Will there be a mouse equivalent of primate extrastriate areas such as MT or IT, in line with the conserved aspects of visual processing seen previously? Or will the commonalities break down in extrastriate cortex? It is possible that either the mouse will lack the sophisticated invariant forms of processing supported by high acuity in primates, or that the higher visual areas might simply be specialized for different tasks that are more appropriate for the mouse’s visual experience. As we delve deeper into mouse vision, these two pioneering studies will provide valuable selleck screening library guidance and new approaches for further exploration of the territory between
primary visual
cortex and the centers for higher motor and cognitive function. “
“Dopamine (DA) neurons of the midbrain usually fire spontaneously at low rates, a firing mode that is called “tonic.” Occasionally, DA neurons fire extra spikes in brief episodes referred to as “phasic” or “burst” firing. Phasic firing is caused by events of motivational significance, such as unexpected primary rewards, and stimuli that predict reward over successive stages of a learning task (Ljungberg et al., 1992). Although DA neurons are sometimes activated by aversive stimuli, the majority of DA neurons CHIR-99021 mw are inhibited by these stimuli (Ungless et al., 2004). In theoretical work, DA neuron firing activity has been modeled as a reward prediction error signal, for example, in the temporal difference (TD) learning framework (Montague et al., 1996). In TD learning, the dopamine neuron firing activity plays the role of a teaching signal,
improving subsequent predictions by strengthening the appropriate synapses. However, although such work offers attractive explanations for observed DA cell activity, which correlates with the predictions of the models, it is important to go beyond correlation and experimentally investigate the causal role of phasic bursts of Dichloromethane dehalogenase DA neurons in animal learning. Previous studies have shown that excitatory drive required for burst firing of DA neurons is mediated by NMDA receptors (Tepper and Lee, 2007). In order to investigate the role of NMDAR-mediated phasic DA activity in behavioral learning, Wang et al. (2011) generated dopamine-neuron-specific NMDAR1 knockout (DAT-NR1-KO) mice. Wang et al. (2011) show that compared with control DA neurons, phasic firing activity was, as expected, greatly reduced in DA neurons of DAT-NR1-KO mice. On the other hand, no difference between controls and DAT-NR1-KO mice was observed in the tonic firing rate. Thus, by using these mice it should be possible to assess which behavioral functions require the phasic firing of dopamine neurons.