Shannon's seminal 1948 work gave rise to two distinct areas of research: information theory and mathematical coding theory. While information theory has had a strong influence on theoretical neuroscience, ideas from mathematical coding theory have received considerably less attention. Here we take a new look at combinatorial neural codes from a mathematical coding theory perspective, examining the error correction capabilities of familiar receptive field codes (RF codes). We find, perhaps surprisingly, that the high levels of redundancy present in these codes does not support accurate error correction, although the error-correcting performance of RF codes "catches up" to that of random comparison codes when a small tolerance to error is introduced. On the other hand, RF codes are good at reflecting distances between represented stimuli, while the random comparison codes are not. We suggest that a compromise in error-correcting capability may be a necessary price to pay for a neural code whose structure serves not only error correction, but must also reflect relationships between stimuli.

Hippocampal place field sequences are supported by sensory cues and network internal mechanisms. In contrast, sharp-wave (SPW) sequences, theta sequences, and episode field sequences are internally generated. The relationship of these sequences to memory is unclear. SPW sequences have been shown to support learning and have been assumed to also support episodic memory. Conversely, we demonstrate these SPW sequences were present in trained rats even after episodic memory was impaired and after other internal sequences – episode field and theta sequences – were eliminated. SPW sequences did not support memory despite continuing to ‘replay’ all task-related sequences – place- field and episode field sequences. Sequence replay occurred selectively during synchronous increases of population excitability -- SPWs. Similarly, theta sequences depended on the presence of repeated synchronized waves of excitability – theta oscillations. Thus, we suggest that either intermittent or rhythmic synchronized changes of excitability trigger sequential firing of neurons, which in turn supports learning and/or memory.DOI: http://dx.doi.org/10.7554/eLife.20697.001

Pharmacologic inhibition of tumor necrosis factor-alpha (TNF-α) has been used in the management of a variety of inflammatory conditions. Recently, reports on the development of sarcoid-like granulomatous disease at multiple systemic sites after treatment with TNF-α inhibitors have emerged, although, to the authors' knowledge, orbital manifestations of this problem have not been previously described. A 48-year-old woman who received injections of adalimumab for the treatment of psoriatic arthritis developed right-sided orbital pain and inflammation. Orbital biopsy of a focal lesion demonstrated sarcoid-like granulomatosis, and a workup for other causes of this problem was noncontributory. This report represents the first documented case of this phenomenon in the orbit, and possible mechanisms are discussed in this presentation. Given the expanding role of TNF-α inhibitors and the increased frequency of their use, clinicians should be aware of this possible side effect.