tailieunhanh - Theory of Brain Function quantum mechanics and superstrings - part 2

Bằng cách nghiên cứu các điện thế gợi lên trong cảm giác kích thích và trong quá trình thử nghiệm học tập, ER John đã có thể cho thấy những tiềm năng gợi phát sinh từ việc sa thải lớn và phân tán các nhóm thần kinh và họ hoàn toàn khác nhau từ những người thu được từ hoạt động vỏ não tự phát ngẫu nhiên | 7 assumed that the EEG waveforms emerge from the summation of local neuron firings but things are a bit more complicated. One would expect that asynchronous firing of randomly distributed neurons would produce a zero net effect on the scalp electrodes. By studying electric potentials evoked during sensory stimulation and during learning trials E. R. John has been able to show that these evoked potentials arise from the firing of large and disperse neural groups and that they are radically different from those obtained by the spontaneous random cortical activity 15 . Temporal rearrangement within the neural groups characterizes the externally evoked potentials. Furthermore Sayers et. al. 16 presented independent evidence strengthening the temporal rearrangement case by studying EEG phase coherence. Frequency components of the EEG spectrum obtained during spontaneous cortical activity show a random configuration of phase relations which shifts to a distinct pattern of phase coherence immediately following sensory stimulation. Amazingly enough imposing the phase characteristics of the evoked potential on the spontaneous waveform we can reproduce the characteristic shape of the observed evoked waveform 16 . These findings support E. R. John s 15 case for temporal rearrangement while at the same time it falsifies the kind of classical expectation that the EEG arises from the summation of neural firings which would imply that just the amplitude characteristics is the only difference between spontaneous and evoked waveforms. Clearly it seems that the external stimulus does not just add energy to the brain but it organizes it in a coherent way in a similar fashion that an external field B acts on a ferromagnet It seems that the analogy between brain function and critical phenomena dynamics may be quite useful and fruitful. In the unified approach suggested here see Eq. 2 the effective mental world W2 is actively interacting with the emerging MQS and thus through the R F .