Impact of the COVID-19 pandemic on paediatric orthopaedic trauma workload in central London: a multi-centre longitudinal observational study over the "golden weeks".

Background and purpose - The COVID-19 pandemic has been recognised as an unprecedented global health crisis. This study assesses the impact on a large acute paediatric hospital service in London, evaluating the trends in the acute paediatric orthopaedic trauma referral caseload and operative casemix before (2019) and during (2020) COVID-19 lockdown. Patients and methods - A longitudinal retrospective observational prevalence study of both acute paediatric orthopaedic trauma referrals and operative caseload was performed for the first 6 "golden weeks" of lockdown. These data were compared with the same period in 2019. Statistical analyses included median (± median absolute deviation), risk and odds ratios as well as Fisher's exact test to calculate the statistical significance, set at p ≤ 0.05. Results - Acute paediatric trauma referrals in 2020 were reduced by two-thirds compared with 2019 (n = 302 vs. 97) with a halving risk (RR 0.55) and odds ratios (OR 0.43) of sporting-related mechanism of injuries (p = 0.002). There was a greater use of outpatient telemedicine in the COVID-19 period with more Virtual Fracture Clinic use (OR 97, RR 84, p < 0.001), and fewer patients being seen for consultation and followed up face to face (OR 0.55, RR 0.05, p < 0.001). Interpretation - The impact of the COVID-19 pandemic has led to a decline in the number of acute paediatric trauma referrals, admissions, and operations during the COVID period. There has also been a significant change in the patient pathway with more being reviewed via the means of telemedicine to reduce the risk of COVID-19 transmission and exposure. More work is required to observe for similar trends nationwide and globally as the pandemic has permanently affected the entire healthcare infrastructure.

Risk factors for postoperative myocardial infarct following cholecystectomy: a population-based study.

BACKGROUND: The aim was to analyse the risk for myocardial infarction (MI) after cholecystectomy. METHODS: The study is based on data from the Swedish Register for Gallstone Surgery (GallRiks) 2006-2014. The cohort was cross-linked with the Swedish Patient Register. Standardised incidence ratio (SIR) was calculated by dividing the observed incidence of MI within 30 days after surgery with the expected incidence of the background population. RESULTS: Altogether 94,577 procedures were included. MI within 30 days postoperatively (30d-po) were registered in 87 cases (0.09%, SIR for MI 3.03; 95% CI 2.43-3.74). MI occurred more often in men (0.15% vs 0.06%), after open surgery (0.34% vs 0.04%), was age related (age >50 years OR 4.05 > 75 years OR 15.70) and occurred more frequently amongst those with gallstone complications and high ASA score (ASA 1; 0.02%, 2; 0.08%, ≥3; 0,64%). The risk for MI within 30d-po was 52.8% if the patient had suffered an infarct within 8 weeks preoperatively. Laparoscopy converted to open and primarily open surgery were independent risk factors (OR 3.05 vs 2.19). The mortality in the group with 30d-po MI was 11.5% vs 0.02%. CONCLUSION: Delaying elective cholecystectomy for at least 8 weeks after a recent MI reduces the risk for postoperative MI.

Defining thalamic nuclei and topographic connectivity gradients in vivo.

The thalamus consists of multiple nuclei that have been previously defined by their chemoarchitectual and cytoarchitectual properties ex vivo. These form discrete, functionally specialized, territories with topographically arranged graduated patterns of connectivity. However, previous in vivo thalamic parcellation with MRI has been hindered by substantial inter-individual variability or discrepancies between MRI derived segmentations and histological sections. Here, we use the Euclidean distance to characterize probabilistic tractography distributions derived from diffusion MRI. We generate 12 feature maps by performing voxel-wise parameterization of the distance histograms (6 feature maps) and the distribution of three-dimensional distance transition gradients generated by applying a Sobel kernel to the distance metrics. We use these 12 feature maps to delineate individual thalamic nuclei, then extract the tractography profiles for each and calculate the voxel-wise tractography gradients. Within each thalamic nucleus, the tractography gradients were topographically arranged as distinct non-overlapping cortical networks with transitory overlapping mid-zones. This work significantly advances quantitative segmentation of the thalamus in vivo using 3T MRI. At an individual subject level, the thalamic segmentations consistently achieve a close relationship with a priori histological atlas information, and resolve in vivo topographic gradients within each thalamic nucleus for the first time. Additionally, these techniques allow individual thalamic nuclei to be closely aligned across large populations and generate measures of inter-individual variability that can be used to study both basic function and pathological processes in vivo.

