Analysis And Modeling Of Hippocampal Neural Signals From Rats In Passive Displacement

The hippocampus is the key brain region to form the spatial recognition and haslong been investigated since last century. There have been numerous studiesinvestigating the hippocampal signals of rats in free roaming and have identified twotypes of theta rhythms in response to their behavioral correlates. In animals’ navigation,proprioception, optic flow and vestibular signals are combined to estimate theirself-motion. The passive displacement paradigm can isolate the sensory pathway ofproprioception, which will enable us to obtain further insights of spatial recognition andnavigation.The dissertation is centered on the speed coding. Based on the passivedisplacement paradigm, both experimental and theoretical investigations have beenconducted, which mainly involve four parts,(1) the set-up of a novel linear passiveparadigm,(2)the analysis of field potentials of hippocampus of rats in passivemovement,(3) the analysis of neuronal spikes and spike-filed potential relations,(4)theoretical discussion of speed perception and spatial recognition in hippocampus andrelated brain regions.We have compared the theta rhythms from rats in free walking and in passivedisplacement. It is verified that the theta rhythms have different characteristics betweenpassive and free movement. There is significant reduction in theta frequency as well astheta amplitude in passive displacement comparing with that in free moving. However,the injection of atropine suggests that the theta rhythms are both non-cholinergic(muscarinic) type I for the two paradigms. Theta I has long been considered as beingcorrelated with voluntary movement. Our results have presented a challenge to thisknowledge. Moving direction has not presented significant impacts on the fieldpotentials.The spike analysis shows that some neurons are correlated with moving speed inpassive paradigm. In addition, comparing to free moving, the modulation depth ofneuronal activities is reduced in passive displacement, as well as the reduction ofspike-field coherence in theta band. This may reflect the reduced coordination betweenindividual neuronal activities and population activities. Similar to field potential analysis, no significant impacts of moving direction were found on the neuronal firingpattern.Based on these results, we proposed that the reason for frequency and amplitudereduction in theta rhythms, as well as the reduction of coordination between thetarhythms and neuronal spikes, may be the reduced speed perception caused by the lackof proprioception. From this assumption, the dissertation has tried to theoretically revealthe role of speed perception in related brain regions from the knowledge we haveobtained in this experiment and literature. An extended velocity-controlled oscillationmodel has been proposed and discussed in concept and in network details.