The Role of Inhibition in Selective Attention

摘要

The phenomenon of attending to a stimulus is at the neuronal level usually assumed to mean an increase in excitation of the neurons representing that stimulus and or its underlying features. This is strongly influenced by the notion that attention works like a spot light. Increased neuronal activity is not only observed in the presence of an attended stimulus [7], but such an increased activity has been also found in the absence of the stimulus as long as it is expected to be present [4]. It is thus demonstrated that attention can be affected by both bottom-up information from the environment, and top-down typically information considered to originate in the prefrontal cortex (PFC). This bottom-up/top-down interaction results in a selection of stimuli to attend to [5]. In the case of visual information, there are established pathways in the human brain that allow for excitatory influences from the frontal cortices on the input processing pathways of the thalamus [1, 2]. However, other puzzling attentional effects, such as inattentional blindness, exist and seem to contradict this mechanism. A complementary view on attention is the concept of the Validation Gate (VG) [6]. It posits that through both excitation and inhibition, predicted features can be downregulated to increase sensitivity to novelty. The same aforementioned pathways could also allow for such indirect inhibition of input to the thalamus via the thalamic reticular nucleus (TRN) [9-11]. Here, we investigate the viability of this thalamocortical substrate by computationally modelling it with a network consisting of four distinct populations of spiking neurons: specific and non-specific nuclei of the thalamus, the thalamic reticular nucleus, and a cortical map [3, 8]. We validate the model using an experimental protocol in which the network has to attend to a region of interest (ROI). Only stimuli appearing within the ROI is task-relevant. We show that in the absence of PFC influence, the modelled cortical map exhibits activity proportional to the size of the stimulus. However, PFC activity can bias the cortical response through a marked decrease in activity in response to stimuli outside of the ROI and a slight increase for that within the ROI. This modulatory effect ensures that stimuli within the ROI consistently elicit stronger activation than those outside of it, regardless of size. Our results thus provide support for the mechanism of inhibitory attention with the TRN as its hub.