Sensory drive

Evolution of a signaling system can also be driven by preexisting sensory biases. The signaler adapts to the receiver s sensory abilities ( sensory drive Endler and MacLellan, 1988). In acoustic communication of frogs, such an evolutionary process has been termed sensory exploitation (Ryan etal., 1990). 

We believe that sensory drive may be an important factor in fish hormonal pheromone systems because of the extreme specificity of the receptors involved, the low cost of expressing these receptors, and the variety of previously abandoned hormonal stimuli to which conspecific receivers might still be receptive. Several apparent examples of the manipulation of receivers by donors which have developed the ability to produce optimal signals that match their sensory capabilities have now been described (Ryan Keddy-Hector, 1992), but this phenomenon has not yet to be examined for pheromones. 

To understand signal amplification, one must understand the biophysics of optimizing signal production and release. Three mechanisms appear important to signal transmission stimulus concentration, temporal release pattern, and matching of stimulus composition with receiver sensitivity (sensory drive). These traits are inter-related, but we consider them individually here. 

The generally accepted view is that the stimulatory drive for the ARAS comes from collaterals of the classical ascending sensory pathways. Indeed, this is another way in which sensory stimuli can affect our state of arousal (Fig. 22.5). The diffuse activating... 

Sensory sensations. Growing stress, rising affluence, and availability of global foods are driving consumer demands for new and more intense taste sensations. 

In a previous paper Bancroft and Richter3 have confirmed the hypothesis of Claude Bernard that anesthesia is due to the reversible coagulation of the colloids of the sensory nerves. It appeared that the proteins were the important factors rather than the lipoid materials. If we have different proteins in different parts of the body we shall expect them to be flocculated reversibly to different extents by different drugs. Claude Bernard pointed out that the anesthetics affect the brain first but the sensory nerves very soon after, while the narcotics affect the brain much more readily than the sensory nerves. Morphine will, therefore, tend to drive chloroform from the brain to the sensory nerves, thereby increasing the anesthetic effect of the chloroform. 

Second, the neural processing of this code defines a percept, called an odor . The first process takes place in a heterogeneous population of olfactory receptor neurons (ORNs) distributed in the epithelium. It determines which volatiles can be detected. The second process occurs in a series of neuropiles in the brain. It leads to some form of perception and can drive a behavioral response, depending on the animal s internal state and integration with other sensory modalities. How do individual neurons handle the transfer of information How do they connect to form a network in which this information is distributed, and what are the coding properties of this network ... 

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