CiteULike: nelmor's olfactory-bulb

Neuronal Activity of Mitral-Tufted Cells in Awake Rats During Passive and Active Odorant Stimulation

Romulo Fuentes — 2008-07-16T09:49:07-00:00

J Neurophysiol, Vol. 100, No. 1. (1 July 2008), pp. 422-430.

Odorants induce specific modulation of mitral/tufted (MT) cells' firing rate in the mammalian olfactory bulb (OB), inducing temporal patterns of neuronal discharge embedded in an oscillatory local field potential (LFP). While most studies have examined anesthetized animals, little is known about the firing rate and temporal patterns of OB single units and population activity in awake behaving mammals. We examined the firing rate and oscillatory activity of MT cells and LFP signals in behaving rats during two olfactory tasks: passive exposure (PE) and two-alternative (TA) choice discrimination. MT inhibitory responses are predominant in the TA task (76.5%), whereas MT excitatory responses predominate in the PE task (59.2%). Rhythmic discharge in the 12- to 100-Hz range was found in 79.0 and 68.9% of MT cells during PE and TA tasks, respectively. Most odorants presented in PE task increase rhythmic discharges at frequencies >50 Hz, whereas in TA, one of four odorants produced a modest increment <40 Hz. LFP oscillations were clearly modulated by odorants during the TA task, increasing their oscillatory power at frequencies centered at 20 Hz and decreasing power at frequencies >50 Hz. Our results indicate that firing rate responses of MT cells in awake animals are behaviorally modulated with inhibition being a prominent feature of this modulation. The occurrence of oscillatory patterns in single- and multiunitary discharge is also related to stimulation and behavioral context, while the oscillatory patterns of the neuronal population showed a strong dependence on odorant stimulation. 10.1152/jn.00095.2008

Dynamic Ensemble Odor Coding in the Mammalian Olfactory Bulb: Sensory Information at Different Timescales

Brice Bathellier — 2008-02-28T13:45:55-00:00

Neuron, Vol. 57, No. 4. (28 February 2008), pp. 586-598.

Summary Neural firing discharges are often temporally patterned, but it is often ambiguous as to whether the temporal features of these patterns constitute a useful code. Here we show in the mouse olfactory bulb that ensembles of projection neurons respond with complex odor- and concentration-specific dynamic activity sequences developing below and above sniffing frequency. Based on this activity, almost optimal discrimination of presented odors was possible during single sniffs, consistent with reported behavioral data. Within a sniff cycle, slower features of the dynamics alone (>100 ms resolution, including mean firing rate) were sufficient for maximal discrimination. A smaller amount of information was also observed in faster features down to 20-40 ms resolution. Therefore, mitral cell ensemble activity contains information at different timescales that could be separately or complementarily exploited by downstream brain centers to make odor discriminations. Our results also support suggestive analogies in the dynamics of odor representations between insects and mammals.

Optimal Time Scale for Spike-Time Reliability: Theory, Simulations, and Experiments

Roberto Galan — 2008-01-15T10:35:24-00:00

J Neurophysiol, Vol. 99, No. 1. (1 January 2008), pp. 277-283.

Use of spike timing to encode information requires that neurons respond with high temporal precision and with high reliability. Fast fluctuating stimuli are known to result in highly reproducible spike times across trials, whereas constant stimuli result in variable spike times. Here, we first studied mathematically how spike-time reliability depends on the rapidness of aperiodic stimuli. Then, we tested our theoretical predictions in computer simulations of neuron models (Hodgkin-Huxley and modified quadratic integrate-and-fire), as well as in patch-clamp experiments with real neurons (mitral cells in the olfactory bulb and pyramidal cells in the neocortex). As predicted by our theory, we found that for firing frequencies in the beta/gamma range, spike-time reliability is maximal when the time scale of the input fluctuations (autocorrelation time) is in the range of a few milliseconds (25 ms), coinciding with the time scale of fast synapses, and decreases substantially for faster and slower inputs. Finally, we comment how these findings relate to mechanisms causing neuronal synchronization. 10.1152/jn.00563.2007

Transient Activity Induces a Long-Lasting Increase in the Excitability of Olfactory Bulb Interneurons

Tsuyoshi Inoue — 2008-01-15T10:31:51-00:00

J Neurophysiol, Vol. 99, No. 1. (1 January 2008), pp. 187-199.

