The Effect of Conductive Hearing Loss on Auditory Skill LearningKevin Dell’Aquila, Antje Ihlefeld, Dan Sanes

Center for Neural Science, New York University,4 Washington Place, New York NY 10003 USA

Introduction One of the most significant consequences for the hearing impaired is the delay in auditory skill acquisition, which may lead to deficits in speech and language acquisition. In this study, we examined the impact of developmental hearing loss on auditory learning, using the Mongolian gerbil, Meriones unguiculatus. The hearing loss did not injure the cochlea, allowing us to attribute perceptual deficits to a CNS locus. The rate at which the gerbils demonstrated auditory skill acquisition was analyzed using signal detection theory. Preliminary results suggest that hearing loss gerbils learned an auditory task at a reduced rate in comparison to gerbils reared with normal hearing.

Materials and Methods

Signal Detection in a Noise Background

Adult gerbils reared with normal hearing (n=5) or reared with bilateral conductive hearing loss (n=6) were trained and tested on a tone detection task. Each animal was tested in an acoustically transparent testing cage (right) that was housed inside a sound attenuation booth. Gerbils were first conditioned to initiate a trial with a nose-poke. They were then trained to obtain a water reward when a tone was presented (Go trials) or withhold a response when no tone was presented (Nogo trial). By varying sound level on Go trials (5 dB steps), psychometric curves for tone detection were derived. Threshold for each session was assigned as a d’=1.

Signal Detection in Quiet

Conclusions

(Left) The first step of the experiment was to condition the gerbils to learn GO versus NOGO at fixed stimuli intensity. On Go trials, the stimulus level was 85 dB SPL for CHL and 65 dB SPL for controls,. Correct responses (hit rate) were obtained for all animals. On Nogo trials, no stimulus was delivered, and the incorrect response rate (false alarm rate, FA) was recorded. Gerbils displayed a reduction in false alarm rate while maintaining a high hit rate.(Right) Number of session required to reach criterion performance (Hit rate > 80% and FA < 20%) was greater for CHL animals, as compared to controls.

Example of performance for a control

This graph displays the threshold TMR on the y-axis (as described in the panel above) plotted as a function of training session number on the x-axis. A range of TMR were delivered in each testing session (5 dB intervals), and we typically presented only one sub-threshold TMR. TMR thresholds were expected to become smaller as task learning occurred. Here, the rate of TMR threshold decrease serves as a proxy for the rate of learning. In this graph, it appears that TMR thresholds for CHL animals did not change during the course of testing (i.e., no learning). Although preliminary, the control animals did display a modest decrease in TMR thresholds (i.e., learning).

The data presented provide preliminary evidence that CHL gerbils do not learn an auditory task at the same rate as controls.

CHL animals required a greater number of sessions to reach criterion performance on a simple tone detection task in quiet.

CHL animals did not display an improvement in TMR threshold over training sessions.

These data suggest that early hearing loss could impair some cognitive skills.

Hit

FA

What is Target to Masker Ratio (TMR)?

What is a masker?

Target to Masker Ratio denotes the difference between the intensity of a target tone relative to the intensity of a masker. Sound intensity is obtained by measuring the pure tone thresholds in decibels (dB) relative to an arbitrary standard (0.0002 dyne/cm2). For humans, 0 dB SPL corresponds to the approximate detection threshold for a 1 kHz tone. In this study, tone thresholds were obtained in the presence of a 60 dB SPL masker (CHL) and 20 dB SPL masker (control). Therefore, if the tone threshold was 20 dB SPL for a control animal, then the TMR would be 0 (i.e., [20 dB SPL tone] - [20 dB SPL masker]).

A masker is any auditory stimulus that makes it more difficult to hear a target sound. In the laboratory, maskers are used to assess the ability of the listener to extract a target sound from competing sounds. In this experiment, the masker was an unmodulated noise band ranging from 500 Hz too 2000 Hz.

What does threshold TMR mean?Threshold TMR is the lowest db SPL relative to the masker that a gerbil consistently responded to at a d’=1. In this example, the threshold for a CHL gerbil during one session was TMR=10.

