Brain and Movement Laboratory, Department of Electrical Engineering, Section of Biomedical Engineering, Danish Technical University, Ørsteds Plads, Building 349, 2800 Kgs. Lyngby, Denmark.
J Physiol. 2011 May 15;589(Pt 10):2515-28. doi: 10.1113/jphysiol.2011.206938. Epub 2011 Mar 21.
Motor cortical points are linked by intrinsic horizontal connections having a recurrent network topology. However, it is not known whether neural activity can propagate over the area covered by these intrinsic connections and whether there are spatial anisotropies of synaptic strength, as opposed to synaptic density. Moreover, the mechanisms by which activity spreads have yet to be determined. To address these issues, an 8 × 8 microelectrode array was inserted in the forelimb area of the cat motor cortex (MCx). The centre of the array had a laser etched hole ∼500 μm in diameter. A microiontophoretic pipette, with a tip diameter of 2-3 μm, containing bicuculline methiodide (BIC) was inserted in the hole and driven to a depth of 1200-1400 μm from the cortical surface. BIC was ejected for ∼2min from the tip of the micropipette with positive direct current ranging between 20 and 40 nA in different experiments. This produced spontaneous nearly periodic bursts (0.2-1.0 Hz) of multi-unit activity in a radius of about 400 μm from the tip of the micropipette. The bursts of neural activity spread at a velocity of 0.11-0.24 ms⁻¹ (mean=0.14 mm ms⁻¹, SD=0.05)with decreasing amplitude.The area activated was on average 7.22 mm² (SD=0.91 mm²), or ∼92% of the area covered by the recording array. The mode of propagation was determined to occur by progressive recruitment of cortical territory, driven by a central locus of activity of some 400 μm in radius. Thus, activity did not propagate as a wave. Transection of the connections between the thalamus and MCx did not significantly alter the propagation velocity or the size of the recruited area, demonstrating that the bursts spread along the routes of intrinsic cortical connectivity. These experiments demonstrate that neural activity initiated within a small motor cortical locus (≤ 400 μm in radius) can recruit a relatively large neighbourhood in which a variety of muscles acting at several forelimb joints are represented. These results support the hypothesis that the MCx controls the forelimb musculature in an integrated and anticipatory manner based on a recurrent network topology
运动皮层点通过具有递归网络拓扑的内在水平连接相连。然而，尚不清楚神经活动是否可以在这些内在连接所覆盖的区域中传播，以及是否存在突触强度的空间各向异性，而不是突触密度。此外，活动传播的机制仍有待确定。为了解决这些问题，在猫运动皮层（MCx）的前肢区域插入了一个 8×8 微电极阵列。该阵列的中心有一个直径约为 500μm 的激光蚀刻孔。一个微离子电泳管，尖端直径为 2-3μm，含有荷包牡丹碱甲碘化物（BIC），插入孔中，并从皮质表面驱动至 1200-1400μm 的深度。在不同的实验中，BIC 从微管尖端用 20-40nA 的正直流喷射约 2min。这在距微管尖端约 400μm 的半径内产生自发的几乎周期性爆发（0.2-1.0Hz）的多单位活动。神经活动的爆发以 0.11-0.24ms⁻¹ 的速度传播（平均=0.14mmms⁻¹，SD=0.05），幅度减小。被激活的区域平均为 7.22mm²（SD=0.91mm²），或记录阵列覆盖面积的约 92%。传播模式被确定为由半径约为 400μm 的活动中心驱动的皮质区域的渐进募集而发生。因此，活动没有像波一样传播。切断丘脑和 MCx 之间的连接不会显著改变传播速度或募集区域的大小，表明爆发沿着内在皮质连接的路径传播。这些实验表明，在小的运动皮层位置（半径≤400μm）内发起的神经活动可以募集相对较大的邻域，其中代表作用于几个前肢关节的各种肌肉。这些结果支持了这样的假设，即 MCx 基于递归网络拓扑以集成和预期的方式控制前肢肌肉。
