Biomedical subjects

David R Moore

Publications and source records attributed to David R Moore.

At least 19 recordsLinked to original sources

PubMed2006

Discrimination learning induced by training with identical stimuli.

Sensory stimuli become easier to detect or distinguish with practice. It is generally assumed that the task-relevant stimulus dimension becomes increasingly more salient as a result of attentively performing the task at a level that is neither too easy nor too difficult. However, here we show improved auditory frequency discrimination following training with physically identical tones that were impossible to discriminate. We also show that learning transfers across tone frequencies and across modalities: training on a silent visuospatial computer game improved thresholds on the auditory discrimination task. We suggest that three processes are necessary for optimal perceptual learning: sensitization through exposure to the stimulus, modality- and dimension-specific attention, and general arousal.

Acoustic Stimulation↗

PubMed2006

The ferret auditory cortex: descending projections to the inferior colliculus.

Descending corticofugal projections are thought to play a critical role in shaping the responses of subcortical neurons. Here, we examine the origins and targets of ferret auditory corticocollicular projections. We show that the ectosylvian gyrus (EG), where the auditory cortex is located, can be subdivided into middle, anterior, and posterior regions according to the pattern of cytochrome oxidase staining and immunoreactivity for the neurofilament antibody SMI32. Injection of retrograde tracers in the inferior colliculus (IC) labeled large layer V pyramidal cells throughout the EG and adjacent sulci. Each region of the EG has a different pattern of descending projections. Neurons in the primary auditory fields in the middle EG project to the lateral nucleus (LN) of the ipsilateral IC and bilaterally to the dorsal cortex and dorsal part of the central nucleus (CN). The projection to these dorsomedial regions of the IC is predominantly ipsilateral and topographically organized. The secondary cortical fields in the posterior EG target the same midbrain areas but exclude the CN of the IC. A smaller projection to the ipsilateral LN also arises from the anterior EG, which is the only region of auditory cortex to target tegmental areas surrounding the IC, including the superior colliculus, periaqueductal gray, intercollicular tegmentum, and cuneiform nucleus. This pattern of corticocollicular connectivity is consistent with regional differences in physiological properties and provides another basis for subdividing ferret auditory cortex into functionally distinct areas.

Animals↗

PubMed2006

Auditory processing disorder (APD)-potential contribution of mouse research.

APD is a common, heterogeneous and poorly understood listening impairment that is receiving increasing recognition, especially in children and the elderly. The primary symptom in humans is poor speech perception despite normal pure tone audiometry. Diagnostic practice is patchy, but current proposals are to distinguish APD by reduced ability to detect, discriminate, localize and order non-speech sounds. APD appears to result predominantly from core malfunctioning of the central auditory system, but with strong cognitive influences and possible additional influences from peripheral auditory and crossmodal sources. APD may be acquired (e.g. through middle ear disease), but it is likely that a more common etiology would involve both environmental and inherited contributions. Mice are increasingly being used for studies of central auditory processing. Most work to date has documented the basic response properties of auditory neurons, or used single gene mutations to investigate specific functions. For high throughput, primary screening, reflex and/or event-related potential measures are required. Pre-pulse inhibition (PPI), the regulation of an acoustic startle reflex by a preceding sound having distinct spatial, temporal or spectral properties, is one way in which auditory processing may be screened. For secondary assessment, standard psychoacoustic tests for mice have been developed.

Animals↗

PubMed2006

A comparison of adaptive procedures for rapid and reliable threshold assessment and training in naive listeners.

In psychoacoustic studies there is often a need to assess performance indices quickly and reliably. The aim of this study was to establish a quick and reliable procedure for evaluating thresholds in backward masking and frequency discrimination tasks. Based on simulations, four procedures likely to produce the best results were selected, and data collected from 20 naive adult listeners on each. Each procedure used one of two adaptive methods (staircase or maximum-likelihood estimation, each targeting the 79% correct point on the psychometric function) and two response paradigms (3-interval, 2-alternative forced-choice AXB or 3-interval; 3-alternative forced-choice oddball). All procedures yielded statistically equivalent threshold estimates in both backward masking and frequency discrimination, with a trend to lower thresholds for oddball procedures in frequency discrimination. Oddball procedures were both more efficient and more reliable (test-retest) in backward masking, but all four procedures were equally efficient and reliable in frequency discrimination. Fitted psychometric functions yielded similar thresholds to averaging over reversals in staircase procedures. Learning was observed across threshold-assessment blocks and experimental sessions. In four additional groups, each of ten listeners, trained on the different procedures, no differences in performance improvement or rate of learning were observed, suggesting that learning is independent of procedure.

