Aoki R, Wake H, Sasaki H, Agata K
Department of Physiology and Biosignaling, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita 565-0871, Japan.
Neuroscience. 2009 Mar 17;159(2):908-14. doi: 10.1016/j.neuroscience.2008.11.011. Epub 2008 Nov 13.
Many animals produce continuous brainwaves, known as the electroencephalogram (EEG), but it is not known at what point in evolution the EEG developed. Planarians possess the most primitive form of brain, but still exhibit learning and memory behaviors. Here, we observed and characterized the EEG waveform of the planarian. We inserted a monopole electrode into the head of a planarian on a cold stage, and were able to observe the EEG at sub-microvolt amplitudes. The EEG had a continuous waveform, similar to that of evolutionarily advanced animals with more developed brains. Occasional myogenic potential spikes were observed in the EEG due to sticking of the electrode, but this was markedly diminished by cooling the sample, which enabled us to investigate the intrinsic character of the continuous EEG waveform. The frequency spectrum of the EEG was observed in the range of 0.1-5 Hz, showing a broad rise below 0.5 Hz and a monotonic decrease above 1 Hz, apparently following the 1/f law. The intensity of the total EEG diminished during anesthesia by cooling to 2-3 degrees C, and recovered when the sample was warmed to about 10 degrees C. The EEG signal was sustained for 30-40 min, and gradually weakened as the animal died. Stimulation of the planarian with water vibration at 0.5-2 Hz induced chaotic resonance with a broad peak spectrum of around the stimulation frequency. Strong illumination suppressed the EEG signals for several minutes, with the degree of suppression positively correlating with the intensity of the light. This provides evidence that the EEG responds to optical signals, although there were no synchronous reactions to light flashes. The continuous EEG waveform suggests the existence of feedback loop circuits in the neural network of the planarian, which was supposed in electric shock memory experiments [McConnell JV, Cornwell P, Clay M (1960) An apparatus for conditioning planaria. Am J Psychol 73:618-622]. However, because of the broad band character of chaotic resonance observed, these loops appear to be loose couplings between ganglia.
许多动物都会产生连续的脑电波，即脑电图（EEG），但目前尚不清楚脑电图是在进化的哪个阶段发展起来的。涡虫拥有最原始的脑形式，但仍表现出学习和记忆行为。在此，我们观察并描述了涡虫的脑电图波形。我们在低温载物台上将一个单极电极插入涡虫头部，能够观察到亚微伏幅度的脑电图。该脑电图具有连续波形，类似于脑发育更高级的进化程度较高的动物的脑电图。由于电极粘贴，在脑电图中偶尔会观察到肌源性电位尖峰，但通过冷却样本这种情况会明显减少，这使我们能够研究连续脑电图波形的内在特征。脑电图的频谱在0.1 - 5赫兹范围内被观察到，在0.5赫兹以下呈现出广泛上升，在1赫兹以上呈单调下降，显然遵循1/f定律。通过冷却至2 - 3摄氏度进行麻醉时，总脑电图强度减弱，当样本升温至约10摄氏度时恢复。脑电图信号持续30 - 40分钟，并随着动物死亡而逐渐减弱。以0.5 - 2赫兹的水振动刺激涡虫会诱发混沌共振，在刺激频率周围有一个宽峰频谱。强光照射会抑制脑电图信号几分钟，抑制程度与光强度呈正相关。这提供了证据表明脑电图对光信号有反应，尽管对光闪烁没有同步反应。连续的脑电图波形表明涡虫神经网络中存在反馈回路，这在电击记忆实验中曾被推测过[麦康奈尔JV、康韦尔P、克莱M（1960年）一种涡虫条件反射装置。《美国心理学杂志》73：618 - 622]。然而，由于观察到的混沌共振具有宽带特性，这些回路似乎是神经节之间的松散耦合。
