Presentation Details
| Temporal-to-spatial code transformation in the piriform cortex Alexei Koulakov. Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, USA |
Abstract
Odor identity is represented by temporal sequences of glomerular activation in the olfactory bulb (OB). One potential function of cortical networks is to decode these sequences to infer odor identity. Chunking models have been proposed to transform a temporal latency code into a spatial representation in the piriform cortex. One prediction of these models is that each piriform neuron has a specific time window within the sniff cycle during which it is responsive to OB inputs, aka the Bulbar Sensitivity Window (BSW). BSW onset is determined by the amount of inhibition received by the piriform neuron: the stronger the inhibition, the later the neuron responds. BSW onset does not depend on odor identity. Due to recurrent circuitry in the cortex, blocking the activation of earlier cortical neurons prevents the activation of later ones. In the simplest form of the chunking model proposed before, the BSW never closes - neurons remain responsive to OB inputs from their onset time until the end of the sniff cycle. Recent data from the piriform cortex suggests that BSW closes before the end of sniff cycle. Here, we propose two mechanisms by which the BSW can be closed. First, inhibition from later-activated cortical neurons may desensitize earlier cells, thereby closing their BSW. This mechanism implies that, in addition to the feedforward excitatory circuitry proposed in earlier models, cortical circuits exhibits biased feedback inhibition. Second, feedback from the cortex to the OB may selectively inhibit inputs to earlier piriform neurons, implementing a form of predictive coding. Together, these two theoretical models implement temporal-to-spatial code transformation in the piriform cortex while accounting for recent cortical data. Both models make specific, testable predictions about cortical circuitry.
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