Development and initial validation of questionnaire on predictors for the use of hearing protection devices among noise exposed manufacturing workers in Tanzania: A methodological study.

Introduction: The use of hearing protection devices (HPDs) has been an intervention of choice in many workplaces such as in the construction industry for quite some time due to impractical effects of engineering and administrative interventions. Questionnaires for assessment for HPDs use among construction workers have been developed and validated in developed countries. However, there is limited knowledge of the same, among manufacturing workers in developing countries that are assumed to have a different culture, work organizations and production processes. Methods: We conducted a stepwise methodological study to develop a questionnaire to predict the use of HPDs among noise exposed workers in manufacturing factories in Tanzania. The questionnaire included 24 items and was developed through rigorous and systematic procedures involving three steps; (i) item formulation that involved two experts, (ii) expert content review and item rating that involving eight experts with vast experience in the field, and (iii) a field pre-test that involved 30 randomly selected workers from a factory with similar characteristics as a planned study site. A modified Pender's Health Promotion Model was adopted in the questionnaire development. We analyzed the questionnaire in terms of content validity and item reliability. Results: The 24 items were categorized into seven domains i.e., perceived self-efficacy, perceived susceptibility, perceived benefits, perceived barriers, interpersonal influences, situational influences and safety climate. The score for content validity for each item was satisfactory as the content validity index ranged between 0.75 to 1.00 for clarity, relevance, and essentiality criteria. Similarly, the scores for the content validity ratio (for all items) were 0.93, 0.88 and 0.93 for clarity, relevance, and essentiality, respectively. In addition, the overall value for Cronbach's alpha was 0.92 with domain coefficients: perceived self-efficacy 0.75; perceived susceptibility 0.74; perceived benefits 0.86; perceived barriers 0.82; interpersonal influences 0.79; situational influences; 0.70; and safety climate 0.79. The mean inter-item correlation was 0.49 suggesting good internal consistency. Discussion and conclusion: The developed and preliminary validated questionnaire can be used to predict the HPDs use among noise exposed manufacturing factory workers. Future surveys using this questionnaires warranted for further validation of the scale developed.

Expansion of the immature B lymphocyte compartment in Graves' disease.

OBJECTIVE: The specific mechanisms driving autoimmunity in Graves' disease (GD) remain largely unknown. Kappa-deleting recombination excision circles (KRECs) are circular DNA molecules generated during B cell maturation in the bone marrow which provide a measure of B cell production and proliferation. We aimed to investigate the association between KRECs and B cell subpopulations, with thyroid status and clinical outcome in GD patients. METHODS: Kappa-deleting recombination excision circles were measured by quantitative real-time PCR using a triple-insert plasmid control in 132 GD patients and 140 healthy controls. In addition, KRECs in GD patients on withdrawal of antithyroid drug (ATD) and 6-10 weeks later were analysed according to a clinical outcome at 1 year. Flow cytometry was performed on isolated CD19+ B cells to quantitate 7 B lymphocyte subpopulations in 65 GD patients. RESULTS: Circulating KRECs were higher in GD vs. controls (P = 1.5 × 10-9) and demonstrated a positive correlation to thyroid hormones and autoantibodies (free thyroxine: P = 2.14 × 10-5, rho = .30; free triiodothyronine: P = 1.99 × 10-7, rho = .37; thyroid stimulating hormone receptor autoantibodies: P = 1.36 × 10-5, rho = .23). Higher KRECs in GD patients 6-10 weeks after ATD withdrawal were associated with relapse of hyperthyroidism at 1 year (P = .04). The KRECs were positively correlated to the total CD19+ B cell count (P = 3.2 × 10-7). CONCLUSIONS: This study reports a robust association between KRECs and GD, highlighting the importance of B cells in the pathogenesis of GD and the influence of thyroid status on B cell activity. The findings indicate a potential role for KRECs as a marker of disease activity and outcome in GD.

