| Recent studies suggested that the hippocampal system receives inputs from multisensory and high order sensory and motor cortical areas, and integrates them with inputs concerning emotion and motivation, including internal sensor signals concerning the degree to which the needs of the organism have been fulfilled. This information is then employed in association with other brain structures for comparing current events and context with previous experiences in order to implement appropriate behaviors, make decisions and form memories. The establishment of trace eyeblink classical conditioning in rabbits depend on hippocampus and cerebellum. Whether the hippocampus participates in auditory discrimination cognition and how the hippocampal neurons encode the information remains controversial. Understanding the role of the hippocampus in the auditory discrimination cognition is important for identifying the neural substrates of vocal communication in mammalians and ultimately, of speech and language in human. With the development of the non-linear theory, it is accepted that the nonlinear dynamics exists in biological system and nonlinear analysis may provide an additional method in the study of information coding in central neuronal system. To study the hippocampal neurons with the help of the linear and nonlinear method may help us deepen the understanding of the dynamical mechanism for the brain. The present research were divided into two parts: Firstly,to explore the spontaneous firing characteristics between the pyramidal cells and interneurons in the CA1 and CA3 regions of dorsal hippocampus. Secondly,to establish a relatively ideal animal model of auditory discrimination cognition which can be trained to eyeblink after hearing the high tone and the firing characteristics and nonlinear dynamics of the hippocampal neurons in passive and active auditory discrimination groups can be observed. The main results are as follows:1. Spontaneous firing characteristics of pyramidal cells and interneurons in the guinea pigsThe spontaneous activities of pyramidal cells and interneurons were different in firing pattern (mean firing frequency and duration of action potential). Action potentials of the interneurons were always of single spike in uniform amplitude with relatively short durationand high spontaneous discharge rate. In contrast, pyramidal cells fired occasionally in multiple-spike bursts with decreasing spike amplitudes or in single spike mode at low rates, with action potentials of long duration. For the same neurons, there was no significant difference in the duration, mean firing frequency, complexity and firing mode between the neurons in the CA1 and CA3 regions.2. Firing characteristics of hippocampal neurons in passive cognition group The neurons firing were recorded in spontaneous state, single low tone (L) and low-high double tones (D, the high tone is the positive stimulus and the low tone is the negative) in passive group for a long time and only a few neurons revealed the increase of firing rate to the high tone.The mean firing frequency and complexity of pyramidal cells in both L and D were higher than that in spontaneous (S) state (p<0.05), but there is no statistical difference between L and D, which suggested the pyramidal cells showed the transient increase of firing rate and changes of complexity, but showed no activation to the high tone. The firing behaviors were nonperiodic burst and the coefficient of variation of interspike interval (ISI ) is over 0.5, the number of favored patterns (FPs) of pyramidal cells exhibited increase, decrease and complete changes. The mean firing frequency of interneurons showed no increase in L and D, but the complexity in L was higher than that in S (p<0.05), and there was no statistical difference between S and D, L and D; it suggested the interneurons in passive group did not change the firing rate,but the complexity of firing sequence may change. The coefficient of variance of ISI of interneurons is over 0.5, showing the...
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