Allison J D, Casagrande V A, Bonds A B
Department of Cell Biology, Vanderbilt University, Nashville, TN, USA.
Vis Neurosci. 1995 Mar-Apr;12(2):309-20. doi: 10.1017/s0952523800007999.
The receptive fields of cells in the primary visual cortex (area 17 or V1) show clear orientation selectivity, unlike those of the lateral geniculate nucleus (LGN) cells which provide their visual input. The intrinsic circuitry of V1 cells is believed to be partly responsible for this selectivity. We investigated the influence of ascending projections from neurons in the lower layers (5 and 6) of V1 on the orientation selectivity of single neurons in the upper layers (2,3, and 4) by reversibly inactivating ("blocking") lower layer neural activity with iontophoretic application of gamma-aminobutyric acid (GABA) while recording from upper layer cells in the prosimian primate, Galago crassicaudatus. During lower layer blocking, the majority (20/28 = 71.4%) of upper layer neurons exhibited a change in the orientation of their preferred stimulus, a reduction in their orientation tuning, and/or an increase in their response amplitude. Twelve (42.9%) neurons exhibited shifts in their preferred orientation averaging 11 (+/- 4) deg. These neurons were located on average, 272 (+/- 120) microns tangential from the vertical axis of the pipette center. Eleven neurons (39.2%) exhibited an average reduced orientation tuning of 52.5%. Their average location was 230 +/- (115) microns away from the vertical axis of the pipette. Five (17.9%) neurons with average location 145 (+/- 75) microns from the vertical axis exhibited both effects. Two (7.1%) neurons that exhibited significant increases in response amplitude to stimulus angles within 10 deg of the peak excitatory stimulus without changes in orientation selectivity or tuning were located less than 100 microns from the vertical axis. The effects on the orientation tuning of cells were restricted in all cases to within +/- 30 deg of the preferred stimulus orientation. This suggests that layer blocking affects cells with preferred stimulus orientations similar to those of the recorded neurons. Only cells located within 500 microns tangential to the vertical axis of the injection site exhibited these effects. These results suggest that cells within layers 5 and 6 provide organized, orientation-tuned inhibition that sharpens the orientation tuning of cells in the upper cortical layers within the same, or closely neighboring, cell columns.
初级视皮层（17区或V1区）细胞的感受野表现出明显的方向选择性，这与提供视觉输入的外侧膝状体核（LGN）细胞不同。V1区细胞的内在神经回路被认为部分导致了这种选择性。我们通过离子电泳施加γ-氨基丁酸（GABA）可逆性地使下层（5层和6层）神经元活动失活（“阻断”），同时在原猴类灵长动物粗尾婴猴的上层（2、3和4层）细胞进行记录，研究了V1区下层神经元的上行投射对上层单个神经元方向选择性的影响。在下层阻断期间，大多数（20/28 = 71.4%）上层神经元表现出其偏好刺激方向的改变、方向调谐的降低和/或反应幅度的增加。12个（42.9%）神经元的偏好方向平均偏移11（±4）度。这些神经元平均位于距移液管中心垂直轴切线方向272（±120）微米处。11个（39.2%）神经元的方向调谐平均降低了52.5%。它们的平均位置距移液管垂直轴230±（115）微米。平均位置距垂直轴145（±75）微米的5个（17.9%）神经元表现出两种效应。2个（7.1%）神经元对峰值兴奋刺激10度范围内的刺激角度反应幅度显著增加，而方向选择性或调谐无变化，它们位于距垂直轴不到100微米处。在所有情况下，对细胞方向调谐的影响都局限于偏好刺激方向的±30度范围内。这表明层阻断影响偏好刺激方向与记录神经元相似的细胞。只有位于注射部位垂直轴切线方向500微米内的细胞表现出这些效应。这些结果表明，5层和6层内的细胞提供有组织的、方向调谐的抑制，从而锐化同一或相邻细胞柱内上层皮质细胞的方向调谐。