Tibial tubercle avulsion fracture during sport activities in adolescent: a case report.

BACKGROUND AND AIM OF WORK: Tibial tubercle avulsion fractures (TTAF) are uncommon condition in children and adolescents. These lesions may be misdiagnosed and consequently not properly treated. Reduction and fixation is indicated if displacement is higher than 2mm or if the extensor apparatus is damaged. Authors present a case of a TTAF associated with a complete lateral patellar retinaculum lesion in a 13-year-old male adolescent non-professional basketball player. METHODS: Surgery consisted of reduction and fixation with 2 half threaded cancellous and washers; TTA was then basted and reinforced with a non absorbable suture according to Krachow technique and finally the patellar lateral retinaculum through a direct repair with absorbable material. RESULTS: Clinical evaluation after 3 years showed bone healing, a complete resolution of pain, complete range of motion, good strength and complete functionality of the operated limb. CONCLUSIONS: Misdiagnosis or delayed treatment of TTAF can often result in nonunion, functional impairment, and persistent pain. For these reasons, authors believe that a stable and quick fixation associated to specialized rehabilitation are crucial for recovery. (www.actabiomedica.it).

Resolution of renal failure 1 month after onset through angioplasty of renal artery stenosis.

The stent placement in patients with atherosclerotic renal artery stenosis and impaired renal function (STAR) and revascularization versus medical therapy for renal-artery stenosis (ASTRAL) trials concluded that renal artery angioplasty was not superior to medical management in delaying progression to renal failure or controlling blood pressure in a selected population. (1,2) There were several criticisms of the STAR trial's methodology, and an important criticism of ASTRAL was that the patient was excluded if their clinician was uncertain of the value in correcting the stenosis. Anuric renal failure by renal artery stenosis is a rare occurrence and falls outside this criteria.

Primary Pericardial Mesothelioma: A Rare but Serious Consideration.

Primary pericardial mesothelioma (PPM) is an extremely rare malignancy with a very poor prognosis. It poses a diagnostic challenge given its often late and non-specific presentation. This report describes a 74-year-old man who presented with central pleuritic chest pain and mild breathlessness. The patient was febrile and mildly tachycardic with crepitations in the right lung base. Blood tests revealed raised inflammatory markers and chest X-ray showed no acute pathology. Following admission, CT pulmonary angiogram showed a large left-sided mediastinal mass (approximately 110 x 70 x 85 mm) centered on the pericardium. Further post venous phase CT imaging identified possible myocardial invasion alongside suspicious liver nodules. Later, outpatient fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging highlighted further FDG avid pleural and liver lesions. CT-guided biopsy of the pericardial lesion was undertaken, with histology and immunohistochemistry indicating epitheliod-type mesothelioma. A significant malignant pericardial effusion was also identified, which ultimately required pericardial window formation. Immunotherapy was commenced utilizing dual nivolumab and ipilimumab, a novel regime for the treatment of mesothelioma. Palliative radiotherapy to the pericardial lesion will also be performed. Here, we demonstrate the diagnostic challenge of this vanishingly rare condition, which is usually diagnosed upon the development of associated complications. Early recognition gives the best chance of improved mortality, however, diagnosis requires a high index of clinical suspicion alongside prompt investigation, primarily involving cross-sectional imaging.

Antibiotic prophylaxis for urinary catheter manipulation following arthroplasty: a systematic review.

