Gap detection threshold in the rat before and after auditory cortex ablation
Introduction
The measurement of gap detection threshold (GDT) is an efficient tool for evaluating the time resolution abilities of the auditory system. The estimation of GDT in man has been the subject of many studies, beginning with the paper by Plomp (1964). Numerous experiments have shown that gap detection ability is dependent on the frequency spectrum and intensity of the continuous noise in which the gaps are embedded (Penner, 1977, Giraudi et al., 1980, Tyler et al., 1982, Florentine and Buus, 1984, Shailer and Moore, 1983, Fitzgibbons, 1983, Snell et al., 1994). Minimal GDTs in human were recorded when the noise signal encompassing the gap was presented at 30–40 dB SL and included frequencies above 5–6 kHz. GDT in this case amounted to about 2–3 ms (Plomp, 1964, Fitzgibbons, 1983). Clinical observations have shown that neurological patients with various types of cerebral lesions have difficulties in temporal resolution tasks, such as reduced gap detection abilities (Buchtel and Stewart, 1989, Albert and Bear, 1974, Efron et al., 1985, Phillips and Farmer, 1990).
Neuronal correlates of gap detection have been studied at different levels of the auditory system (for review see Frisina, 2001). The fundamental mechanism of coding sound gaps at the level of the auditory nerve fibres is through a cessation of activity in response to a gap (Relkin and Turner, 1988, Zhang et al., 1990), whereas at the level of cochlear nuclei and the inferior colliculus the mechanism switches to an increase in the spike firing rate at the conclusion of the gap (Boettcher et al., 1990, Kaltenbach et al., 1993, Palombi et al., 1994, Walton et al., 1997, Barsz et al., 1998). Walton et al. (1997) concluded that the gap encoding capabilities of inferior colliculus neurones in the CBA mouse were similar to the behavioural gap functions. Neural correlates of gap detection were studied in the auditory cortex of the cat by Eggermont, 1995, Eggermont, 1999. In these experiments gaps inserted either early (after 5 ms) or late (after 500 ms) in a 1 s duration noise burst were used. The neural detection threshold for the ‘late gap’ was found to be similar to the psychophysical gap threshold (around 5 ms) and was not significantly different from that found in the inferior colliculus (Walton et al., 1997). Significantly larger minimum late-gap durations were found in the anterior auditory field in comparison with the primary and secondary auditory fields.
The measurement of GDT may be used for investigating pathologies of temporal resolution ability and for estimating their severity. For this purpose, studies dealing with the influence of experimentally produced impairments in gap detection in animals may be of importance. The aim of such studies is usually to determine the involvement of individual structures of the auditory system in temporal resolution. Only a few papers on gap detection in animals with a cortical lesion have been published so far (in rat: Ison et al., 1991; in ferret: Kelly et al., 1996). The purpose of this study was to examine the role of the auditory cortex in the ability to detect gaps in noise. GDT was measured in pigmented rats before and after bilateral ablation of the auditory cortex.
Section snippets
Subjects
The ability to detect gaps in a continuously present noise was tested in five adult (8–13 months old) pigmented female rats (strain Long–Evans) with no primary pathology, before and after bilateral lesions of the primary auditory cortex. GDT measurements after a bilateral lesion of the auditory cortex began on the fifth day after surgery and continued for 2 months. In addition, the dependence of GDT on the frequency spectrum and intensity of the carrier noise was studied in three other rats.
Behavioural apparatus and procedures
The
Results
Control experiments revealed that the GDT depends on the spectral characteristics and intensity levels of the continuous noise in which the gaps are embedded. The mean values of GDT measured in eight normal rats when the gaps were embedded in a continuous white noise of 70 dB SPL were significantly smaller (P<0.05, tested with the paired t-test) than when the gaps were embedded in a low-frequency noise of the same intensity; the values were 1.57±0.07 ms and 2.9±0.34 ms, respectively. The
Discussion
The lowest GDTs for rats, measured in our experiments under optimal stimulus conditions (in a broadband noise at an intensity above 40 dB SPL) by an operant conditioning method, fluctuated about 1.6 ms and were slightly smaller than those obtained in previous investigations using a startle amplitude reduction paradigm (Ison, 1982, Ison et al., 1991, Leitner et al., 1993). The examination of Ison (Ison, 1982, Ison et al., 1991) of acoustic startle reflex inhibition by brief gaps in noise showed
Acknowledgements
This work was supported by grants of the Grant Agency of the Czech Republic (309/01/1063) and the Grant Agency of the Ministry of Health (NK/6454-3).
References (44)
- et al.
Gap encoding by inferior collicular neurons is altered by minimal changes in signal envelope
Hear. Res.
(1998) - et al.
Recovery from short term adaptation in single neurons in the cochlear nucleus
Hear. Res.
(1990) - et al.
Auditory agnosia: apperceptive or associative disorder?
Brain Lang.
(1989) - et al.
An ear asymmetry for gap detection following anterior temporal lobectomy
Neuropsychologia
(1985) Subcortical neural coding mechanisms for auditory temporal processing
Hear. Res.
(2001)- et al.
Behavioral hearing range of the chinchilla
Hear. Res.
(1991) - et al.
Audiogram of the hooded Norway rat
Hear. Res.
(1994) The effects of insular and temporal lesions in cats on two types of auditory pattern discrimination
Brain Res.
(1973)- et al.
Hearing in the ferret (Mustela putorius): thresholds for pure tone detection
Hear. Res.
(1986) - et al.
Detection of gaps in noise by budgerigars (Melopsittacus undulatus) and zebra finches (Poephila guttata)
Hear. Res.
(1990)
Paired tone facilitation in dorsal cochlear nucleus neurons: a short-term potentiation model testable in vivo
Hear. Res.
Acquired word deafness, and the temporal grain of sound representation in the primary auditory cortex
Behav. Brain Res.
Auditory frequency and intensity discrimination in pigmented rats
Hear. Res.
Threshold shifts and enhancement of cortical evoked responses after noise exposure in rats
Hear. Res.
Neural correlates of gap detection in auditory nerve fibers of the chinchilla
Hear. Res.
Time to understand: a case study of word deafness with reference to the role of time in auditory comprehension
Brain
Neural correlates of gap detection and auditory fusion in cat auditory cortex
NeuroReport
Neural correlates of gap detection in three auditory cortical fields in the cat
J. Neurophysiol.
The auditory cortex. Review
J. Comp. Physiol.
Temporal gap detection in noise as a function of frequency, bandwidth, and level
J. Acoust. Soc. Am.
Temporal gap detection in sensorineural and simulated hearing impairments
J. Speech Hear. Res.
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