Biomedical subjects

D D Gehr

Publications and source records attributed to D D Gehr.

4 recordsLinked to original sources

PubMed2003

[Automated hearing threshold estimation in newborns using extrapolated DPOAE input/output functions].

BACKGROUND AND AIM: A new method for automatically assessing hearing loss by means of extrapolated DPOAE I/O-functions was applied for the first time in newborns. METHODS: DPOAE I/O-functions were recorded in 118 ears of 93 newborns (mean age 3 days) at 12 frequencies between 1 and 8 kHz. L(2) was varied between 20 and 65 dB SPL with L(1)=0.4L(2)+39 and f(2)/f(1)=1.2. Auditory thresholds were constructed using the estimated DPOAE threshold level from extrapolated DPOAE I/O-functions. Follow-up measurements were conducted in 15 ears 4 weeks later. RESULTS: The first measurement revealed a high-frequency hearing loss. The second measurement showed normal hearing function. This fact and the decrease of DPOAE level in the frequency range of the hearing loss, while keeping the compressive shape of the DPOAE I/O-functions, indicate that transitory sound conduction disturbance may be due to amniotic fluid. CONCLUSIONS: The method fulfils the essential criteria for screening newborn hearing. It is fast and easy to handle, and measurement and data analysis are performed automatically. Preliminary results suggest that the new method is able to differentiate between transitory middle-ear dysfunction and persisting cochlear disorders. Due to its better diagnostic capabilities in comparison to TEOAE, DPOAE, and FAEP, this method may provide a new instrument with which to make a fast evaluation of hearing function in children.

Acoustic Stimulation↗

PubMed2000

Functional changes in field L complex during song development of juvenile male zebra finches.

The field L complex is the highest station of the ascending auditory pathway and is thought to be the input stage of auditory information into the song system in birds. Multi-unit recordings were performed in awake, socially reared zebra finches, 30 and 60 days of age. The responses of the field L complex to synthetic and natural stimuli during important periods of song learning were investigated. According to neural responses in field L, three different functional areas could be distinguished, NA-L(30), NA2b(30) and NA2c(30,) in 30 days old birds. In 60 days old birds five different functional areas, NA-L(60), NA2a(60), NA2b(60), NA2c(60) and NA3(60), were recognised. Especially, NA-L increases its functional volume between the developmental stages. The different areas showed already mature neuronal response behaviours. No preference for a certain song type could be found at all ages. The incomplete functional organisation of the field L complex in young birds (30 days) is a possible reason for the nonselectivity in the song system at this age.

Age Factors↗

PubMed2000

Neuronal responses in cat primary auditory cortex to natural and altered species-specific calls.

We investigated how natural and morphed cat vocalizations are represented in primary auditory cortex (AI). About 40% of the neurons showed time-locked responses to major peaks in the vocalization envelope, 60% only responded at the onset. Simultaneously recorded multi-unit (MU) activity of these peak-tracking neurons on separate electrodes was significantly more synchronous during stimulation than under silence. Thus, the representation of the vocalizations is likely synchronously distributed across the cortex. The sum of the responses to the low and high frequency part of the meow, with the boundary at 2.5 kHz, was larger than the neuronal response to the natural meow itself, suggesting that strong lateral inhibition is shaping the response to the natural meow. In this sense, the neurons are combination-sensitive. The frequency-tuning properties and the response to amplitude-modulated tones of the MU recordings can explain the responses to natural, and temporally and spectrally altered vocalizations. Analysis of the mutual information in the firing rate suggests that the activity of at least 95 recording sites in AI would be needed to reliably distinguish between the nine different vocalizations. This suggests that a distributed representation based on temporal stimulus aspects may be more efficient than one based on firing rate.

Acoustic Stimulation↗

PubMed1999

Functional organisation of the field-L-complex of adult male zebra finches.

Functional maps of auditory response areas were established from multiunit recordings in the caudal telencephalon of male zebra finches. The response criterion was a difference of activity from the spontaneous discharge level. Pure tones and conspecific song were used as stimuli. The auditory part of the caudal telencephalon in zebra finches can be subdivided into six functionally separated centres. The definition of separate areas is based on the existence of tonotopic gradients in each single area and on differences in neural response behaviour between areas. The anatomical area L2a is functionally subdivided into two tonotopic centres. Other areas can be identified by anatomy and function. The borders vary slightly depending on the description method.

Acoustic Stimulation↗