Cycle-to-Cycle Variability of Neuromuscular Activity in Aplysia Feeding Behavior

2004 ◽  
Vol 92 (1) ◽  
pp. 157-180 ◽  
Author(s):  
Charles C. Horn ◽  
Yuriy Zhurov ◽  
Irina V. Orekhova ◽  
Alex Proekt ◽  
Irving Kupfermann ◽  
...  
Keyword(s):  
Feeding Behavior ◽  
Motor Neurons ◽  
Motor Program ◽  
Neuromuscular System ◽  
Motor Programs ◽  
Large Variability ◽  
Implanted Electrodes ◽  
Functional Behavior ◽  
High Level ◽  
Stimulation Of

Aplysia consummatory feeding behavior, a rhythmic cycling of biting, swallowing, and rejection movements, is often said to be stereotyped. Yet closer examination shows that cycles of the behavior are very variable. Here we have quantified and analyzed the variability at several complementary levels in the neuromuscular system. In reduced preparations, we recorded the motor programs produced by the central pattern generator, firing of the motor neurons B15 and B16, and contractions of the accessory radula closer (ARC) muscle while repetitive programs were elicited by stimulation of the esophageal nerve. In other similar experiments, we recorded firing of motor neuron B48 and contractions of the radula opener muscle. In intact animals, we implanted electrodes to record nerve or ARC muscle activity while the animals swallowed controlled strips of seaweed or fed freely. In all cases, we found large variability in all parameters examined. Some of this variability reflected systematic, slow, history-dependent changes in the character of the central motor programs. Even when these trends were factored out, however, by focusing only on the differences between successive cycles, considerable variability remained. This variability was apparently random. Nevertheless, it too was the product of central history dependency because regularizing merely the high-level timing of the programs also regularized many of the downstream neuromuscular parameters. Central motor program variability thus appears directly in the behavior. With regard to the production of functional behavior in any one cycle, the large variability may indicate broad tolerances in the operation of the neuromuscular system. Alternatively, some cycles of the behavior may be dysfunctional. Overall, the variability may be part of an optimal strategy of trial, error, and stabilization that the CNS adopts in an uncertain environment.

Tight or Loose Coupling Between Components of the Feeding Neuromusculature of Aplysia?

2005 ◽  
Vol 94 (1) ◽  
pp. 531-549 ◽  
Author(s):  
Yuriy Zhurov ◽  
Klaudiusz R. Weiss ◽  
Vladimir Brezina
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Neuromuscular System ◽  
Loose Coupling ◽  
Tight Coupling ◽  
Feeding Behaviors ◽  
Motor Programs ◽  
Firing Patterns ◽  
Functional Behavior ◽  
Tightly Coupled

Like other complex behaviors, the cyclical, rhythmic consummatory feeding behaviors of Aplysia—biting, swallowing, and rejection of unsuitable food—are produced by a complex neuromuscular system: the animal's buccal mass, with numerous pairs of antagonistic muscles, controlled by the firing of numerous motor neurons, all driven by the motor programs of a central pattern generator (CPG) in the buccal ganglia. In such a complex neuromuscular system, it has always been assumed that the activities of the various components must necessarily be tightly coupled and coordinated if successful functional behavior is to be produced. However, we have recently found that the CPG generates extremely variable motor programs from one cycle to the next, and so very variable motor neuron firing patterns and contractions of individual muscles. Here we show that this variability extends even to higher-level parameters of the operation of the neuromuscular system such as the coordination between entire antagonistic subsystems within the buccal neuromusculature. In motor programs elicited by stimulation of the esophageal nerve, we have studied the relationship between the contractions of the accessory radula closer (ARC) muscle, and the firing patterns of its motor neurons B15 and B16, with those of its antagonist, the radula opener (I7) muscle, and its motor neuron B48. There are two separate B15/B16-ARC subsystems, one on each side of the animal, and these are indeed very tightly coupled. Tight coupling can, therefore, be achieved in this neuromuscular system where required. Yet there is essentially no coupling at all between the contractions of the ARC muscles and those of the antagonistic radula opener muscle. We interpret this result in terms of a hypothesis that ascribes a higher-order benefit to such loose coupling in the neuromusculature. The variability, emerging in the successive feeding movements made by the animal, diversifies the range of movements and thereby implements a trial-and-error search through the space of movements that might be successful, an optimal strategy for the animal in an unknown, rapidly changing feeding environment.

