f/f/p mice was decreased by 50% compared with wild-type mice, whereas baseline ventilation and the hypoxic ventilatory response were normal. In addition, Lmx1b f/f/p mice rapidly became hypothermic when exposed to an ambient temperature of 4°C, decreasing core temperature to 30°C within 120 min. This failure of thermoregulation was caused by impaired shivering and nonshivering thermogenesis, whereas thermosensory perception and heat conservation were normal. Finally, intracerebroventricular infusion of 5-HT stimulated baseline ventilation, and rescued the blunted hypercapnic ventilatory response. These data identify a previously unrecognized role of 5-HT neurons in the CO 2 chemoreflex, whereby they enhance the response of the rest of the respiratory network to CO 2 . We conclude that the proper function of the 5-HT system is particularly important under conditions of environmental stress and contributes significantly to the hypercapnic ventilatory response and thermoregulatory cold defense.

Objective The objective was to determine the impact of the COVID-19 pandemic on operative case volume in 8 US neurosurgical residency training programs in early 2020 and to survey these programs regarding training activities during this period. Methods A retrospective review was conducted of monthly operative case volumes and types for 8 residency programs for 2019 and January-April 2020. Cases were grouped as elective cranial, elective spine, and non-elective emergent cases. Programs were surveyed regarding residents’ perceptions of the impact of COVID-19 on surgical training, didactics, and research participation. Data was analyzed for individual programs and pooled across programs. Results Across programs, the 2019 monthly case average was 211 (SD ± 82); 2020 average case volumes for January, February, March, and April were 228±93, 214±84, 180±73, and 107±45, respectively. Compared with 2019, March and April 2020 average cases declined 15% (p=0.003) and 49% (p=0.002), respectively. COVID-19 affected surgical case volume for all programs; 75% reported didactics negatively affected, and 90% reported COVID-19 resulted in increased research time. Several neurosurgery residents have required COVID-19 testing, however, to our knowledge, only one resident from the participating programs tested positive. Conclusions This study documents a significant reduction in operative volume in 8 neurosurgery residency training programs in early 2020. During this time, neurosurgery residents engaged in online didactics and research-related activities, reporting increased research productivity. Residency programs should collect data to determine the educational impact of the pandemic on resident operative case volumes, identify deficiencies, and develop plans to mitigate any effects.

Therapeutic parent artery occlusion has been routinely utilized for management of some intracranial aneurysms. One possible long-term complication of this procedure is ''de novo'' formation of aneurysms. The purpose of this paper is to estimate the incidence of de novo aneurysm formation, the time period between occlusion and formation, and the most common sites of formation. A PubMed search was performed for all articles between 1970 and 2008 reporting cases of both therapeutic carotid occlusion and de novo cerebral aneurysms. The 20 papers reviewed reported 187 patients having undergone therapeutic carotid occlusion. Of the 163 patients reported in complete-case series, seven developed new aneurysms (4.3%). Thirty-six total new aneurysms were reported, ranging from 1 to 5 per patient. The average time period between occlusion and detection of de novo aneurysm was 9.1 years (range: 2 to 20 years). These aneurysms occurred mostly in the anterior circulation, predominately the anterior communicating artery and posterior communicating artery, and frequently occurred contralateral to the site of occlusion. Therapeutic parent artery occlusion is a likely risk factor for de novo aneurysm formation. Noninvasive follow-up studies should be performed, especially between 2 and 10 years after occlusion.

Change blindness (CB), the inability to detect changes in visual scenes, may increase with age and early Alzheimer’s disease (AD). To test this hypothesis, participants were asked to localize changes in natural scenes. Dependent measures were response time (RT), hit rate, false positives (FP), and true sensitivity (d′). Increased age correlated with increased sensitivity and RT; AD predicted even slower RT. Accuracy and RT were negatively correlated. Differences in FP were nonsignificant. CB correlated with impaired attention, working memory, and executive function. Advanced age and AD were associated with increased CB, perhaps due to declining memory and attention. CB could affect real-world tasks, like automobile driving.