Biomedical subjects

Anne Hsu

Publications and source records attributed to Anne Hsu.

7 recordsLinked to original sources

PubMed2006

Topical mitomycin-C for obstructing endobronchial granuloma.

An elderly woman with post-tuberculous stricture of the lower trachea and main bronchi underwent laser re-canalization, balloon dilation, and silicone stent insertion in the lower trachea and main bronchi. Subsequently she had recurrent dyspnea develop due to obstructing granulomas, which necessitated four endoscopic procedures in 2 years. The tracheal stent was removed and topical mitomycin-C was applied using saturated pledgets at a dose of 0.5 mg/mL for 2 minutes each over the lower trachea and both orifices of the main bronchi. Follow-up for 24 months showed no recurrence of symptoms. Bronchoscopy and spirometry performed at 2, 6, and 12 months showed resolution of the granulomas.

Administration, Topical↗

PubMed2005

Tuning for spectro-temporal modulations as a mechanism for auditory discrimination of natural sounds.

Vocal communicators discriminate conspecific vocalizations from other sounds and recognize the vocalizations of individuals. To identify neural mechanisms for the discrimination of such natural sounds, we compared the linear spectro-temporal tuning properties of auditory midbrain and forebrain neurons in zebra finches with the statistics of natural sounds, including song. Here, we demonstrate that ensembles of auditory neurons are tuned to auditory features that enhance the acoustic differences between classes of natural sounds, and among the songs of individual birds. Tuning specifically avoids the spectro-temporal modulations that are redundant across natural sounds and therefore provide little information; rather, it overlaps with the temporal modulations that differ most across sounds. By comparing the real tuning and a less selective model of spectro-temporal tuning, we found that the real modulation tuning increases the neural discrimination of different sounds. Additionally, auditory neurons discriminate among zebra finch song segments better than among synthetic sound segments.

Acoustic Stimulation↗

PubMed2004

Modulation power and phase spectrum of natural sounds enhance neural encoding performed by single auditory neurons.

We examined the neural encoding of synthetic and natural sounds by single neurons in the auditory system of male zebra finches by estimating the mutual information in the time-varying mean firing rate of the neuronal response. Using a novel parametric method for estimating mutual information with limited data, we tested the hypothesis that song and song-like synthetic sounds would be preferentially encoded relative to other complex, but non-song-like synthetic sounds. To test this hypothesis, we designed two synthetic stimuli: synthetic songs that matched the power of spectral-temporal modulations but lacked the modulation phase structure of zebra finch song and noise with uniform band-limited spectral-temporal modulations. By defining neural selectivity as relative mutual information, we found that the auditory system of songbirds showed selectivity for song-like sounds. This selectivity increased in a hierarchical manner along ascending processing stages in the auditory system. Midbrain neurons responded with highest information rates and efficiency to synthetic songs and thus were selective for the spectral-temporal modulations of song. Primary forebrain neurons showed increased information to zebra finch song and synthetic song equally over noise stimuli. Secondary forebrain neurons responded with the highest information to zebra finch song relative to other stimuli and thus were selective for its specific modulation phase relationships. We also assessed the relative contribution of three response properties to this selectivity: (1) spiking reliability, (2) rate distribution entropy, and (3) bandwidth. We found that rate distribution and bandwidth but not reliability were responsible for the higher average information rates found for song-like sounds.

Acoustic Stimulation↗

PubMed2004

Methods for the analysis of auditory processing in the brain.

Understanding song perception and singing behavior in birds requires the study of auditory processing of complex sounds throughout the avian brain. We can divide the basics of auditory perception into two general processes: (1) encoding, the process whereby sound is transformed into neural activity and (2) decoding, the process whereby patterns of neural activity take on perceptual meaning and therefore guide behavioral responses to sounds. In birdsong research, most studies have focused on the decoding process: What are the responses of the specialized auditory neurons in the song control system? and What do they mean for the bird? Recently, new techniques addressing both encoding and decoding have been developed for use in songbirds. Here, we first describe some powerful methods for analyzing what acoustical aspects of complex sounds like songs are encoded by auditory processing neurons in songbird brain. These methods include the estimation and analysis of spectro-temporal receptive fields (STRFs) for auditory neurons. Then we discuss the decoding methods that have been used to understand how songbird neurons may discriminate among different songs and other sounds based on mean spike-count rates.

