Grent-'t-Jong Tineke, Oostenveld Robert, Jensen Ole, Medendorp W Pieter, Praamstra Peter
Department of Neurology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; and Donders Institute for Brain, Cognition, and Behaviour, Radboud University Nijmegen, Nijmegen, The Netherlands
Donders Institute for Brain, Cognition, and Behaviour, Radboud University Nijmegen, Nijmegen, The Netherlands.
J Neurophysiol. 2014 Jul 15;112(2):224-32. doi: 10.1152/jn.00127.2014. Epub 2014 Apr 23.
Choice behavior is influenced by factors such as reward and number of alternatives but also by physical context, for instance, the relative position of alternative movement targets. At small separation, speeded eye or hand movements are more likely to land between targets (spatial averaging) than at larger separation. Neurocomputational models explain such behavior in terms of cortical activity being preshaped by the movement environment. Here, we manipulate target separation, as a determinant of motor cortical activity in choice behavior, to address neural mechanisms of response selection. Specifically, we investigate whether context-induced changes in the balance of cooperative and competitive interactions between competing groups of neurons are expressed in the power spectrum of sensorimotor rhythms. We recorded magnetoencephalography while participants were precued to two possible movement target locations at different angles of separation (30, 60, or 90°). After a delay, one of the locations was cued as the target for a joystick pointing movement. We found that late delay-period movement-preparatory activity increased more strongly for alternative targets at 30 than at 60 or 90° of separation. This nonlinear pattern was evident in slow event-related fields as well as in beta- and low-gamma-band suppression. A comparable pattern was found within an earlier window for theta-band synchronization. We interpret the late delay effects in terms of increased movement-preparatory activity when there is greater overlap and hence less competition between groups of neurons encoding two response alternatives. Early delay-period theta-band synchronization may reflect covert response activation relevant to behavioral spatial averaging effects.
选择行为受到诸如奖励和备选方案数量等因素的影响，但也受到物理环境的影响，例如，备选运动目标的相对位置。在较小的间隔下，与较大间隔相比，快速的眼部或手部运动更有可能落在目标之间（空间平均）。神经计算模型根据运动环境预先塑造的皮层活动来解释这种行为。在这里，我们操纵目标间隔，作为选择行为中运动皮层活动的一个决定因素，以探讨反应选择的神经机制。具体而言，我们研究了在感觉运动节律的功率谱中，竞争神经元群体之间合作与竞争相互作用平衡的上下文诱导变化是否有所体现。我们记录了参与者的脑磁图，同时他们被预先提示了两个可能的运动目标位置，这两个位置以不同的间隔角度（30°、60°或90°）呈现。经过延迟后，其中一个位置被提示为操纵杆指向运动的目标。我们发现，在延迟后期，对于间隔为30°的备选目标，运动准备活动的增加比间隔为60°或90°时更为强烈。这种非线性模式在缓慢的事件相关场以及β和低γ波段抑制中都很明显。在较早的窗口中，对于θ波段同步也发现了类似的模式。我们将延迟后期的效应解释为，当编码两个反应备选方案的神经元群体之间有更大的重叠，从而竞争较少时，运动准备活动增加。延迟早期的θ波段同步可能反映了与行为空间平均效应相关的隐蔽反应激活。
