A specific role for septohippocampal acetylcholine in memory?

Abstract

Acetylcholine has long been implicated in memory, including hippocampal-dependent memory, but the specific role for this neurotransmitter is difficult to identify in human neuropsychology. Here, we review the evidence for a mechanistic model of acetylcholine function within the hippocampus and consider its explanatory power for interpreting effects resulting from both pharmacological anticholinergic manipulations and lesions of the cholinergic input to the hippocampus in animals. We argue that these effects indicate that acetylcholine is necessary for some, but not all, hippocampal-dependent processes. We review recent evidence from lesion, pharmacological and electrophysiological studies to support the view that a primary function of septohippocampal acetylcholine is to reduce interference in the learning process by adaptively timing and separating encoding and retrieval processes. We reinterpret cholinergic-lesion based deficits according to this view and propose that acetylcholine reduces the interference elicited by the movement of salient locations between events.

Hypothalamic melanin-concentrating hormone projections to the septo-hippocampal complex in the rat

“…However, after the first experience the animal would dispense the cholinergic activation promoted by the MCH-ir fibers. This is supported by the explanation from Easton et al (2012) that say that the cholinergic input to the hippocampus is especially involved when the reduction of acetylcholine, through lesions, in interference relates specifically to locations and contexts, but not to the object identity attached to these representations. Despite the previously described importance of the septohippocampal cholinergic pathway, Parent & Baxter (2004) stated that, for some aspects of the hippocampal memory function, the acetylcholine (Ach) appears to be unnecessary.…”

Basal Forebrain Cholinergic Circuits and Signaling in Cognition and Cognitive Decline

“…The separation between encoding and retrieval is considered vital for formation of accurate associations (Easton et al, 2012; Hasselmo and Stern, 2014; Kunec et al, 2005). In support of an essential role for cholinergic signaling in facilitating encoding, muscarinic blockade has been shown both to shift CA1 pyramidal cell firing towards theta trough (thus away from the encoding peak) during exploration of a novel environment and to impair the encoding of an experimental environment (Douchamps et al, 2013; Newman et al, 2014).…”

Alterations of Coherent Theta and Gamma Network Oscillations as an Early Biomarker of Temporal Lobe Epilepsy and Alzheimer’s Disease

“…This neuronal coding is precisely organized within a time scale, which is controlled by ongoing oscillations, especially by the hippocampal theta and gamma rhythms (Bland and Oddie, 2001; Hasselmo et al, 2002; Huxter et al, 2008; Mizuseki et al, 2009; Easton et al, 2012; Buzsáki and Moser, 2013; Lisman and Jensen, 2013). A careful measurement of the proximodistal coherence of the theta activity in the dorsal hippocampus of normal and epileptic animals showed that healthy rats exhibited a stronger coordination between the temporoammonic and perforant entorhinal inputs near CA3 field (at proximal locations), while epileptic rats showed stronger coordination near subiculum (at distal locations; Laurent et al, 2015).…”