paws in late-spinal animals produced two patterns of activity distinctly different from the locomotor pattern. of activity distinctly different from the locomotor pattern. One was a short sequence of high-frequency rhythmic activity (at approximately 8 c/s) in response to gently stimulating one paw with a water jet, and the other was a slow rhythm in flexor nerves in response to squeezing the paw. 7. The main conclusion of this investigation is that three distinctly different fictive motor patterns can be generated in chronic spinal cats depending on the method and site of stimulation. These patterns correspond to three different behaviors (locomotion, paw shake, and rhythmic leg flexion) that can be elicited in behaving chronic spinal cats in response to the same stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Local anesthetic action of phentolamine on insect mechanoreceptors.

1. The effect of phentolamine on the response properties of insect mechanoreceptors and on the conduction in their axons was examined using electrophysiological techniques. 2. Phentolamine blocked conduction of action potentials along axons, an effect which exhibited 3 characteristics typical of local anesthetics: the effect was frequency-dependent, reversible and varied for nerves with different diameters. 3. The concentration of phentolamine required to block axonal conduction (1-2 x 10(-3) M) was significantly higher than that required to abolish the response of receptors to mechanical stimulation (3-5 x 10(-4) M). 4. All mechanoreceptors that were examined in Locusta migratoria and Periplaneta americana were inactivated by phentolamine (Table 1). The type I receptors (chordotonal, campaniform and hair sensilla) were inactivated within 5-15 min following phentolamine application. The only type II receptor examined (forewing stretch-receptor) underwent a phase of repetitive discharge before being inactivated. 5. Tolazoline and metoclopramide inactivated, like phentolamine, mechanoreceptors at lower concentrations than necessary to block axonal conduction. However, yohimbine and chlorpromazine inactivated mechanoreceptors and blocked axonal conduction at similar concentrations. 6. These findings suggest that phentolamine affects sense-organ specific ionic processes that are more sensitive to the drug than the ionic processes along the axons.

Action Potentials↗
PubMed1990

Chemical deafferentation of the locust flight system by phentolamine.

1. Phentolamine was injected into the haemolymph of locusts, Locusta migratoria, and its effects on the flight system were analyzed using electrophysiological techniques. 2. Doses of 150 microliters at 10(-2) M phentolamine inactivated the wing stretch-receptors and tegulae without influencing the central nervous system (CNS). The lack of effect on the CNS was demonstrated by the absence of any effect on the flight motor pattern in animals that had been mechanically deafferented prior to the administration of phentolamine. From these observations we conclude that phentolamine can be used to chemically deafferent the flight system of the locust. Consistent with this conclusion is that the administration of phentolamine in intact animals changed the flight motor pattern so that it resembled the pattern occurring in mechanically deafferented animals. 3. The two main advantages of deafferenting the flight system by injecting phentolamine were a) intracellular recordings from central neurons could be easily maintained during the process of deafferentation, and b) the contribution of different groups of proprioceptors to the generation of the motor pattern could be assessed since not all proprioceptors were inactivated simultaneously. 4. By intracellularly recording from elevator motoneurons and administering phentolamine we confirmed a number of previous results related to the function of the wing stretch-receptors and the tegulae.

Animals↗
PubMed1989

An evaluation of the role of identified interneurons in triggering kicks and jumps in the locust.

