Alloway Kevin D, Zhang Mengliang, Dick Susan H, Roy Stephane A
Department of Neuroscience and Anatomy, Milton S. Hershey Medical Center, Penn State University College of Medicine, Hershey, PA 17033-2255, USA.
Exp Brain Res. 2002 Nov;147(2):227-42. doi: 10.1007/s00221-002-1233-3. Epub 2002 Oct 1.
Extracellular discharges were recorded from 205 neurons in the secondary somatosensory (SII) cortex of isoflurane-anesthetized cats. Cross-correlation analysis was used to characterize the temporal coordination of SII neurons recorded during cutaneous stimulation with a focal air jet that moved back-and-forth across the distal forelimb. Over two-thirds of the recorded neuron pairs ( n=357) displayed significant levels of synchronized activity during one or both directions of air-jet movement. The probability of detecting correlated activity varied according to the distance separating the neurons. Whereas synchronized responses were observed in 82.3% of the pairs in which the neurons were separated by 200-300 micro m, the incidence of synchronization declined to 52.3% for neurons that were separated by 600-800 micro m. The distance between neurons also had a significant effect on the temporal precision of correlated activity. For neurons that were separated by 200-300 micro m, synchronized responses in the cross-correlograms (CCGs) were characterized by narrow (0.5-1.0 ms) peaks at time zero. For SII neurons that were more widely separated, the peak half-widths were substantially broader and more likely to be displaced from time zero. Analysis of directional sensitivity indicated that only 14.2% of the correlated neurons displayed a directional preference for synchronized activity. By comparison, 63.4% of the neurons displayed a directional preference in their discharge rate. These results indicate that stimulus-induced synchronization is a prominent feature among local populations of SII neurons, but synchronization does not appear to play a critical role in coding the direction of stimulus movement. A comparison of these results with those obtained from similar experiments conducted in primary somatosensory (SI) cortex indicates that neuronal synchronization is more likely in SII cortex. This finding is discussed with respect to the known functional differences between the SI and SII cortical areas.
在异氟烷麻醉的猫的次级体感（SII）皮层中，记录了205个神经元的细胞外放电。使用互相关分析来表征在皮肤刺激期间记录的SII神经元的时间协调性，刺激采用聚焦空气喷射，该喷射在远端前肢上来回移动。在记录的神经元对中（n = 357），超过三分之二在空气喷射移动的一个或两个方向上表现出显著水平的同步活动。检测到相关活动的概率根据神经元之间的距离而变化。当神经元之间的距离为200 - 300微米时，82.3%的神经元对观察到同步反应，而当神经元之间的距离为600 - 800微米时，同步发生率降至52.3%。神经元之间的距离对相关活动的时间精度也有显著影响。对于距离为200 - 300微米的神经元，互相关图（CCG）中的同步反应在时间零点处的峰值较窄（0.5 - 1.0毫秒）。对于距离更远的SII神经元，峰值半高宽明显更宽，并且更有可能偏离时间零点。方向敏感性分析表明，只有14.2%的相关神经元在同步活动中表现出方向偏好。相比之下，63.4%的神经元在放电率上表现出方向偏好。这些结果表明，刺激诱导的同步是SII神经元局部群体中的一个突出特征，但同步似乎在编码刺激运动方向方面不发挥关键作用。将这些结果与在初级体感（SI）皮层中进行的类似实验获得的结果进行比较表明，SII皮层中神经元同步的可能性更大。结合SI和SII皮层区域已知的功能差异对这一发现进行了讨论。