Adult↗

PubMed2005

Allograft reconstruction for massive, irreparable rotator cuff tears.

BACKGROUND: There is currently no widely accepted treatment for massive, irreparable rotator cuff tears. HYPOTHESIS: Allograft reconstruction to span the remaining defect in massive, irreparable rotator cuff tears will lead to increased functional results and will demonstrate healing of the allograft on follow-up magnetic resonance imaging studies. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Between 1989 and 2003, 32 patients underwent allograft reconstruction of massive rotator cuff tears. University of California, Los Angeles shoulder scores were compared preoperatively and postoperatively and analyzed using paired Student t tests. In addition, 15 patients underwent postoperative magnetic resonance imaging to evaluate the structural integrity of the allograft reconstruction at the greater tuberosity insertion. RESULTS: Of 32 patients, 28 were available for review at a mean follow-up of 31.3 months; 23 of the 28 patients were satisfied with their outcome. There was 1 postoperative infection and 1 acute allograft rejection. The mean University of California, Los Angeles score increased from 12.1 preoperatively to 26.1 postoperatively (P < .001). All 15 patients evaluated with postoperative magnetic resonance imaging arthrograms demonstrated complete radiographic failure of the allograft rotator cuff reconstruction. Despite radiographic failure, the mean University of California, Los Angeles score increased from 13.2 preoperatively to 28.3 postoperatively in this subset of patients. CONCLUSION: The functional results of this reconstruction method are similar to those reported for debridement and subacromial decompression alone and are satisfactory, despite magnetic resonance imaging arthrogram evaluation demonstrating failure of the structural integrity of the allograft. Allograft reconstruction carries increased risk of infection and rejection and is technically more difficult than other less expensive treatment options with similar functional results. Therefore, we do not recommend allograft reconstruction of massive and otherwise irreparable rotator cuff tears.

Adult↗

PubMed2005

Descending projections from the auditory cortex to the inferior colliculus in the gerbil, Meriones unguiculatus.

Corticofugal projections to the auditory midbrain, the inferior colliculus (IC), influence the way in which specific sets of IC neurons process acoustic signals. We used retrograde tracer (Fluorogold, Fluororuby, microbeads) injections in the IC to study the morphology and location of cortico-collicular projecting neurons and anterograde tracer (dextran biotin) injections in auditory cortical fields to describe the distribution of terminals in the IC. Nissl staining, cytochrome oxidase activity, and neurofilament SMI32 immunostaining were used to delimit the different auditory areas. We defined a primary or "core" auditory cortex and a secondary "caudal" auditory area containing layer V pyramidal neurons that project to the IC. These projections target the central nucleus of the IC (CNIC) ipsilaterally and the IC cortices bilaterally, with the ipsilateral component predominant. Other secondary auditory areas, dorsal and ventral to the core, do not directly participate in this projection. The ventral secondary cortex targets midbrain periaqueductal gray. The projection from the core cortex originates from two classes of layer V pyramidal cells. Cells presenting a tufted apical dendrite in layer I have dense terminal fields in the IC cortices. Pyramids lacking layer I dendritic tufts target the CNIC in a less dense but tonotopic manner. The caudal cortex projection originates from smaller layer V pyramids and targets the IC cortices with dense terminal fields. Descending auditory inputs from the core and caudal areas converge in the dorsal and external cortices of the IC. Descending connections to the gerbil IC form a segregated system in which multiple descending channels originating from different neuronal subpopulations may modulate specific aspects of ascending auditory information.

Animals↗

PubMed2005

Effects of otitis media with effusion on auditory temporal resolution.