Rate of Learning in Background Noise

CHLCtl

Mean Sessions to Criterion

d’

TMR

Session Number

The Effect of Conductive Hearing Loss on Auditory Skill LearningKevin Dell’Aquila, Antje Ihlefeld, Dan Sanes

Center for Neural Science, New York University,4 Washington Place, New York NY 10003 USA

Introduction One of the most significant consequences for the hearing impaired is the delay in auditory skill acquisition, which may lead to deficits in speech and language acquisition. In this study, we examined the impact of developmental hearing loss on auditory learning, using the Mongolian gerbil, Meriones unguiculatus. The hearing loss did not injure the cochlea, allowing us to attribute perceptual deficits to a CNS locus. The rate at which the gerbils demonstrated auditory skill acquisition was analyzed using signal detection theory. Preliminary results suggest that hearing loss gerbils learned an auditory task at a reduced rate in comparison to gerbils reared with normal hearing.

Materials and Methods

Signal Detection in a Noise Background

Adult gerbils reared with normal hearing (n=5) or reared with bilateral conductive hearing loss (n=6) were trained and tested on a tone detection task. Each animal was tested in an acoustically transparent testing cage (right) that was housed inside a sound attenuation booth. Gerbils were first conditioned to initiate a trial with a nose-poke. They were then trained to obtain a water reward when a tone was presented (Go trials) or withhold a response when no tone was presented (Nogo trial). By varying sound level on Go trials (5 dB steps), psychometric curves for tone detection were derived. Threshold for each session was assigned as a d’=1.

Rate of Learning in Background Noise

Signal Detection in Quiet

Conclusions(Left) The first step of the experiment was to condition the gerbils to learn GO versus NOGO at fixed stimuli intensity. On Go trials, a stimulus of 85 dB SPL was delivered, and the correct responses (hit rate) were obtained. On Nogo trials, no stimulus was delivered, and the incorrect responses (false alarm rate, FA) was recorded. For this stage of training, animals displayed a reduction in false alarm rate while maintaining a high hit rate.

(Right) Number of session required to reach criterion performance (FA < 20%).

Performance of gerbil with normal hearing

Figure 5 (Left)- Psychometric functions for CHL gerbils interpolated against d’=1 for visualization of perceptual thresholdsFigure 6 (Right)- Psychometric functions for NH gerbils interpolated aginst d’=1 for visualization of perceptual thresholds

Discriminability index (d’) is a measurement of behavioral performance and can be used to determine perceptual thresholds by defining d’ greater or equal to one as level of performance as a strong indicator for perceiving the tone. The psychometric functions of conductive hearing loss gerbils were expect to shift to the left a reduced rate relative to normal hearing gerbils (corresponding to reduced rate of reaching true thresholds and optimal behavior). From the visuals above, two key observations are a greater relative density of sessions with TMRs below d’=1 for CHLs, and also less spacing between subsequent trials for CHLs. This suggests both raised perceptual threshold and reduced learning rates for CHLs.

There is evidence to suggest CHL gerbils not only have higher perceptual thresholds for tone intensity, but also an impaired ability to learn auditory skills. Because the bilateral incus removal does not damage the ear, the deficient learning ability can be attributed to a CNS locus, the auditory cortex. With gerbils as model for the mammalian brain, impaired auditory learning for the CHL implicates language comprehension impairments for humans born with hearing loss is attributable to altered neural mechanisms in auditory cortex (A1).

Hit

FA

What is TMR?

What is a masker?

TMR stands for Target to Masker Ratio. It is an expression of intensity of pure tone stimuli relative to the masker background. In a sound attenuated booth, perceptual thresholds are understood in db SPL rather than just db. A TMR of 5 corresponds to a pure tone stimulus 5 db above intensity of background masker.

A masker is any sound that masks the target stimulus. Maskers are used to analyze the ability of the listener to extract a target stimulus from different qualities of background noise. The spectral features of the masker can be manipulated to determine the ability to extract

CHL d’ across session for TMR=15

CHL d’ against TMR per session

See Word document for Rest!

Normal hearing d’ across session for TMR=15

Normal hearing d’ against TMR per session

Normal hearing operant conditioning

Role of Hydrogenase in Metabolic pathway of Hydrogenosome

Figure 7- Metabolic pathways in the hydrogenosome (left). Hydrogenase (Hy) reduce 2H+ from electron transport chain into molecular hydrogen by interaction with oxidase and ferredoxin enzymes. (Carlton, et al., 2007)

Hydrogenase transfection

Potential for modifying hydrogenase activity?

