Zhang, Jiping, Kyle T. Nakamoto, and Leonard M. Kitzes. Modulation of level response areas and stimulus selectivity of neurons in cat primary auditory cortex. J Neurophysiol 94: 2263-2274, 2005. First published May 25, 2005 10.1152/jn.01207.2004. Sounds commonly occur in sequences, such as in speech. It is therefore important to understand how the occurrence of one sound affects the response to a subsequent sound. We approached this question by determining how a conditioning stimulus alters the response areas of single neurons in the primary auditory cortex (AI) of barbiturate-anesthetized cats. The response areas consisted of responses to stimuli that varied in level at the two ears and delivered at the characteristic frequency of each cell. A binaural conditioning stimulus was then presented Ն50 ms before each of the stimuli comprising the level response area. An effective preceding stimulus alters the shape and severely reduces the size and response magnitude of the level response area. This ability of the preceding stimulus depends on its proximity in the level domain to the level response area, not on its absolute level or on the size of the response it evokes. Preceding stimuli evoke a nonlinear inhibition across the level response area that results in an increased selectivity of a cortical neuron for its preferred binaural stimuli. The selectivity of AI neurons during the processing of a stream of acoustic stimuli is likely to be restricted to a portion of their level response areas apparent in the tone-alone condition. Thus rather than being static, level response areas are fluid; they can vary greatly in extent, shape and response magnitude. The dynamic modulation of the level response area and level selectivity of AI neurons might be related to several tasks confronting the central auditory system.
I N T R O D U C T I O NAs acoustic stimuli commonly occur in a temporal relation to other acoustic stimuli, it is important to understand how responses of cortical neurons vary during the processing of a stream of acoustic signals. Throughout the auditory neuroaxis, discharge rate as a function of monaural stimulus level (so called rate-level functions) have been shown to be displaced to higher stimulus levels when stimuli are presented either during or after a conditioning stimulus (Boettcher et