BACKGROUND: Urinary catheter use in the peri- and post-operative phase following arthroplasty may be associated with urinary tract infection (UTI) and deep prosthetic joint infection (PJI). These can be catastrophic complications in joint arthroplasty. We performed a systematic review of the evidence on use of antibiotics for urinary catheter insertion and removal following arthroplasty. METHODS: Electronic databases were searched using the Healthcare Databases Advanced Search interface. Grey literature was searched. From 219 citations, six studies were deemed eligible for review. Due to study heterogeneity, a narrative approach was adopted. Methodological quality of each study was assessed using the Critical Appraisal Skills Programme appraisal tool. RESULTS: A total of 4696 hip and knee arthroplasties were performed on 4578 participants across all studies. Of these, 1475 (31%) were on men and 3189 (68%) on women. The mean age of study participants was 69 years. Three thousand four hundred and eighty-nine cases (74.3%) were related to hip arthroplasty and 629 (13.4%) to knee arthroplasty. Five hundred and seventy-eight (12.3%) were either hip or knee arthroplasty. Forty-five PJIs were reported across all studies (0.96%). Two studies found either no PJI or no statistical difference in the rate of PJI when no antibiotic prophylaxis was used for catheter manipulation. Another study found no statistical difference in PJI rates between patients with or without preoperative bacteriuria. Where studies report potential haematogenous spread from UTIs, this association can only be assumed. Increased duration of urinary catheterization is positively associated with UTI. CONCLUSION: It remains difficult to justify the use of prophylactic antibiotics for catheter manipulation in well patients. Their use is not recommended for this indication.

In-car particulate matter exposure across ten global cities.

Cars are a commuting lifeline worldwide, despite contributing significantly to air pollution. This is the first global assessment on air pollution exposure in cars across ten cities: Dhaka (Bangladesh); Chennai (India); Guangzhou (China); Medellín (Colombia); São Paulo (Brazil); Cairo (Egypt); Sulaymaniyah (Iraq); Addis Ababa (Ethiopia); Blantyre (Malawi); and Dar-es-Salaam (Tanzania). Portable laser particle counters were used to develop a proxy of car-user exposure profiles and analyse the factors affecting particulate matter ≤2.5 µm (PM2.5; fine fraction) and ≤10 µm (PM2.5-10; coarse fraction). Measurements were carried out during morning, off- and evening-peak hours under windows-open and windows-closed (fan-on and recirculation) conditions on predefined routes. For all cities, PM2.5 and PM10 concentrations were highest during windows-open, followed by fan-on and recirculation. Compared with recirculation, PM2.5 and PM10 were higher by up to 589% (Blantyre) and 1020% (São Paulo), during windows-open and higher by up to 385% (São Paulo) and 390% (São Paulo) during fan-on, respectively. Coarse particles dominated the PM fraction during windows-open while fine particles dominated during fan-on and recirculation, indicating filter effectiveness in removing coarse particles and a need for filters that limit the ingress of fine particles. Spatial variation analysis during windows-open showed that pollution hotspots make up to a third of the total route-length. PM2.5 exposure for windows-open during off-peak hours was 91% and 40% less than morning and evening peak hours, respectively. Across cities, determinants of relatively high personal exposure doses included lower car speeds, temporally longer journeys, and higher in-car concentrations. It was also concluded that car-users in the least affluent cities experienced disproportionately higher in-car PM2.5 exposures. Cities were classified into three groups according to low, intermediate and high levels of PM exposure to car commuters, allowing to draw similarities and highlight best practices.

An Intronic HCP5 Variant Is Associated With Age of Onset and Susceptibility to Graves Disease in UK and Polish Cohorts.

