Neural correlates of single-vessel haemodynamic responses in vivo

Abstract

Neural activation increases blood flow locally. This vascular signal is used by functional imaging techniques to infer the location and strength of neural activity 1,2 . However, the precise spatial scale over which neural and vascular signals are correlated is unknown. Furthermore, the relative role of synaptic and spiking activity in driving hemodynamic signals is controversial [3][4][5][6][7][8][9] . Prior studies recorded local field potentials (LFPs) as a measure of synaptic activity together with spiking activity and low-resolution hemodynamic imaging. Here we used two-photon microscopy to measure sensory-evoked responses of individual blood vessels (dilation, blood velocity) while imaging synaptic and spiking activity in the surrounding tissue using fluorescent glutamate and calcium sensors. In cat primary visual cortex, where neurons are clustered by their preference for stimulus orientation, we discovered new maps for excitatory synaptic activity, which were organized similar to spiking activity but were less selective for stimulus orientation and direction. We generated tuning curves for individual vessel responses for the first time and found that parenchymal vessels in cortical layer 2/3 were orientation selective. Neighboring penetrating arterioles had different orientation preferences. Pial surface arteries in cats, as well as surface arteries and penetrating arterioles in rat visual cortex (where orientation maps do not exist 10 ), responded to visual stimuli but had no orientation selectivity. We integrated synaptic or spiking responses around individual parenchymal vessels in cats and established that the vascular and neural responses had the same orientation preference. However, synaptic and spiking responses were more selective than vascular responses-vessels frequently responded robustly to stimuli that evoked little to no neural activity in the surrounding tissue. Thus, local neural and hemodynamic signals were partly decoupled. Together, these results indicate that intrinsic cortical properties, such as propagation of vascular dilation between neighboring columns, need to be accounted for when decoding hemodynamic signals.To determine how neural activity leads to changes in cerebral blood flow, the hemodynamic responses of individual vessels need to be compared to neural activity in the surrounding tissue 11 . While sensory-evoked responses of individual vessels have been measured in the Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

In vivo real-time imaging of cutaneous hemoglobin concentration, oxygen saturation, scattering properties, melanin content, and epidermal thickness with visible spatially modulated light

“…Since 200mmHg pressure was enforced by the cuff, no arterial blood flew into the forearm area while the tissue was in acute hypoxia. To meet the needs of distal tissue oxygen consumption, the arterial smooth muscle contracted and relaxed slowly, pumping blood to the aerobic tissue to maintain its basic metabolism [43]. Blood filled into the capillary microcirculation intermittently.…”

Stability, affinity and chromatic variants of the glutamate sensor iGluSnFR

“…The intensity-based glutamate-sensing fluorescent reporter (iGluSnFR) 1 has become an invaluable tool for studying glutamate dynamics in diverse systems, including retina 2,3 , olfactory bulb 4 and visual cortex 5 . iGluSnFR also allows mesoscale "functional connectomic" mapping 6 and mechanistic studies of Huntington's disease 7 , synaptic spillover 8 , cortical spreading depression 9 and exocytotic vesicle fusion 10 .…”

Fast fMRI can detect oscillatory neural activity in humans

“…fMRI measures brain function by tracking focal changes in blood flow and oxygenation and therefore is an indirect measure of neuronal activity, with spatial and temporal specificity intrinsically limited by the precision and responsiveness of the coordinated regulation of blood delivery in the brain (7,8). Typical fMRI experiments use stimuli or tasks designed to elicit large, easily detectable hemodynamic responses, which lag the onset of neuronal activation by several seconds, suggesting that these hemodynamic signals are too slow to capture many aspects of ongoing neuronal activity.…”