scholarly journals Functional Genetic Screen to Identify Interneurons Governing Behaviorally Distinct Aspects of Drosophila Larval Motor Programs

2016 ◽  
Author(s):  
Matt Q. Clark ◽  
Stephanie J. McCumsey ◽  
Sereno Lopez-Darwin ◽  
Ellie S. Heckscher ◽  
Chris Q. Doe
Keyword(s):  
Motor Neurons ◽  
Animal Behavior ◽  
Motor Program ◽  
Genetic Screen ◽  
Muscle Contractions ◽  
Specific Expression ◽  
Motor Programs ◽  
Secondary Screen ◽  
Forward Locomotion ◽  
Sparse Pattern

AbstractDrosophila larval crawling is an attractive system to study patterned motor output at the level of animal behavior. Larval crawling consists of waves of muscle contractions generating forward or reverse locomotion. In addition, larvae undergo additional behaviors including head casts, turning, and feeding. It is likely that some neurons are used in all these behaviors (e.g. motor neurons), but the identity (or even existence) of neurons dedicated to specific aspects of behavior is unclear. To identify neurons that regulate specific aspects of larval locomotion, we performed a genetic screen to identify neurons that, when activated, could elicit distinct motor programs. We used 165 Janelia CRM-Gal4 lines – chosen for sparse neuronal expression – to express the warmth-inducible neuronal activator TrpA1 and screened for locomotor defects. The primary screen measured forward locomotion velocity, and we identified 63 lines that had locomotion velocities significantly slower than controls following TrpA1 activation (28°C). A secondary screen was performed on these lines, revealing multiple discrete behavioral phenotypes including slow forward locomotion, excessive reverse locomotion, excessive turning, excessive feeding, immobile, rigid paralysis, and delayed paralysis. While many of the Gal4 lines had motor, sensory, or muscle expression that may account for some or all of the phenotype, some lines showed specific expression in a sparse pattern of interneurons. Our results show that distinct motor programs utilize distinct subsets of interneurons, and provide an entry point for characterizing interneurons governing different elements of the larval motor program.

Afferent-Induced Changes in Rhythmic Motor Programs in the Feeding Circuitry of Aplysia

2004 ◽  
Vol 92 (4) ◽  
pp. 2312-2322 ◽  
Author(s):  
Avniel N. Shetreat-Klein ◽  
Elizabeth C. Cropper
Keyword(s):  
Sensory Neurons ◽  
Motor Neurons ◽  
Rhythmic Activity ◽  
Motor Program ◽  
Firing Frequency ◽  
Afferent Activity ◽  
Motor Programs ◽  
Rhythmic Motor ◽  
Induced Changes ◽  
The Impact

A manipulation often used to determine whether a neuron plays a role in the generation of a motor program involves injecting current into the cell during rhythmic activity to determine whether activity is modified. We perform this type of manipulation to study the impact of afferent activity on feeding-like motor programs in Aplysia. We trigger biting-like programs and manipulate sensory neurons that have been implicated in producing the changes in activity that occur when food is ingested, i.e., when bites are converted to bite-swallows. Sensory neurons that are manipulated are the radula mechanoafferent B21 and the retraction proprioceptor B51. Data suggest that both cells are peripherally activated during radula closing/retraction when food is ingested. We found that phasic subthreshold depolarization of a single sensory neuron can significantly prolong radula closing/retraction, as determined by recording both from interneurons (e.g., B64), and motor neurons (e.g., B15 and B8). Additionally, afferent activity produces a delay in the onset of the subsequent radula opening/protraction, and increases the firing frequency of motor neurons. These are the changes in activity that are seen when food is ingested. These results add to the growing data that implicate B21 and B51 in bite to bite-swallow conversions and indicate that afferent activity is important during feeding in Aplysia.

