Lee C C, Schreiner C E, Imaizumi K, Winer J A
Division of Neurobiology, Department of Molecular and Cell Biology, Room 285 Life Sciences Addition, University of California at Berkeley, Berkeley, CA 94720-3200, USA.
Neuroscience. 2004;128(4):871-87. doi: 10.1016/j.neuroscience.2004.06.062.
Combined physiological and connectional studies show significant non-topographic extrinsic projections to frequency-specific domains in the cat auditory cortex. These frequency-mismatched loci in the thalamus, ipsilateral cortex, and commissural system complement the predicted topographic and tonotopic projections. Two tonotopic areas, the primary auditory cortex (AI) and the anterior auditory field (AAF), were electrophysiologically characterized by their frequency organization. Next, either cholera toxin beta subunit or cholera toxin beta subunit gold conjugate was injected into frequency-matched locations in each area to reveal the projection pattern from the thalamus and cortex. Most retrograde labeling was found at tonotopically appropriate locations within a 1 mm-wide strip in the thalamus and a 2-3 mm-wide expanse of cortex (approximately 85%). However, approximately 13-30% of the neurons originated from frequency-mismatched locations far from their predicted positions in thalamic nuclei and cortical areas, respectively. We propose that these heterotopic projections satisfy at least three criteria that may be necessary to support the magnitude and character of plastic changes in physiological studies. First, they are found in the thalamus, ipsilateral and commissural cortex; since this reorganization could arise from any of these routes and may involve each, such projections ought to occur in them. Second, they originate from nuclei and areas with or without tonotopy; it is likely that plasticity is not exclusively shaped by spectral influences and not limited to cochleotopic regions. Finally, the projections are appropriate in magnitude and sign to plausibly support such rearrangements; given the rapidity of some aspects of plastic changes, they should be mediated by substantial existing connections. Alternative roles for these heterotopic projections are also considered.
生理学和连接性的联合研究表明，猫听觉皮层中存在对频率特异性区域的显著非拓扑性外在投射。丘脑、同侧皮层和连合系统中这些频率不匹配的位点补充了预测的拓扑性和音频拓扑性投射。两个音频拓扑区域，即初级听觉皮层（AI）和前听觉场（AAF），通过其频率组织进行了电生理特征描述。接下来，将霍乱毒素β亚基或霍乱毒素β亚基金偶联物注射到每个区域的频率匹配位置，以揭示来自丘脑和皮层的投射模式。在丘脑1毫米宽的条带内和2 - 3毫米宽的皮层区域（约85%）的音频拓扑合适位置发现了大多数逆行标记。然而，分别约13 - 30%的神经元起源于远离丘脑核和皮层区域中预测位置的频率不匹配位置。我们提出，这些异位投射至少满足三个标准，这些标准可能是支持生理学研究中可塑性变化的幅度和特征所必需的。首先，它们存在于丘脑、同侧和连合皮层中；由于这种重组可能源于这些途径中的任何一条，并且可能涉及每一条途径，所以这种投射应该出现在这些区域。其次，它们起源于有或没有音频拓扑的核和区域；可塑性可能并非仅由频谱影响塑造，也不限于耳蜗拓扑区域。最后，这些投射在幅度和特征上合适，能够合理地支持这种重新排列；鉴于可塑性变化某些方面的快速性，它们应该由大量现有的连接介导。还考虑了这些异位投射的其他作用。
