UC Irvine

Neuroanatomical studies play a key role in developing an understanding of neural connectivity and providing insight into how structure leads to function. Cell-type specific tracing methods have been utilized to identify distinct projection neurons originating from the basal forebrain and terminating in the primary visual cortex (V1). These neurons have been exclusively labeled using cell type-specific helper viruses, which allow for selective infection and spread of modified rabies viruses to label the projection neurons terminating onto specific neuron types in V1. While basal forebrain afferents terminate in the infragranular layers of V1, acetylcholine is delivered to more superficial layers through volume transmission. This study was designed to determine the synaptic targets and functional implications of this projection pathway utilizing a retrograde-tracing method to deliver light-gated ion channels to basal forebrain projection neurons. This allowed for direct optogenetic manipulation during single unit recording in V1 of anaesthetized rats. In doing so, we found significant suppression of cell response to the preferred stimulus with basal forebrain activation. Conversely, we found that responses to stimuli smaller than the optimal size were facilitated during basal forebrain activation. Thus, basal forebrain effects on V1 neurons depend on stimulus size. We examine the differences among cortical layers to further distinguish the role acetylcholine plays in the cortex. provide insight into the mechanism of cholinergic modulation from visual processing.