1. We have used intracellular recording and staining techniques to examine the importance of certain identified interneurons within the system responsible for triggering kicks and jumps in the locust, Locusta migratoria. In particular, our study focused on a pair of metathoracic interneurons called the M-neurons. These cells make strong inhibitory connections to hind-leg flexor motoneurons and are thought to play a key role in the termination of flexor activity which causes kicks and jumps to be triggered (8, 20, 24). 2. Simultaneous recordings from M-neurons and flexor motoneurons during bilateral hindleg kicks revealed that in most cases the onset of the M-neuron's high-frequency discharge coincided precisely with the start of the flexor's rapid repolarization. This result demonstrated that M's activity had the correct timing to be involved in the triggering process and so confirmed suggestions made in previous studies. At times, however, the flexor motoneurons began to repolarize slowly prior to the first spike in the M-neuron, indicating that triggering must involve other neurons and perhaps also an additional mechanism such as a reduction of flexor excitation. 3. The sufficiency and necessity of the M-neurons for triggering kicks were tested by experiments involving intracellular current injections. The application of a brief pulse of depolarizing current to an M-neuron, in order to evoke a burst of spikes in the cell prior to the time it would normally have become active, caused extension of the ipsilateral leg to be triggered prematurely but did not influence the motor program in the contralateral leg. This effect was only observed when the discharge frequency evoked artificially in the M-neuron was greater than that seen during natural performance of the behavior. Even then, the repolarization produced in the flexor motoneurons by the current pulses was not the same as occurs normally. We conclude that under natural circumstances the M-neurons, by themselves, are not sufficient to trigger kicks. 4. When the usual discharge in an M-neuron was prevented by the injection of hyperpolarizing current, both legs were still able to kick. This lack of necessity of the M-neurons confirms that additional neurons must be involved in the triggering process. The rate of repolarization of the flexor motoneurons during kicks in which M activity had been abolished was slower and more variable than is seen in normal kicks but this did not appear to alter the timing of leg extension.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Generation of motor patterns for walking and flight in motoneurons supplying bifunctional muscles in the locust.

In the flight system of Locusta migratoria certain muscles move a wing and a leg (bifunctional muscles) and are active during the performance of walking and flight. A preparation that allowed intracellular recordings during these behaviors was developed to analyze the activity of motoneurons supplying these and other muscles. Motoneurons innervating bifunctional muscles were active during walking and flight, whereas motoneurons innervating unifunctional flight muscles were active only during flight. Both motor patterns, walking and flight, were sometimes generated simultaneously in our preparation. In bifunctional motoneurons the two patterns were superimposed, whereas in unifunctional motoneurons only the flight motor pattern was observed. All flight interneurons we examined were either inactive or tonically inhibited during walking. All interneurons that were strongly modulated during walking were either inactive, inhibited, or only weakly modulated during flight. Anatomical investigations showed that unifunctional flight motoneurons have their main processes in the extreme dorsal region of neuropil. With the exception of the second basalar motoneurons, all bifunctional motoneurons have their processes extending more ventrally in the neuropil. Flight interneurons have their processes restricted to the dorsal neuropil. Interneurons that were rhythmically active during walking had their processes distributed more ventrally. We conclude that motoneurons innervating bifunctional muscles are active during both motor patterns, walking and flight, and that these patterns are produced by two distinct interneuronal networks. The pattern-generating network for flight appears to be located in the extreme dorsal regions of the thoracic ganglia, and the network for walking is located more ventrally.

Animals↗
PubMed1988

Proprioceptive input patterns elevator activity in the locust flight system.

1. In the locust, Locusta migratoria, the roles of two groups of wing sense organs, hind wing tegulae and wing-hinge stretch receptors, in the generation of the flight motor pattern were investigated. A preparation was employed that allowed the intracellular recording of neural activity in almost intact tethered flying locusts or after selective manipulations of sensory input. The functions of the two sets of receptors were assessed 1) by studying the phases of their discharges in the wingbeat cycle (Fig. 3), 2) by the selective ablation of input from the receptors (Figs. 4-7), and 3) by the selective stimulation of the receptor afferents (Figs. 8-12). 2. Input from the tegulae was found to be responsible for the initiation of elevator activity (Figs. 9 and 10) and for the generation of a distinct initial rapid depolarization (Figs. 4, 5, and 8) characteristic of elevator motor neuron activity in intact locusts (Figs. 1 and 16). 3. Input from the wing-hinge stretch receptors was found to control the duration of elevator depolarizations by the graded suppression of a second late component of the elevator depolarizations as wingbeat frequency increased (Figs. 6, 7, 11, and 12). The characteristics of this late component of elevator activity suggested that it is generated by the same (central nervous) mechanism that produces the elevator depolarizations recorded in deafferented animals (Fig. 2). Apparently this late component contributes to the intact pattern of elevator depolarizations only at lower wingbeat frequencies and is abolished by the action of stretch-receptor input at frequencies above approximately 15 Hz (Figs. 1, 2, and 4). At these high wingbeat frequencies elevator activity is dominated by the rapid depolarizations generated as a result of tegula input. 4. The present study demonstrates 1) that the timing of elevator motor neuron activity is determined by phasic afferent input from tegulae and stretch receptors and 2) that input from the stretch receptors controls the duration of elevator activity in the wingbeat cycle following the wing movement that was responsible for the generation of the receptor discharge.

