A NOVEL MECHANISM FOR FREQUENCY DISCRIMINATION IN THE AUDITORY MIDBRAIN
Document Type
Presentation
Start Date
22-10-2010 3:00 PM
End Date
22-10-2010 4:30 PM
Description
Several speech sounds are characterized by a change in frequency, either continuous frequency modulation (FM) or rapid transients. We discovered that adaptation, the reduction in response to an ongoing stimulus, may process such frequency changes by causing a release from adaptation when novel frequencies are presented. We term this, Frequency Specific Adaptation (FSA) and test it at the level of the Inferior Colliculus (IC), where neural convergence results in auditory sensitivity to broad frequency bands. Approximately 25% of auditory units in the torus semicircularis of frogs (IC homologue) exhibit rapid adaptation (phasic) to tones. If a cell exhibits FSA, a change in tone frequencywill illicit release from that adaptation. Using free field broadcasts and extracellular isolated recordings of these units we first characterize the extent to which phasic units exhibit FSA in the IC. This was tested using a 200 ms stimulus consisting of two 100 ms tones: F1, at the characteristic frequency (CF) and F2 varied across the cells sensitivity band. Following adaptation to F1, a neuron was classified as having FSA if F2 elicited a response at least ( 17 /20) during presentation and is not sensitive to amplitude change. We then tested the hypothesis that FSA units are better at detecting novel frequencies produced by the spectral splatter of gaps or the ongoing frequency change in an FM stimulus. For transients, this was tested using either pure tones or noise with a centered gap of varying duration. FSA cells detected shorter gaps better than non-FSA cells, confirming their ability to detect the novel frequencies in spectral splatter. This ability was also confirmed using FM stimuli, as FSA cells showed an increase in the number of action potentials for FM vs. pure tone stimuli. Our results reveal that about 30% of phasic neurons in IC exhibit FSA, a novel mechanism for frequency discrimination that could be employed during the processing of spectrally complicated communication sounds.
Recommended Citation
Ponnath, Abhilash and Farris, H. E., "A NOVEL MECHANISM FOR FREQUENCY DISCRIMINATION IN THE AUDITORY MIDBRAIN" (2010). Dr. Joseph M. Moerschbaecher, III Graduate Research Day. 16.
https://digitalscholar.lsuhsc.edu/grad_rs/2010/poster2/16
A NOVEL MECHANISM FOR FREQUENCY DISCRIMINATION IN THE AUDITORY MIDBRAIN
Several speech sounds are characterized by a change in frequency, either continuous frequency modulation (FM) or rapid transients. We discovered that adaptation, the reduction in response to an ongoing stimulus, may process such frequency changes by causing a release from adaptation when novel frequencies are presented. We term this, Frequency Specific Adaptation (FSA) and test it at the level of the Inferior Colliculus (IC), where neural convergence results in auditory sensitivity to broad frequency bands. Approximately 25% of auditory units in the torus semicircularis of frogs (IC homologue) exhibit rapid adaptation (phasic) to tones. If a cell exhibits FSA, a change in tone frequencywill illicit release from that adaptation. Using free field broadcasts and extracellular isolated recordings of these units we first characterize the extent to which phasic units exhibit FSA in the IC. This was tested using a 200 ms stimulus consisting of two 100 ms tones: F1, at the characteristic frequency (CF) and F2 varied across the cells sensitivity band. Following adaptation to F1, a neuron was classified as having FSA if F2 elicited a response at least ( 17 /20) during presentation and is not sensitive to amplitude change. We then tested the hypothesis that FSA units are better at detecting novel frequencies produced by the spectral splatter of gaps or the ongoing frequency change in an FM stimulus. For transients, this was tested using either pure tones or noise with a centered gap of varying duration. FSA cells detected shorter gaps better than non-FSA cells, confirming their ability to detect the novel frequencies in spectral splatter. This ability was also confirmed using FM stimuli, as FSA cells showed an increase in the number of action potentials for FM vs. pure tone stimuli. Our results reveal that about 30% of phasic neurons in IC exhibit FSA, a novel mechanism for frequency discrimination that could be employed during the processing of spectrally complicated communication sounds.
Comments
See abstract book page 60