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Table 1. 

Summary of internal versus external mode examples.

TimescaleSpatial scaleInternal modeExternal mode
Hippocampal encoding vs. retrieval 10s ms Single circuit: hippocampal trisynaptic loop Trough of CA1pyramidal theta: CA3 input to CA1 stronger than entorhinal input Peak of CA1pyramidal theta: entorhinal input to CA1 stronger than CA3 input 
 
Hippocampal encoding vs. retrieval 100s ms Multiple circuits: hippocampus and septal circuits Retrieval: lower cholinergic tone; CA3 drives CA1 activity Encoding: higher cholinergic tone; entorhinal cortex drives CA1 activity 
 
Neocortical feedforward vs. feedback 100s ms to 10s s Changes often coherent over ∼5–50 mm of neocortex Field potential filtered in 4–35 Hz range is high and high variance; lower; cholinergic tone; inhibition of core thalamic input and feedforward corticocortical drive Field potential filtered in 4-35 Hz range is low and low variance; higher cholinergic tone; elevated asynchronous firing, detectable as increase in broadband power 
 
Active vs. resting wake periods seconds–minutes Most of brain Lower cholinergic tone; higher overall activity in default mode network Higher cholinergic tone; lower overall activity in default mode network 
 
Non-REM vs. REM 10s minutes Entire brain REM: exploration of cortical networks containing long-term memories Non-REM: dominance of hippocampus, containing more recent memories 
 
Wake vs. sleep Hours Entire brain Sleep: minimal influence of environment; relatively lower cholinergic tone in cortex on average Wake: (potential for) strong influence of environment; relatively higher cholinergic tone in cortex on average 
TimescaleSpatial scaleInternal modeExternal mode
Hippocampal encoding vs. retrieval 10s ms Single circuit: hippocampal trisynaptic loop Trough of CA1pyramidal theta: CA3 input to CA1 stronger than entorhinal input Peak of CA1pyramidal theta: entorhinal input to CA1 stronger than CA3 input 
 
Hippocampal encoding vs. retrieval 100s ms Multiple circuits: hippocampus and septal circuits Retrieval: lower cholinergic tone; CA3 drives CA1 activity Encoding: higher cholinergic tone; entorhinal cortex drives CA1 activity 
 
Neocortical feedforward vs. feedback 100s ms to 10s s Changes often coherent over ∼5–50 mm of neocortex Field potential filtered in 4–35 Hz range is high and high variance; lower; cholinergic tone; inhibition of core thalamic input and feedforward corticocortical drive Field potential filtered in 4-35 Hz range is low and low variance; higher cholinergic tone; elevated asynchronous firing, detectable as increase in broadband power 
 
Active vs. resting wake periods seconds–minutes Most of brain Lower cholinergic tone; higher overall activity in default mode network Higher cholinergic tone; lower overall activity in default mode network 
 
Non-REM vs. REM 10s minutes Entire brain REM: exploration of cortical networks containing long-term memories Non-REM: dominance of hippocampus, containing more recent memories 
 
Wake vs. sleep Hours Entire brain Sleep: minimal influence of environment; relatively lower cholinergic tone in cortex on average Wake: (potential for) strong influence of environment; relatively higher cholinergic tone in cortex on average 
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