Bonham Ben H, Cheung Steven W, Godey Benoit, Schreiner Christoph E
Department of Otolaryngology-Head and Neck Surgery, and W. M. Keck Center for Integrative Neuroscience, University of California, San Francisco, California 94143, USA.
J Neurophysiol. 2004 Feb;91(2):841-54. doi: 10.1152/jn.00017.2003. Epub 2003 Oct 8.
The current study was conducted to extend our understanding of changes in spatial organization and response properties of cortical neurons in the developing mammalian forebrain. Extracellular multiunit responses to tones were recorded from a dense array of penetrations covering entire isofrequency contours in the primary auditory cortex (AI) of pentobarbital anesthetized kittens. Ages ranged from postnatal day 14 (P14), shortly after acquisition of normal auditory response thresholds, through postnatal day 111 (P111), when the kittens were largely mature. Spatial organization of the AI was tonotopically ordered by P14. The tonotopic gradient decreased with chronological maturation. At P14 the gradient was about 3.5 kHz/mm. By P111 it had declined to about 2.5 kHz/mm, so that the cortical region encompassing a fixed 3- to 15-kHz frequency range enlarged along its posterior-anterior dimension. Response properties of developing AI neurons changed in both frequency selectivity and intensity selectivity. The mean frequency tuning bandwidth increased with age. Initially, tuning bandwidths were narrow throughout the entire AI. With progressive maturation, broader bandwidths were observed in areas dorsal and ventral to a central region in which neurons remained narrowly tuned. The resulting spatial organization of tuning bandwidth was similar to that reported in adult cats. The majority of recording sites manifested nonmonotonic rate/level functions at all ages. However, the proportion of sites with monotonic rate/level functions increased with age. No spatial organization of rate/level functions (monotonic and nonmonotonic) was observed through P111. The relatively late development of bandwidth tuning in the AI compared with the early presence of tonotopic organization suggests that different developmental processes are responsible for structuring these two dimensions of acoustic selectivity.
本研究旨在拓展我们对发育中的哺乳动物前脑皮质神经元空间组织和反应特性变化的理解。在戊巴比妥麻醉的小猫初级听觉皮层（AI）中，通过覆盖整个等频轮廓的密集穿刺阵列记录了对音调的细胞外多单位反应。年龄范围从出生后第14天（P14），即刚获得正常听觉反应阈值后不久，到出生后第111天（P111），此时小猫基本成熟。到P14时，AI的空间组织呈音调拓扑有序。音调拓扑梯度随时间成熟而降低。在P14时，梯度约为3.5kHz/mm。到P111时，它已降至约2.5kHz/mm，因此包含固定3至15kHz频率范围的皮质区域沿其后 - 前维度扩大。发育中的AI神经元的反应特性在频率选择性和强度选择性方面均发生了变化。平均频率调谐带宽随年龄增加。最初，整个AI的调谐带宽都很窄。随着逐渐成熟，在中央区域背侧和腹侧的区域观察到更宽的带宽，而中央区域的神经元仍保持窄调谐。由此产生的调谐带宽空间组织与成年猫中报道的相似。在所有年龄，大多数记录位点表现出非单调的速率/电平函数。然而，具有单调速率/电平函数的位点比例随年龄增加。直到P111都未观察到速率/电平函数（单调和非单调）的空间组织。与音调组织的早期出现相比，AI中带宽调谐的发育相对较晚，这表明不同的发育过程负责构建声学选择性的这两个维度。
