Cross-modal and cross-temporal association in neurons of frontal cortex

The prefrontal cortex is essential for the temporal integration of sensory information in behavioural and linguistic sequences. Such information is commonly encoded in more than one sense modality, notably sight and sound. Connections from sensory cortices to the prefrontal cortex support its integrative function. Here we present the first evidence that prefrontal cortex cells associate visual and auditory stimuli across time. We gave monkeys the task of remembering a tone of a certain pitch for 10 s and then choosing the colour associated with it. In this task, prefrontal cortex cells responded selectively to tones, and most of them also responded to colours according to the task rule. Thus, their reaction to a tone was correlated with their subsequent reaction to the associated colour. This correlation faltered in trials ending in behavioural error. We conclude that prefrontal cortex neurons are part of integrative networks that represent behaviourally meaningful cross-modal associations. The orderly and timely activation of neurons in such networks is crucial for the temporal transfer of information in the structuring of behaviour, reasoning and language.     

地球在碰撞中运行

对太阳系的探测表明,陨石撞击是行星表面的形成及日后演变的一个重要进程。例如,月亮表面满是陨痕累累的高地及低洼的、布满熔岩的盆地。遍布陨石坑的高地表明,最初的月球外壳及盆地是38亿年以前、月球形成最后阶段中所发生的巨大碰撞的结果。这些盆地是由直径为10～50公里的物体撞击出来的,后来,陨石坑为大熔岩所填充,就成了现在大家所熟知的平坦的玄武岩平原,即月球海。地球表面一定也曾发生过类似的碰撞。这些巨大的碰撞可能是地壳由早先的模样演变成现今海洋和大陆板