Neural Changes in Cat Auditory Cortex After a Transient Pure-Tone Trauma

Abstract

Noreñ a, Arnaud J., Masahiko Tomita, and Jos J. Eggermont. Neural changes in cat auditory cortex after a transient pure-tone trauma. J Neurophysiol 90: 2387-2401, 2003. First published May 28, 2003 10.1152/jn.00139.2003. Here we present the changes in cortical activity occurring within a few hours after a 1-h exposure to a 120-dB SPL pure tone (5 or 6 kHz). The changes in primary auditory cortex of 16 ketamine-anesthetized cats were assessed by recording, with two 8-microelectrode arrays, from the same multiunit clusters before and after the trauma. The exposure resulted in a peripheral threshold increase that stabilized after a few hours to on average 40 dB in the frequency range of 6 -32 kHz, as measured by the auditory brain stem response. The trauma induced a shift in characteristic frequency toward lower frequencies, an emergence of new responses, a broadening of the tuning curve, and an increase in the maximum of driven discharges. In addition, the onset response after the trauma was of shorter duration than before the trauma. The results suggest the involvement of both a decrease and an increase in inhibition. They are discussed in terms of changes in central inhibition and its implications for tonotopic map plasticity.

Effects of Noise-Induced Hearing Loss at Young Age on Voice Onset Time and Gap-in-Noise Representations in Adult Cat Primary Auditory Cortex

“…This is comparable to the change found by Noreñ a et al (2003), within a few hours after the noise trauma, in the CF range one octave above the trauma-tone frequency.…”

“…It was surprising that the noise-induced hearing loss was frequency-independent over a wide range, albeit there was about 10 dB more hearing loss in the 16-to 24-kHz range, as measured by ABR, and up to 20 dB more above 16 kHz as measured by multiunit thresholds in the cortex. This is different from that observed about 5 h after a noise trauma; here, the loss is negligible up to 4 kHz and then rapidly increases to about 40 dB for frequencies above 6 kHz (Noreñ a et al 2003;Tomita et al 2004). At longer times, after the trauma, the loss typically reduces somewhat but does not spread to frequencies below 4 kHz (Seki and Eggermont 2002;Noreñ a and Eggermont 2005).…”

“…A model for the effect of the duration of the leading noise burst on the minimum detectable early gap (Eggermont 2000) predicts that increased postactivation suppression, as found within the first few hours after a noise trauma (Noreñ a et al 2003), would shift the FR max -gap duration curve to larger gap durations without affecting the shape thereof. Thus, one needs a postactivation suppression in the noise-exposed animals that becomes progressively stronger with time after the response to the leading noise burst to explain the observed changes.…”

“…Previously, we have shown that in the first few hours after noise exposure in adult cats, the VOT threshold for a /ba/-/pa/ continuum shifted to higher values and that the peak firing rate-VOT function became shallower, suggesting that the discrimination boundary between /ba/ and /pa/ became less well defined (Tomita et al 2004). This study also showed a comparable change in the threshold for a double-onset response to a noise burst with a gap inserted 5 ms after the onset: a socalled Bearly gap.Î t is likely that immediately after a noise trauma, the neurons in the auditory cortex are subject to a different combination of excitation and inhibition strengths than several months later when a new balance has emerged (Noreñ a et al 2003;Noreña and Eggermont 2005). We also have to consider that behaviorally measured hearing loss induced by noise exposure in young rats was larger than that in the adults, and there was also relatively more hearing loss for the lower frequencies in young animals compared to adults (Rybalko and Syka 2001).…”

Enduring effects of early structured noise exposure on temporal modulation in the primary auditory cortex

“…Earlier studies demonstrated that cochlear injury can be generated by high intensity sound exposure (100-120 dB SPL). This damage is usually accompanied by elevated sound intensity thresholds (18)(19)(20)(21). It was recently shown that such noise-induced peripheral hearing loss also affects cortical tMTFs to amplitudemodulated noises in cats (22).…”