OBJECTIVE: There is mounting evidence to suggest that otitis media with effusion (OME) is associated with auditory processing deficits that persist beyond the resolution of the peripheral hearing loss. This study investigated the residual effects of OME on auditory temporal resolution. EXPERIMENT 1: METHODS: Experiment 1 measured detection thresholds for a brief tone presented either before (backward masking) or during (simultaneous masking) a masking noise, in 6- and 8-year-old children. Six-year-olds were selected from a prospectively studied group with a lifetime known history of OME. Eight-year-old children, with a retrospectively determined history of OME, were also recruited. All children were free of OME at the time of testing. RESULTS: Regardless of OME history, 6-year-old children had similar tone thresholds on all masking tasks. In contrast, 8-year-olds with a history of recurrent OME had 18 and 4dB higher mean thresholds for the backward and simultaneous masking conditions, respectively, compared with age-matched controls. Possible explanations for these results included (i) recruitment bias, rather than OME, contributed to differences in auditory processing abilities amongst 8-year-old children, or (ii) OME impaired performance at both ages, but this was not seen in 6-year-olds due to 'ceiling' effects. EXPERIMENT 2: METHODS: To distinguish between these possibilities, Experiment 2 measured temporal resolution, using backward masking and amplitude modulation detection, in the prospectively studied group of children when they were 8 years old. RESULTS: Regardless of OME history, these 8-year-olds had similar auditory temporal processing abilities. Results from Experiment 2 suggested that recruitment bias was the most likely explanation for the difference in auditory processing abilities between 8-year-old children with and without a history of OME found in Experiment 1. Consistent with previous data, associations were found between backward masking, age and cognitive ability. CONCLUSION: There is no evidence to suggest that OME effects temporal resolution after the recovery of normal pure-tone thresholds.

Age Factors↗

PubMed2005

Discrimination training of phonemic contrasts enhances phonological processing in mainstream school children.

Auditory perceptual learning has been proposed as effective for remediating impaired language and for enhancing normal language development. We examined the effect of phonemic contrast discrimination training on the discrimination of whole words and on phonological awareness in 8- to 10-year-old mainstream school children. Eleven phonemic contrast continua were synthesised using linear interpolation coding from real speaker endpoints. Thirty children were pre-tested on the Word Discrimination Test (WDT) and the Phonological Assessment Battery (PhAB). Eighteen then trained for 12 x 30min sessions over 4 weeks using an adaptive three interval two alternative phonemic matching task. The remaining children participated in regular classroom activities. In Post-testing, trained children significantly increased their age-equivalent scores on both the WDT and PhAB by about 2 years. For the PhAB, no improvement was found in the controls. Enhanced performance in the trained children was maintained in a delayed test 5-6 weeks following training. Enhancements on the trained discriminations were weak and variable. The results indicate a dramatic improvement in phonological awareness following phonemic discrimination training without matching perceptual learning.

Child↗

PubMed2005

Allograft ankle arthrodesis: a limb salvage technique for distal tibial tumors.

UNLABELLED: Allograft ankle arthrodesis using a retrograde intramedullary tibial nail is a new strategy in limb salvage for treatment of distal intraarticular tibial tumors. After tumor resection, the ankle is reconstructed using an intercalary allograft and retrograde intramedullary fixation. We retrospectively reviewed nine consecutive patients with intraarticular resection of distal tibial tumors who had allograft ankle arthrodesis reconstruction between April 1994 and August 2000. Patient charts were reviewed for: (1) local recurrence, new metastases, and survival; (2) Musculoskeletal Tumor Society score; and (3) complications or reoperations or both. Only one of nine patients had a local recurrence. Eight of nine patients achieved independent ambulation. Eight of nine patients had a Musculoskeletal Tumor Society score greater than 73%. Six of nine patients required nine additional operations. No patients required flap coverage. There were no superficial or deep infections. Allograft ankle arthrodesis is a new alternative in limb salvage for distal tibial tumors. It has oncologic outcomes (rate of local recurrence, new metastases, and survival from time of diagnosis) and functional outcomes (Musculoskeletal Tumor Society score and rates of reoperation) comparable to previously reported and accepted methods of limb salvage. LEVEL OF EVIDENCE: Therapeutic study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Adolescent↗

PubMed2005

Auditory frequency discrimination learning is affected by stimulus variability.

