Abstract 545, Date 1:00 pm, Wednesday, February 14, 2007 (24 hours)|
Session W8: Poster
|Acoustic Trauma Induces Long-Term Temporal Correlations in DCN|
|*Benjamin Letham, Wei-Li D. Ma, Shanqing Cai, Eric D. Young|
Changes to the functional properties of the dorsal cochlear nucleus (DCN) that follow acoustic trauma are not well understood. Past studies (e.g. Kaltenbach et al.) have reported an increase in mean spontaneous firing rates following acoustic trauma. However, recent work from our lab in DCN principal cells has found no change in mean spontaneous firing rate. This finding has led us to study temporal patterns in DCN spontaneous activity that may change independent of the mean rate. One pattern of specific interest is long-range dependence (LRD). LRD is an effect of fractal rate fluctuations, where rate fluctuations have weak correlations on the scale of minutes.
Cats were acoustically traumatized by exposure to 10kHz noise at 107dB SPL for four hours. Compound action potentials showed a >60dB threshold shift at and above 10kHz. Ten minutes of spontaneous activity were recorded from isolated single DCN units in these deaf cats as well as a group of normal hearing cats. LRD can be quantified by computing the Fano factor for a range of counting times. The Fano factor has a power-law dependence on counting time, and the exponent of the power-law is called the fractal dimension. This dimension is a measure of the spike count variance and LRD.
The average fractal dimension of the 10kHz-exposed DCN units is significantly higher than that of normal DCN units. Surprisingly, there is no correlation between higher fractal dimension and the degree of threshold shift (or spontaneous activity). The increased fractal dimension implies that neurons in exposed cats have more long-term correlations and higher spike count variance. Increased spike count variance could contribute to tinnitus by providing a fluctuating rate signal that would be interpreted as resulting from a fluctuating sound.
(Supported by NIH grant DC00109 and the Tinnitus Consortium).