[Comparison of 2 models for lateral inhibition]

Information processing in the mammalian olfactory system

Recently, modern neuroscience has made considerable progress in understanding how the brain perceives, discriminates, and recognizes odorant molecules. This growing knowledge took over when the sense of smell was no longer considered only as a matter for poetry or the perfume industry. Over the last decades, chemical senses captured the attention of scientists who started to investigate the different stages of olfactory pathways. Distinct fields such as genetic, biochemistry, cellular biology, neurophysiology, and behavior have contributed to provide a picture of how odor information is processed in the olfactory system as it moves from the periphery to higher areas of the brain. So far, the combination of these approaches has been most effective at the cellular level, but there are already signs, and even greater hope, that the same is gradually happening at the systems level. This review summarizes the current ideas concerning the cellular mechanisms and organizational strategies used by the olfactory system to process olfactory information. We present findings that exemplified the high degree of olfactory plasticity, with special emphasis on the first central relay of the olfactory system. Recent observations supporting the necessity of such plasticity for adult brain functions are also discussed. Due to space constraints, this review focuses mainly on the olfactory systems of vertebrates, and primarily those of mammals.

Response vs excitation in response-dependent and stimulus-dependent lateral inhibitory networks

Response-dependent and stimulus-dependent lateral inhibitory networks may be distinguished by differences in their net response vs net excitation functions. It is shown that the net response of a stable, response-dependent network is a monotonically increasing function of the net excitation. By contrast, the response of a stimulus-dependent lateral inhibitory network can either increase, decrease or remain constant as the net excitation of the network is increased, depending on the relation of the inhibition to the excitation. These differences make it possible to determine that the inhibition produced by a lateral inhibitory network is stimulus-dependent if the net response of the network declines as the network excitation increases.

Electrical coupling of photoreceptors in retinal network models

The spatial width of photoreceptor receptive fields affects the processing of signals in neural networks of the retina. This effect has been examined using the simple recurrent and non-recurrent network models, where lateral interaction strength was adjusted to approximate a prescribed receptive field profile. The results indicate that the optimal performance of the networks is obtained with photoreceptor receptive fields wider than the ganglion cell sepration. It is thus concluded that while electrical coupling of photoreceptors in the retina reduces the intrinsic noise in the system, it also improves the sampling efficiency of the laterally coupled neural network of the retina.

Release from masking as a means of studying hair cell function

If mutual inhibition exists among the neural elements of the auditory pathway, then tonal contours should be enchanced by analogy with the mechanisms of Mach bands in vision. Experimental evidence is presented for enhancement or sharpening of contours by means of direct masking of pure tones by narrow-band noise. These results suggested that sharply defined regions of loss of hair cells in sharply delimited regions of the basilar membrane ought to be associated with gains in hearing level due to release from inhibition. Support for this notion was found in both the experimental and clinical literature.