Bon L, Lucchetti C
Istituto di Fisiologia, Università di Trieste, Italy.
Exp Brain Res. 1992;89(3):571-80. doi: 10.1007/BF00229882.
The activity of 249 neurons in the dorsomedial frontal cortex was studied in two macaque monkeys. The animals were trained to release a bar when a visual stimulus changed color in order to receive reward. An acoustic cue signaled the start of a series of trials to the animal, which was then free to begin each trial at will. The monkeys tended to fixate the visual stimuli and to make saccades when the stimuli moved. The monkeys were neither rewarded for making proper eye movements nor punished for making extraneous ones. We found neurons whose discharge was related to various movements including those of the eye, neck, and arm. In this report, we describe the properties of neurons that showed activity related to visual fixation and saccadic eye movement. Fixation neurons discharged during active fixation with the eye in a given position in the orbit, but did not discharge when the eye occupied the same orbital positions during nonactive fixation. These neurons showed neither a classic nor a complex visual receptive field, nor a foveal receptive visual field. Electrical stimulation at the site of the fixation neurons often drove the eye to the orbital position associated with maximal activity of the cell. Several different kinds of neurons were found to discharge before saccades: 1) checking-saccade neurons, which discharged when the monkeys made self-generated saccades to extinguish LED's; 2) novelty-detection saccade neurons, which discharged before the first saccade made to a new visual target but whose activity waned with successive presentations of the same target. These results suggest that the dorsomedial frontal cortex is involved in attentive fixation. We hypothesize that the fixation neurons may be involved in codifying the saccade toward a target. We propose that their involvement in arm-eye-head motor-planning rests primarily in targeting the goal of the movement. The fact that saccade-related neurons discharge when the saccades are self initiated, implies that this area of the cortex may share the control of voluntary saccades with the frontal eye fields and that the activation is involved in intentional motor processes.
在两只猕猴身上研究了背内侧前额叶皮层中249个神经元的活动。训练动物在视觉刺激颜色变化时松开杠杆以获得奖励。一个声音提示向动物发出一系列试验开始的信号，然后动物可以随意开始每次试验。猴子倾向于注视视觉刺激，并在刺激移动时进行扫视。猴子做出正确的眼球运动既不会得到奖励，做出无关的眼球运动也不会受到惩罚。我们发现了一些神经元，其放电与包括眼睛、颈部和手臂在内的各种运动有关。在本报告中，我们描述了显示与视觉注视和眼球扫视运动相关活动的神经元的特性。注视神经元在眼睛处于眼眶中给定位置的主动注视期间放电，但在非主动注视期间眼睛占据相同眼眶位置时不放电。这些神经元既没有经典的也没有复杂的视觉感受野，也没有中央凹视觉感受野。在注视神经元所在部位进行电刺激常常会驱使眼睛移向与该细胞最大活动相关的眼眶位置。发现有几种不同类型的神经元在扫视之前放电：1）检查性扫视神经元，当猴子为熄灭发光二极管而进行自主扫视时放电；2）新奇检测扫视神经元，在首次扫视新视觉目标之前放电，但其活动会随着同一目标的连续呈现而减弱。这些结果表明背内侧前额叶皮层参与了注意力集中的注视。我们假设注视神经元可能参与对朝向目标的扫视进行编码。我们提出它们参与手臂 - 眼睛 - 头部运动规划主要在于确定运动的目标。当扫视是自主发起时与扫视相关的神经元放电这一事实，意味着该皮层区域可能与额叶眼区共同控制自主扫视，并且这种激活参与了有意的运动过程。