We explored the effects of training set variability on learning and generalization of pure-tone frequency discrimination (FD) in three groups of untrained, normally hearing adult listeners. Group 1 trained using a fixed standard tone at 1 kHz (fixed), Group 2 on slightly varying (roving) tones around 1 kHz, and Group 3 on widely varying standard frequencies (wide-roving). Initially, two thirds of all listeners had low FD thresholds (good listeners) and one third had intermediate to high thresholds (poor listeners). For good listeners, slight variations in the training set slowed learning but wide variations did not. Transfer to untrained frequencies (up to 4 kHz) and to the fixed condition was equivalent regardless of training condition, but Group 1 listeners did not fully transfer learning to the roving condition. For poor listeners, any variation in the training condition slowed learning and impaired transfer to other frequencies but did not affect transfer to untrained conditions. Thus, the effects of training set on progress and outcome depend on set variability and individual FD ability.

Adult↗

PubMed2004

Discrete metal-based catalysts for the copolymerization of CO2 and epoxides: discovery, reactivity, optimization, and mechanism.

Most synthetic polymers are made from petroleum feedstocks. Given the non-renewable nature of these materials, there is increasing interest in developing routes to polymeric materials from renewable resources. In addition, there is a growing demand for biodegradable polymeric materials. Polycarbonates made from CO(2) and epoxides have the potential to meet these goals. Since the discovery of catalysts for the copolymerization of CO(2) and epoxides in the late 1960's by Inoue, a significant amount of research has been directed toward the development of catalysts of improved activity and selectivity. Reviewed here are well-defined catalysts for epoxide-CO(2) copolymerization and related reactions.

Journal Article↗

PubMed2004

Early and rapid perceptual learning.

Major, rapid performance improvements in perceptual training are often dismissed as 'task' or 'procedural' learning because they are fast and generalize within a task. We assessed the contributions of perceptual and procedural learning to improvement in an auditory tone frequency learning task in humans and found that perceptual learning accounted for between 76% and 98% of the rapid early performance improvement.

Acoustic Stimulation↗

PubMed2004

Auditory processing efficiency and temporal resolution in children and adults.

Children have higher auditory backward masking (BM) thresholds than adults. One explanation for this is poor temporal resolution, resulting in difficulty separating brief or rapidly presented sounds. This implies that the auditory temporal window is broader in children than in adults. Alternatively, elevated BM thresholds in children may indicate poor processing efficiency. In this case, children would need a higher signal-to-masker ratio than adults to detect the presence of a signal. This would result in poor performance on a number of psychoacoustic tasks but would be particularly marked in BM due to the compressive nonlinearity of the basilar membrane. The objective of the present study was to examine the competing hypotheses of "temporal resolution" and "efficiency" by measuring BM as a function of signal-to-masker interval in children and adults. The children had significantly higher thresholds than the adults at each of the intervals. Subsequent modeling and analyses showed that the data for both children and adults were best fitted using the same, fixed temporal window. Therefore, the differences in BM threshold between adults and children were not due to differences in temporal resolution but to reduced detection efficiency in the children.

Acoustic Stimulation↗

PubMed2004

Unilateral cochlear ablation produces greater loss of inhibition in the contralateral inferior colliculus.

Bilateral cochlear ablation leads to a profound weakening of synaptic inhibition within the inferior colliculus (IC) of gerbils [Vale & Sanes (2000) J. Neurosci., 20, 1912-1921]. To examine whether unilateral deafening leads to similar functional alterations, we studied the effect of unilateral cochlear ablation on inhibitory synaptic properties both ipsilateral and contralateral to the deafened ear. Lateral lemniscal and commissure of the IC-evoked inhibitory postsynaptic currents (IPSCs) were recorded in an IC brain slice preparation using whole-cell and gramicidin perforated-patch electrodes in the presence of kynurenic acid. Unilateral cochlear ablation led to a 23 mV depolarizing shift in the IPSC equilibrium potential for IC neurons contralateral to the deafened ear, but only a 10 mV depolarization in the ipsilateral IC. Lateral lemniscal-evoked inhibitory synaptic conductance declined significantly in the ipsilateral and contralateral IC, whereas commissural-evoked inhibitory synaptic conductance declined only contralateral to the ablated cochlea. An analysis of paired-pulse facilitation showed that inhibitory transmitter release was more affected ipsilateral to the ablated cochlea. Thus, unilateral cochlear ablation modifies inhibitory synapses in the inferior colliculus, but these changes appear to be dominated by postsynaptic alterations in the contralateral IC, and by presynaptic changes in the ipsilateral IC.

