title: Dynamic coupling of excitatory and inhibitory responses in the medial nucleus of the trapezoid body.
abstract: The neuronal representation of acoustic amplitude modulations is an important prerequisite for understanding the processing of natural sounds. We investigated this representation in the medial nucleus of the trapezoid body (MNTB) of the Mongolian gerbil using sinusoidal amplitude modulations (SAM). Depending on the SAM's carrier frequency (f(C)) MNTB cells either increase or decrease their discharge rates, indicating underlying excitatory and inhibitory/suppressive mechanisms. As natural sounds typically are composed of multiple spectral components we investigated how stimuli containing two spectral components are represented in the MNTB, especially when they have opposing effects on the discharge rate. Three conditions were compared: SAM stimuli (1) with rate-increasing f(C), (2) with rate-increasing f(C) and an additional unmodulated rate-decreasing pure tone, and (3) with rate-decreasing f(C) and an unmodulated, rate-increasing pure tone. We found that responses under all three conditions showed comparable strength of phase-locking. Adding a rate-decreasing tone to a rate-increasing SAM increased phase-locking for modulation frequencies (f(AM)) of < or = 600 Hz. A comparison of two possible coding strategies--phase-locking vs. envelope reproduction--indicates that both strategies are realized to different degrees depending on the f(AM). We measured latencies for following modulations in rate-increasing and rate-decreasing SAMs using a modified reverse correlation approach. Although latencies varied between 2.5 and 5 ms between cells, a decrease in rate consistently followed an increase in rate with a delay of about 0.2 ms in each cell. These results suggest a temporally precise representation of rate-increasing and rate-decreasing stimuli at the level of the MNTB during dynamic stimulation.
authors.affiliation: Institute of Biology II, University of Leipzig, Talstr. 33, 04103 Leipzig, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Tolnai
authors.forename: Bernhard
authors.initials: B
authors.lastname: Englitz
authors.forename: Cornelia
authors.initials: C
authors.lastname: Kopp-Scheinpflug
authors.forename: Susanne
authors.initials: S
authors.lastname: Dehmel
authors.forename: Jürgen
authors.initials: J
authors.lastname: Jost
authors.forename: Rudolf
authors.initials: R
authors.lastname: Rübsamen
mesh_terms: D000161:Acoustic Stimulation; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001306:Auditory Pathways / Q000166:cytology / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005849:Gerbillinae; D053444:Inhibitory Postsynaptic Potentials / Q000502:physiology; D008959:Models, Neurological; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009847:Olivary Nucleus / Q000166:cytology / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology