Abstract
Suppression of cholinergic receptors and inactivation of the septum impair short-term memory, and disrupt place cell and grid cell activity in the medial temporal lobe (MTL). Location-dependent hippocampal place cell firing during active waking, when the acetylcholine level is high, switches to time-compressed replay activity during quiet waking and slow-wave-sleep (SWS), when the acetylcholine level is low. However, it remains largely unknown how acetylcholine supports short-term memory, spatial navigation, and the functional switch to replay mode in the MTL. In this paper, we focus on the role of the calcium-activated non-specific cationic (CAN) current which is activated by acetylcholine. The CAN current is known to underlie persistent firing, which could serve as a memory trace in many neurons in the MTL. Here, we review the CAN current and discuss possible roles of the CAN current in short-term memory and spatial navigation. We further propose a novel theoretical model where the CAN current switches the hippocampal place cell activity between real-time and time-compressed sequential activity during encoding and consolidation, respectively.
Highlights
It has been suggested that the medial temporal lobe (MTL) supports memory formation through two distinct processes: encoding and consolidation (Buzsáki, 1989; McClelland et al, 1995; reviewed by McGaugh, 2000)
The cholinergic system is believed to modulate the dynamics of the MTL between active waking, quiet waking, and SWS modes in the hippocampus, making the information flow suitable for encoding and consolidation (Hasselmo, 1999)
Others, suggest this feature could be directly useful for the short-term memory function of the MTL
Summary
It has been suggested that the medial temporal lobe (MTL) supports memory formation through two distinct processes: encoding and consolidation (Buzsáki, 1989; McClelland et al, 1995; reviewed by McGaugh, 2000). PERSISTENT FIRING MAY CONTRIBUTE TO SHORT-TERM MEMORY Sustained increased activity in MTL areas has been observed in the trace period of trace conditioning tasks, or during the delay period of DNMS tasks, using in vivo electrophysiological recordings in animals, and using fMRI in humans. Aged animals that were impaired in acquiring this trace conditioning task, showed significantly fewer cells responding during the delay period (McEchron et al, 2001) These results suggest that sustained firing activity of the hippocampal neurons is necessary for acquiring this type of task. Each cell showed persistent firing at the same frequency, these neurons fired at slightly different timings from each other with a specific delay, which was equal to one gamma cycle (∼40 Hz; Lisman and Idiart, 1995; Jensen and Lisman, 1996). Koene and Hasselmo (2008) further suggested that memory items in the nested theta and gamma model can
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