2. Nongraded amnesia (Spatial memory tasks)
Remote memory
Hippocampus
Neocortex
Retrograde amnesia
Nongraded amnesia (Spatial memory tasks)
Multiple trace theory

3. methods
Physical studies Pharmacological studies Genetic lesion studies Cellular and temporal precise Optogenetics (Opsin Genes)

5. Specific Optogenetic Inhibition (OGI)of Excitatory Neurons in Dorsal CA1 Reduces Neuronal Activity

8. A temporally precise, stable and reversible manner

9. CA1 OGI Blocks Contextual Fear Acquisition and Retrirval
A real-time involvement of CA1 excitatory cells, during acquisition and recall

11. No difference in exploration

12. Acquisition and expression of fear denpend on the amygdala

13. CA1 OGI Reversibly Interferes with Remote Fear Memory Recall

14. Ongoing involvement, default activator of the memory trace

15. Disturb only recent but not remote
OPI limits expression of compensatory mechanisms

16. Precise but Not Prolonged CA1 OGI Blocks Remote Contextual Fear Recall

18. Interrupted in the midst of a behavioral session
Hippocampus participate in remote memory trace maintenance

19. Brain-wide Mapping of Circuit Activity Controlled by the Hippocampus during Remote Recall

21. CA1 recruiting brain-wide fear memory activity
Increased activity compensating for hippocampal inactivation

23. OGI of Anterior Cingulate Cortex (ACC) Inhibits Remote but Not Recent Contextual Memory

24. Olfactory bulbs (OB), no effect

25. Point not clear
This result at once demonstrates that a sudden drop in a major source of synaptic input to cortex need not nonspecifically influence recall (without ruling out a contribution from such an effect) and also points to the specificity of ACC in remote memory (consistent with prior work).