Abstract
BackgroundHow do neural networks encode sensory information? Following sensory stimulation, neural coding is commonly assumed to be based on neurons changing their firing rate. In contrast, both theoretical works and experiments in several sensory systems showed that neurons could encode information as coordinated cell assemblies by adjusting their spike timing and without changing their firing rate. Nevertheless, in the olfactory system, there is little experimental evidence supporting such model.Methodology/Principal FindingsTo study these issues, we implanted tetrodes in the olfactory bulb of awake mice to record the odorant-evoked activity of mitral/tufted (M/T) cells. We showed that following odorant presentation, most M/T neurons do not significantly change their firing rate over a breathing cycle but rather respond to odorant stimulation by redistributing their firing activity within respiratory cycles. In addition, we showed that sensory information can be encoded by cell assemblies composed of such neurons, thus supporting the idea that coordinated populations of globally rate-invariant neurons could be efficiently used to convey information about the odorant identity. We showed that different coding schemes can convey high amount of odorant information for specific read-out time window. Finally we showed that the optimal readout time window corresponds to the duration of gamma oscillations cycles.ConclusionWe propose that odorant can be encoded by population of cells that exhibit fine temporal tuning of spiking activity while displaying weak or no firing rate change. These cell assemblies may transfer sensory information in spiking packets sequence using the gamma oscillations as a clock. This would allow the system to reach a tradeoff between rapid and accurate odorant discrimination.
Highlights
Sensory perception is driven in the brain by specific coding strategies defined as modification of firing patterns in particular subpopulations of neurons
We propose that odorant can be encoded by population of cells that exhibit fine temporal tuning of spiking activity while displaying weak or no firing rate change
Odorants evoke weak rate change in mitral cells recorded in awake mice In order to study the potential coding mechanisms in M/T cells underlying odor representation, we recorded ensembles of neurons from the mouse olfactory bulb (OB) in both anesthetized and awake mice (Fig. 2A– B) [22]
Summary
Sensory perception is driven in the brain by specific coding strategies defined as modification of firing patterns in particular subpopulations of neurons. Other codes are considered since they may carry complementary information and/or may be more resistant to noise or fluctuations of the stimulus These include, temporal codes such as synchronized firing of neurons [1,2,3,4,5,6,7], first spike latency following stimulus onset [8,9,10,11,12] or firing in a specific phase of particular rhythms [13,14,15,16]. Neural coding is commonly assumed to be based on neurons changing their firing rate. In the olfactory system, there is little experimental evidence supporting such model
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