Great strides in this direction have been made by Florian Engert and his colleagues, who have recently created zebrafish in which GCaMPs are expressed in all neurons, allowing activity to be assessed in multiple regions of the brain while filming the motor behavior elicited by visual stimulation (Ahrens et al., 2012). An important challenge for the future will be to transfer these optical approaches for assessing signal transfer between brain Dinaciclib regions to mammals such as mice. How will the mouse’s eye tell the mouse’s brain about important features of
the visual world? It has been suggested that specificity coding, epitomized by the “bug detector,” is a specialization of cold-blooded creatures, while mammals use the cortex for detection BMS-777607 price of such high-level features. Or, to put it more pithily, “the dumber the animal, the smarter its retina” (Dennis Baylor, personal communication). Nonetheless, it is increasingly apparent that individual ganglion cells of mammals can also transmit the results of some surprisingly complex computations (Gollisch and Meister, 2010), and recently a “hawk detector” has been identified in the retinae of mice: a very numerous type of motion-sensitive
ON-OFF ganglion cell that is likely to respond found vigorously to circling birds of prey (Zhang et al., 2012). To understand the relative importance of such “specificity coding” compared to a distributed code, we will have to be able to monitor the signals transmitted by the complete population of retinal ganglion cells in a relatively unbiased way. Nikolaou et al. (2012) now show us that the use of SyGCaMPs to image the synaptic output is a feasible approach for making such population measurements.
We hope that this experimental strategy might also be able to tell us what the “mouse’s eye tells the mouse’s brain. “
“A fundamental property of the brain is that perceptual experiences drive modifications in number and strength of synaptic connections among neurons. These modifications of synaptic strength and connectivity are thought to be the neural correlates of cognition, which is constantly shaped by experience. Because synapse specificity is fundamental to neuronal plasticity, local protein synthesis at activated synapses plays a key role in establishing this spatial specificity. Although the mechanisms governing synapse-specific protein translation are not fully understood, a “synaptic tagging” mechanism that restricts new protein synthesis to activated synapses has been proposed (Redondo and Morris, 2011).