The best method to distinguish between these two possibilities is to generate map plasticity

using a method that is independent of learning and then test the behavioral consequences. A finding that map plasticity has no effect on learning would suggest map plasticity is an epiphenomenon; the finding that map plasticity improves learning would indicate that map plasticity is indeed functionally relevant, even if unnecessary for continued task performance. Nucleus basalis stimulation (NBS) can be used to create cortical plasticity outside of a behavioral context. NBS during tone presentation leads to stimulus-specific map expansions in both primary and secondary auditory cortex (Bakin and selleck inhibitor Weinberger, 1996, Froemke et al., 2007, Kilgard and Merzenich, 1998 and Puckett et al., 2007). Plasticity has also been observed in the inferior colliculus and auditory thalamus after NBS-tone pairing, apparently due to the influence of cortical feedback connections onto these subcortical stations (Ma and Suga, 2003 and Zhang and Yan, 2008). Although nucleus

basalis is active during both aversive and appetitive behavioral tasks, NBS is motivationally neutral (Miasnikov et al., 2008). Previous studies have demonstrated that NBS-tone pairing causes map expansions that are similar to the plasticity Selleckchem RAD001 seen after tone discrimination learning (Bakin and Weinberger, 1996, Bjordahl

et al., 1998 and Kilgard and Merzenich, 1998). NBS and tone exposure must occur within a few seconds of each other for stimulus-specific map plasticity to occur (Kilgard and Merzenich, 1998 and Metherate and Ashe, 1991). Passive exposure to tones without NBS does not result in map reorganization (Bakin and Weinberger, 1996, Bao et al., 2001 and Recanzone et al., 1993). In the current study, we used NBS paired with tones to determine the functional consequence of auditory cortex map plasticity. In the first experiment, we used NBS-tone pairing to cause auditory Suplatast tosilate cortex map expansions before discrimination learning. In the second experiment, we used NBS-tone pairing in animals that had already learned to perform the discrimination task. We performed neurophysiological recordings in all groups of animals to measure cortical map plasticity after NBS-tone pairing and behavioral training. For our study, it was important that the map expansions caused by NBS-tone pairing last long enough to evaluate the behavioral consequences of map plasticity. We have previously reported that 20 days of NBS-tone pairing results in map expansions in the primary auditory cortex (A1) that last at least 48 hr after the end of pairing (Kilgard and Merzenich, 1998).