Spatial Navigation Flashcards
What is particular with ant spatial navigation?
- They always chose the shortest path even in a feature less environment
- Use polarized light to orient themselves using their dorsal rim area + have an integrated odometer (elongated legs = go too far)
What are the 5 types of neurons involved in spatial navigation and mapping?
- Place cells
- Grid cells
- Head direction cells
- Border cells
- Speed cells
What is the brain part implicated in memory and what proved that?
The hippocampus : Henry Molaison (HM = Hippocampal man) saw a part of his temporal lobe being removed to treat epilepsy, including most of his hippocampus and that destroyed his capacity to form any new long-term memories.
What is the difference in structure of the hippocampus in London taxi drivers? What is it giving them?
Anterior H : significantly smaller
Body H : same size
Posterir H : significantly bigger
They are better to orient themselves in London crazy streets
What are the 3 major subregions of hippocampus and their type of cells?
- Dentate gyrus (granule cells) = linked toentorhinal cortex and receives inputs from it
- CA3 (pyramidal cells)
- CA1 (pyramidal cells)
Place cells characteristics (6)
- Located in hippocampus
- Fire in a particular place but there is no obvious relationships between place fields of neighboring cells
- Fire only under light
- Are environment specific (same cylinder of a different color = not the same place cells activated in the same region)
- Replay in order of activation during sleep really fast (about 20X)
- Inputs from EC are important for persistance of place fields
Grid cells characteristics
- Located in the entorhinal cortex
- Have firing fields across the entire environment organized in a hexagonal lattice structure that are evenly spaced apart. Grid spacing increase along the DV axis
- Shoot in the dark and fields remain stable across trials
- Have a spatial organization of grid cells : neighboring ones have a similar spacing that is typically offset (not overlapping)
- Fire according to info coming directly from path integration : head direction + speed
What are the biomarkers of AD and what should be their levels in the CSF (cerebrospinal spinal fluids) of a human?
Plaque of Aβ oligomers and hyperphosphorylation of tau damaging microtubules. In CSF, you should get a lot of hyperphophorylized tau proteins and not a lot of Aβ because they form sticky plaques.
What is the 4-MT test and what can it prove?
The 4 mountains Test is a hippocampus-dependent test of spatial memory where participants have to recognize a set of 4 mountains they saw for 2 seconds arranged differently. People with AD do worst at that test than controls and people suffering from a mild cognitive impairment.
Are grid cells or place cells dependent on one another according to research?
According to research, location of place fields may be determined by integrating inputs from many grid cells whose fields overlap. However, when medial septum is inactivated, you don’t have grid cell activity anymore (linked to medial entorhinal cortex), but you still have place fields that remain constant anyway.
What is the difference of the non-amyloidogenic pathway vs. the amyloidogenic one?
Non-amyloidogenic pathway : APP cleaved by α-secretase, then by 𝜸-secretase, leaving a healthy p3 piece.
Amyloidogenic pathway: APP cleaved first by β-secretase then by 𝜸-secreatase, leaving an Aβ piece which will form oligomers.
What is the effect of Aβ oligomers?
They are neurotoxins (they induce neuronal death at high concentration) and inhibit long term potentiation (increase in synaptic strength after exposition to constant stimuli). However, they use REALLY high concentrations that 1000X higher than physiological ones.
What was the Morris Water Maze (MWM) experiment?
Put a platform in a water tank and looked at swimming speed, time spent in the target quadrant, the distance swam in the quadrant and the crossing between platforms. They started by testing rats with hippocampal lesions that were slower to find the platform. Then, they induced mutations in genesregulafting APP cleavage and saw the OLDER mice with mutations were significantly slower finding the platform.
Do endogenous and low levels of Aβ have a role in learning and memory? How can it be tested ?
Healthy mice where they block Aβ cleaving site showed impaired learning and it inhibited hippocampal long term potentiation, so Aβ at low levels is necessary. It is in line with the Goldilocks Principle.
What is the effect of AD on place fields?
Place fields are degraded, but only in old transgenic mice.
