Parallel Odor Processing by Two Anatomically Distinct Olfactory Bulb Target Structures

The olfactory cortex encompasses several anatomically distinct regions each hypothesized to provide differential representation and processing of specific odors. Studies exploring whether or not the diversity of olfactory bulb input to olfactory cortices has functional meaning, however, are lacking. Here we tested whether two anatomically major olfactory cortical structures, the olfactory tubercle (OT) and piriform cortex (PCX), differ in their neural representation and processing dynamics of a small set of diverse odors by performing in vivo extracellular recordings from the OT and PCX of anesthetized mice. We found a wealth of similarities between structures, including odor-evoked response magnitudes, breadth of odor tuning, and odor-evoked firing latencies. In contrast, only few differences between structures were found, including spontaneous activity rates and odor signal-to-noise ratios. These results suggest that despite major anatomical differences in innervation by olfactory bulb mitral/tufted cells, the basic features of odor representation and processing, at least within this limited odor set, are similar within the OT and PCX. We predict that the olfactory code follows a distributed processing stream in transmitting behaviorally and perceptually-relevant information from low-level stations

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

OT and PCX Odor signal∶noise.

<p>(<b>A</b>) Average signal∶noise (s∶n, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034926#s2" target="_blank">Methods</a>) in OT and PCX units. Each point represents average s∶n of each unit, across all odor presentations (>4 trials/unit) and odors. Horizontal bars = average s∶n across units ± SEM. *<i>p</i><0.05, ANOVA followed by Fisher's PLSD.</p

Electrode tip locations verifying extent of OT and PCX recording sites.

<p>Coronal stereotaxic panels showing the approximate location of electrode tips from records used for analysis. Coronal sections span from 2.0 – 0.5 mm anterior of bregma, in 0.5 mm intervals. Panels adapted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034926#pone.0034926-Paxinos1" target="_blank">[61]</a>.</p

Onset of odor input is similar between OT and PCX.

<p>(<b>A</b>) Example traces of unit firing and respiration over the course of 1 sec. Inhalation in respiratory trace is an upward deflection. Hash marks represent unit responses (spikes). t_onset = latency from first inhalation initiation during odor (circle) until the time of the first action potential (depicted here by the green horizontal arrow). (<b>B</b>) Average t_onset values ± SEM within the OT (red) and PCX (blue). (<b>C</b>) Cumulative probability plot of t_onset values (same data as in (B)). Dashed lines = normal fits of OT (red) and PCX (blue) cumulative probability data.</p

Temporal dynamics of odor-evoked activity in OT and PCX neural ensembles.

<p>(<b>A</b>) 3-dimensional histograms of average firing frequency for each unit across the five odors within the OT (top) and the PCX (bottom). Diversity of intensity in spontaneous firing and odor-evoked changes in firing are visible within both structures. Units arrangement (#1,2,3, etc.) is arbitrary but consistent across panels within regions. (<b>B</b>) Average firing frequency of OT (top) and PCX (bottom) units relative to odor onset sorted by odors. (<b>C</b>) Raw (top) and normalized (bottom) average firing frequency of OT and PCX units sorted by odors (left to right). (<b>D</b>) Average firing frequency across all odors and units. Data displayed as mean ± SEM. Vertical magenta dashed line = odor onset.</p