CONTEXT: The genetic background of young-onset Graves disease (GD) remains largely unknown. An intronic variant in human leukocyte antigen (HLA) complex P5 (HCP5) has previously been associated with GD susceptibility and age of onset in a cohort of Polish patients. OBJECTIVE: We aimed to investigate the association of the HCP5 variant rs3094228 with GD susceptibility and age of onset in a UK cohort and conduct a meta-analysis of UK and Polish data. DESIGN AND PARTICIPANTS: rs3094228 was genotyped in 469 UK patients with GD using Taqman chemistry. Genotype frequencies were compared with genotypic data available from the Wellcome Trust case-control consortium using logistic regression analysis. To determine whether rs3094228 is independently associated with age of GD onset, the HLA DRB1*0301 tagging variant, rs535777, was also genotyped. RESULTS: The C allele of rs3094228 was overrepresented in the UK GD cohort compared with controls (P allele=5.08 × 10-9, odds ratio 1.76; [95% confidence interval, 1.46-2.13]). This association was more marked in young-onset GD (<30 years) (P allele=1.70 × 10-10 vs P allele=0.0008). The meta-analysis of UK and Polish data supported the association of the C allele with GD susceptibility (P allele=1.79 × 10-5) and age of onset (P allele=5.63 × 10-8). Haplotype analysis demonstrated that rs3094228 is associated with age of GD onset (P = 2.39 × 10-6) independent of linkage disequilibrium with HLA DRB1*0301. CONCLUSION: The rs3094228 HCP5 polymorphism is independently associated with GD susceptibility and age of onset in a UK GD cohort. Our findings indicate a potential role of long noncoding ribonucleic acids, including HCP5, in GD pathogenesis, particularly in the younger population.

Pesticide Exposure and Health Problems Among Female Horticulture Workers in Tanzania.

Commercialization of horticulture farming, expansion of farms, and the practice of monoculture favor the proliferation of pests, which in turn increases the need for pesticides. Increased exposure to pesticides is associated with inadequate knowledge on the hazardous nature of pesticides, poor hygiene practices, lack of availability of washing facilities, and insufficient adherence to precautionary instructions on pesticide labels. Mitigating the risks posed by pesticides is considered a less compelling interest than alleviating poverty. Women working in horticulture in Tanzania usually have low levels of education and income and lack decision-making power even on matters relating to their own health. This contributes to pesticide exposure and other health challenges. Because of multiple factors, some of which act as study confounders, few studies on exposure to pesticides and health effects have been conducted among women. This review identified factors that contribute to the increased health effects among women working in the horticultural industry and how these effects relate to pesticide exposure.

Endotoxin, dust and exhaled nitrogen oxide among hand pickers of coffee; a cross-sectional study.

BACKGROUND: Primary coffee processing takes place in countries where coffee is grown, and may include hand picking of coffee to remove low quality beans. Hand picking is mostly performed by women. No previous studies on dust and respiratory health have been performed in this occupational group, although studies indicate respiratory problems among other coffee production workers. FINDINGS: Our aim was to assess dust and endotoxin exposure among hand pickers in a coffee factory and compare the levels with limit values. In addition we wanted to examine the fraction of exhaled nitric oxide (FeNO) as a possible inflammatory marker in the airways among the hand pickers and evaluate the association between FeNO and years of hand picking. All hand pickers in a factory were examined during 1 week. The response was 100 %; 69 participated. FeNO was measured using an electrochemistry-based NIOX MINO device. Nine out of 69 workers (13 %) had levels of FeNO above 25 ppb, indicating presence of respiratory inflammation. A significant positive association was found between increasing FeNO and years of hand picking. Nine personal samples of total dust and endotoxin were taken. None of the dust samples exceeded the occupational limit value for total organic dust of 5 mg/m(3). Three samples of endotoxin (33 %) were above the recommended value of 90 EU/m(3). CONCLUSIONS: Levels of endotoxin were higher than recommended standards among hand pickers, and there was a positive association between the level of exhaled nitrogen oxide and years of work with hand picking coffee.

[Extramedullary hematopoiesis in the paravertebral space]. / Extramedulläre Blutbildung im paravertebralen Raum.

