The entorhinal cortex (EC) (ento = interior, rhino = nose, entorhinal = interior to the rhinal sulcus) is an area located in the medial temporal lobe and functioning as a hub in a widespread network for memory and navigation. The EC is the main interface between the hippocampus and neocortex. The EC-hippocampus system plays an important role in declarative (autobiographical/episodic/semantic) memories and in particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane response of classical trace conditioning, the association of impulses from the eye and the ear occurs in the entorhinal cortex.
The perforant pathway projection from layer II of the entorhinal cortex to the hippocampal dentate gyrus is especially important for long term memory formation, and is preferentially vulnerable to developing a degenerative tauopathy early in Alzheimer disease (AD) that may spread over time trans-synaptically.
A study showed that DBS in the entorhinal region improved the accuracy of human spatial memory. Based on this line of work, Jacobs et al performed a series of experiments to more fully characterize the effects of DBS in the medial temporal lobe on human memory. Neurosurgical patients with implanted electrodes performed spatial and verbal-episodic memory tasks. During the encoding periods of both tasks, subjects received electrical stimulation at 50 Hz. In contrast to earlier work, electrical stimulation impaired memory performance significantly in both spatial and verbal tasks. Stimulation in both the entorhinal region and hippocampus caused decreased memory performance. These findings indicate that the entorhinal region and hippocampus are causally involved in human memory and suggest that refined methods are needed to use DBS in these regions to improve memory 1).