Feature-Dependent Sensitive Periods in the Development of Complex Sound Representation

Abstract

Simple tonal stimuli can shape spectral tuning of cortical neurons during an early epoch of brain development. The effects of complex sound experience on cortical development remain to be determined. We exposed rat pups to a frequency-modulated (FM) sweep in different time windows during early development, and examined the effects of such sensory experience on sound representations in the primary auditory cortex (AI). We found that early exposure to a FM sound resulted in altered characteristic frequency representations and broadened spectral tuning in AI neurons, whereas later exposure to the same sound only led to greater selectivity for the sweep rate and direction of the experienced FM sound. These results indicate that cortical representations of different acoustic features are shaped by complex sounds in a series of distinct sensitive periods.

Natural Restoration of Critical Period Plasticity in the Juvenile and Adult Primary Auditory Cortex

“…5A). As has been recorded in previous studies (de VillersSidani et al, 2007;Insanally et al, 2009), in striking contrast to rats in the normal early critical period, this exposure produced no measurable alteration of A1 tonotopy compared with agematched control rats [ Fig. 5B, tone-exposed (TE) vs control] (t test, all p Ͼ 0.3).…”

“…As has been shown in many previous studies (Zhang et al, 2001;Polley et al, 2007;Insanally et al, 2009), A1 was relatively predictably topographically (tonotopically) organized in control rats, with isofrequency bands oriented approximately orthogonal to a systematic rostrocaudal frequency representation gradient. A1 tonotopy was distorted in NE rats, to proportionally exaggerate and proportionally reduce the territories representing higher and lower frequencies, respectively (Fig.…”

“…It should be noted that the magnitudes of these sound exposureinduced changes paralleled those resulting from a matched period of exposure in the critical period in infant rats. As in those infants (Zhang et al, 2001;de Villers-Sidani et al, 2007;Insanally et al, 2009), the percentages of A1 area tuned to frequencies that were just below or just above the exposed tone frequency were also reduced (Fig. 6 D, NEϩTE vs control) (ANOVA with post hoc Student-Newman-Keuls test, p Ͻ 0.05 at 9.9 kHz).…”

“…At this age, the rat is approaching sexual maturity, and A1 has matured far beyond the normal closure of the critical period window (a month after the birth) (Zhang et al, 2001;Hsieh et al, 2002;Insanally et al, 2009) for passive sound exposure-driven plasticity. Since tone-specific enlargement in A1 representation resulting from transient exposure to sound stimuli is one basic index of critical period plasticity (Zhang et al, 2001), we directly confirmed the postcritical period status of normal rats at this age by exposing them to pulsed 7 kHz tone pips over a week (Fig.…”

“…In the auditory system, previous studies have documented a well defined, acoustic environment-dependent critical period in the primary auditory cortex (A1) in the rat (Zhang et al, 2001;de VillersSidani et al, 2007;Insanally et al, 2009). Within this developmental epoch, cortical representations of spectral, temporal, intensive, or combined features of sound can be greatly distorted (plausibly specialized for their representations) by passive exposure to sound stimuli.…”