Afferent Pathways↗
PubMed1987

Intracellular recordings from interneurons and motoneurons in intact flying locusts.

A preparation is described in which it is possible to record intracellularly from identified motoneurons and interneurons during flight in intact tethered locusts. Intracellular recordings could be obtained from either the large somata of the motoneurons or from the neuropil processes of interneurons and motoneurons in either the meso- or metathoracic ganglion. Intracellular recordings from motoneuron somata were sufficiently stable to allow surgical manipulations, e.g. deafferentation, of the nervous system without the loss of penetration. Recordings from neuropil processes required stabilizing the ganglion by sandwiching it between two supports. The preparation is suitable for the cellular analysis of many aspects of motor patterning in the flight system of the locust. So far we have used it to make a direct comparison between the patterns of synaptic activity in intact and deafferented animals. This comparison shows that sensory feedback from wing proprioceptors strongly influences the activity in elevator motoneurons and flight interneurons. From these and other observations we conclude that proprioceptive feedback is essential for generating important features of the intact motor pattern and that wing receptors are integral elements of the intact flight pattern generator.

Animals↗
PubMed1987

Projections of the wing stretch receptors to central flight neurons in the locust.

To investigate the cellular mechanisms by which proprioceptors modify the activity of a central neuronal oscillator, we identified flight motoneurons and interneurons in the thoracic ganglia of the locust Locusta migratoria, which receive constant short-latency PSPs from the wing stretch receptors (SRs). We also examined the changes in membrane potential oscillations of individual neurons when the SRs were stimulated on every cycle so as to mimic their discharge in intact animals. The SRs evoked constant short-latency (4 msec or less) EPSPs of 2 mV or less in depressor motoneurons. In general, the hindwing SRs project to both forewing and hindwing depressor motoneurons, whereas the forewing SRs project only to forewing depressor motoneurons. The SRs did not evoke IPSPs in elevator motoneurons. Twenty-one thoracic interneurons were identified that receive short-latency (4 msec or less) EPSPs from the forewing and/or hindwing SRs. Amplitudes varied from 1 to 6 mV, depending on the particular neuron. Only one neuron was found that responded with an IPSP to each SR afferent spike, but the longer latency (5-8 msec) and the different polarity suggest at least a disynaptic pathway. Fourteen interneurons received input from more than one SR. Of these, 12 neurons received EPSPs from the forewing and hindwing SRs ipsilateral to each neuron's soma, while 3 received bilateral forewing SR input. Convergence of more than one SR with the remaining 7 interneurons cannot be ruled out. Most EPSPs were evoked in interneurons depolarized in the depressor phase of the central oscillator cycle, which corresponds to the natural phase of SR activity in intact animals. However, elevator, nonrhythmic, and tonically active cells also received short-latency EPSPs from the SRs. Stimulating the SRs with trains of stimuli on every cycle produced pronounced changes in the membrane potential oscillations of several neurons, including phase-shifts, increased burst frequency, prolonged bursts, and abolition of activity. These observations suggest that the concepts of proprioceptors as error detectors and of the central oscillator as the primary generator of the movement are too simplistic to be applied to the locust flight system.

Animals↗