Animals↗

PubMed2004

Quantifying variability in neural responses and its application for the validation of model predictions.

A rate code assumes that a neuron's response is completely characterized by its time-varying mean firing rate. This assumption has successfully described neural responses in many systems. The noise in rate coding neurons can be quantified by the coherence function or the correlation coefficient between the neuron's deterministic time-varying mean rate and noise corrupted single spike trains. Because of the finite data size, the mean rate cannot be known exactly and must be approximated. We introduce novel unbiased estimators for the measures of coherence and correlation which are based on the extrapolation of the signal to noise ratio in the neural response to infinite data size. We then describe the application of these estimates to the validation of the class of stimulus-response models that assume that the mean firing rate captures all the information embedded in the neural response. We explain how these quantifiers can be used to separate response prediction errors that are due to inaccurate model assumptions from errors due to noise inherent in neuronal spike trains.

Action Potentials↗

PubMed2003

The clinical predictors of sleepiness correlated with the multiple sleep latency test in an Asian Singapore population.

STUDY OBJECTIVES: To explore the clinical predictors of sleepiness as objectively determined by the Multiple Sleep Latency Test with the Epworth Sleepiness Scale, age, body mass index, and overnight polysomnographic parameters at a tertiary referral center Sleep Disorders Unit. DESIGN: Retrospective, consecutive case series review. SETTING: A multidisciplinary sleep disorders unit in Singapore General Hospital, a tertiary-care university-affiliated hospital. PATIENTS: 72 consecutive patients evaluated for sleep disorders with overnight polysomnograms and Multiple Sleep Latency Tests between March 2002 and September 2002. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Mean sleep latency on the Multiple Sleep Latency Test was 9.0 +/- 4.4 minutes, and mean Epworth Sleepiness Scale score was 10.8 +/- 5.8. On univariate analysis, mean sleep latency on the Multiple Sleep Latency Test showed a significant negative correlation with the Epworth Sleepiness Scale score, apnea-hypopnea index, body mass index, arousal index, and time spent below 90% oxygen saturation during overnight polysomnography. After performing multiple linear regression, only Epworth Sleepiness Scale score and apnea-hypopnea index remained significantly correlated (P = .039 and P = .008, respectively). An Epworth Sleepiness Scale score of 8 or above predicted a mean sleep latency on the Multiple Sleep Latency Test of less than 10 minutes with a sensitivity of 73.9% and specificity of 50.0%. CONCLUSIONS: The Epworth Sleepiness Scale and apnea-hypopnea index are useful predictors of sleepiness in our Asian Singapore population.

Adult↗

PubMed2002

Mitochondrial destabilisation and caspase-3 activation are involved in the apoptosis of Jurkat cells induced by gaudichaudione A, a cytotoxic xanthone.

Gaudichaudione A, a cytotoxic xanthone obtained from Garcinia gaudichaudii, displayed strong growth inhibitory effects against Jurkat human leukemic cells, parental murine leukemic P388 and P388/DOX-resistant cell lines, and exhibited similar cytotoxicity against P388/DOX as well as P388, but was less toxic toward normal human Chang liver cells. A variety of apoptotic events induced by gaudichaudione A at the mitochondrial and nuclear levels has been characterized. It appears that gaudichaudione A induced a collapse of the mitochondrial transmembrane potential. Caspase-3 was activated and induced internucleosomal DNA fragmentation and externalization of PS residues. The apoptotic features were also observed in ultrastructural studies.

Animals↗