BACKGROUND: Extramedullary hematopoiesis is a response of the organism to a deficient production of blood-forming cells within the bone marrow. It may coincide with some hematologic diseases. Two patients with paravertebral mass lesions representing extramedullary hematopoiesis are discussed. Characteristic findings of extramedullary hematopoiesis are presented along with a review of the literature on this topic. CASE REPORTS: A 76-year-old male with a known myelodysplastic syndrome presented with pneumonia. In addition, he had symptoms of a cauda equina syndrome with complaints of pain and hypesthesia of the lower limbs as well as urinary retention. A 63-year-old female presented with aggravated complaints of the lower thorax, low back pain radiating to the upper left leg, and dysesthesia of both feet. In her past medical history, she had polycythemia vera and a splenectomy. Both patients showed paravertebral and intraspinal lesions located in the thoracic and sacral spine which were regarded as extramedullary hematopoiesis according to the imaging findings in MRI and CT. Radiation therapy showed marked improvement in their neurologic complaints following the initial sessions. CONCLUSION: Clinical presentation, knowledge of the underlying disease and of imaging findings are essential in the diagnosis of extramedullary hematopoiesis. MRI is the imaging modality of choice in the primary diagnosis of extramedullary hematopoiesis. Possible extension of the disease into the intraspinal space can be evaluated with high accuracy and differential diagnosis can be facilitated. In addition, MRI is of use in the accurate planning of radiation fields as well as during follow-up of extramedullary hematopoiesis.

Registration of health-related quality of life in a cohort of patients undergoing cholecystectomy.

Background. Assessment of gallstone surgery's impact on quality of life (QoL) requires a reliable instrument with sufficient responsiveness. The instrument should also enable estimation of each individual's expected condition in an unaffected state. Materials and Methods. The Swedish Register for Gallstone Surgery and ERCP (GallRiks) registers indications, complications, results, and QoL-outcome of gallstone surgery. In 2008, 68 hospitals were registered in GallRiks. Between 2007 and 2008, SF-36 (a short form health survey) was filled in 1-2 weeks pre- and 6-9 months postoperatively at five of the units. Expected scores were determined from an age- and gender-matched Swedish population (AGMSP). Results. Of the 330 patients, 212 responded to SF36 pre- and postoperatively (RR = 64%; 212/330). Standardized response means ranged from 0.20 to 0.93 for the SF-36 subscores. Highest responsiveness was seen for bodily pain. Preoperatively, all subscores were significantly lower than in the AGMSP (all P < .05). Six months postoperatively, there was no significant difference between any of the observed and expected quality of life subscales. Conclusion. SF-36 is a useful instrument for measuring the impact of gallstone surgery on QoL. The postinterventional health status equalled or even exceeded the AGMSP for all subscales.

The clinically meaningful change in physical performance scores in an elderly cohort.

BACKGROUND AND AIMS: The aim of this study was to assess annual changes in the continuous summary physical performance score (CSPPS) and the quartile summary physical performance (QSPPS) score, evaluate how these changes relate to self-reported changes in physical function and to examine clinically meaningful changes in CSPPS and QSPPS. METHODS: This was a longitudinal study of an elderly cohort of men and women (age>65) reporting at least two domains of disability from 5 centers in the US and Europe. Subjects completed assessments of mobility, ability to perform activities of daily living (ADLs), and the physical component of the SF-36 at both baseline and at 1- year, as well as a self-report of change in function over the year. Timed physical performance tests including walking speed, repeated chair stands and balance were used to calculate QSPPS and CSPPS at baseline and one year. RESULTS: Regardless of the tool used to evaluate clinical significance (ADL, SF- 36 PF, mobility disability, self-rating of physical performance) or a determination of the small meaningful change estimates based on effect size, it appears that a change of approximately 3 points in the CSPPS or 0.6 points in the QSPPS is clinically meaningful. CONCLUSION: In this cohort with moderate to severe disability, an annual change of approximately 3 points in CSPPS and 0.6 points in QSPPS are clinically meaningful and these changes are evident at one year.

Evaluation of continuous summary physical performance scores (CSPPS) in an elderly cohort.

