The contribution of glomerular activity maps to olfactory perceptual judgements in mice

Odours are first represented in the brain as spatiotemporal maps of activity in the olfactory bulb (OB). Imaging and electrophysiological studies have shown that these maps are both temporally and spatially complex and unique to each odour. Behavioural tasks that probe perceptual differences between odours suggest that odours that evoke similar spatial activity maps in the OB are perceived as similar. However, combination of lesion and behavioural experiments of either the olfactory epithelium or bulb has suggested that rodents can detect and discriminate between odours using minimal stimulus-related input. This has led to a consensus in the field that sensory inputs to the olfactory system contain significant redundant signal and that spatial activity maps are unnecessary for odour coding. The work presented here used a go/no-go behavioural paradigm to investigate the ability of mice not just to detect or discriminate odours after nasal epithelial lesion but also to recognise odours – which enables odour quality perception to be probed. Intrinsic optical imaging was used in the same animals, to observe changes in odour-evoked signals in the OB before and after lesion. The results revealed that even moderatechanges to intrinsic activity maps caused deficits in both odour discrimination and recognition, suggesting that perception of odour quality was significantly altered. Reduction in odour inputs could be equivalent to reducing the intensity of inputs, so alterations to odour quality perception after changes in odour concentration were also examined. Recognition scores were reduced when mice were presented with a familiar odour at an unfamiliar concentration, suggesting odour perception was also significantly altered by reduction of stimulus intensity. In order to determine whether reductions in recognition score caused by lesioning and change in odour concentration had different perceptual origins, mice were trained to generalise across odour concentrations and tested for recognition after lesion. This revealed that impaired recognition after lesion resulted, not from experiencing an altered odour concentration, but from perception of apparent novel odour qualities. Consistent with this, intrinsic imaging data revealed that relative intensity of glomerular activity following lesions was altered compared with maps recorded in shams or by varying odour concentration. Long-standing theories of sensory coding suggest that sensory systems actively match odours in the environment with stored stimulus templates. Odours familiar before lesioning were re-learnt more rapidly after lesioning than novel odours were learnt either before or after lesioning. This suggests that stored templates of familiar odours were compared to moderately altered incoming inputs and, with reinforcement, were rapidly incorporated into those templates. In all, this work suggests that odour quality perception requires comprehensive matching of input patterns to stored representations, suggesting that spatial activity maps are a crucial component of odour coding

Multisensory coding of angular head velocity in the retrosplenial cortex

To successfully navigate the environment, animals depend on their ability to continuously track their heading direction and speed. Neurons that encode angular head velocity (AHV) are fundamental to this process, yet the contribution of various motion signals to AHV coding in the cortex remains elusive. By performing chronic single-unit recordings in the retrosplenial cortex (RSP) of the mouse and tracking the activity of individual AHV cells between freely moving and head-restrained conditions, we find that vestibular inputs dominate AHV signaling. Moreover, the addition of visual inputs onto these neurons increases the gain and signal-to-noise ratio of their tuning during active exploration. Psychophysical experiments and neural decoding further reveal that vestibular-visual integration increases the perceptual accuracy of angular self-motion and the fidelity of its representation by RSP ensembles. We conclude that while cortical AHV coding requires vestibular input, where possible, it also uses vision to optimize heading estimation during navigation

A sociological dilemma: race, segregation, and US sociology

US sociology has been historically segregated in that, at least until the 1960s, there were two distinct institutionally organized traditions of sociological thought – one black and one white. For the most part, however, dominant historiographies have been silent on that segregation and, at best, reproduce it when addressing the US sociological tradition. This is evident in the rarity with which scholars such as WEB Du Bois, E Franklin Frazier, Oliver Cromwell Cox, or other ‘African American Pioneers of Sociology’, as Saint-Arnaud calls them, are presented as core sociological voices within histories of the discipline. This article addresses the absence of African American sociologists from the US sociological canon and, further, discusses the implications of this absence for our understanding of core sociological concepts. With regard to the latter, the article focuses in particular on the debates around equality and emancipation and discusses the ways in which our understanding of these concepts could be extended by taking into account the work of African American sociologists and their different interpretations of core themes