Graded persistent activity in entorhinal cortex neurons

Abstract

Working memory represents the ability of the brain to hold externally or internally driven information for relatively short periods of time. Persistent neuronal activity is the elementary process underlying working memory but its cellular basis remains unknown. The most widely accepted hypothesis is that persistent activity is based on synaptic reverberations in recurrent circuits. The entorhinal cortex in the parahippocampal region is crucially involved in the acquisition, consolidation and retrieval of long-term memory traces for which working memory operations are essential. Here we show that individual neurons from layer V of the entorhinal cortex-which link the hippocampus to extensive cortical regions-respond to consecutive stimuli with graded changes in firing frequency that remain stable after each stimulus presentation. In addition, the sustained levels of firing frequency can be either increased or decreased in an input-specific manner. This firing behaviour displays robustness to distractors; it is linked to cholinergic muscarinic receptor activation, and relies on activity-dependent changes of a Ca2+-sensitive cationic current. Such an intrinsic neuronal ability to generate graded persistent activity constitutes an elementary mechanism for working memory.

The Temporal Context Model in Spatial Navigation and Relational Learning: Toward a Common Explanation of Medial Temporal Lobe Function Across Domains.

“…the firing on the center arm in Figure 10c-d). Another aspect of the Egorov et al (2002) study that we neglected was the rate of change of firing rate in response to an input. Here we assumed that the response of the integrator cells to an input was essentially instantaneous.…”

“…6 ( Figure 6) using a model intended to represent EC. The simulation was populated of integrator cells modeled after those in EC layer V (Egorov et al, 2002) and provided with input from the head direction system (Taube, 1998), which are known to synapse on EC layer V (Haeften et al, 2000). Normalization of the integrator cell population was accomplished by means of a gain modulation where the gain varied inversely with the activity in the network (Chance et al, 2002).…”

“…The existence of a stable firing rate in the absence of input observed by Egorov et al (2002) provides the capability to implement this property. Further, Egorov et al (2002) observed that these cells respond to subsequent suprathreshold inputs by adopting a new stable firing rate (see Figure 5). Depolarizing (positive) inputs resulted in a higher stable firing rate.…”

Somato-dendritic mechanisms underlying the electrophysiological properties of hypothalamic magnocellular neuroendocrine cells: A multicompartmental model study

“…CAN channels exist in the membranes of a variety of mammalian cells, both excitable and non-excitable, and support important cellular responses such as neuronal bursting, secretion, and cardiac rhythmicity (Siemen 1993;Thorn and Petersen 1993;Partridge et al 1994;Teulon 2000). For example, CAN channels take part in plateau potential generation and persistent spiking in entorhinal cortex neurons (Egorov et al 2002), in DAPs in myenteric neurons (Vogalis et al 2002), and in after-depolarization and burst after discharge in rat neocortical neurons (Kang et al 1998;Aoyagi et al 2002). I CAN appears to have higher calcium sensitivity than other Ca 2+ -activated currents, such as I BK and I SK (Zhu et al 2004).…”

Regulation of neuromodulator receptor efficacy—implications for whole-neuron and synaptic plasticity

“…(107; 150)). The alteration of membrane properties due to neuromodulation or a specific composition of ion channels induces a 'filter' on signal transmission that may affect gain modulation (151) or short-term retention of spike input patterns (152). A significant difference in receptor density and sensitivity will affect the efficacy of the intrinsic 'filter' for each individual neuron.…”