Distribution of olfactory epithelium in the primate nasal cavity: are microsmia and macrosmia valid morphological concepts?

Perinatal size and maturation of the olfactory and vomeronasal neuroepithelia in lorisoids and lemuroids

Explanations for the chemosensory abilities of newborn mammals focus primarily on food (milk) acquisition and communication (e.g., maternal-infant bonding). However, the relative importance of the main and accessory (vomeronasal) olfactory systems is hypothesized to differ at birth between altricial and precocial mammals. Strepsirrhines (lemurs and lorises) possess main and accessory olfactory systems, and vary in life-history traits related to infant dependency and maturation. Accordingly, this study examines the size and maturational characteristics of vomeronasal (VNNE) and olfactory (OE) neuroepithelia in strepsirrhines. Serially sectioned heads of 18 infant cadavers were examined microscopically for neuroepithelial distribution. Measurements were taken on the length of the nasal fossa on one side that was occupied by VNNE and OE. The data were corrected for body size using the cranial length or body mass, and were then examined for correlation with several life-history variables, as well as activity pattern. In addition, immunohistochemistry was used to identify cells in the VNNE and OE that express olfactory marker protein (OMP), a marker of mature olfactory neurons. Relative OE extent was not significantly correlated with any of the life-history variables. Relative VNNE length was negatively correlated with relative gestation length and relative neonatal mass (P<0.05). However, when we corrected for phylogenetic relationships, we found no significant correlations between either of the neuroepithelial measurements and life-history variables. Immunohistochemical findings suggest that OE has more OMP-reactive cells than VNNE in all species. OMP-reactive cells appear to be less numerous in diurnal species compared to most nocturnal species. These results indicate that the VNNE may be relatively longer at birth in altricial species. However, it remains uncertain how phylogeny and/or ontogeny may explain these findings.

Quantitative EEG analysis in post-traumatic anosmia

Many objective and quantitative methods have been developed to create a procedure or a device to prove, describe and quantify olfactory deficit and anosmia, especially after a head trauma. Electrophysiological testing throughout olfactoelectroencephalography (olfactoEEG) is based on brain activity desynchronisation, and on the subsequent disappearance of alpha activity on the posterior regions after an olfactory stimulus. Yet traditional evaluation of EEG can be difficult, because of little or hardly detectable alpha activity on the posterior regions ('alpha rare'). The aim of this study was to evaluate the Olfactory Stop Reaction (OSR) by means of frequency band power calculation and subsequent topographical mapping in patients with post-traumatic anosmia, who presented 'alpha rare' EEG. Twenty-five consecutive patients, affected by anosmia caused by head trauma, were submitted to an EEG recording with olfactory stimulation. After signal processing and analysis, an Olfactory Stop Reaction was detected in 17 out of 25 patients; moreover, in these patients we detected a significant decrease in alpha band power in the occipital regions and an increase in theta band power on midline frontal and central regions after olfactory stimulation. In the remaining eight patients, no significant variation in band power was observed. In conclusion, an objective evaluation of the olfactory function with this method of automatic EEG signal analysis allows the limits given by psychophysical methods and traditional EEG to be overcome and attempts to fulfil the requirements for standardization of olfactory function evalution.

Evolution of the special senses in primates: past, present, and future

The present special issue of The Anatomical Record is the result of a symposium entitled Evolution of the Special Senses in Primates. Considered together, the special senses of primates are remarkable because they constitute a singular and definitive suite of mammalian characteristics. Examining their evolution is pivotal for understanding the origin and present-day variation of primate behavior and ecology. Accordingly, the 14 articles assembled here consider the different constraints and opportunities associated with the uptake and use of physical and chemical stimuli. The present issue brings together experts on different primate sensory modalities and stresses events at the sensory periphery, where the organism is exposed to and comes into contact with its environment. Key topics include color vision, the genetics of olfaction, the morphological basis and significance of chemical communication, and the neural organization and scaling of primate sensory systems. The result is a special issue that both reflects our current understanding of primate sensory modalities and challenges certain fundamental assumptions concerning their evolution.