Age-related Changes in Auditory Cortex Without Detectable Peripheral Alterations: A Multi-level Study in Sprague–Dawley Rats

Florian Occelli (1) , Florian Hasselmann (2) , Julien Bourien (2) , Michel Eybalin (2) , Jean-Luc Puel (2) , Nathalie Desvignes (1) , Bernadette Wiszniowski (1) , Jean-Marc Edeline (1) , Boris Gourévitch (1)

1 NeuroPSI - Institut des Neurosciences Paris-Saclay
2 INM - Institut des Neurosciences de Montpellier

Aging is often considered to affect both the peripheral (i.e. the cochlea) and central (brainstem and thalamus-cortex) auditory systems. We investigated the effects of aging on the cochlea, brainstem and cortex of female Sprague-Dawley rats. The auditory nerve threshold remained stable between the ages of nine and 21 months, as did distortion product otoa-coustic emissions and the number of ribbon synapses between inner hair cells and nerve fibers. The first clear signs of aging appeared in the brainstem, in which response amplitude decreased, with thresholds remaining stable until the age of 15 months, and increasing slightly thereafter. The responses of primary auditory cortex neurons revealed specific effects of aging: at 21 months, receptive fields were spectrally narrower and the temporal reliability of responses to communication sounds was lower. However, aging had a null or even positive effect on neuronal responses in the presence of background noise, responses to amplitude-modulated sounds, and responses in gap-detection protocols. Overall, inter-animal variability remained high relative to the variability across groups of different ages, for all parameters tested. Beha-vioral performance for the modulation depth of amplitude modulation noise was worse in 21-month old animals than in other animals. Age-related alterations of cortical and behavioral responses were thus observed in animals displaying no signs of aging at the peripheral level. These results suggest that intrinsic, central aging effects can affect the perception of acoustic stimuli independently of the effects of aging on peripheral receptors.

Mots clés: synaptic ribbons; multi-unit recordings; compound action potential; central auditory system; behavioral task

Domaines: Sciences du Vivant [q-bio]; Neurosciences [q-bio.NC]; Neurobiologie

Florian Occelli, Florian Hasselmann, Julien Bourien, Michel Eybalin, Jean-Luc Puel, et al.. Age-related Changes in Auditory Cortex Without Detectable Peripheral Alterations: A Multi-level Study in Sprague–Dawley Rats. Neuroscience, 2019, 404, pp.184-204. ⟨10.1016/j.neuroscience.2019.02.002⟩. ⟨hal-02111931⟩