Abstract
Throughout life, sensory systems adapt to the sensory environment to provide optimal responses to relevant tasks. In the case of a developing system, sensory inputs induce changes that are permanent and detectable up to adulthood. Previously, we have shown that rearing rat pups in a complex acoustic environment (spectrally and temporally modulated sound) from postnatal day 14 (P14) to P28 permanently improves the response characteristics of neurons in the inferior colliculus and auditory cortex, influencing tonotopical arrangement, response thresholds and strength, and frequency selectivity, along with stochasticity and the reproducibility of neuronal spiking patterns. In this study, we used a set of behavioral tests based on a recording of the acoustic startle response (ASR) and its prepulse inhibition (PPI), with the aim to extend the evidence of the persistent beneficial effects of the developmental acoustical enrichment. The enriched animals were generally not more sensitive to startling sounds, and also, their PPI of ASR, induced by noise or pure tone pulses, was comparable to the controls. They did, however, exhibit a more pronounced PPI when the prepulse stimulus was represented either by a change in the frequency of a background tone or by a silent gap in background noise. The differences in the PPI of ASR between the enriched and control animals were significant at lower (55 dB SPL), but not at higher (65-75 dB SPL), intensities of background sound. Thus, rearing pups in the acoustically enriched environment led to an improvement of the frequency resolution and gap detection ability under more difficult testing conditions, i.e., with a worsened stimulus clarity. We confirmed, using behavioral tests, that an acoustically enriched environment during the critical period of development influences the frequency and temporal processing in the auditory system, and these changes persist until adulthood.
Highlights
Development of the juvenile sensory systems passes through a critical period (CP), a period of increased sensory receptivity and plasticity, during which a particular experience could have a life-long effect
We described the changes of the responses in the inferior colliculus (IC) [9] and auditory cortical (AC) neurons [19, 20] after the application of an acoustically enriched environment (AEE) during the critical period of development
We have shown that rats reared in a complex acoustic environment exhibited permanently improved response characteristics; in particular, the neurons of the enriched animals had lower excitatory thresholds, sharper frequency selectivity, and lower proportion of nonmonotonic rate-intensity functions [9, 19]
Summary
Development of the juvenile sensory systems passes through a critical period (CP), a period of increased sensory receptivity and plasticity, during which a particular experience could have a life-long effect. Rat pups show an onset of hearing at around P11-P12, with the CP extended to the first month of postnatal life [1, 2] During this period, auditory cortical (AC) neurons demonstrate poor spectral selectivity, weak tonotopic organization, and broad tuning curves, with spectrally broad. Neural Plasticity and temporally extended sideband inhibitory receptive fields in comparison with adult animals, but they appear to be better suited for spectral and temporal integration across a very broad range of acoustic inputs [3]. For these reasons, rat pups are a suitable model for studying the influence of the acoustic environment on the auditory system during its maturation. The exposure to an acoustically enriched environment during the critical developmental period can induce permanent changes in the structure of neurons in the central auditory system, such as changes in the dendritic length and volume and density of spines [14]
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