FMRI and electrophysiology of cortical layer-dependent processes in primary sensory cortex

Abstract

To understand cortical function, it is important to better understand the cortical functional units, i.e., its columns and layers. High-resolution fMRI can offer tremendous advantages for the study of cortical circuits in vivo, evidenced by the increasing interest in high-resolution fMRI. However, many questions remain about the size of the cortical features that can be resolved, and how neural activity gives rise to the blood oxygenation dependent (BOLD) signal measured with fMRI. We use high-resolution fMRI combined with electrophysiology to study laminar processing, with the aim of gaining insight into the layer-dependent neural processing and the mechanisms of neurovascular coupling in the primary visual cortex (V1) and temporal lobe of awake and anesthetized macaques. We investigated whether laminar differences in the BOLD, cerebral blood flow (CBF), and volume (CBV) responses can be detected for excitatory and inhibitory stimuli, and found that the mechanisms for positive and negative BOLD responses differ, but also that neurovascular coupling differs in the cortical layers. Furthermore, neuromodulators such as dopamine can alter neurovascular coupling. Our results suggest that neurovascular coupling depends on multiple factors, and that the combination of high-resolution fMRI with electrophysiology can be used to resolve neurovascular coupling in functional microcircuits.