Regional variations of noise-induced changes in operating range in cat AI

Regional differences in spectral integration of neurons in cat primary auditory cortex (AI) suggest that regions differ in effects of background noise on operating characteristics of neurons. Therefore, tone-response threshold, best level (peak-rate intensity), dynamic range, and sharpness of tuning in quiet and in continuous broadband noise were mapped for single neurons along the isofrequency domain of AI. Neurons did not show an excitatory response to the noise. Noise invariably increased the tone-response threshold and best levels. Consequently, the dynamic ranges and receptive fields shifted to higher intensity levels without changes of average sharpness of tuning. These shifts were linearly related to noise level and showed little inter-neuronal variability for neurons in the central, mostly sharply tuned part of AI. In more dorsal and ventral parts of AI, neurons were more variable in tone-response threshold, dynamic range and best level, and no systematic relationship between increase in noise level, threshold increase and best-level increase was observed. We conclude that linear shifts in the operating range of neurons in central AI in the presence of continuous noise backgrounds do not affect other response properties and may relate to the unaltered analysis and representation of spectral components of sounds. In contrast, neurons in dorsal and ventral AI change response properties in a non-predictable way in the presence of noise in accordance with the more complex receptive field properties in those areas.

[1]  Peter Heil,et al.  Topographic representation of tone intensity along the isofrequency axis of cat primary auditory cortex , 1994, Hearing Research.

[2]  M. L. Sutter,et al.  Functional topography of cat primary auditory cortex: response latencies , 1997, Journal of Comparative Physiology A.

[3]  F. de Ribaupierre,et al.  Changes of single unit activity in the cat's auditory thalamus and cortex associated to different anesthetic conditions , 1994, Neuroscience Research.

[4]  Raimond L Winslow,et al.  Single-tone intensity discrimination based on auditory-nerve rate responses in backgrounds of quiet, noise, and with stimulation of the crossed olivocochlear bundle , 1988, Hearing Research.

[5]  R A Reale,et al.  Spatial receptive fields of primary auditory cortical neurons in quiet and in the presence of continuous background noise. , 1998, Journal of neurophysiology.

[6]  D. P. Phillips,et al.  Some neural mechanisms in the cat's auditory cortex underlying sensitivity to combined tone and wide-spectrum noise stimuli , 1985, Hearing Research.

[7]  D. P. Phillips.  Neural representation of sound amplitude in the auditory cortex: effects of noise masking , 1990, Behavioural Brain Research.

[8]  Joachim Krauth,et al.  Distribution-Free Statistics: An Application-Oriented Approach , 1988 .

[9]  Christoph E. Schreiner,et al.  Spatial Distribution of Responses to Simple and Complex Sounds in the Primary Auditory Cortex , 1998, Audiology and Neurotology.

[10]  C E Schreiner,et al.  Topography of excitatory bandwidth in cat primary auditory cortex: single-neuron versus multiple-neuron recordings. , 1992, Journal of neurophysiology.

[11]  C. Schreiner,et al.  Physiology and topography of neurons with multipeaked tuning curves in cat primary auditory cortex. , 1991, Journal of neurophysiology.

[12]  A. J. Moffat,et al.  Noise masking of tone responses and critical ratios in single units of the mouse cochlear nerve and cochlear nucleus , 1984, Hearing Research.

[13]  Günter Ehret,et al.  Complex sound analysis (frequency resolution, filtering and spectral integration) by single units of the inferior colliculus of the cat , 1988, Brain Research Reviews.

[14]  D. P. Phillips.  Temporal response features of cat auditory cortex neurons contributing to sensitivity to tones delivered in the presence of continuous noise , 1985, Hearing Research.

[15]  D. D. Greenwood,et al.  Response of neurons in the cochlear nuclei to variations in noise bandwidth and to tone-noise combinations. , 1970, The Journal of the Acoustical Society of America.

[16]  E D Young,et al.  Rate responses of auditory nerve fibers to tones in noise near masked threshold. , 1986, The Journal of the Acoustical Society of America.

[17]  G. Ehret.  The auditory cortex , 1997, Journal of Comparative Physiology A.

[18]  Inferior colliculus of the house mouse , 1985 .

[19]  R. Christopher deCharms,et al.  Primary cortical representation of sounds by the coordination of action-potential timing , 1996, Nature.

[20]  C E Schreiner,et al.  Functional topography of cat primary auditory cortex: distribution of integrated excitation. , 1990, Journal of neurophysiology.

[21]  E D Young,et al.  Effects of continuous noise backgrounds on rate response of auditory nerve fibers in cat. , 1984, Journal of neurophysiology.

[22]  C. Schreiner,et al.  Modular organization of frequency integration in primary auditory cortex. , 2000, Annual review of neuroscience.

[23]  D. Irvine,et al.  Sensitivity of neurons in cat primary auditory cortex to tones and frequency-modulated stimuli. II: Organization of response properties along the ‘isofrequency’ dimension , 1992, Hearing Research.

[24]  D P Phillips,et al.  Spike-rate intensity functions of cat cortical neurons studied with combined tone-noise stimuli. , 1986, The Journal of the Acoustical Society of America.

[25]  Günter Ehret,et al.  The Central Auditory System , 1996 .

[26]  A R Palmer,et al.  Rate-intensity functions and their modification by broadband noise for neurons in the guinea pig inferior colliculus. , 1988, The Journal of the Acoustical Society of America.

[27]  E. Young,et al.  Responses to tones and noise of single cells in dorsal cochlear nucleus of unanesthetized cats. , 1976, Journal of neurophysiology.

[28]  M. Goldstein,et al.  Single-unit activity in the primary auditory cortex of unanesthetized cats. , 1968, The Journal of the Acoustical Society of America.

[29]  C. Schreiner,et al.  Frequency resolution and spectral integration (critical band analysis) in single units of the cat primary auditory cortex , 1997, Journal of Comparative Physiology A.

[30]  J O Pickles,et al.  Auditory-nerve-fiber bandwidths and critical bandwidths in the cat. , 1976, The Journal of the Acoustical Society of America.

[31]  C D Geisler,et al.  Auditory nerve fiber response to wide-band noise and tone combinations. , 1978, Journal of neurophysiology.

[32]  T. Imig,et al.  Functional organization of sound direction and sound pressure level in primary auditory cortex of the cat. , 1994, Journal of neurophysiology.

[33]  C E Schreiner,et al.  Topography of intensity tuning in cat primary auditory cortex: single-neuron versus multiple-neuron recordings. , 1995, Journal of neurophysiology.