Noradrenaline facilitates working memory for gamma-modulated low coherence stimuli

MIGUELEZ FERNÁNDEZ A. M. M; ZANUTTO B. S; LEW S. E.

New Orleans, LA, USA

Congreso; Annual Meeting of the Society for Neuroscience.; 2012

Society for Neuroscience.

The locus coeruleus (LC) is a noradrenergic brainstem structure and the sole source of noradrenaline (NA) to the neocortex. One of its functions is to regulate waking and arousal by changing the level and mode of LC activity. During focused attention, LC cells exhibit phasic activation for target stimuli and a moderate level of tonic discharge whereas in inattentive states there is a very low level LC activity in general. Gamma-band oscillation is observed in many cortical areas under different conditions and has been implicated in several aspects of cognition and attention. In particular, high values of gamma-band power indicate an activated state of cortical networks. In addition, in early visual areas levels of gamma-band synchronization among neurons is related to the level of attention directed to a visual stimulus. In this study we propose a novel mechanism that connects attentional states induced by NA levels in the neocortex with the power of gamma oscillations. In order to understand how NA affect working memory, we use a recurrent neural network able to sustain working memory composed by 1600 pyramidal and 400 inhibitory integrate and fire neurons. In this model, an increased noradrenergic tone reduces HCN after-hiperpolarization conductance. As a result, NA blocks HCN currents delaying membrane repolarization and changing the permeability of the whole system to some frequencies. A tonic increase in NA levels enhanced working memory for gamma-band modulated stimuli, especially for low coherence ones. Thus, for gamma modulated stimuli, NA focuses the system increasing its ability to sustain low coherence stimuli, resembling a high attentional state.