Submitted on May 5, 2006
Accepted on August 19, 2006
Responses of Neurons in the Rat’s Ventral Nucleus of the Lateral Lemniscus to Amplitude Modulated Tones
Huiming Zhang1 and Jack B. Kelly1*
1 Psychology, Carleton University, Ottawa, Canada
* To whom correspondence should be addressed. E-mail: jkelly{at}ccs.carleton.ca.
Recordings were made from single neurons in the rat’s ventral nucleus of the lateral lemniscus (VNLL) to determine responses to amplitude modulated (AM) tones. The neurons were first characterized on the basis of their response to tone bursts presented to the contralateral ear and a distinction was made between those with transient onset responses and those with sustained responses. Sinusoidal AM tones were then presented to the contralateral ear with a carrier that matched the neuron’s characteristic frequency (CF). Modulation transfer functions were generated on the basis of firing rate (MTFFR) and vector strength (MTFVS). Ninety-two percent of onset neurons had band-pass MTFFR’s with best modulation frequencies distributed from 10 to 300 Hz. Fifty-four percent of sustained neurons had band-pass MTFFR’s with best modulation frequencies from 10-500 Hz; other neurons had band-suppressed, all-pass, low-pass or high-pass functions. Most neurons showed either band-pass or low-pass MTFVS. Responses were well synchronized to the modulation cycle with maximum vector strengths ranging from 0.37 to 0.98 for sustained neurons, and 0.78 to 0.99 for onset neurons. The upper frequency limit for response synchrony was higher than reported for IC, but lower than seen in more peripheral structures. Results suggest that VNLL neurons, especially ones with onset responses to tone bursts, are sensitive to temporal features of sounds and narrowly tuned to different modulation rates. However, there was no evidence of a topographic relation between dorsoventral position along the length of VNLL and best modulation frequency as determined by either firing rate or vector strength.