Little is known about the cellular mechanisms that underlie the processing and storage of sensory in the mammalian olfactory system. Here we show that persistent spiking, an activity pattern associated with working memory in other brain regions, can be evoked in the olfactory bulb by stimuli that mimic physiological patterns of synaptic input. We find that brief discharges trigger persistent activity in individual interneurons that receive slow, subthreshold oscillatory input in acute rat olfactory bulb slices. A 2- to 5-Hz oscillatory input, which resembles the synaptic drive that the olfactory bulb receives during sniffing, is required to maintain persistent firing. Persistent activity depends on muscarinic receptor activation and results from interactions between calcium-dependent afterdepolarizations and low-threshold Ca spikes in granule cells. Computer simulations suggest that intrinsically generated persistent activity in granule cells can evoke correlated spiking in reciprocally connected mitral cells. The interaction between the intrinsic currents present in reciprocally connected olfactory bulb neurons constitutes a novel mechanism for synchronized firing in subpopulations of neurons during olfactory processing. 10.1152/jn.00526.2007

Olfactory Coding With All-or-Nothing Glomeruli

Alexei Koulakov — 2007-12-20T19:29:05-00:00

J Neurophysiol, Vol. 98, No. 6. (1 December 2007), pp. 3134-3142.

We present a model for olfactory coding based on spatial representation of glomerular responses. In this model distinct odorants activate specific subsets of glomeruli, dependent on the odorant's chemical identity and concentration. The glomerular response specificities are understood statistically, based on experimentally measured distributions of activation thresholds. A simple version of the model, in which glomerular responses are binary (the all-or-nothing model), allows us to account quantitatively for the following results of human/rodent olfactory psychophysics: 1) just noticeable differences in the perceived concentration of a single odor (Weber ratios) are as low as dC/C [~=] 0.04; 2) the number of simultaneously perceived odors can be as high as 12; and 3) extensive lesions of the olfactory bulb do not lead to significant changes in detection or discrimination thresholds. We conclude that a combinatorial code based on a binary glomerular response is sufficient to account for several important features of the discrimination capacity of the mammalian olfactory system. 10.1152/jn.00560.2007

Activity-dependent gating of lateral inhibition in the mouse olfactory bulb

Armen Arevian — 2007-12-27T17:57:48-00:00

Nature Neuroscience, Vol. 11, No. 1. (16 December 2007), pp. 80-87.

An Olfacto-Hippocampal Network Is Dynamically Involved in Odor-Discrimination Learning

Claire Martin — 2007-10-16T03:51:23-00:00

J Neurophysiol, Vol. 98, No. 4. (1 October 2007), pp. 2196-2205.

Several studies have shown that memory consolidation relies partly on interactions between sensory and limbic areas. The functional loop formed by the olfactory system and the hippocampus represents an experimentally tractable model that can provide insight into this question. It had been shown previously that odor-learning associated beta band oscillations (1530 Hz) of the local field potential in the rat olfactory system are enhanced with criterion performance, but it was unknown if these involve networks beyond the olfactory system. We recorded local field potentials from the olfactory bulb (OB) and dorsal and ventral hippocampus during acquisition of odor discriminations in a go/no-go task. These regions showed increased beta oscillation power during odor sampling, accompanied by a coherence increase in this frequency band between the OB and both hippocampal subfields. This coherence between the OB and the hippocampus increased with the onset of the first rule transfer to a new odor set and remained high for all learning phases and subsequent odor sets. However, coherence between the two hippocampal fields reset to baseline levels with each new odor set and increased again with criterion performance. These data support hippocampal involvement in the network underlying odor-discrimination learning and also suggest that cooperation between the dorsal and ventral hippocampus varies with learning progress. Oscillatory activity in the beta range may thus provide a mechanism by which these areas are linked during memory consolidation, similar to proposed roles of beta oscillations in other systems with long-range connections. 10.1152/jn.00524.2007