External stimulation induces switches between oscillations in certain frequency bands in the mammalian olfactory bulb and the weakly electric fish: an illustrative feedback model.

Abstract

Event Abstract Back to Event External stimulation induces switches between oscillations in certain frequency bands in the mammalian olfactory bulb and the weakly electric fish: an illustrative feedback model. Axel Hutt1*, Thomas Voegtlin1, Nathalie Buonviso2, Nicolas Fourcaud-Trocmé2 and Philippe Litaudon2 1 INRIA Nancy – Grand Est, Equipe Cortex, France 2 CNRS UMR, Equipe Neurosciences et Systèmes sensoriels, France Oscillatory activity in neural systems plays an important role to process information. For instance, different cognitive tasks evoke certain frequency bands which are characteristic for the corresponding experimental paradigm. Examples are the theta-rhythm (4-8Hz) in memory tasks or the gamma-rhythm (30-60Hz) in visual binding tasks. Moreover, changing the external activation of a neural system may lead to the activation of additional oscillations in specific frequency bands or may even yield a switch between specific frequency bands. In the last years, such a switch has been found experimentally in-vivo in some neural systems, such as in the mammalian olfactory bulb [1] and in the primary sensory area of weakly electric fish [2]. Both systems exhibit a feedback topology between two or more interacting populations and an external stimulation that originates from another brain area. More detailed, the mammalian olfactory bulb is subject to activation by the receptor cells which are rhythmically activated by odours due to the breathing cycle. Applying an odour, the Local Field Potentials (LFP) exhibit high gamma-activity in the inhalation phase and switches to high beta-activity in the exhalation phase. In weakly electric fish, the primary sensory area ELL receives input from electro-receptors on the skin of the fish. In the case of spatially-uncorrelated input on the skin, single neurons fire mainly in the beta-band while a strong spatial input correlation switches to spiking activity in the gamma-band.To explain such switches in frequency bands in feedback systems, the presented work discusses a neural population model of a rather general feedback system [3] that allows to derive mathematical conditions for the switch between frequency bands subject to the spatial correlation of an external input. The proposed model explains the switch between frequency bands as a selective activation of linear spatial oscillation modes. The centre frequency and the width of the bands and the spatial properties of the spatial oscillation modes to be activated result from the intrinsic properties of the feedback system. Such properties are the synaptic time constants and delays between system components. Moreover, the spatial interactions in the feedback system determines the spatial frequency of the oscillation modes. The essential selection of the frequency band appens via the coupling of the spatially extended external input with the spatial modes. For illustration reasons, one might think of a guitar string whose oscillation frequency depends on the manner of it is stricken.