Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0029713 (immaturity)
 4,335 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The absolute auditory sensitivity of the human newborn infant was investigated using auditory brainstem response thresholds (ABR). ABRs were elicited with clicks and tone-bursts of 0.5, 1.5, 4.0 and 8.0 kHz, embedded in notched noise, in healthy, full-term human neonates and young adults with known, normal-hearing sensitivity. Stimuli were calibrated using a probe microphone positioned near the tympanic membrane in the ear canal of each subject to control for differences in resonance characteristics of infant and adult ear canals. ABR thresholds were also characterized relative to group psychophysical thresholds (nHL) and relative to individual psychophysical threshold or sensation level (SL) for the adult subjects. Infant ABR thresholds measured in p.e. SPL for all stimuli are elevated by to 3-25 dB relative to adult thresholds. Threshold elevation is greatest for the high-frequency stimuli. Result are consistent with neural immaturity for high-frequency stimuli in the auditory system of human neonates.
 ...
PMID:Auditory threshold sensitivity of the human neonate as measured by the auditory brainstem response. 911 64

The growth of distortion product otoacoustic emission (DPOAE) suppression follows a systematic, frequency-dependent pattern. The pattern is consistent with direct measures of basilar-membrane response growth, psychoacoustic measures of masking growth, and measures of neural rate growth. This pattern has its basis in the recognized nonlinear properties of basilar-membrane motion and, as such, the DPOAE suppression growth paradigm can be applied to human neonates to study the maturation of cochlear nonlinearity. The objective of this experiment was to investigate the maturation of human cochlear nonlinearity and define the time course for this maturational process. Normal-hearing adults, children, term-born neonates, and premature neonates, plus a small number of children with sensorineural hearing loss, were included in this experiment. DPOAE suppression growth was measured at two f2 frequencies (1500 and 6000 Hz) and three primary tone levels (55-45, 65-55, and 75-65 dB SPL). Slope of DPOAE suppression growth, as well as an asymmetry ratio (to compare slope for suppressor tones below and above f2 frequency), were generated. Suppression threshold was also measured in all subjects. Findings indicate that both term-born neonates and premature neonates who have attained term-like age, show non-adult-like DPOAE suppression growth for low-frequency suppressor tones. These age effects are most evident at f2 = 6000 Hz. In neonates, suppression growth is shallower and suppression thresholds are elevated for suppressor tones lower in frequency than f2. Additionally, the asymmetry ratio is smaller in neonates, indicating that the typical frequency-dependent pattern of suppression growth is not present. These findings suggest that an immaturity of cochlear nonlinearity persists into the first months of postnatal life. DPOAE suppression growth examined for a small group of hearing-impaired children also showed abnormalities.
 ...
PMID:Maturation of cochlear nonlinearity as measured by distortion product otoacoustic emission suppression growth in humans. 1294 74

The complete timeline for maturation of human cochlear function has not been defined. Distortion product otoacoustic emission (DPOAE)-based measures of cochlear function show non-adult-like responses from premature and term-born neonates at high f2 frequencies; however, older infants were not included in these studies. In the present experiment, previously collected DPOAE ipsilateral suppression data from premature neonates were combined with new data collected from adults, term-born neonates, and 3-month-old infants to further examine the time course for maturation of cochlear function. DPOAE suppression tuning curves (STC) and suppression growth patterns were measured in the three age groups at f2 = 6000 Hz, L1 = 65, L2 = 55 dB SPL, with an f2/f1 of 1.2. Results indicate that term-born neonates and 3-month-old infants have non-adult-like STC width, slope on the low-frequency flank, and tip features. However, the two infant groups are not significantly different from one another. Suppression growth patterns for low-frequency suppressor tones show a clear developmental progression. In general, the younger the infant, the more shallow and compressive the suppression growth for the lowest suppressor frequencies. These findings suggest a high-frequency postnatal immaturity in cochlear function as measured by DPOAE suppression. Results may have been influenced by noncochlear factors, such as middle-ear immaturity. These factors are reviewed and considered.
 ...
PMID:Distortion product otoacoustic emission (2f1-f2) suppression in 3-month-old infants: evidence for postnatal maturation of human cochlear function? 1565 8