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Trace conditioning in insects-keep the trace!

Dylla KV, Galili DS, Szyszka P, Lüdke A - Front Physiol (2013)

Bottom Line: It is still unknown how the brain encodes CS traces and how they are associated with a US in trace conditioning.In this review we summarize the recent progress in insect trace conditioning on the behavioral and physiological level and emphasize similarities and differences compared to delay conditioning.Moreover, we examine proposed molecular and computational models and reassess different experimental approaches used for trace conditioning.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Neurobiology, University of Konstanz Konstanz, Germany.

ABSTRACT
Trace conditioning is a form of associative learning that can be induced by presenting a conditioned stimulus (CS) and an unconditioned stimulus (US) following each other, but separated by a temporal gap. This gap distinguishes trace conditioning from classical delay conditioning, where the CS and US overlap. To bridge the temporal gap between both stimuli and to form an association between CS and US in trace conditioning, the brain must keep a neural representation of the CS after its termination-a stimulus trace. Behavioral and physiological studies on trace and delay conditioning revealed similarities between the two forms of learning, like similar memory decay and similar odor identity perception in invertebrates. On the other hand differences were reported also, like the requirement of distinct brain structures in vertebrates or disparities in molecular mechanisms in both vertebrates and invertebrates. For example, in commonly used vertebrate conditioning paradigms the hippocampus is necessary for trace but not for delay conditioning, and Drosophila delay conditioning requires the Rutabaga adenylyl cyclase (Rut-AC), which is dispensable in trace conditioning. It is still unknown how the brain encodes CS traces and how they are associated with a US in trace conditioning. Insects serve as powerful models to address the mechanisms underlying trace conditioning, due to their simple brain anatomy, behavioral accessibility and established methods of genetic interference. In this review we summarize the recent progress in insect trace conditioning on the behavioral and physiological level and emphasize similarities and differences compared to delay conditioning. Moreover, we examine proposed molecular and computational models and reassess different experimental approaches used for trace conditioning.

No MeSH data available.


Related in: MedlinePlus

Simplified diagram of olfactory processing in Drosophila melanogaster. Odors activate distinct sets of olfactory receptor neurons (ORNs) in the fly's antenna. ORNs which express the same receptor converge onto the same glomerulus in the antennal lobe. Thus, each odor induces a unique glomerular activity pattern. This pattern is modulated by the interaction between ORNs, excitatory and inhibitory local interneurons (LNs) and projection neurons (PNs). The PNs relay the odor information to the lateral horn (which is assumed to mediate the innate odor response) and to the mushroom body intrinsic Kenyon cells (KCs). Upon reinforcement, KCs receive input from modulatory neurons, signaling either punishment or reward. Coincident activation of these neurons and the odor-responsive KCs in delay conditioning is believed to modify the output in these KCs. This modification changes the fly's behavior to the previously reinforced odor stimulus. For trace conditioning the underlying mechanism is yet unknown, but it seems likely that the necessary modifications occur in the olfactory pathway and/or pathway-associated neurons.
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Figure 2: Simplified diagram of olfactory processing in Drosophila melanogaster. Odors activate distinct sets of olfactory receptor neurons (ORNs) in the fly's antenna. ORNs which express the same receptor converge onto the same glomerulus in the antennal lobe. Thus, each odor induces a unique glomerular activity pattern. This pattern is modulated by the interaction between ORNs, excitatory and inhibitory local interneurons (LNs) and projection neurons (PNs). The PNs relay the odor information to the lateral horn (which is assumed to mediate the innate odor response) and to the mushroom body intrinsic Kenyon cells (KCs). Upon reinforcement, KCs receive input from modulatory neurons, signaling either punishment or reward. Coincident activation of these neurons and the odor-responsive KCs in delay conditioning is believed to modify the output in these KCs. This modification changes the fly's behavior to the previously reinforced odor stimulus. For trace conditioning the underlying mechanism is yet unknown, but it seems likely that the necessary modifications occur in the olfactory pathway and/or pathway-associated neurons.

Mentions: Where is the information about the CS stored until the US arrives? The insect olfactory pathway (Figure 2) starts at the antennae where odors activate odor-specific subsets of olfactory receptor neurons (ORNs). ORNs transmit odor information to the antennal lobe, the primary brain area for olfactory processing. Here, ORN axons interact with excitatory and inhibitory local interneurons (LNs) and with projection neurons (PNs) which conduct the information to higher order neurons, like the Kenyon cells (KCs) in the mushroom body and lateral horn neurons (Figure 2). The olfactory trace might be located in any of these neuron types or in other neurons outside the olfactory pathway.


