Gender Differences in Human Single Neuron Responses to Male Emotional Faces

Well-documented differences in the psychology and behavior of men and women have spurred extensive exploration of gender€™s role within the brain, particularly regarding emotional processing. While neuroanatomical studies clearly show differences between the sexes, the functional effects of these differences are less understood. Neuroimaging studies have shown inconsistent locations and magnitudes of gender differences in brain hemodynamic responses to emotion. To better understand the neurophysiology of these gender differences, we analyzed recordings of single neuron activity in the human brain as subjects of both genders viewed emotional expressions. This study included recordings of single-neuron activity of 14 (6 male) epileptic patients in four brain areas: amygdala (236 neurons), hippocampus (n = 270), anterior cingulate cortex (n = 256), and ventromedial prefrontal cortex (n = 174). Neural activity was recorded while participants viewed a series of avatar male faces portraying positive, negative or neutral expressions. Significant gender differences were found in the left amygdala, where 23% (n = 15/66) of neurons in men were significantly affected by facial emotion, vs. 8% (n = 6/76) of neurons in women. A Fisher€™s exact test comparing the two ratios found a highly significant difference between the two (p \u3c 0.01). These results show specific differences between genders at the single-neuron level in the human amygdala. These differences may reflect gender-based distinctions in evolved capacities for emotional processing and also demonstrate the importance of including subject gender as an independent factor in future studies of emotional processing by single neurons in the human amygdala

Radiographic Prevalence of Osteoarthritis of the Scaphotrapeziotrapezoid Joint in Patients With Carpometacarpal Osteoarthritis of the Thumb: A Retrospective Case Series

Background: In planning operative treatment of thumb carpometacarpal (CMC) joint osteoarthritis, surgeons should consider the presence of an arthritic scaphotrapeziotrapezoid (STT) joint. We aimed to determine the radiographic prevalence of concomitant (STT) osteoarthritis with thumb CMC osteoarthritis in patients who underwent surgical treatment at our institution. We hypothesized that the prevalence of concomitant arthritis at these 2 joints (STT and CMC) would be lower than previously reported. Methods: Between September 2005 and July 2012, a total of 417 patients were identified from our institution using the Current Procedural Terminology code for thumb CMC joint arthroplasty (25447). After applying exclusion criteria and identifying patients who underwent treatment, a total of 194 patients were included and 218 preoperative radiographs were available for review. Each radiograph was categorized according to the Eaton classification of thumb CMC osteoarthritis, with stage 4 involving the (STT) joint. Evaluation was performed by four reviewers independently. Results: A total of 47 (21.6%) patients had varying degrees of concomitant (STT) joint osteoarthritis with the thumb CMC joint osteoarthritis. Stage 4 was reported in 6.4% (14) of the radiographs. Conclusions: The radiographic prevalence of concomitant (STT) osteoarthritis with thumb CMC osteoarthritis may be lower than previously reported. Further studies that include a similarly large sample size and additional radiographic views can help evaluate the likelihood of these conditions in patients who elect to undergo surgical treatment of thumb CMC osteoarthritis

Third Extensor Compartment Disruption and the Biomechanics of Thumb Extension

Background: Procedures involving release of the third dorsal wrist compartment have been thought to transpose the extensor pollicis longus (EPL) tendon from its anatomical position. Few studies, however, have reported on the effects this might have on function and mechanics of the thumb. We analyzed the impacts of intact extensor retinaculum, release of the third dorsal compartment, and removal of Lister’s tubercle on thumb extension. Methods: A total of 15 fresh-frozen cadaveric upper extremities (eight male, seven female; mean age, 52 years; range, 38-59 years) were used. For each specimen, three phases of testing were analyzed: the extensor retinaculum was intact, third dorsal compartment was released, and Lister’s tubercle was released. Force-displacement measurements were obtained to determine maximum extension and stiffness of the thumb by applying 1 N increments on the EPL until full extension of the thumb occurred. A one-way analysis of variance was used for statistical comparison. Results: In 14 of 15 specimens, the EPL tendon transposed during the first trial after release of the extensor retinaculum. No significant difference in mean maximum extension or stiffness of the thumb was found (P = 0.45 and P = 0.74, respectively). Conclusion: Functional loss of thumb extension may not occur with EPL transposition after release of the third dorsal compartment or removal of Lister’s tubercle. In patients with weakness in thumb extension, repairing the third dorsal compartment or creating a new pulley may not be effective