Progressing Toward Hearing Loss

At this point (week 6), I have successfully moved into ISC, have completed a pair of experiments, and just this past week begun another two.

The completed pair consists of 4 birds that all received 1 hour of noise at approximately 110dB.  [This is different than described in my previous post.]  Looking at the data from these 4 birds, two exhibit slight hearing loss and a third is inconclusive.

To come to that conclusion, I use excel to look at the data generated by Arduino VS which analyzes the data of the ABR Waveform.  Arduino VS takes in information of the brain’s electric response to 1400 repeats of specific frequency and decibel combinations.  It averages these repeats together to eliminate the electric noise and present only the waveform in response to the stimuli.  This waveform is unique to each frequency and decibel combination in each individual bird.  A good example is as follows.

ABR Wave (each different color is a different dB of the same frequency)

The peaks labeled 1 and 2 are the most reliable to identify and give a consistent measurement across trials, so the measure of amplitude I use is the vertical distance between peak 1 and 2. The solid black line reaching from the y-axis to the location of the first peak is the latency of that peak.

The data collected from the most recent experiments are shown below.

105 106 Intensity Data

This first graph is a chart of the amplitude of each ABR Wave for each of 4 birds for two specific days. The days shown are the first day of recording after the noise event (hearing loss inducing event) and the third day of recording (about a week) after the noise event. Normally the comparison is made between a day of recording the bird’s ability to hear before the noise event and the first or second recording after; however, in this circumstance the recording prior to the noise event is unusual in all of the birds.

RMSOutside is a qualifier of the data.  The red dots have a more acceptable RMSOutside and thus are of a higher quality of data, so the data was restricted to include a range of acceptable quality in this regard and a few others.

According to the comparison within the same bird between days (column), three of these birds exhibit slight hearing loss.  This judgement is made by comparing the amplitude heights (on the y-axis). Higher values indicate that the bird heard the sound better and had a larger electric response in the brain to that sound.  You can see in this comparison that the amplitudes in first row in the three columns indicated are smaller than the amplitudes in the second row of the same three columns.  This is promising data – informing me that this method of hearing loss induction is much closer to successful (obvious hearing loss) than my previous attempts.

 

105 106 Latency Data

This graph is a second way to assess a bird’s ability to hear.  The latency of the first peak will be longer when the sound is not heard well by the bird and will be shorter when the sound is heard well.  This derives from the brain responding slower or quicker to the noise.

Each bar within the set of bars indicates a day and each set indicates a particular decibel.  The height of the bar is the average latency across various frequencies at the same decibel.  Without hearing loss the expectation is that across decibels the latency will decrease (subsequent groups) and within the same decibel across multiple days the latency would be approximately the same with some variation(group of 4 colors).  However with hearing loss, the expectation is that the latency of the day before hearing loss will be lower than of the day or two after the noise event.  In this graph it appears this is true and the latency of the fourth day of testing (about a week after the noise event inducing hearing loss) returns to a more normal length (it appears even shorter, so perhaps the birds hear better and compensate for a day?).  This particular pattern suggests that hearing was hindered in the middle two days of testing.

Two birds showed this pattern and the other two did not.

Thus two birds exhibited slight hearing loss while a third bird is inconclusive.

Since the progression toward more hearing loss occurs in junction with the increase in dB of the noise event (induce hearing loss), I increased the dB of the noise event in the current experiment to 115dB.  Thus far all of the four birds I am testing appear to have lost some hearing ability.  We shall see if this remains true when I analyze the complete set of data and assess what patterns arise.

Comments

  1. smalapati01 says:

    Great post! Its great to hear that all of the birds have had some hearing loss, and I am looking forward to hear more about the analysis of the complete data set. I have a question, so it would be great if you can answer it. In hearing loss induced by loud noises, what is the process by which neurons degenerate. Please let me know as I will be all ears.

  2. micailya says:

    Hi! Thanks for such a great question. The neurons will initiate axon degeneration due to lack of stimuli and use. The hair cells will be damaged by the noise and thus not communicate with the axons as they once did. A protein called SARM1 will become active in the neuron and start the process of Wallerian degeneration (an active process), which destroys the axon of a neuron.
    The neurons may themselves receive stress and damage from the noise if it is severe enough. SARM1 will be activated by the structural stress and damage inflicted on the axon if it were so injured and initiate degeneration just as with the lack of stimulus.The current intensity of noise I am using to induce hearing loss is not expected to damage the axon of the neuron directly, so the previously stated method is most likely.