Luethke L E, Krubitzer L A, Kaas J H
Department of Hearing and Speech Sciences, Vanderbilt University, Nashville, Tennessee 37240.
J Comp Neurol. 1988 Feb 8;268(2):181-203. doi: 10.1002/cne.902680205.
Multiunit recordings with microelectrodes were used to identify and delimit subdivision of auditory cortex in squirrels. In the same animals, cortical connections of subdivisions of auditory cortex were determined by placing injections of the tracer wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) into electrophysiologically defined locations. The electrophysiological results and patterns of connections were later related to myeloarchitectonic distinctions in brain sections cut parallel to the surface of the artificially flattened cortex. As previously described (Merzenich et al.: J. Comp. Neurol. 166:387-402, '76), a primary auditory field, A-I, was characterized by (1) neurons narrowly tuned to tone frequency; (2) a tonotopic map with high frequencies, which represented caudal to low frequencies; and (3) dense myelination. A-I was reciprocally connected with a rostral field, R, a parietal ventral somatosensory representation, PV, cortex ventral to A-I, and other nearby regions of cortex of the same hemisphere. Callosal connections of A-I were with A-I, R, and two or more other regions of temporal cortex. The less densely myelinated rostral field, R, also had neurons that were frequency tuned, but the neurons were often less securely driven. R appeared to have a tonotopic organization that roughly mirrored that of A-I. Ipsilateral connections of R included A-I, PV, and cortex ventral and caudal to R. Callosal connections were with R, A-I, PV, and cortex ventral and caudal to R. Callosal connections were with R, A-I, PV, and other locations in temporal cortex. Cortex in caudal PV, ventral to A-I, and ventral to R was responsive to auditory stimuli, but responses to pure tones were weak and inconsistent, and habituation to a repeated stimulus was rapid. The cortex responsive to auditory stimuli included some but not all of the cortex connected with A-I and R. The results lead to the conclusion that auditory cortex of squirrels contains at least two tonotopically organized fields, possibly as many as five or more auditory fields, and at least two auditory-somatosensory fields.
用微电极进行多单元记录，以识别和界定松鼠听觉皮层的分区。在同一批动物中，通过将与辣根过氧化物酶结合的示踪剂小麦胚芽凝集素（WGA-HRP）注射到电生理学确定的位置，来确定听觉皮层各分区的皮层连接。随后，将电生理结果和连接模式与平行于人工扁平化皮层表面切割的脑切片中的髓鞘构筑差异联系起来。如前所述（梅尔泽尼希等人：《比较神经学杂志》166:387 - 402，1976年），初级听觉区A-I的特征为：（1）神经元对音调频率的调谐范围狭窄；（2）具有高频到低频的音调定位图，高频代表尾侧，低频代表头侧；（3）髓鞘密集。A-I与一个头侧区R、顶叶腹侧体感代表区PV、A-I腹侧的皮层以及同一半球的其他附近皮层区域相互连接。A-I的胼胝体连接是与A-I、R以及颞叶皮层的两个或更多其他区域。髓鞘密度较低的头侧区R也有频率调谐的神经元，但这些神经元的驱动往往不太稳定。R似乎具有大致与A-I镜像的音调定位组织。R的同侧连接包括A-I、PV以及R腹侧和尾侧的皮层。胼胝体连接是与R、A-I、PV以及颞叶皮层的其他位置。A-I腹侧、R腹侧以及尾侧PV中的皮层对听觉刺激有反应，但对纯音的反应微弱且不一致，对重复刺激的习惯化很快。对听觉刺激有反应的皮层包括与A-I和R相连的部分但不是全部皮层。结果得出结论，松鼠的听觉皮层至少包含两个音调定位组织的区域，可能多达五个或更多听觉区域，以及至少两个听觉 - 体感区域。
