**5. Limitations and future research**

The approach which we have proposed is supposed to enable an insight into the neural signaling of the monoaminergic systems through measuring and processing of the behavioral variables such as skin conductance response. Although the monoaminergic neural signaling is a net result of the subtle neurochemical processes such as neurotransmitters' release, reuptake, and receptor binding the present method does not allow a direct insight into the relationship between our estimations of the neural signaling and the pharmacological actions such as processes of down- or up-regulation of receptors, inhibition of transporters, and intracellular changes (Leonard, 2000). But there is a possibility to overcome this limitation of the present method. It could be done through an integration of the present model with the existing mathematical models of the cellular mechanisms of the dopaminergic and serotonergic signaling (Best et al., 2009; Best, Nijhout & Reed, 2010; Best, Reed & Nijhout, 2010; Best et al., 2011). The later models are models of the processes of synthesis, release, and reuptake of brainstem monoamines. Establishing the link between the SCR model and these models could bring to a deeper insight into the monoaminergic processes specifying the deviation in the processes through knowing the vales of the SCR system parameters. It could enable even more informed choice of psychotropic drugs (e.g. is it more appropriate to intervene with a postsynaptic receptor agent or with a drug acting on the reuptake transporters). Agreement between our findings on the change of SCR system's indicators of tonic and phasic monoaminergic functions due to serotonergic treatment, and theoretical assumptions derived from the model of serotonergic signaling (Best at al., 2011) render the task feasible.

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In this study we did not examine the effect of dopaminergic agents on the SCR system parameters what could be done in the future research. Further work could be also aimed to determine normative values of the hidden-input measures and the SCR system's parameters in larger samples of healthy individuals and to compare them with different populations of individuals currently experiencing an episode of a mental disorder.
