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The Role of Cortical Cholinergic Inputs in a Selective Attentional Suppression Task

Visual stimuli are in constant competition with one another because of the limited processing capacity in the visual system (Desimone and Duncan, 1995). Selective attention is therefore necessary to suppress distractor stimuli and enhance perceptual processing of target stimuli (Desimone and Duncan, 1995). Cholinergic projections from the nucleus basalis magnocellularis (NBM), found in the basal forebrain, to the prefrontal (PFC) and posterior parietal (PPC) cortices play a significant role in the modulation of selective attention (Nelson et al, 2005). These two cortical areas work together to modulate attentional processing to amplify the signals of the attended stimulus in order to overcome those elicited by the unattended stimuli, thus increasing the signal-to-noise ratio (Reynolds and Desimone, 2003). In the present study, rats performed a learning-to-ignore (LI) task initially designed for human participants (Dixon et al, 2009) where they learned to respond to a stimulus that they had previously ignored in two different contexts. The cholinergic neurons of the NBM were lesioned with the selective cholinergic immunotoxin 192 IgG-saporin (SAP) to reduce cholinergic cortical afferentation. Selective attention was impaired in the SAP group; this was evidenced by the SAP rats’ better performance in the LI task. As hypothesized, the reduction in cortical levels of ACh impaired their ability to ignore distractor stimuli.