Different Roles of Neurons B63 and B34 That Are Active During the Protraction Phase of Buccal Motor Programs in Aplysia californica

1997 ◽  
Vol 78 (3) ◽  
pp. 1305-1319 ◽  
Author(s):  
Itay Hurwitz ◽  
Irving Kupfermann ◽  
Abraham J. Susswein
Keyword(s):  
Motor Neurons ◽  
Aplysia Californica ◽  
Motor Program ◽  
Excitatory Postsynaptic Potential ◽  
Strongly Correlated ◽  
Excitatory Effect ◽  
Buccal Ganglion ◽  
Motor Programs ◽  
Pattern Characteristic ◽  
Protraction Phase

Hurwitz, Itay, Irving Kupfermann, and Abraham J. Susswein. Different roles of neurons B63 and B34 that are active during the protraction phase of buccal motor programs in Aplysia californica. J. Neurophysiol. 78: 1305–1319, 1997. The buccal ganglion of Aplysia contains a central pattern generator (CPG) that organizes sequences of radula protraction and retraction during food ingestion and egestion. Neurons B63 and B34 have access to, or are elements of, the CPG. Both neurons are depolarized along with B31/B32 during the protraction phase of buccal motor programs. Both cells excite the contralateral B31/B32 neurons and inhibit B64 and other neurons active during the retraction phase. B63 and B34 also both have an axon exiting the buccal ganglia via the contralateral cerebrobuccal connective. Despite their similarities, B63 and B34 differ in a number of properties, which reflects their different functions. B63 fires during both ingestion and egestion-like buccal motor programs, whereas B34 fires only during egestion-like programs. The bilateral B63 neurons, along with the bilateral B31 and B32 neurons, act as a single functional unit. Sufficient depolarization of any of these neurons activates them all and initiates a buccal motor program. B63 is electrically coupled to both the ipsilateral and the contralateral B31/B32 neurons but monosynaptically excites the contralateral neurons with a mixed electrical and chemical excitatory postsynaptic potential (EPSP). Positive feedback caused by electrical and chemical EPSPs between B63 and B31/B32 contributes to the sustained depolarization in B31/B32 and the firing of B63 during the protraction phase of a buccal motor program. B34 is excited during the protraction phase of all buccal motor programs, but, unlike B63, it does not always reach firing threshold. The neuron fires in response to current injection only after it is depolarized for 1–2 s or after preceding buccal motor programs in which it is depolarized. Firing of B34 produces facilitating EPSPs in the contralateral B31/B32 and B63 neurons and can initiate a buccal motor program. Firing in B34 is strongly correlated with firing in the B61/B62 motor neurons, which innervate the muscle (I2) responsible for much of protraction. B34 monosynaptically excites these motor neurons. B34 firing is also correlated with firing in motor neuron B8 during the protraction phase of a buccal motor program. B8 innervates the I4 radula closer muscle, which in egestion movements is active during protraction and in ingestion movements is active during retraction. B34 has a mixed, but predominantly excitatory, effect on B8 via a slow conductance-decrease EPSP. Thus firing in B34 leads to amplification of radula protraction that is coupled with radula closing, a pattern characteristic of egestion.

scholarly journals Interneuronal and Peptidergic Control of Motor Pattern Switching in Aplysia

2002 ◽  
Vol 87 (1) ◽  
pp. 49-61 ◽  
Author(s):  
Peter T. Morgan ◽  
Jian Jing ◽  
Ferdinand S. Vilim ◽  
Klaudiusz R. Weiss
Keyword(s):  
Motor Pattern ◽  
Electrical Coupling ◽  
Motor Program ◽  
Pattern Generator ◽  
Higher Order ◽  
Pattern Selection ◽  
Motor Programs ◽  
Additional Support ◽  
Selection Of ◽  
Stimulation Of

It has been proposed that a choice of specific behaviors can be mediated either by activation of behavior-specific higher order neurons or by distinct combinations of such neurons in different behaviors. We examined the role that two higher order neurons, CBI-2 and CBI-3, play in the selection of motor programs that correspond to ingestion and egestion, two stimulus-dependent behaviors that are generated by a single central pattern generator (CPG) of Aplysia. We found that CBI-2 could evoke either ingestive, egestive, or ambiguous motor programs depending on the regime of stimulation. When CBI-2 recruited CBI-3 firing via electrical coupling, the motor program tended to be ingestive. In the absence of CBI-3 activation, the program was usually egestive. When CBI-2 was stimulated to produce ingestive programs, hyperpolarization of CBI-3 converted the programs to egestive or ambiguous. When CBI-2 was stimulated to produce egestive or ambiguous programs, co-stimulation of CBI-3 converted them into ingestive. These findings are consistent with the idea that combinatorial commands are responsible for the choice of specific behaviors. Additional support for this view comes from the observations that appropriate stimulus conditions exist both for activation of CBI-2 together with CBI-3, and for activation of CBI-2 without a concomitant activation of CBI-3. The ability of CBI-3 to convert egestive and ambiguous programs into ingestive ones was mimicked by application of APGWamide, a neuropeptide that we have detected in CBI-3 by immunostaining. Thus combinatorial actions of higher order neurons that underlie pattern selection may involve the use of modulators released by specific higher order neurons.

