Attention: oscillations and neuropharmacology

Abstract

Attention is a rich psychological and neurobiological construct that influences almost all aspects of cognitive behaviour. It enables enhanced processing of behaviourally relevant stimuli at the expense of irrelevant stimuli. At the cellular level, rhythmic synchronization at local and long-range spatial scales complements the attention-induced firing rate changes of neurons. The former is hypothesized to enable efficient communication between neuronal ensembles tuned to spatial and featural aspects of the attended stimulus. Recent modelling studies suggest that the rhythmic synchronization in the gamma range may be mediated by a fine balance between N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate postsynaptic currents, whereas other studies have highlighted the possible contribution of the neuromodulator acetylcholine. This review summarizes some recent modelling and experimental studies investigating mechanisms of attention in sensory areas and discusses possibilities of how glutamatergic and cholinergic systems could contribute to increased processing abilities at the cellular and network level during states of top-down attention.

Fig. 1

Attention-induced rate modulation (solid line) and gamma modulation (dashed line) as a function of the g_AMPA:g_NMDA ratio in a network model. The initial main effect of increasing the g_AMPA:g_NMDA ratio (with or without attention) was an increase in the network synchronization in the gamma band (dotted line), i.e. in the overall gamma power. The rate modulation decreased monotonically with the g_AMPA:g_NMDA ratio. Attention-mediated gamma modulation (irrespective of overall power) increased to a g_AMPA:g_NMDA ratio of 0.12 and then decreased quickly to almost 0. Attention-induced modulation of gamma synchrony depended on a fine balance of NMDA/AMPA receptor activation, whereas attention-induced rate changes were less susceptible to small changes in this ratio. The x-axis shows the ratio of AMPA:NMDA conductance (for details see Buehlmann & Deco, 2008) and the y-axis shows the percentage of modulation of gamma band frequency for the rate and gamma modulation data; it shows the percentage of gamma power relative to overall spectral power for the gamma power curve.

Fig. 2

Influence of ACh on attentional modulation in V1. (A) Example of a single cell where the application of ACh resulted in enhanced attentional modulation. In the absence of ACh application the attentional modulation was small but significant (P < 0.05). Left plot shows single trial activity for the four conditions and the corresponding peri-stimulus time histograms. Right plot shows mean activity obtained from the time period of 200–500 ms after stimulus onset. (B) Mean attentional modulation index for our population of V1 cells. Attentional modulation was significantly increased when ACh was applied. RF, receptive field.