Learning to Like Your Voice Developing Selectivity to Birdsong

lease has been proposed as a mechanism of activity-dependent changes in neurotransmitter release (Herring-to Birdsong ton et al., 1996; Tang and Zucker, 1997). Mitochondrial uptake and release of Ca 2ϩ was inconsistently observed in Mb1 synaptic terminals, and it typically required high (Ͼ800 nM) cytosolic Ca 2ϩ (Zenisek and Matthews, 2000). A basic principle of functional brain organization is that Such high cytosolic Ca 2ϩ can be achieved following a stimuli in the environment are coded by selective neu-Ca 2ϩ action potential (Zenisek and Matthews, 1998) or a ronal responsiveness. Classic examples of such neu-long depolarization (Heidelberger and Matthews, 1992). ronal selectivity range from cells in the visual cortex that However, the amount of Ca 2ϩ that was released from fire only in response to simple visual stimuli to the more mitochondria did not correlate with the magnitude of complex cells in the inferotemporal cortex of primates the Ca 2ϩ load. Thus, it would seem that using the release that are selective only for conspecific faces. Although of Ca 2ϩ from mitochondria as a way of modulating syn-the existence of such neuronal selectivity is axiomatic aptic efficacy in Mb1 synaptic terminals would be capri-in cognitive neuroscience, the way in which such striking cious at best, and it is tempting to speculate that if selectivity develops remains an important topic of re-these neurons undergo a meaningful, activity-depen-search. The classic work of Hubel and Wiesel on the dent change in neurotransmitter release, another mech-development of neuronal selectivity in the visual system anism must be at work. demonstrated that this selectivity is not entirely pre-In summary, some bipolar cells of the vertebrate retina specified or necessarily intrinsic to a neuronal cell type. seem to be electrically excitable, contrary to the com-In fact, severe developmental perturbations can extin-monly held belief that they are only capable of graded guish or profoundly modify the occurrence of cortical responses. Ca 2ϩ-based action potentials in the Mb1 bi-neurons that fire selectively to simple visual stimuli. But polar cell are likely to contribute to signal amplification what types of normal experiences can induce such se-and enhancement of synaptic gain in the high-sensitivity lectivity? Is learning involved? How enduring are such rod pathway. Consistent with the generation of these experiential effects? action potentials, the synaptic terminals of Mb1 neurons Insight into these processes is provided by a paper are well equipped for effectively handling large presyn-in this issue of Neuron …