Animals↗

PubMed2003

Functional asymmetry for auditory processing in human primary auditory cortex.

Structural asymmetries in the supratemporal plane of the human brain are often cited as the anatomical basis for the lateralization of language predominantly to the left hemisphere. However, similar asymmetries are found for structures mediating earlier events in the auditory processing stream, suggesting that functional lateralization may occur even at the level of primary auditory cortex. We tested this hypothesis using functional magnetic resonance imaging to evaluate human auditory cortex responses to monaurally presented tones. Relative to silence, tones presented separately to either ear produced greater activation in left than right Heschl's gyrus, the location of primary auditory cortex. This functional lateralization for primary auditory cortex is distinct from the contralateral dominance reported for other mammals, including nonhuman primates, and may have contributed to the evolution of a unique role for the left hemisphere in language processing.

Adult↗

PubMed2003

Mechanism of the alternating copolymerization of epoxides and CO2 using beta-diiminate zinc catalysts: evidence for a bimetallic epoxide enchainment.

A series of zinc beta-diiminate (BDI) complexes and their solid-state structures, solution dynamics, and copolymerization behavior with CO(2) and cyclohexene oxide (CHO) are reported. Stoichiometric reactions of the copolymerization initiation steps show that zinc alkoxide and bis(trimethylsilyl)amido complexes insert CO(2), whereas zinc acetates react with CHO. [(BDI-2)ZnOMe](2) [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene] and (BDI-1)ZnO(i)Pr [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene] react with CO(2) to form [(BDI-2)Zn(mu-OMe)(mu,eta(2)-O(2)COMe)Zn(BDI-2)] and [(BDI-1)Zn(mu,eta(2)-O(2)CO(i)Pr)](2), respectively. (BDI-2)ZnN(SiMe(3))(2) inserts CO(2) and eliminates trimethylsilyl isocyanate to give [(BDI-2)Zn(mu-OSiMe(3))](2). [(BDI-7)Zn(mu-OAc)](2) [(BDI-7) = 3-cyano-2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene] reacts with 1.0 equiv of CHO to yield [(BDI-7)Zn(mu,eta(2)-OAc)(mu,eta(1)-OCyOAc)Zn(BDI-7)]. Under typical polymerization conditions, rate studies on the copolymerization exhibit no dependence in [CO(2)], a first-order dependence in [CHO], and orders in [Zn](tot) ranging from 1.0 to 1.8 for [(BDI)ZnOAc] complexes. The copolymerizations of CHO (1.98 M in toluene) and 300 psi CO(2) at 50 degrees C using [(BDI-1)ZnOAc] and [(BDI-2)ZnOAc] show orders in [Zn](tot) of 1.73 +/- 0.06 and 1.02 +/- 0.03, respectively. We propose that two zinc complexes are involved in the transition state of the epoxide ring-opening event.

Journal Article↗

PubMed2003

Auditory neuroscience: the salience of looming sounds.

Sounds that move towards us have a greater biological salience than those that move away. Recent studies in human and non-human primates have demonstrated a perceptual and behavioural priority for such looming sounds that is also reflected in an asymmetric pattern of cortical activation.

Animals↗

PubMed2003

Impaired binaural hearing in children produced by a threshold level of middle ear disease.

Otitis media with effusion (OME), a form of middle ear disease, is the most common reason for young children both to visit their family doctor and to have surgery. Almost all children have at least a single episode of OME before their first birthday and annual incidence rates exceed 50% in each of the first five years. For most children, OME occurs infrequently, but about 10-15% of children have OME during more than half of their first six years. Middle ear effusions attenuate and delay sound, causing conductive sound distortion during the crucial years for language acquisition. The many studies of OME effects on language and other indices of development have produced mixed results. However, a consensus is emerging of mild language impairment in the preschool years, with subsequent performance, emotional, and behavioral difficulties. In addition to the peripheral hearing loss produced directly by the disease, binaural and other central auditory deficits can outlive the OME. It has been unclear which children are at risk of central impairment following OME, since the children studied have generally been recruited from otolaryngology clinics. Consequently, a detailed prospective history of the middle ear status of participants has not been available. By studying six-year-old children with a lifetime known history of OME, we show in this study that only those children with a cumulative OME experience of more than about half the time during the first five years consistently have residual impaired binaural hearing.

Audiometry↗