| Spatial learning is a kind of behavior pattern to evaluate the cognition level by detecting the abilities of spatial orientation,reaction time,visual and sensation et al, and it is the learning and memory about scenes and memories. It is widely known that hippocampus plays an important role in the spatial learning. Most of these results were derived from the research on hippocampal place cell and spatial cognitive deficit caused by the damage of hippocampus, but few researches had been carried out to study the spatial information encoding of single cell in the hippocampus when rodents were in fixed position and the character of hippocampal potential during the spatial learning. As a result, this research is designed to study the characteristic changes of hippocampal neurons and hippocampal potential under the model of spatial discrimination cognition, so as to discuss the role of hippocampus during the spatial information encoding and spatial learning. It has been proved that nervous system is the complicated system composed of large quantities of nonlinear elements that connected by extensive connection, and it has the characteristic dynamics changes. Consequently, the nonlinear analytical method is much better to study the function of cerebra neuron during the cognitive process and the changing regularity of EGG that composed of large quantities of nonlinear elements information. The combination of linear and nonlinear analytical methods is helpful to study the dynamics mechanism, thus providing the beneficial suggestion in revealing the basic regularity of cognitive activation. This research is to be divided into two parts: Firstly, to synchronized collect the potential and neural spontaneous firing sequence in the dorsal hippocampus of the awaked guinea pigs, analyzing the characteristics of spontaneous fire between CA1 and CA3 regions in the dorsal hippocampus, and then to conclude the general electrophysiological characteristics of the neuron and hippocampal potential; Secondly, to establish the model of guinea pig in spatial discrimination cognition, combining the linear and non-linear analytical methods and observing the firing of different neurons in the hippocampus and the characteristic changes of hippocampal potential in the active and passive state during the spatial discrimination cognition, so as to discuss the role of hippocampus neuron in the spatial discrimination cognition and the relationship between hippocampal potential and the brain function. The main results are as follows: 1. The general electrophysiological character of hippocampal potential and neuron in the guinea pigs The hippocampus pyramidal cells and interneurons can be discriminated by the firing frequency,action potential durations and patterns. The differences are: The AP of the pyramidal cells are long duration (usually>1.2 ms), with lower mean firing frequency (usually<10Hz), and its firing patterns are mainly single spike potential (occasionally in CS potential composed of 2~10 action potentials); In contrast, The AP duration of the interneurons are quite short (usually<1.2ms), with higher mean firing frequency (usually>10Hz), and its firing patterns are single spike potential. On the contrary, there is no significant difference in mean firing frequency,complexity between the neurons in the CA1 and CA3 regions. 2. The relationship between spatial discrimination cognition and the changes of hippocampal neural firing and hippocampal potential. 2.1 Hippocampal pyramidal cells in the guinea pigs and the spatial discrimination cognition In this research, the study on the passive cognition group reveals that there are the pyramidal cells that can take part in the reaction to the positive lamp in the guinea pigs'hippocampus, and these pyramidal cells might encode the information of environmental clues and the stimulation of senses. In addition, the study reveals that there is significant difference between the active cognition group and passive cognition group in the firing frequency and complexity (P<0.05), but there is no significant difference between them in the spontaneous state (P>0.05). What's more, the number of the cells in the active cognition group that take part in the reaction to the positive lamp has increased significantly (P<0.05), which means that the characteristic changes of hippocampus pyramidal cells have close relationship with the spatial cognition and learning. Moreover, the firing pattern of the pyramidal cells that take part in the reaction to the positive lamp has showed positive andnegative correlation frequency models, which reveals that these pyramidal cells might act their respective functions in spatial cognition. 2.2 Hippocampal interneurons in the guinea pigs and the spatial discrimination cognition In the spontaneous state, there is significant difference between the active cognition group and passive cognition group in complexity (P<0.05), which means that the activities of hippocampus interneurons have relationship with the maintenance of conscious and alert state. At the same time, this research have found that the interneurons in both passive cognition group and active cognition group can be reactive to the negative lamp, which reveals that the interneurons can take part in the processing of sensation information. The further studies have found that it has no significant difference between the passive cognition state and active cognition state in complexity and the cell proportions that take part in the reaction to the positive lamp, which means that the hippocampus interneurons may have relations with position detection and stimulation, and play a reasonable role in the cognitive activity, 2.3 Hippocampal potentials in the guinea pigs and the spatial discrimination cognition This research indicates that no matter in the spontaneous state or cognitive state of active cognition group and passive cognition group, there is apparent θ-rhythm in the hippocampal potential. The results of ApEn in the cognition state of active cognition group and passive cognition group have increased significantly than in the spontaneous state (P<0.05); At the same time, the results of ApEn in the active cognition group (no matter in the spontaneous state or cognitive state) have increased significantly than the results in the passive cognition group (P<0.05). These results indicate that the brain functional status can be reflected by the result of ApEn. Conclusions 1.This research has carried out the vivo synchronous recording of the hippocampal neuron firing and hippocampal potential in the awaked guinea pigs, observed the electrophysiological characteristics of the pyramidal cells and interneurons and the character of hippocampus potential; And the study on the pyramidal cells and interneurons in the CA1 and CA3 regions of dorsal hippocampus indicates that the general electrophysiological character of the neuron spontaneous firing between the two regions hasno significant difference. 2. The study on the spatial discrimination cognition reveals that both pyramidal cells and interneurons in the hippocampus can take part in the encoding of sensation stimulation and discrimination of spatial location. Besides, these two cells can adjust the each other's activities through the abundant feedforward and feedback pathway,thus forms the hippocampal spatial cognition network. The fact that hippocampus can encode the information about the surroundings indicts that hippocampus may produce a marked effect on the formation of declarative memory. 3. The study on the hippocampal potential indicates that the nonlinear analytical method on ApEn is reliable to reflect the brain functional status, and the method has close correlations with the functional status. As a result, this analytical method has important significance in the research on the brain functional status and advanced functional activity mechanism. |
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