The effect of hippocampal activity to auditory evoked responses in guinea pig revealed by optical imaging

We observed the spatio-temporal representation of auditory cortex against the information processing in the hippocampus CA1 field. To clarify the dynamical interaction between the cortex and the hippocampus is a basic approach to investigate the systematic mechanism of memory system in the brain. The networks in the auditory cortex shows the representations of information for auditory recognition, while the hippocampus plays an important role in the course of storing and retrieving memory. In order to capture the spatio-temporal activity of auditory cortex, we used an optical imaging method with the aid of voltage sensitive dye. To make a comparison with the regular response of auditory cortex, a different spatio-temporal representation of neural networks in the auditory cortex of guinea pigs was measured by the method when a stimuli was simultaneously applied to the hippocampus CA1 and the auditory cortex. In the result of the experiment, the simultaneous stimuli to the hippocampus in addition to the auditory stimuli cause depression in the auditory cortex. From the viewpoint of memory of the brain, the effect of depression induced by the hippocampal activity seems to be important for selecting a certain region on the cortical memory space. This result suggest that connection from the hippocampus to the auditory cortex plays an important role for an attention to the memory system.