Lateral inhibition in the olfactory bulb and in olfaction
Section snippets
Lateral inhibition in the olfactory bulb
The known anatomy and physiology of the olfactory bulb (and similarly the antenna lobe of insects) suggest that activity of a cluster of nearby mitral cells (the principal neurons of the olfactory bulb) will result in inhibition of other mitral cells located at some distance from the active cells. The synaptic circuitry mediating this inhibition consists of reciprocal dendrodendritic synapses made between excitatory mitral cells and inhibitory granule cells. Active mitral cells release
Filters and lateral inhibition
Before detailing the properties of lateral inhibition in the olfactory bulb, I consider what properties a circuit must have in order to mediate lateral inhibition at the functional level; that is, to cause the sharpening of receptive fields and the enhancing of contrast that are the functional hallmarks of lateral inhibition. To help understand what properties are required, one can begin with the simplification of viewing lateral inhibition as a simple linear filter. Such filters are used in
Physiological implementation of filters
To make use of this analogy between filtering of images and lateral inhibition, one must be able to determine (or at least approximate) the kernel function of the filtering that is performed by a given brain network. To estimate the kernel function, one can take advantage of the fact that if a filter is applied to an image that consists of a single pixel (with all other pixels of amplitude zero), then the resulting filtered image is just the kernel function itself, scaled by the amplitude of
The spatial properties of lateral inhibition in the olfactory bulb
In image filtering, the spatial requirement for filter design is clear: signals such as edges are enhanced best when their spatial frequency is similar to the spatial frequency of the filter. In this case, nearby activated pixels cause mutual enhancement and distant activated pixels cause mutual inhibition. On this analogy, for lateral inhibition to cause sharpening of spatial signals in the bulb, activation of one cell or a small population of cells with similar receptive fields must result in
The functional roles of local inhibition in olfaction
In the mammalian olfactory bulb, a general blockade of inhibition clearly results in an overall increase in spontaneous and odor-evoked mitral cell firing [4], [21] that may result in a broadening of the tuning curves of mitral cells that are activated by straight chain aldehydes of differing lengths [4]. A simple prediction for the effects of lateral inhibition on olfactory behavior would be that impairment of lateral inhibition should impair performance on olfactory discrimination tasks, and
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