L37-41 Flashcards
What is the memory engram?
Long-lasting biological changes that take place in the brain to encode specific experiences.
Basic unit of memory.
How are engrams thought store memories?
- Greater synaptic strength = higher AMPA/NMDA ratio
- Increased spine density
- Engram cells that fire together, wire together
How can engrams be studied?
- in vivo electrophysiology
- in vivo Ca2+ imaging
Transgenic mice/viral expression system, e.g.:
- loss-of-function study where a virus expressing CREB and an inducible construct ==> cell ablation was used to specifically kill allocated neurons after training 00> disrupted freezing
- gain of function study, with optogenesis (ChrOpsin2) ==> sufficient to induce freezing in a non-training setting
How are engrams distributed across brain areas and regions?
In engram cell ensembles (ECEs): ECEs in different regions in the brain may support distinct aspects of an experince, e.g., in contextual fear memory hippocampal ESEs may represent context, whereas amygdala ECEs may represent valence info, and cortical ECEs may represent distinct sensory info
How are engram cells connected to other engram cells and brain circuits in general?
- preferentially connected to other engram cells by stronger synaptic connections than non-engram cells
- spine density and size are selectively increased in engram cell assemblies, and this is positively correlated to memory strength
How are engrams altered in disease conditions?
- mutations in specific components of the activity-dependent transcriptional pathways has been implicated with various neurodeveopmental and neurological disorders
- Alzheimers: fewer re-activated neurons - contextual memories can be stored but not adequetely retrieved
Mention some IEGs.
cFOS, Arc, Zif/268, Npas4
What are CREB, and what are the function of CREB?
- cAMP element binding protein
- a transcription factor that binds cAMP response element (CRE) sites in the DNA
- required for fear memory expression
- neurons with relatively increased CREB expression “win” the competition for allocating towards an engram supporting a fear memory
What did Karl Lashley do, and what did he find?
Cortical cuts in rats, failed to locate memory to a specific area ==> the engram is everywhere (in the cortex), but nowhere specifically
Describe and identify the neocortex and distinguish it from allocortex.
Neo: 6 histological layers
Allo: 3 histological layers (e.g., hippocampus)
Subdivide the telencephalon in lobes.
Frontal, parietal, occipital, temporal
Describe the anatomy of the medial temporal lobe memory system.
Hippocampus + parahippocampal cortex + rhinal cortex (peri + ento, parahippocampal + the rhinal cortices = parahippocampal gyrus)
(the amygdala is not considered part of the memory system per se)
