A rat learns to navigate maze A over several days, developing a stable pattern of place cell activity. It is then placed in maze B, which has the same shape but different wall colors and odors. What will happen to the place cell population?
AThe same place cells will fire in the same relative locations, since the maze shape is identical
BThe place cells will fire randomly until the rat learns the new maze
CAn entirely new map will be generated — cells that fired in maze A may fire in different locations or not at all in maze B
DPlace cells will be silent in maze B because the rat already has a map from maze A
This is global remapping: when an animal enters a genuinely novel environment, the hippocampus generates a completely new population-level map. Cells that fired in specific locations in maze A reorganize to new fields or go silent in maze B. This is not failure or confusion — it is the system's solution to the problem of memory interference. Each distinct environment gets a distinct neural representation, preventing the maps from overlapping and degrading. The remapping is rapid and complete, not gradual, and it means the hippocampus can store many separate spatial memories without them corrupting each other.
Question 2 Multiple Choice
Grid cells in the medial entorhinal cortex are thought to contribute to spatial memory primarily by providing what to the hippocampus?
AA catalog of visual landmarks from the environment
BA metric coordinate framework — regularly spaced firing fields that allow distances and directions to be computed
CEmotional salience signals that mark which locations in a map are important
DDirect input from the vestibular system about head direction
Grid cells fire at multiple locations arranged in a precise triangular (hexagonal) lattice as an animal moves through space. Different grid cells have different lattice spacings and orientations, effectively tiling the environment at multiple scales. This regular, metric structure is thought to provide the hippocampus with a coordinate system for computing distances and directions — a kind of internal ruler. Place cells combine this metric input from grid cells with sensory landmark information to build unique, context-specific maps. Grid cells supply the geometric scaffold; place cells construct the environment-specific representation on top of it.
Question 3 True / False
A single hippocampal place cell fires throughout an entire environment at a roughly uniform rate, signaling the animal's general presence in that space.
TTrue
FFalse
Answer: False
Place cells are spatially tuned: each cell fires selectively within a restricted region of the environment called its place field, which might cover only a fraction of a large space. Outside the place field, the cell is largely silent. It is the *population* of place cells — each contributing its own localized firing — that provides a complete spatial map. At any location, only a subset of place cells are active, and the identity of that active subset uniquely encodes position. Thinking of spatial coding as distributed across a population is essential; no single cell represents the whole environment.
Question 4 True / False
Global remapping — generating an entirely new place cell map for a novel environment — occurs rapidly and prevents spatial memories from different environments from interfering with each other.
TTrue
FFalse
Answer: True
Global remapping is thought to be the hippocampus's solution to the interference problem: if the same cells fired in the same places across different environments, the maps would overlap and degrade. Instead, each environment gets an orthogonal (statistically independent) representation — the same cell population generates a completely different firing pattern configuration. This decorrelation means dozens or hundreds of distinct spatial memories can be stored without corrupting each other. The remapping is rapid (apparent within seconds of entering a new environment) and is one of the key computational advantages of the hippocampal spatial coding strategy.
Question 5 Short Answer
Why is it inaccurate to say that the hippocampus permanently stores spatial memories, and what actually happens to those memories over time?
Think about your answer, then reveal below.
Model answer: The hippocampus plays a time-limited role in spatial memory. It is critical for initially encoding spatial memories and for consolidation — the process of stabilizing and organizing memories during sleep and rest, involving hippocampal replay of place cell sequences. Over time, however, well-consolidated spatial memories are transferred to and can be retrieved from neocortical areas, particularly retrosplenial and parietal cortices. The hippocampus becomes less critical for accessing remote spatial memories (those formed long ago) while remaining essential for recent ones. Patients with hippocampal damage lose recently formed memories but can often still access old, well-consolidated ones — a temporal gradient that reflects this consolidation-and-transfer process.
This relates to the standard model of systems consolidation (Squire's model), where the hippocampus acts as a temporary binding site that gradually transfers representations to distributed cortical storage. The misconception that 'memories are stored in the hippocampus permanently' conflates the site of initial encoding and consolidation with the final storage location. For spatial memories in particular, the cortical storage eventually allows retrieval without hippocampal involvement.