Delay-specific deficits of medial septum suppression on a spatial working memory task

Abstract

Spatial working memory (SWM) is defined as the ability to process and maintain spatially-relevant, goal-directed information over a temporal gap. Several brain regions are known to be essential for successful SWM performance, including the hippocampus (HPC). One way to characterize the activity of the HPC is by measuring the local field potential (LFP) within the structure. LFP is the summated electrical activity of a population of cells, made up of the graded potentials of the neurons. One of the most prominent oscillations in the HPC is theta, which is known to support SWM processes. The medial septum (MS) is one of the septal nuclei that projects to all cell fields of the HPC and provides the rhythmic drive for theta oscillations. We investigated whether disrupting the normal temporal organization of the HPC via suppression of MS activity could cause task-specific deficits on a delayed non-match to position (DNMP) task by suppression MS activity during the sample, delay, or choice phases of the task. We found deficits specific to the delay period of the task. This indicates that the MS supports the maintenance of goal-relevant information over a temporal delay during SWM tasks. This deficit may be due to an interruption of planning abilities, where the disruption of normal theta causes deficits in the rats’ ability to plan a future decision using previously acquired information.