Trace conditioning in insects-keep the trace!

Dylla KV, Galili DS, Szyszka P, Lüdke A - Front Physiol (2013)

Simplified diagram of olfactory processing in Drosophila melanogaster. Odors activate distinct sets of olfactory receptor neurons (ORNs) in the fly's antenna. ORNs which express the same receptor converge onto the same glomerulus in the antennal lobe. Thus, each odor induces a unique glomerular activity pattern. This pattern is modulated by the interaction between ORNs, excitatory and inhibitory local interneurons (LNs) and projection neurons (PNs). The PNs relay the odor information to the lateral horn (which is assumed to mediate the innate odor response) and to the mushroom body intrinsic Kenyon cells (KCs). Upon reinforcement, KCs receive input from modulatory neurons, signaling either punishment or reward. Coincident activation of these neurons and the odor-responsive KCs in delay conditioning is believed to modify the output in these KCs. This modification changes the fly's behavior to the previously reinforced odor stimulus. For trace conditioning the underlying mechanism is yet unknown, but it seems likely that the necessary modifications occur in the olfactory pathway and/or pathway-associated neurons.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750952&req=5

Figure 2: Simplified diagram of olfactory processing in Drosophila melanogaster. Odors activate distinct sets of olfactory receptor neurons (ORNs) in the fly's antenna. ORNs which express the same receptor converge onto the same glomerulus in the antennal lobe. Thus, each odor induces a unique glomerular activity pattern. This pattern is modulated by the interaction between ORNs, excitatory and inhibitory local interneurons (LNs) and projection neurons (PNs). The PNs relay the odor information to the lateral horn (which is assumed to mediate the innate odor response) and to the mushroom body intrinsic Kenyon cells (KCs). Upon reinforcement, KCs receive input from modulatory neurons, signaling either punishment or reward. Coincident activation of these neurons and the odor-responsive KCs in delay conditioning is believed to modify the output in these KCs. This modification changes the fly's behavior to the previously reinforced odor stimulus. For trace conditioning the underlying mechanism is yet unknown, but it seems likely that the necessary modifications occur in the olfactory pathway and/or pathway-associated neurons.
Mentions: Where is the information about the CS stored until the US arrives? The insect olfactory pathway (Figure 2) starts at the antennae where odors activate odor-specific subsets of olfactory receptor neurons (ORNs). ORNs transmit odor information to the antennal lobe, the primary brain area for olfactory processing. Here, ORN axons interact with excitatory and inhibitory local interneurons (LNs) and with projection neurons (PNs) which conduct the information to higher order neurons, like the Kenyon cells (KCs) in the mushroom body and lateral horn neurons (Figure 2). The olfactory trace might be located in any of these neuron types or in other neurons outside the olfactory pathway.

Bottom Line: It is still unknown how the brain encodes CS traces and how they are associated with a US in trace conditioning.In this review we summarize the recent progress in insect trace conditioning on the behavioral and physiological level and emphasize similarities and differences compared to delay conditioning.Moreover, we examine proposed molecular and computational models and reassess different experimental approaches used for trace conditioning.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Neurobiology, University of Konstanz Konstanz, Germany.

ABSTRACT
Trace conditioning is a form of associative learning that can be induced by presenting a conditioned stimulus (CS) and an unconditioned stimulus (US) following each other, but separated by a temporal gap. This gap distinguishes trace conditioning from classical delay conditioning, where the CS and US overlap. To bridge the temporal gap between both stimuli and to form an association between CS and US in trace conditioning, the brain must keep a neural representation of the CS after its termination-a stimulus trace. Behavioral and physiological studies on trace and delay conditioning revealed similarities between the two forms of learning, like similar memory decay and similar odor identity perception in invertebrates. On the other hand differences were reported also, like the requirement of distinct brain structures in vertebrates or disparities in molecular mechanisms in both vertebrates and invertebrates. For example, in commonly used vertebrate conditioning paradigms the hippocampus is necessary for trace but not for delay conditioning, and Drosophila delay conditioning requires the Rutabaga adenylyl cyclase (Rut-AC), which is dispensable in trace conditioning. It is still unknown how the brain encodes CS traces and how they are associated with a US in trace conditioning. Insects serve as powerful models to address the mechanisms underlying trace conditioning, due to their simple brain anatomy, behavioral accessibility and established methods of genetic interference. In this review we summarize the recent progress in insect trace conditioning on the behavioral and physiological level and emphasize similarities and differences compared to delay conditioning. Moreover, we examine proposed molecular and computational models and reassess different experimental approaches used for trace conditioning.

No MeSH data available.


Related in: MedlinePlus