Serotonergic Neurons Differentially Modulate the Efficacy of Two Motor Neurons Innervating the Same Muscle Fibers in Aplysia

1998 ◽  
Vol 80 (2) ◽  
pp. 647-655 ◽  
Author(s):  
Lyle E. Fox ◽  
Philip E. Lloyd
Keyword(s):  
Feeding Behavior ◽  
Motor Neurons ◽  
Muscle Fibers ◽  
Short Term ◽  
Serotonergic Neurons ◽  
Anterior Portion ◽  
Excitatory Junction Potentials ◽  
Evoked Contractions ◽  
Stimulation Of ◽  
Short Term Effects

Fox, Lyle E. and Philip E. Lloyd. Serotonergic neurons differentially modulate the efficacy of two motor neurons innervating the same muscle fibers in Aplysia. J. Neurophysiol. 80: 647–655, 1998. Feeding behavior in Aplysia shows substantial plasticity. An important site for the generation of this plasticity is the modulation of synaptic transmission between motor neurons and the buccal muscles that generate feeding movements. We have been studying this modulation in the anterior portion of intrinsic buccal muscle 3 (I3a), which is innervated by two excitatory motor neurons and identified serotonergic modulatory neurons, the metacerebral cells (MCCs). We have shown previously that serotonin (5-HT) applied selectively to the muscle potently modulates excitatory junction potentials (EJPs) and contractions. All the effects of 5-HT were persistent, lasting many hours after wash out. We examined whether the release of endogenous 5-HT from the MCC could produce effects similar to the application of 5-HT. Stimulation of the MCCs did produce similar short-term effects to the application of 5-HT. MCC stimulation facilitates EJPs, potentiates contractions, and decreases the latency between the onset of a motor neuron burst and the onset of the evoked contraction. The effects of MCC stimulation reached a maximum at quite low firing frequencies, which were in the range of those previously recorded during feeding behavior. The maximal effects were similar to those produced by superfusion with ∼0.1 μM 5-HT. Although the effects of MCC stimulation on EJPs were persistent, they were less persistent than the effects of 0.1 μM 5-HT. Mechanisms that may account for differences in the persistence between released and superfused 5-HT are discussed. Thus activity in the MCCs has dramatic short-term effects on the behavioral output of motor neurons, increasing the amplitude and relaxation rate of contractions evoked by both B3 and B38 and shifting the temporal relationship between B38 bursts and evoked contractions.

Sonometric Measurements of Motor-Neuron-Evoked Movements of an Internal Feeding Structure (the Radula) in Aplysia

2001 ◽  
Vol 86 (2) ◽  
pp. 1057-1061 ◽  
Author(s):  
Irina V. Orekhova ◽  
Jian Jing ◽  
Vladimir Brezina ◽  
Ralph A. DiCaprio ◽  
Klaudiusz R. Weiss ◽  
...  
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Neural Control ◽  
Feeding System ◽  
Motor Programs ◽  
Rhythmic Motor ◽  
Feeding Structure ◽  
Intracellular Stimulation ◽  
Functional Movements ◽  
Stimulation Of

In many systems used to study rhythmic motor programs, the structures that generate behavior are at least partially internal. In these systems, it is often difficult to directly monitor neurally evoked movements. As a consequence, although motor programs are relatively well characterized, it is generally less clear how neural activity is translated into functional movements. This is the case for the feeding system of the mollusk Aplysia. Here we used sonomicrometry to monitor neurally evoked movements of the food-grasping organ in Aplysia, the radula. Movements were evoked by intracellular stimulation of motor neurons that innervate radula muscles that have been extensively studied in reduced preparations. Nevertheless our results indicate that the movements and neural control of the radula are more complex than has been assumed. We demonstrate that motor neurons previously characterized as radula openers (B48) and closers (B8, B15, B16) additionally produce other movements. Moreover, we show that the size of the movement evoked by a motor neuron can depend on the preexisting state of the radula. Specifically, the motor neurons B15 and B16 produce large closing movements when the radula is partially open but produce relatively weak closing movements in a preparation at rest. Thus the efficacy of B15 and B16 as radula closers is context dependent.

