Electrical stimulus amplitude

Likewise, mechanoreceptors in the skin can be made more sensitive by applying a small-amplitude random signal (Figure 8.2.21). By itself, this electrical or mechanical noise is less than the sensor threshold, and not detectable. When added to a small primary signal, however, some of the noise pulses exceed the threshold, and the sensor fires. Thus, the magnitude of the adequate stimulus has been made smaller. 

Fig. 5 Theoretical and experimental descriptions of the impact of uptake inhibition (a) and enhancement of release (b) of the responses recorded at microdisk electrodes. Theoretical curves Numerical solutions of Eq. (3) were used to generate predicted concentration profiles at various times during a simulated period of stimulation. The calculated concentration profiles shown in the main panel of the top and bottom portion of this figure were obtained at the end of the simulated stimulus. The top panel shows how an increase in the Michaelis constant (/fm) changes the concentration profile, while the bottom panel shows the effect of an increase in the magnitude the simulated stimulus (further details can be found in Ref [25]). Stimulation responses The inset panels show experimental stimulus responses recorded in the rat brain with microdisk electrodes. Open circles denote the beginning and end of the electrical stimulation. Predrug responses (solid lines) were recorded prior to systemic administration of either 20 mg kg nomifensine (a) or 250 mg kg L-DOPA (b). Postdrug responses (dotted lines) were recorded 25 min after nomifensine administration or 55 min after L-DOPA administration. Note that the trends in the amplitude of the experimental signals correspond very well to those apparent in the theoretical concentration profiles.

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