Rapid event-related, BOLD fMRI, non-human primates (NHP): choose two out of three

Abstract

Human functional magnetic resonance imaging (fMRi) typically employs the blood-oxygen-leveldependent (BoLD) contrast mechanism. in non-human primates (nHp), contrast enhancement is possible using monocrystalline iron-oxide nanoparticles (Mion) contrast agent, which has a more temporally extended response function. However, using BoLD fMRi in nHp is desirable for interspecies comparison, and the BOLD signal's faster response function promises to be beneficial for rapid event-related (reR) designs. Here, we used reR BoLD fMRi in macaque monkeys while viewing realworld images, and found visual responses and category selectivity consistent with previous studies. However, activity estimates were very noisy, suggesting that the lower contrast-to-noise ratio of BoLD, suboptimal behavioural performance, and motion artefacts, in combination, render reR BoLD fMRi challenging in nHp. previous studies have shown that reR fMRi is possible in macaques with Mion, despite Mion's prolonged response function. to understand this, we conducted simulations of the BoLD and Mion response during reR, and found that no matter how fast the design, the greater amplitude of the Mion response outweighs the contrast loss caused by greater temporal smoothing. We conclude that although any two of the three elements (reR, BoLD, nHp) have been shown to work well, the combination of all three is particularly challenging.

Corticocortical and Thalamocortical Changes in Functional Connectivity and White Matter Structural Integrity after Reward-Guided Learning of Visuospatial Discriminations in Rhesus Monkeys

“…Our study also uniquely shows that thalamocortical functional connectivity from the inferotemporal and entorhinal cortex to the DM_Th was increased after learning, while the VP white matter tract had reduced FA. Connectivity changes in the Experimental group were larger than in an age-and cohort-matched control group, who had learned an unrelated visual task (Pelekanos et al, 2020). In accord with our findings, strong links between functional and structural connectivity have been reported in the healthy brain (Honey et al, 2007(Honey et al, , 2009O'Reilly et al, 2013).…”

“…In contrast to the complex cognitive training of the Experimental group, the Control group completed a passive visual fixation task. The task, stimuli, and training protocol of our control monkeys are described in detail previously (Pelekanos et al, 2020). Briefly, control monkeys were trained to fixate a cue that appeared in the center of a computer screen.…”

Ultra-high field (10.5 T) resting state fMRI in the macaque

“…One tool to improve SNR is using monocrystalline iron oxide nanoparticles (MION) as a contrast agent (Moeller et al, 2009;Tsao et al, 2003;Vanduffel et al, 2001). However, this has several disadvantages: (1) the signal then reflects blood volume changes (Leite et al, 2002) rather than the typical BOLD response, complicating its translatability to typical human studies, (2) it has a slower hemodynamic response (Leite et al, 2002;Pelekanos et al, 2020), exacerbating an already major problem with fMRI, and (3) it accumulates in the brain and causes potentially longlasting health disadvantages. The SNR problem can to some degree also be overcome with larger datasets (i.e.…”

Model-based dynamic off-resonance correction for improved accelerated fMRI in awake behaving non-human primates

“…In awake NHP imaging, the reduced functional sensitivity is conventionally addressed by using contrast agents [36][37][38][39] or detecting and discarding data frames with excessive motion 40,41 . Using contrast agents biases the functional signal by changing the hemodynamic response functions, hindering direct comparison between findings in NHPs and human studies 42 .…”