, 2003). The organization found by Bathellier et al. (2012)—which contained a small number of discrete, spatially separated modes—could thus be a more natural behavior for locally recurrent circuits that are not fine tuned. Like all surprising results, this study raises many questions. First, how general is this organization of neuronal activity? Evidence for attractor dynamics in other networks has been inconsistent (e.g., Wills et al., 2005; Leutgeb et al., 2005). Is a similar organization of discrete modes Fludarabine molecular weight seen in other cortical regions, other cortical layers,

and other brain structures? Second, would a similar pattern be seen in actively behaving animals, as well as the anesthetized and awake passive mice studied here? Third, what causes particular groups of cells to form an assembly? In Hebb’s original theory, the composition of cell assemblies was determined by experience. But Bathellier et al. (2012) could predict one mouse’s classification choices from the mode organization observed in different animals, suggesting that auditory cortical assemblies arise either from an innate process, or at least from commonalities in the sensory experience of these mice. Finally, why should the cortex work like this, using hundreds of neurons

do convey a single number? Although this may seem inefficient from the perspective of information coding, the brain is not just there to represent external stimuli, but to act on them. Is cortical attractor dynamics in fact a fundamental mechanism

of decision making? Characterizing cortical dynamics in behaving animals, and how it changes Androgen Receptor phosphorylation with learning, may well answer these questions. “
“Charles Darwin famously wrote that the eye caused him to doubt that random selection could create the intricacies of nature. Fortunately, Darwin did not know the structure of the else retina: if he had, his slowly gestating treatise on evolution might never have been published at all. Among other wonders, the neurons of the retina are tiny (Figure 1). The ∼100 million rod photoreceptors appear to be the second most numerous neurons of the human body, after only the cerebellar granule cells. The retina’s projection neuron, the retinal ganglion cell, has less than 1% the soma-dendritic volume of a cortical or hippocampal pyramidal cell. Although the retina forms a sheet of tissue only ∼200 μm thick, its neural networks carry out feats of image processing that were unimagined even a few years ago (Gollisch and Meister, 2010). They require a rethinking not only of the retina’s function, but of the brain mechanisms that shape these signals into behaviorally useful visual perception. The retinal neurome—the census of its component cells—continues to be refined. An initial estimate of 55 cell types in the retina (Masland, 2001) appears to have been something of an underestimate.