Sensory Information Processing In Hippocampal CA1

The hippocampus is a major component of the brains of humans and vertebrates. It belongs to the limbic system and is associated with higher nervous activity, behavioral response and autonomic nervous function. Histologically, since different neuronal cell types are neatly organized into layers in the hippocampus, it has frequently been used as a model system for studying neuroanatomy and neurophysiology.The basis of hippocampal function is to process and integrate multimodal information, it is also one of the few brain regions that receive highly processed, multimodal sensory information from a variety of neocortical sources. And its own system of widely distributed intrinsic neuronal networks is ideally suited for further mixing or comparing this information. Sensory information of the various sorts is funneled down to the hippocampus via the perirhinal and entorhinal cortices, the outputs of the perirhinal and entorhinal cortices project to the dentate gyrus, CA3and CA1. The axons of CA1neurons project back to the entorhinal cortex, as well as other structures. Thus, via this general circuit, sensory information enters the hippocampus, is processed in the local hippocampal circuit, and then goes out of the hippocampus and ultimately back up into the cortex.Previous studies have proposed that the sensory information is represented in the hippocampus by sparsely distributed neurons, which is distinct from unimodal information processing in the primary sensory cortices. This notion is best embodied in hippocampal place cells, which discharge when the animal is in the particular location in the environment. It's also supported by the evidence of sparse code of non-spatial information in the hippocampus, including real-time information processing, relationships among objects and complexities encoding (e.g.face recognition), etc.As previously reported, the hippocampus encodes spatial or non-spatial information sparsely, however, not much is known about the individual cellular properties, thus, we used in vivo whole-cell patch-clamp recordings from CA1pyramidal neurons of anaesthetized adult rats to monitor membrane potential changes in current clamp mode. By presenting a brief flash of light at the contralateral eye, we found that about30%CA1pyramidal neurons were responsive to this sensory stimulation. Both depolarizing and hyperpolarizing membrane potential responses to the flash stimulus in CA1exhibited much longer latencies than those in primary visual cortex. On the other hand, the amplitudes of the depolarizing and hyperpolarizing membrane potential responses of CA1pyramidal neurons to the flash stimulus were much smaller than in primary visual cortex. These results indicate that CA1pyramidal neurons could perceive information of vision, but this ability of perception is weak.In addition, we found CA1pyramidal neurons could exhibit large, putatively calcium-based depolarization that often follow a burst of action potentials, which can last for>50ms. Studies on this point are major on hippocampus in vitro since this cutting of hippocampus damages many fibers, leading to disrupt intrinsic connections of hippocampus, various stimulation protocols were applied to generate burst firing. While direct evidence in vivo is more similar as physiological level.