Immediate early gene regulation in the auditory system

Immediate early genes (IEGs) are genes whose expression in the brain is sensitive to the activation state of neuronal cells (see other chapters in this book and the reviews in Kaczmarek and Robertson, 2002). Although the exact relationship between neuronal activation and IEG expression is not entirely understood, the analysis of induced expression of IEGs has been extremely useful in the identification and study of brain regions activated by specific sensory stimuli or behavioral conditions. This is the case because IEG studies are non-invasive, allowing the mapping of brain activation without interfering with the animal's ability to behave or respond to the stimulus being presented. In addition, although IEG expression studies generally lack temporal resolution (but see the chapter by Guzowski in this volume), this type of analysis allows for the mapping of global patterns of activation with cellular resolution. Furthermore, some IEGs have been linked to neuronal plasticity (Guzowski et al., 1999; Jones et al., 2001) and their activation may indicate sites where experience-dependent changes take place in the brain. The present chapter discusses the use of IEG expression analysis to study brain regions and pathways involved in the processing of auditory stimuli in vertebrates (for previous reviews on related topics, see Chaudhuri, 1997; Clayton, 2000; Chaudhuri and Zangenehpour, 2002; Mello, 2002a, 2004; Mello et al., 2004).