Potential roles of cholinergic modulation in the neural coding of location and movement speed

Abstract

Behavioral data suggest that cholinergic modulation may play a role in certain aspects of spatial memory, and neurophysiological data demonstrate neurons that fire in response to spatial dimensions, including grid cells and place cells that respond on the basis of location and running speed. These neurons show firing responses that depend upon the visual configuration of the environment, due to coding in visually-responsive regions of the neocortex. This review focuses on the physiological effects of acetylcholine that may influence the sensory coding of spatial dimensions relevant to behavior. In particular, the local circuit effects of acetylcholine within the cortex regulate the influence of sensory input relative to internal memory representations via presynaptic inhibition of excitatory and inhibitory synaptic transmission, and the modulation of intrinsic currents in cortical excitatory and inhibitory neurons. In addition, circuit effects of acetylcholine regulate the dynamics of cortical circuits including oscillations at theta and gamma frequencies. These effects of acetylcholine on local circuits and network dynamics could underlie the role of acetylcholine in coding of spatial information for the performance of spatial memory tasks.

Keywords: Basal forebrain; Entorhinal cortex; Grid cells; Medial septum; Place cells; Spatial navigation; Theta rhythm.

Figure 1

Cholinergic modulation of rodent cortical structures described in this review. A. Schematic dorsal view of mouse brain showing cholinergic neurons in the medial septum and vertical limb of the diagonal band (MSDB) that innervate the hippocampus (HC) and the medial entorhinal cortex (MEC). B. Cholinergic neurons in the substantia innominata and horizontal limb of the diagonal band (SI & DB) activate cholinergic receptors in neocortical regions including the medial prefrontal cortex (MPFC) and primary visual cortex (V1), primary somatosensory cortex (S1), primary auditory cortex (A1) and retrosplenial cortex (RSC) as well as higher order visual areas. Higher order visual areas in the rodent include areas LM, AL, RL, AM and PM (Wang et al., 2011). C. Saggital view of the mouse brain schematically showing cholinergic innervation arising from the MSDB to innervate hippocampus and entorhinal cortex and from SI to innervate neocortical regions including V1 and MPFC. Schematic diagrams based on (Oh et al., 2014)