Effects of pre-exposure were assessed by comparing the percentages of active males (males moving towards plus males moving against the stimulus) between treatments. Changes in the oriented response of males caused by pre-exposure were analyzed by comparing the proportion of males walking ‘‘towards’’ or ‘‘away from’’ the stimulus source between treatments. Chi-square tests for homogeneity were performed for comparing percentages of activated or oriented males of different groups. Differences in individual trajectories were analyzed and compared between treatments by calculating 4 kinetic parameters: – latency of response (s): time until males activated (non-stop walk for at least 100 mm) – walked distance (mm): displacement in any direction – walked time (s): active time within the total assay duration – mean speed (mm/s): ‘‘walked distance’’ divided by ‘‘walked time’’ Non-parametrical comparisons between these kinetic parame- ters of na¨ıve and pre-exposed males and changes in parameters associated to the tested PHE dose were assessed using the Median test. Behavioural gustatory tests Gustatory tests were done by using the PER paradigm. A toothpick soaked with different aqueous solutions was moved evenly over the antenna during 10 s to make sure that a maximum number of gustatory sensilla got in contact with the solution and the occurrence of a PER was registered. The following experimental series were performed: – pre-exposure to SUC or QUI, test with SUC – pre-exposure to SUC, test with SUC on the ipsi- or contra- lateral antenna – pre-exposure to PHE, test with SUC – pre-exposure to shaking, test with SUC Different concentrations of SUC were used in different experiments because ‘‘absolute’’ response thresholds to SUC varied between time periods. As for pheromone tests, a sub- optimal sucrose concentration depending on the ‘‘absolute’’ threshold during a given test-period was chosen to reveal possible differences between pre-exposed and na¨ıve males for each experimental series. The proportion of males extending the proboscis was calculated for each group and compared by means of a Chi-Square test for homogeneity. Intracellular recordings from AL neurons Pre-exposed males were mounted and prepared for electro- physiology as previously described [19]. Intracellular recordings of pheromone sensitive neurons within the MGC were performed using standard recording techniques [54]. When intracellular References 1. Crair MC, Gillespie DC, Stryker MP (1998) The role of visual experience in the development of columns in cat visual cortex. Science 279: 566–570. 2. Fox K, Wong ROL (2005) A comparison of experience-dependent plasticity in the visual and somatosensory systems. Neuron 48: 465–477. 3. Chang EF, Merzenich MM (2003) Environmental noise retards auditory cortical development. Science 300: 498–502. 4. Hudson R (1999) From molecule to mind: the role of experience in shaping olfactory function. J Comp Physiol A 185: 297–304. 5. Oboti L, Savalli G, Giachino C, De Marchis S, Panzica GC, et al. (2009) Integration and sensory experience-dependent survival of newly generated neurons in the accessory olfactory bulb of female mice. Eur J Neurosci 29: 679–692. Sensitization after Brief Pre-Exposure in a Moth contact had been established, a 500 ms pheromone stimulus was introduced into a constant air stream (7 ml/s) using a stimulus controller (CS 55, Syntech, Kirchzarten, Germany). A minimum of 10 s elapsed between individual pheromone stimulations. Recorded signals were amplified (Axoclamp-2B, Axon Instru- ments, Foster City, USA), digitalized and analyzed with Autospike 32 software (Syntech, Kirchzarten, Germany). We counted the number of action potentials during the excitatory response period of the neuron and subtracted the spontaneous activity during the same duration of time before the stimulus onset. A neuron was classified as responding to the different concentrations of the pheromone when the response exceeded the response to a control stimulus (the solvent hexane) by at least 10%. The percentage of AL neurons responding at different thresholds was calculated and compared between na¨ıve and pre-exposed males with a G-Test (applying Williams correction). Extracellular recordings from antennal gustatory sensilla Neural activity of gustatory receptor neurons was studied using the tip recording technique [55]. Insects were fixed in tight-fitting plastic tubes with their head and antennae protruding. The glass capillary containing the stimulus, and an electrolyte (1 mM KCl) was fitted onto a silver wire connected to the probe of a preamplifier and brought in contact with the tip of a Sensillum chaeticum (TastePROBE DTP-02, Syntech, Kirchzarten, Ger- many). Data acquisition and storage was triggered by voltage signals when contact between the sensillum and the stimulus solution was established. Electrical signals were further amplified (CyberAmp 320, Axon Instruments, Foster City, USA) and filtered (band-pass 10–2800 Hz). 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