, 2007 and Zhang and Yan, 2008). However, similar studies have not yet been done in the auditory system after operant discrimination training. In the visual system, there is some evidence that map expansions after training may either develop or renormalize at different rates in secondary versus primary cortical areas (Ghose et al., 2002 and Yang and Maunsell, 2004). More

studies are necessary to determine whether Caspase inhibitor review plasticity develops in multiple brain regions, whether plasticity renormalizes at the same rate in different brain regions, and what factors may inhibit or enhance expansion and renormalization. Although the map renormalization stage has been less well-studied than map expansion, several recent studies have reported renormalization after behavior training. In our study, we found map expansions renormalized 35 days after the beginning of low-frequency discrimination training or NBS pairing with low-frequency

tones. Similar map renormalization has now been observed in the auditory, visual, and motor cortex (Ma et al., 2010, Molina-Luna et al., 2008, Takahashi et al., 2010 and Yotsumoto et al., 2008). Renormalization has also been observed after the cortical plasticity associated with recovery from stroke and brain injury (Tombari et al., 2004 and Ward et al., 2003). These findings indicate that cortical map expansion is not usually this website the method by which skills are permanently stored in the brain but rather that map expansion is an important mechanism to generate efficient circuitry to perform behaviorally important tasks. The time required to pass through the map expansion and map renormalization

stages is likely to be affected by many factors. Many studies have shown that rates of learning and map expansion are affected by task difficulty and by motivation (Rutkowski and Weinberger, 2005). Demanding tasks are more below likely to cause plasticity because they lead to increased neuromodulator release compared to tasks that are easy to perform (Arnold et al., 2002 and Himmelheber et al., 2000). We propose that when subjects are required to perform demanding tasks or are highly motivated, they may transition to the map renormalization stage more slowly than when subjects are required to perform easy tasks. In some previous studies, map expansions persisted for several months after the beginning of behavior training, implying that these subjects never reached the map renormalization stage (Polley et al., 2006, Recanzone et al., 1992a, Recanzone et al., 1992b and Recanzone et al., 1993). In studies with persistent map expansions, subjects were often trained using adaptive tracking so that the difficulty of the task changed on a trial-by-trial basis and subjects never achieved >70% correct performance during a session.

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