Spatial Navigation in Rats Flashcards
Tolman (1930) experiment with cognitive maps
Used a radial arm maze, each arm was baited with food (to eliminate fear of danger) before a few had their food removed
Rats produced a cognitive map by relating arms to landmarks, moving in a clockwise manner, or by marking each arm
Tolman (1930) experiment with cognitive maps alteration
Arms were rotated after rats made 3 correct choices (cues were the same, marked arms were no longer helpful)
Rats continued to avoid arms that did not have food before even if they did not visit them → used working memory to store information about the spatial relationships in the maze
Morris water maze experiment
Hidden platform was placed in a 1/4 quadrant of a bath of water → rats are placed in the water and are able to locate the platform → water becomes clouded in order to obstruct platform from view → rats associate quadrant containing the platform with landmarks outside of the pool
Role of hippocampus in spatial learning - what sections of the hippocampus are involved?
Trisynaptic circuit (1, 2, 3)
1. Perforant pathway connects entorhinal cortex (EC) to hippocampus
2. Mossy fibers connect dentate granule cells to CA3 pyramidal cells
3. Schaffer collaterals of the CA3 pyramidal axons make synaptic connections to the CA1 pyramidal cells
Place cells
Neurons in the hippocampus that show firing patterns related to the animal’s position in space (firing field = spatial area within which the place cell is active)
Form a spatial map of the local spatial environment
Plasticity of place cells
Place cell preferences are not predefined but are established in a novel environment
Place cells can code for more than one place field (can also have two different place fields within the same environment)
Experiment with the plasticity of place cells
Visual cues are placed in an experimental setup → cues are rotated once place cell preferences are established → cells fire to the new locations of cues (i.e. cell firing SW will now fire NW)
Preferences remain even if all cues are removed (“dead reckoning”) → consist of visual motion and vestibular cues
Grid cells
Multiple locations at which an entorhinal cell fires forms the vertices of a hexagon (grid cells are vertices)
Provide info about distance and direction using internal cues w/o relying on inputs from the environment
Spacing of hexagonal elements that create spatial map change when moving from top to bottom in the EC (30-35 cm from one vertex to another at the top, as far as several meters between vertices at the bottom)
Differences between place and grid cells
Place cells form unique spatial map specific to local environment, grid cells fire together at a particular set of locations on the grid map for one environment as well as analogous positions on the map for another location
Head direction cells
Act like a compass (become active only when facing a particular direction)
No plasticity (fire in the same pattern regardless of novelty)
Neural oscillation/brain waves
Repetitive patterns of neural activity → rhythmic activations of groups of neurons
Types: Alpha (8-12 Hz), Theta (4-8 Hz), low Gamma (30-70 Hz), high Gamma (70-150 Hz)
Purpose of neural oscillations
Feature binding, information transfer, and rhythmic motor activity
Phase precession
During navigation sequential activation of hippocampal place cells requires spiking of individual cells and the spiking correlates with the phase of theta → phase precession
Neural signatures of place fields
- An asymmetric ramp-like depolarization of the baseline membrane potential
- An increase in the amplitude of membrane potential theta oscillations
- A phase precession, such that spike times of place cells advanced relative to LFP theta
