Age-Related Alteration in Processing of Temporal Sound Features in the Auditory Midbrain of the CBA Mouse

Abstract

The perception of complex sounds, such as speech and animal vocalizations, requires the central auditory system to analyze rapid, ongoing fluctuations in sound frequency and intensity. A decline in temporal acuity has been identified as one component of age-related hearing loss. The detection of short, silent gaps is thought to reflect an important fundamental dimension of temporal resolution. In this study we compared the neural response elicited by silent gaps imbedded in noise of single neurons in the inferior colliculus (IC) of young and old CBA mice. IC neurons were classified by their temporal discharge patterns. Phasic units, which accounted for the majority of response types encountered, tended to have the shortest minimal gap thresholds (MGTs), regardless of age. We report three age-related changes in neural processing of silent gaps. First, although the shortest MGTs (1-2 msec) were observed in phasic units from both young and old animals, the number of neurons exhibiting the shortest MGTs was much lower in old mice, regardless of the presentation level. Second, in the majority of phasic units, recovery of response to the stimulus after the silent gap was of a lower magnitude and much slower in units from old mice. Finally, the neuronal map representing response latency versus best frequency was found to be altered in the old IC. These results demonstrate a central auditory system correlate for age-related decline in temporal processing at the level of the auditory midbrain.

Age-related changes in GAD levels in the central auditory system of the rat

“…A similar situation exists in another species, in mice: hearing function in the CBA/CaJ strain of mice deteriorates very slowly as in the Long-Evans strain of rats, whereas the C57BL/6J strain is known to undergo rapid deterioration with early deafness (Parham, 1997, Spongr et al, 1997. In spite of these differences in age-related defects of auditory function, which are mostly caused by pathologies in the inner ear, significant age-related alterations of the inhibitory function in the central auditory system were reported in both strains of mice (Walton et al, 1998(Walton et al, , 2002Felix and Portfors, 2007). Therefore, we may tentatively suggest that the age-related decline in GAD expression in the IC and AC demonstrated in our experiments does not depend primarily on peripheral deafferentation but is, at least partially, of central origin.…”

“…For example, single unit recordings illustrate the presence of a less precise processing of complex sounds and extended excitatory areas in the IC (Palombi and Caspari 1996;Walton et al, 1998;Walton et al, 2002;Simon et al, 2004). Age-related alterations in the fine-tuned receptive fields and a relative increase in poorly tuned receptive fields could influence the processing of sounds in the central auditory system (Turner et al, 2005a,b).…”

Inhibitory neurotransmission, plasticity and aging in the mammalian central auditory system

“…Increasingly, recent studies suggest that a selective loss of normal adult inhibitory neurotransmission may subserve this loss of sensory function. This review is focused on aging in inhibitory neurotransmitter systems; however, it is important to understand that age-related changes occur in other neurotransmitter systems, including serotonergic (Tadros et al, 2007a), cholinergic (Caspary et al, 1990) and excitant amino acids (Banay-Schwartz et al, 1989a; Banay-Schwartz et al, 1989b;Tadros et al, 2007b).Accurate temporal processing depends on the ability of inhibitory circuits to sharpen responses to rapidly time-varying signals (Walton et al, 1997;Walton et al, 1998;Krishna and Semple, 2000;Frisina, 2001; Caspary et al, 2002;Liang et al, 2002). Rapidly time-varying signals play an important role in communication and socialization among mammals.…”

Development of large-scale functional networks over the lifespan

“…First, an age-dependent decrease of intracortical inhibition may account for the enhanced long-range connectivity in older age. Animal studies on gamma aminobutyric acid (GABA), which is the most important inhibitory neurotransmitter of the brain, have consistently shown an age-related decrease of GABA effectiveness in the auditory pathways (Caspary et al, 1995(Caspary et al, , 1999Ling et al, 2005;Walton et al, 1998Walton et al, , 2002. Similar findings exist for the visual system which also show a decrease of GABA functioning (Liang et al, 2010;Yang et al, 2008).…”