BACKGROUND AND AIMS: Physical performance is an important predictor of quality of life among the elderly. A valid and sensitive measure of physical performance is needed in order to evaluate possible interventions. The aim of this study was to examine the validity and reliability of the Continuous Summary Physical Performance Score (CSPPS) and its relationship to the Quartile Summary Physical Performance Score (QSPPS). METHODS: This cross-sectional study of an elderly cohort from 5 centers in the US and Europe included men and women (> age 65) reporting at least two domains of disability. Subjects completed assessments of mobility and ability to perform activities of daily living (ADLs), the physical component of the SF-36, and a self-rating of physical performance. Timed physical performance tests were used to calculate the CSPPS and QSPPS. RESULTS: 216 subjects took part (mean age = 81 years). The distribution of CSPPS scores was similar for men and women, with a mean of 59.2 (SD 17.8), median of 64.3, and range from 1.3 to 91. Subjects with older age, higher degree of disability, and lower self-rated physical performance had lower CSPPS scores. The CSPPS had good test-retest reliability (r = 0.92), and CSPPS and QSPPS are highly correlated (r = 0.94, p < 0.001). However, the QSPPS appears to lack the linearity, and the ranges of the CSPPS for each score of the QSPPS overlap substantially. CONCLUSIONS: In a cohort with moderate to severe disability, the CSPPS appears to be a valid, reproducible measure that can discriminate smaller yet clinically meaningful differences in physical function, as compared with the QSPPS.

Age-related alterations in the neural coding of envelope periodicities.

This research was guided by the working hypothesis that the aging auditory system progressively loses its ability to process rapid acoustic transients efficiently, and in elderly listeners, this results in difficulties in speech perception. Neural correlates of age-related deficits in temporal processing were investigated by recording from inferior colliculus (IC) neurons from young adult and old CBA mice. Single-unit responses were recorded to sinusoidally amplitude-modulated (SAM) noise carriers, presented at 65-80 dB SPL, having modulation frequencies (MFs) that ranged from 10 to 800 Hz. Because phasic-type temporal response patterns dominate responses to tone and noise in mammalian IC, we limited our analyses to only phasic units. Modulation transfer functions (MTF) for both rate (rMTF) and synchronization (sMTF) measures were used to derive respective best modulation frequencies (rBMF and sBMF). The main age-related finding was that there was an overall increase in response rate to SAM noise carriers and a decrease in the median upper cutoff frequency in units from old mice. At rBMF, the median spike count from units from old animals was 1.63 times greater, and at the sBMF, the median spike count was 2.29 times greater than the young adult sample. We explored whether the increase in driven activity was due to a change in the transient (first cycle response) or periodic (remaining response) component of the response to SAM noise. Median spike counts of the transient component decreased with increasing MF for both young adult and old units, with median counts consistently greater in the old sample as compared with young. Median spike counts for the periodic response remained relatively constant as a function of MF; however, there was a significantly greater (3 times) response for older units in a restricted range of MFs. The greater median spike counts found for the transient and periodic response was also evident when we analyzed the cycle-by-cycle response. The magnitude of the differences between the young adult and the old spike median responses was greatest at low MFs and then declined as MF increased. Finally, the young adult distribution of rBMFs extends to higher MFs than the old, with 36.0% of units having rBMFs >100 Hz as compared with only 12.5% of the old unit sample. We postulate that this age-related difference in rate coding of SAM noise carriers is consistent with a loss, or imbalance, of excitatory and inhibitory neural mechanisms known to shape encoding of envelope periodicities in the IC.

Age reduces response latency of mouse inferior colliculus neurons to AM sounds.

Age and stimulus rise time (RT) effects on response latency were investigated for inferior colliculus (IC) neurons in young-adult and old CBA mice. Single-unit responses were recorded to unmodulated and sinusoidal amplitude modulated (SAM) broadband noise carriers, presented at 35 to 80 dB SPL. Data from 63 young-adult and 76 old phasic units were analyzed to identify the time interval between stimulus onset and driven-response onset (latency). When controlling for stimulus sound level and AM frequency, significant age-related changes in latency were identified. Absolute latency decreased with age at all stimulus AM frequencies, significantly so for equivalent rise times (RT) < or = 12.5 ms. The linear correlation of latency with AM stimulus RT was significant for both young-adult and old units, and increased significantly with age. It is likely that both the decrease in absolute latency and the increase in latency/RT correlation with age are consistent with a reduction of inhibitory drive with age in the IC. These latency changes will result in age-related timing variations in brainstem responses to stimulus onsets, and therefore affect the encoding of complex sounds.