Hydrogenase Activity in the Hydrogenosome of Trichomonas vaginalisKevin Dell’Aquila, Andrew Gorman and Jane M. Carlton

Center for Genomics and Systems Biology, Department of Biology, New York University,12 Waverly Place, New York NY 10003 USA

Introduction Trichomonas Vaginalis is a facultative anaerobic microorganism with a relatively unique organelle, the hydrogenosome. This organelle is a reduced mitochondrion, which means it doesn’t have a lipid bilayer and more importantly, it produces molecular hydrogen gas, H2, as waste. This rare function is the focus of the research. Thanks to the fact that the T. Vaginalis is fully sequenced, nine genes were found to putatively code for the enzymes responsible for hydrogen production, hydrogenases. The sequence and putative activity of three of the genes in various articles were first validated by PCR and RT-PCR. The next steps of the research is to potentially manipulate the activity of these hydrogenase genes in order to assess whether the activity of the gene can be made more efficient, effectively producing more units of molecular hydrogen output per unit of metabolic input.

What are the hydrogenases?Figure 3- The four hypothetical hydrogenase genes are represented (left) as I through IV. The three that were chosen were II, III, and IV. The names of these genes, respectively are, TVAG_377820, TVAG_ 160930,

and TVAG_4836890. Each of

these genes have four sets of function domains and are unusually diverse buth all are ion-only and have a conserved H cluster. (Carlton, et al., 2007)

Phenotypic assay Conclusion and ongoing work

Figure 4 (left)- Colony PCR of three different colonies using same primers for TVAG_377820 clone. Lane 4 is probably from a microsatellite E.Coli with no plasmid. in order using different primers for the first two genes. Figure 5 (right)- Plasmid analysis by restriction digestion.

What is Trichomonas vaginalis?Trichomonas Vaginalis is a flagellated protist that causes trichomoniasis and is an extracellular parasite which resides in the urogenital tract of both sexes. The T. Vaginalis is useful for genetic analysis because of its fully sequenced genome, generated by whole genome shotgun methodology (Carlton, et al., 2007).

A potential outcome of the research is modification ofhydrogenase activity. If the hydrogenase enzyme’s activitywas made more efficient, more units of hydrogen outputcould be produced per unit of metabolic input. One possiblemethod for accomplishing this is analyzing the effect differentiron concentrations have on gene activity {Tsai, 2001). Another way would be to silence one gene, to see its relative contribution,and find the most productive hydrogenase, and transfect that gene into the less productive loci.

Hydrogenase genes are transcribed under in vitro culturing conditionsFigure 6- RT-PCR of TVAG_1608930, TVAG_4836890, TVAG_160930 in order. Two different forward primers were used for the first two lanes with the same reverse, two different forward and reverse primers for the next two lanes, and only one forward and reverse for the last. Usingdifferent primers allows for selection of the most optimal primer construction.

References: Carlton et al Science 2007;315, 207-12; Malik et al PLoS One 2007;3, e2879; Yu, L. and Wolin, J. Journal of Bacteriology 1968;98, 51-5; Tsai, Chu-Dang et al Journal of Biological Chemistry 2001;277, 5153-62

Acknowledgements: Supported by the Dean Undergraduate Research Fund. We thank Jeff Mertz for his contributions to the research up until January 2013.

Figure 8 and 9-Reduced methyl viologen can beused in reaction with isolated hydrogenases asthe electron donors for reduction.The absorbance peak (left) can also help determine relativeconcentrations and extinction rate (right) of reducedmethyl viologen per unit time.

Figure 1 and 2- Electron microscopyof T. Vaginalis on vaginal epithelial cell(left) as seen on the January 2007Science Magazine cover. Asexual lifecycle (right) shows no distinct sexual stages. (Malik, et. al., 2008)

Figure 7a- Every T. Vaginalis hydrogenase has a [Fe/S] cluster which has some role in reduction.Iron may also play a role as a gene promoter, andupregulate hydrogenase transcription.

(Yu, L. 2006)