Visual Motion Processing Investigated Using Contrast Agent-Enhanced fMRI in Awake Behaving Monkeys

Abstract

To reduce the information gap between human neuroimaging and macaque physiology and anatomy, we mapped fMRI signals produced by moving and stationary stimuli (random dots or lines) in fixating monkeys. Functional sensitivity was increased by a factor of approximately 5 relative to the BOLD technique by injecting a contrast agent (monocrystalline iron oxide nanoparticle [MION]). Areas identified as motion sensitive included V2, V3, MT/V5, vMST, FST, VIP, and FEF (with moving dots), as well as V4, TE, LIP, and PIP (with random lines). These regions sensitive for moving dots are largely in agreement with monkey single unit data and (except for V3A) with human fMRI results. Moving lines activate some regions that have not been previously implicated in motion processing. Overall, the results clarify the relationship between the motion pathway and the dorsal stream in primates.

Lessons from fMRI about Mapping Cortical Columns

“…Dextran-coated iron oxide nanoparticles have been used as a long half-life intravascular susceptibility contrast agent (Kennan et al, 1998;Mandeville et al, 1998;van Bruggen et al, 1998), similar to endogenous irons in dHb molecules (used for the BOLD contrast). The half-life of the iron oxides in blood is dependent on particle size and species; the typical half-life of 20-30 μm diameter particles is >4 hours in rats (Mandeville et al, 1998), 3-6 hours in cats (in our observation), and >18 hours in non-human primates (Vanduffel et al, 2001). During a steadystate condition established following the infusion of an intravascular contrast agent (reached within a few minutes), an increase in CBV during stimulation will induce an increase in intravoxel contrast agent, and consequently a decrease in MRI signal.…”

The neural basis of the blood–oxygen–level–dependent functional magnetic resonance imaging signal

“…BOLD fMRI has also been applied successfully in anaesthetized or conscious animals, including rodents (Hsu et al 1998;Lahti et al 1998;Bock et al 1998;Tuor et al 2000;Burke et al 2000;Ances et al 2000;Burke et al 2000;Chang & Shyu 2001), rabbits (Wyrwicz et al 2000), cats ( Jezzard et al 1997), bats (Kamada et al 1999), and recently monkeys (Nakahara et al 2002;Logothetis et al 1998Logothetis et al , 1999Disbrow et al 1999;Zhang et al 2000;Disbrow et al 2000;Vanduffel et al 2001;Dubowitz et al 2001). What follows describes the use of BOLD fMRI in monkeys (Macaca mulatta) and its combination with electrophysiological measurements in an attempt to investigate the neural basis of the BOLD response.…”

Setup and data analysis for functional magnetic resonance imaging of awake cat visual cortex

“…An MRI-compatible head-post implanted on the skull is the most commonly used device for head fi xation [9,15,[17][18][19][20][21][22][23][24]26] . Although noninvasive methods have been proposed for monkey studies [27] , a plastic head-post is still the best choice if we are to extend fMRI experiments to cats, due to the complexity of the noninvasive methods.…”

“…Most of the studies scanning behaving monkeys have developed similar methods [9,10,[14][15][16][17][18][19][20][21][22][23][24][25][26] . One of the most important aspects in the awake monkey fMRI scan is to keep the monkey's head in position by invasively implanting a headpost on the skull or by noninvasive techniques, such as a vacuum helmet [27] .…”