I’ve decided to take a step back from the trace studies and check out this book written by some of the most influential hippocampal researchers. This book was written specifically to allow newcomers to hippocampal research to catch up on the latest trends emerging from the systems view of the hippocampus.
Chapter 1 starts by pointing out that the Cognitive Map Theory (CMT) of the hippocampus is often misconstrued solely as a theory of spatial cognition, but is rather a theory of how the hippocampus is involved in episodic memory. Then, the authors provide an overview of the rest of the book and describe briefly what makes place cells (the physiological foundation of CMT) fire. The hippocampus receives input from the medial entohorinal cortex, an area that seems to convey information about space, and the lateral entorhinal cortex, which, for the most part, conveys object information (though whether or not this is the case will be discussed in a later chapter). Thus, the processing of the hippocampus is made possible through a complex cortical-hippocampal system that includes many areas of specialization, all of which, in the view of CMT, allow for the binding and association of spatial and object information into events which can then later be used to guide behavior in familiar situations. In addition to external sensory information regarding objects and landmarks, spatial computations involve internal input, such as from the vestibular system, to compute how an organism’s position in space changes over time in relation to the world around it.
Since most of the information in this first chapter will be discussed in detail later, I wanted to instead point out an interesting study mentioned about the role of NMDA receptor-dependent LTP and their role in place field formation. It was shown early on that NMDAR’s are necessary for spatial memory recall. However, Kentros et al. (1998) demonstrated that place fields could form in the absence of NMDAR activity, but that these fields would not bind to the cognitive map in the long run. Certainly, this would be an interesting read when revisiting Ryan et al.