Dynamic Influence Of Environment Cues On Place Cells In Hippocampus CA1Area

In hippocampus there were a group of neurons that showed specific reaction to certain locations. Such neurons were defined as place cells, the specific area that triggered place cells to fire was called place field. Here we designed a U-shape two-dimensional linear track to investigate the firing properties of place cells and the influences on the hippocampus place cells under different space features.There were two parts of experiments in this dissertation, one was to change the direction of the U-shape track,180degrees rotation without location shift, to investigate the influence of the changed relative space location of the track on the firing activities of place cells in hippocampus CA1area. The other was to study the time effect of the influence discussed above by repeating the protocol one week later. We recorded5Long-Evans rats altogether and obtained intact data which were discussed in this paper from3of them. Totally239neurons in the CA1area were recorded from the first recording protocol, while repeated it one week later we recorded301neurons.Firstly, according to the directionality and numbers of place field, we sorted these neurons into four categories:unidirectional neuron with single place field, unidirectional neuron with multiple place fields, bidirectional neuron with double place fields and bidirectional neuron with multiple place fields. Either forward or reverse, bidirectional neurons were more than the unidirectional ones, of which, the bidirectional neuron with double place fields occupied the largest proportion.Secondly, place cells with different place fields properties showed variations in firing features. Take the S2period of the first recording as an example, the fluctuation range of the average peak firing rate of all the four kinds of place cells was relatively large, with most of which under20Hz. Specifically, unidirectional neuron with single place field:15.19±14.73; unidirectional neuron with multiple place fields:6.24±2.93Hz; bidirectional neuron with double place fields12.07±11.11Hz; and bidirectional neuron with multiple place fields11.59±10.16Hz. The fluctuation range of the length of the place fields was also relatively large, most of them distributed between20and40cm, specifically they were:26.46±8.34cm,31.26±10.39cm,32.02±13.41cm and 40.87±23.45cm.Meanwhile, the activity of hippocampal place cells was influenced by mainly three types of stimuli, distal visual cues, local visual cues and self-motion cues. The180-degrees-rotation of the track mainly changed the relative position of the local cues while had little effect on the other stimulation factors. Based on the variation pattern of the place fields during the experiment, we sorted the place cells into three categories:local-cue-domain-effect, distal-cue-domain-effect and irregular. It was very interesting that, during the two experiments with one week gap, the number of place cells affected by the local cue decreased significantly, the average proportion of the local-cue-domain-effect in the three rats from60.57%of the first time to4.69%one week later, while the number of place cells affected by the distal cue increased apparently, the average proportion of the distal-cue-domain-effect from28%of the first time to54.6%one week later.In summary, our study showed that during the back and forth of a rat ran along a U shaped linear track, hippocampal place cells showed directionality. Also, we recorded place cells with local-cue-domain effect and distal-cue-domain effect, and their firing varied with time:first showed obvious local-cue-domain effect and then distal-cue-domain effect apparently one week later. This discovery could help us get a better understanding of the information processing of place cells in the hippocampus.