Activity patterns of the B31/B32 pattern initiators innervating the I2 muscle of the buccal mass during normal feeding movements in Aplysia californica

1996 ◽  
Vol 75 (4) ◽  
pp. 1309-1326 ◽  
Author(s):  
I. Hurwitz ◽  
D. Neustadter ◽  
D. W. Morton ◽  
H. J. Chiel ◽  
A. J. Susswein
Keyword(s):  
Feeding Behavior ◽  
Motor Neurons ◽  
Activity Patterns ◽  
Aplysia Californica ◽  
Motor Programs ◽  
Physiological Functions ◽  
Rest Position ◽  
Buccal Ganglia ◽  
Normal Feeding ◽  
Protraction Phase

1. B31 and B32 are pattern-initiator neurons in the buccal ganglia of Aplysia. Along with the B61/B62 neurons, B31/B32 are also motor neurons that innervate the 12 buccal muscle via the I2 nerve. This research was aimed at determining the physiological functions of the B31/B32 and B61/B62 neurons, and of the I2 muscle. 2. Stimulating the I2 muscle in the radula rest position produces radula protraction. In addition, in behaving animals lesioning either the muscle or the I2 nerve greatly reduces radula protraction. 3. During buccal motor programs in reduced preparations, B31/B32 and B61/62 fire preceding activity in neuron B4, whose firing indicates the onset of radula retraction. In addition, during both ingestion-like and rejection-like patterns the activity in the I2 nerve is correlated with protraction. 4. B31/B32 fire at frequencies of 15-25 Hz. Neither B31/B32 nor B61/B62 elicit facilitating end-junction potentials (EJPs) and electromyograms (EMGs) in the I2 muscle. EMGs from B31/B32 are smaller than those from B61/B62. B31/B32 and B61/B62 innervate all areas of the muscle approximately uniformly. 5. In behaving animals, EMGs consistent with B31/B32 activity are seen in the I2 muscle during the protraction phase of biting, swallowing, and rejection movements. In addition, the I2 muscle receives inputs that cannot be attributed to either the B31/B32 or B61/B62 neurons, either because the potentials are too large, firing frequencies are too low, or a prominent facilitation is seen. Such potentials are associated with lip movements, and also with radula retraction. 6. EMGs were recorded from the I2 muscle during feeding behavior after a lesion of the I2 nerve. Animals that had severe deficits in protraction showed no activity consistent with B31/B32 or B61/B62, but did show activity during retraction. 7. Our data indicate that the I2 muscle and the B31/B32 motor neurons are essential constituents contributing to protraction movements. Activity in these neurons is associated with radula protraction, which occurs as a component of a number of different feeding movements. The I2 muscle may also contribute to retraction, via activation by other motor neurons.

Activity of multiple identified motor neurons recorded intracellularly during evoked feedinglike motor programs in Aplysia

1994 ◽  
Vol 72 (4) ◽  
pp. 1794-1809 ◽  
Author(s):  
P. J. Church ◽  
P. E. Lloyd
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Muscle Fibers ◽  
Inhibitory Neuron ◽  
Motor Programs ◽  
Firing Patterns ◽  
Complex Interactions ◽  
Intracellular Stimulation ◽  
Evoked Contractions ◽  
Stimulation Of

