Kay L M, Lancaster L R, Freeman W J
Graduate Group in Biophysics, University of California at Berkeley 94720, USA.
Int J Neural Syst. 1996 Sep;7(4):489-95. doi: 10.1142/s0129065796000476.
Olfactory bulb activity has been postulated to be chaotic, as measured in the EEG, and to be subject to an attractor with many "wings" enabling classification of different learned odor classes. Two parallel questions are thus addressed by the work presented here: (1) what is the evidence for attractors in the olfactory system, which can mediate learned odor classes? and (2) how does the olfactory system enter a specific attractor or attractor wing associated with the learned odor during the classification process? Both of these questions address the wider notion of endogenous activity preparing the system for an expected stimulus, which is at the basis of the reafference principle. By viewing the brain as a distributed complex dynamical system with global attractors, these questions can be answered together. Rats were implanted with bipolar macroelectrodes in the Olfactory Bulb (OB), Prepyriform Cortex (PPC), Entorhinal Cortex (EC), and Dentate Gyrus (DG), and then trained in an operant paradigm to press a bar for a reward in the presence of one odor and to receive no reward in the presence of another odor. Local Field Potentials (LFP) were recorded simultaneously from the structures during the operant task. We present evidence for three endogenous events: (1) preafference, which is manifested both by the EC entering an attractor and a mid-range signal (15-30 Hz) which appears to be passed from the EC to the OB just before the OB enters an attractor; (2) afference, where the OB enters an attractor during the odor recognition period of the experiment and the LFP recordings indicate that the OB drives the other structures in all frequency bands, especially the high gamma band (65-100 Hz) associated with the OB burst frequency; and (3) reafference or post-afference, which is accompanied by a lower frequency gamma band signal (40-60 Hz) originating in the PPC and passed to both the OB and the EC just before the onset of the motor response to the odor. We use a new method, NECTAR (Nonparametric Exact Contingency Table Association Routine), related to mutual information, to verify what is seen with coherence and phase estimates, the apparent driving of each structure at different times in the odor trials, and to display evidence for non-periodic attractors governing both individual physiological structures and the system of structures. This is the first evidence of an endogenous, limbic event associated with sensory perceptual tuning in a mammal. These results are also the first experimental confirmation that the attractors governing olfactory activity involve multiple sites in the olfactory/limbic system and implement the process of attention.
嗅球活动据推测是混沌的，如脑电图所测，并且受一个具有许多“翼”的吸引子影响，从而能够对不同的习得气味类别进行分类。因此，本文所呈现的研究解决了两个平行的问题：（1）嗅觉系统中存在吸引子的证据是什么，这种吸引子能够介导习得的气味类别？（2）在分类过程中，嗅觉系统如何进入与习得气味相关的特定吸引子或吸引子翼？这两个问题都涉及到内源性活动为预期刺激准备系统这一更广泛的概念，而这正是再传入原则的基础。通过将大脑视为一个具有全局吸引子的分布式复杂动力系统，这些问题可以一并得到解答。给大鼠在嗅球（OB）、梨状前皮质（PPC）、内嗅皮质（EC）和齿状回（DG）植入双极宏观电极，然后在操作性范式中进行训练，使其在一种气味出现时按压杠杆以获得奖励，而在另一种气味出现时不获得奖励。在操作性任务期间，同时记录这些结构的局部场电位（LFP）。我们提供了三个内源性事件的证据：（1）预传入，表现为EC进入一个吸引子以及一个中频信号（15 - 30赫兹），该信号似乎在OB进入吸引子之前从EC传递到OB；（2）传入，在实验的气味识别期OB进入一个吸引子，并且LFP记录表明OB在所有频段驱动其他结构，特别是与OB爆发频率相关的高伽马频段（65 - 100赫兹）；（3）再传入或后传入，伴随着一个低频伽马频段信号（40 - 60赫兹），该信号起源于PPC，在对气味的运动反应开始之前传递到OB和EC。我们使用一种与互信息相关的新方法NECTAR（非参数精确列联表关联程序）来验证通过相干性和相位估计所观察到的现象，即在气味试验的不同时间每个结构的明显驱动，并展示支配个体生理结构和结构系统的非周期性吸引子的证据。这是首次在哺乳动物中发现与感觉知觉调谐相关的内源性边缘系统事件的证据。这些结果也是首次实验证实支配嗅觉活动的吸引子涉及嗅觉/边缘系统中的多个位点并实现注意力过程。
