Jahanshahi M, Profice P, Brown R G, Ridding M C, Dirnberger G, Rothwell J C
Department of Clinical Neurology, Institute of Neurology, The National Hospital for Neurology and Neurosurgery, London, UK.
Brain. 1998 Aug;121 ( Pt 8):1533-44. doi: 10.1093/brain/121.8.1533.
Random number generation is an attention-demanding task that engages working memory and executive processes. Random number generation requires holding information 'on line', suppression of habitual counting, internally driven response generation and monitoring of responses. Evidence from PET studies suggests that the dorsolateral prefrontal cortex (DLPFC) is involved in the generation of random responses. We examined the effects of short trains of transcranial magnetic stimulation (TMS) over the left or right DLPFC or medial frontal cortex on random number generation in healthy normal participants. As in previous evidence, in control trials without stimulation participants performed poorly on the random number generation task, showing repetition avoidance and a tendency to count. Brief disruption of processing with TMS over the left DLPFC changed the balance of the individuals' counting bias, increasing the most habitual counting in ones and reducing the lower probability response of counting in twos. This differential effect of TMS over the left DLPFC on the balance of the subject's counting bias was not obtained with TMS over the right DLPFC or the medial frontal cortex. The results suggest that, with disruption of the left DLPFC with TMS, habitual counting in ones that has previously been suppressed is released from inhibition. From these findings a network modulation model of random number generation is proposed, whereby suppression of habitual responses is achieved through the modulatory influence of the left DLPFC over a number-associative network in the superior temporal cortex. To allow emergence of appropriate random responses, the left DLPFC inhibits the superior temporal cortex to prevent spreading activation and habitual counting in ones.
随机数生成是一项需要注意力的任务，涉及工作记忆和执行过程。随机数生成需要在线保留信息、抑制习惯性计数、内部驱动反应生成以及对反应进行监控。正电子发射断层扫描（PET）研究的证据表明，背外侧前额叶皮层（DLPFC）参与随机反应的生成。我们研究了对健康正常参与者左侧或右侧DLPFC或内侧额叶皮层进行短串经颅磁刺激（TMS）对随机数生成的影响。与之前的证据一致，在无刺激的对照试验中，参与者在随机数生成任务上表现不佳，表现出避免重复和计数倾向。对左侧DLPFC进行TMS短暂干扰处理改变了个体计数偏差的平衡，增加了最常见的以1计数的频率，并降低了以2计数的较低概率反应。对右侧DLPFC或内侧额叶皮层进行TMS未获得TMS对左侧DLPFC在受试者计数偏差平衡上的这种差异效应。结果表明，通过TMS干扰左侧DLPFC，先前被抑制的以1计数的习惯性计数从抑制中释放出来。基于这些发现，提出了一个随机数生成的网络调制模型，即通过左侧DLPFC对颞上叶皮层中数字关联网络的调制影响来实现对习惯性反应 的抑制。为了使适当的随机反应出现，左侧DLPFC抑制颞上叶皮层以防止扩散激活和以1计数的习惯性计数。