1. The firing patterns of 22 motor neurons were determined by simultaneously recording intracellularly from up to 7 neurons during evoked feedinglike buccal motor programs (BMPs). Intracellular stimulation of cerebral-buccal interneuron 2 (CBI-2) or tactile stimulation of the odontophore were used to elicit BMPs in a reduced preparation. 2. Evoked BMPs were identified as either ingestive-like (iBMP) or egestive-like (eBMP) on the basis of their similarity to those previously recorded in select neurons in freely behaving animals. Neurons were divided into the p-group, r-group, or c-group, on the basis of the phase relationships of rhythmic membrane depolarizations and hyperpolarizations during evoked BMPs. Depolarization of the p-, r-, and c-group neurons was associated with radular protraction, retraction, and closure, respectively. With one exception, the motor neurons segregated into the same groups during iBMPs and eBMPs. The exception, B7, was categorized as a c-group neuron during iBMPs, but as an r-group neuron during eBMPs. 3. Every motor neuron exhibited cyclic membrane depolarizations and hyperpolarizations, and over one-half of the neurons fired bursts of action potentials, during both iBMPs and eBMPs. The neurons fired in patterns that would be likely to release both their conventional and peptide transmitters. 4. A marked hyperpolarizing step in the p-group neurons coincident with a depolarization in the r-group neurons was observed during both iBMPs and eBMPs, suggesting a degree of shared premotor circuitry for the two BMPs. 5. A shift in the timing of activity in c-group neurons relative to that in p- and r-group neurons during iBMPs and eBMPs was observed and correlates well with the shift in phase of radular closure relative to protraction and retraction, which is useful in distinguishing ingestion from egestion in the behaving animal. 6. The firing patterns recorded in neurons that innervate overlapping populations of muscle fibers suggested that there would be complex interactions of multiple transmitters. This is particularly intriguing in the case of I3a muscle fibers, which are innervated by two excitatory and one inhibitory neuron. The firing patterns recorded in these neurons suggest that the inhibitory motor neuron may serve to not only block inappropriate contractions, but also to specifically shape evoked contractions during feeding.

scholarly journals Outputs of Radula Mechanoafferent Neurons inAplysia are Modulated by Motor Neurons, Interneurons, and Sensory Neurons

2000 ◽  
Vol 83 (3) ◽  
pp. 1621-1636 ◽  
Author(s):  
Steven C. Rosen ◽  
Mark W. Miller ◽  
Elizabeth C. Cropper ◽  
Irving Kupfermann
Keyword(s):  
Membrane Potential ◽  
Sensory Neurons ◽  
Motor Neurons ◽  
Activity Patterns ◽  
Motor Program ◽  
Cell Types ◽  
Afferent Input ◽  
Sensory Cells ◽  
Motor Programs ◽  
Sensory Inputs

The gain of sensory inputs into the nervous system can be modulated so that the nature and intensity of afferent input is variable. Sometimes the variability is a function of other sensory inputs or of the state of motor systems that generate behavior. A form of sensory modulation was investigated in the Aplysiafeeding system at the level of a radula mechanoafferent neuron (B21) that provides chemical synaptic input to a group of motor neurons (B8a/b, B15) that control closure and retraction movements of the radula, a food grasping structure. B21 has been shown to receive both excitatory and inhibitory synaptic inputs from a variety of neuron types. The current study investigated the morphological basis of these heterosynaptic inputs, whether the inputs could serve to modulate the chemical synaptic outputs of B21, and whether the neurons producing the heterosynaptic inputs were periodically active during feeding motor programs that might modulate B21 outputs in a phase-specific manner. Four cell types making monosynaptic connections to B21 were found capable of heterosynaptically modulating the chemical synaptic output of B21 to motor neurons B8a and B15. These included the following: 1) other sensory neurons, e.g., B22; 2) interneurons, e.g., B19; 3) motor neurons, e.g., B82; and 4) multifunction neurons that have sensory, motor, and interneuronal functions, e.g., B4/5. Each cell type was phasically active in one or more feeding motor programs driven by command-like interneurons, including an egestive motor program driven by CBI-1 and an ingestive motor program driven by CBI-2. Moreover, the phase of activity differed for each of the modulator cells. During the motor programs, shifts in B21 membrane potential were related to the activity patterns of some of the modulator cells. Inhibitory chemical synapses mediated the modulation produced by B4/5, whereas excitatory and/or electrical synapses were involved in the other instances. The data indicate that modulation is due to block of action potential invasion into synaptic release regions or to alterations of transmitter release as a function of the presynaptic membrane potential. The results indicate that just as the motor system of Aplysia can be modulated by intrinsic mechanisms that can enhance its efficiency, the properties of primary sensory cells can be modified by diverse inputs from mediating circuitry. Such modulation could serve to optimize sensory cells for the different roles they might play.

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