Comparison of medial and lateral septal neuron activity during performanceof spatial tasks in rats

The septal complex, having close and reciprocal connections with the hippoc ampus, is known to play an important role in learning and memory Anatomical ly, the septal complex is divided into the medial and lateral areas (MS and LS). In the present study, in order to elucidate functional differences be tween the MS and LS, we recorded single unit activity in the MS or LS and e lectroencephalogram (EEG) in the hippocampus simultaneously while the rats performed the following 2 spatial tasks in an open-field chamber. In task 1 , the rat received rewarding intracranial electrical stimulation (ICES) whe n it entered in a reward place that was set randomly in the open field in e ach trial. In task 2, the rat received rewarding ICES when it alternately v isited two fixed reward places in the open field. Unit activity was analyze d in relation to the pattern of hippocampal EEC, and rat's location, locomo tion direction and locomotion speed in the spatial tasks. A total of 47 neu rons were recorded in the septal complex (MS, 19; LS, 28). The majority of neurons with activity correlated with hippocampal EEG were found in the MS (14/19). All of the neurons with place-related activity (an increase in uni t activity when the rat was in a specific location in the open field) were found in the LS (n = 15). The majority of neurons with direction-related ac tivity were found in the LS (18/23). Twenty-one neurons displayed speed-rel ated activity (MS, 9; LS, 12). The present results indicate that (1) the MS is directly involved in the formation and control of hippocampal EEG patte rns, and (2) the LS is important for the processing and integration of spat ial information in the environment. (C) 1999 Wiley-Liss, Inc.