Corticofugal Shaping of Frequency Tuning Curves in the Central Nucleus of the Inferior Colliculus of Mice

• Published in: Journal of neurophysiology Vol. 93; no. 1; pp. 71 - 83
• Main Authors: Yan, Jun, Zhang, Yunfeng, Ehret, Gunter
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01-01-2005
• Subjects: Acoustic Stimulation - methods; Action Potentials - physiology; Action Potentials - radiation effects; Analysis of Variance; Animals; Auditory Cortex - physiology; Auditory Cortex - radiation effects; Auditory Pathways - physiology; Auditory Pathways - radiation effects; Cell Count; Chi-Square Distribution; Dose-Response Relationship, Radiation; Electric Stimulation - methods; Female; Inferior Colliculi - cytology; Inferior Colliculi - physiology; Mice; Neuronal Plasticity - physiology; Neuronal Plasticity - radiation effects; Neurons - physiology; Neurons - radiation effects; Sensory Thresholds - physiology; Sensory Thresholds - radiation effects; Time Factors
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00348.2004

1 Department of Physiology and Biophysics, Neuroscience Research Group, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada; and 2 Department of Neurobiology, University of Ulm, Ulm, Germany
Submitted 5 April 2004;
accepted in final form 17 August 2004
Plasticity of the auditory cortex can be induced by conditioning or focal cortical stimulation. The latter was used here to measure how stimulation in the tonotopy of the mouse primary auditory cortex influences frequency tuning in the midbrain central nucleus of the inferior colliculus (ICC). Shapes of collicular frequency tuning curves (FTCs) were quantified before and after cortical activation by measuring best frequencies, FTC bandwidths at various sound levels, level tolerance, Q-values, steepness of low- and high-frequency slopes, and asymmetries. We show here that all of these measures were significantly changed by focal cortical activation. The changes were dependent not only on the relationship of physiological properties between the stimulated cortical neurons and recorded collicular neurons but also on the tuning curve class of the collicular neuron. Cortical activation assimilated collicular FTC shapes; sharp and broad FTCs were changed to the shapes comparable to those of auditory nerve fibers. Plasticity in the ICC was organized in a center (excitatory)-surround (inhibitory) way with regard to the stimulated location (i.e., the frequency) of cortical tonotopy. This ensures, together with the spatial gradients of distribution of collicular FTC shapes, a sharp spectral filtering at the core of collicular frequency-band laminae and an increase in frequency selectivity at the periphery of the laminae. Mechanisms of FTC plasticity were suggested to comprise both corticofugal and local ICC components of excitatory and inhibitory modulation leading to a temporary change of the balance between excitation and inhibition in the ICC.
Address for reprint requests and other correspondence: J. Yan, Dept. of Physiology and Biophysics, Neuroscience Research Group, Faculty of Medicine, University of Calgary, 3330 Hospital Drive, N.W., Rm193B, Calgary, Alberta, T2N 4N1, Canada, (E-mail: juyan{at}ucalgary.ca )