A Readout Mechanism for Latency Codes

Franks

2018

Preprint

122

Although the ability to reliably identify objects over a large range of stimulus intensities is a fundamental feature of all sensory systems, the neural circuit mechanisms that implement intensity invariance remain poorly understood. In mammals, odors are detected by individual olfactory sensory neurons expressing just one out of ~1,000 different types of odorant receptor, each of which projects to a specific pair of glomeruli in the olfactory bulb (OB). At low concentrations, odorants selectively bind high-affinity receptors, activating a sparse combination of responsive glomeruli. However, receptor activation, and thus glomerular activation, becomes less specific at higher odorant concentrations (1-4), potentially degrading the representation of odor identity. However, psychophysical studies indicate that odors retain their perceptual identities while concentration varies over several orders of magnitude (5-7). The olfactory system must therefore transform these concentration-dependent odor responses at early stages of processing into concentration-invariant representations of odor identity.Animals rely on olfaction to find food, attract mates and avoid predators. To support these behaviors, animals must reliably identify odors across different odorant concentrations. The neural circuit operations that implement this concentration invariance remain unclear. Here we demonstrate that, despite concentration-dependence in olfactory bulb (OB), representations of odor identity are preserved downstream, in piriform cortex (PCx). The OB cells responding earliest after inhalation drive robust responses in a sparse subset of PCx neurons. Recurrent collateral connections broadcast their activation across PCx, recruiting strong, global feedback inhibition that rapidly suppresses cortical activity for the remainder of the sniff, thereby discounting the impact of slower, concentration-dependent OB inputs. Eliminating recurrent collateral output dramatically amplifies PCx odor responses, renders cortex steeply concentration-dependent, and abolishes concentration-invariant identity decoding.

Section: Recurrent Circuitry Is Required For Concentration-invariant mentioning

confidence: 75%

Recurrent cortical circuits implement concentration-invariant odor coding

Franks

2018

Preprint

122

“…Although spike timing information is often used to encode features of a stimulus ( Panzeri et al, 2001 ; Thorpe et al, 2001 ; Gollisch and Meister, 2008 ; Zohar et al, 2011 ; Gütig et al, 2013 ; Zohar and Shamir, 2016 ), it is not clear how this information is decoded by downstream areas ( Buzsáki, 2010 ; Panzeri et al, 2014 ; Zohar and Shamir, 2016 ). In olfaction, a latency code is thought to be used in olfactory bulb (OB) to represent odor identity ( Bathellier et al, 2008 ; Cury and Uchida, 2010 ; Shusterman et al, 2011 ; Gschwend et al, 2012 ).…”

Section: Introductionmentioning

confidence: 99%

A transformation from temporal to ensemble coding in a model of piriform cortex

Stern

Abbott

et al. 2018

eLife

Different coding strategies are used to represent odor information at various stages of the mammalian olfactory system. A temporal latency code represents odor identity in olfactory bulb (OB), but this temporal information is discarded in piriform cortex (PCx) where odor identity is instead encoded through ensemble membership. We developed a spiking PCx network model to understand how this transformation is implemented. In the model, the impact of OB inputs activated earliest after inhalation is amplified within PCx by diffuse recurrent collateral excitation, which then recruits strong, sustained feedback inhibition that suppresses the impact of later-responding glomeruli. We model increasing odor concentrations by decreasing glomerulus onset latencies while preserving their activation sequences. This produces a multiplexed cortical odor code in which activated ensembles are robust to concentration changes while concentration information is encoded through population synchrony. Our model demonstrates how PCx circuitry can implement multiplexed ensemble-identity/temporal-concentration odor coding.

“…Spike timing information is often used to encode features of a stimulus (Panzeri et al 2001, Thorpe et al 2001, Gollisch and Meister 2008, Zohar et al 2011, Gutig et al 2013, Zohar and Shamir 2016, but it is not clear how this information is decoded (Buzsaki 2010, Panzeri et al 2014, Zohar and Shamir 2016. In olfaction, a latency code is used in olfactory bulb (OB) to represent odor identity (Bathellier et al 2008, Cury and Uchida 2010, Gschwend et al 2012).…”

Section: Introductionmentioning

confidence: 99%

A transformation from temporal to ensemble coding in a model of piriform cortex

Stern

Abbott

et al. 2017

Preprint

Different coding strategies are used to represent odor information at various stages of the mammalian olfactory system. A temporal latency code represents odor identity in olfactory bulb (OB), but this temporal information is discarded in piriform cortex (PCx) where odor identity is instead encoded through ensemble membership. We developed a spiking PCx network model to understand how this transformation is implemented. In the model, the impact of OB inputs activated earliest after inhalation is amplified within PCx by diffuse recurrent collateral excitation, which then recruits strong, sustained feedback inhibition that suppresses the impact of later-responding glomeruli. Simultaneous OB-PCx recordings indicate that indeed, over a single sniff, the earliest-active OB inputs are most effective at driving PCx activity. We model increasing odor concentrations by decreasing glomerulus onset latencies while preserving their activation sequences. This produces a multiplexed cortical odor code in which activated ensembles are robust to concentration changes while concentration information is encoded through population synchrony. Our model demonstrates how PCx circuitry can implement multiplexed ensemble-identity/temporal-concentration odor coding.