Functional magnetic resonance imaging (fMRI) has been widely used to study human tactile perception. To reveal many unsolved problems to human tactile perception, developing complex and fMRI-compatible stimulation devices are crucial for tactile perception research. These stimulation devices, combined with functional magnetic resonance imaging (fMRI), can assist researchers in analyzing human brain activity. Through analyzing human brain activity, researchers can clarify how the human brain controls the body. Meanwhile, these device scan provide the best rehabilitation program for patients. This chapter presents previous fMRI-compatible stimulation devices, including texture stimulation, shape stimulation, vibrotactile stimulation, etc., which involve the hands, face, ears, legs and other parts of the body. In this chapter, we examine the design of the devices in greater detail. Finally, we summarize the characteristics of these devices and create an outlook for future fMRI-compatible devices.
TopBackground
Since the early 1990s, fMRI has dominated brain mapping research because it does not require people to undergo surgery, shots, be exposed to ionizing radiation, etc. (Huettel, S. A, et al., 2009). During the late 19th century, Angelo Mosso invented the 'human circulation balance', which worked like a seesaw to measure blood flow changes in the brain (Sandrone S, et al., 2012).
However, although briefly mentioned by William James in 1890, the precise workings of this balance and the experiments remained unclear until the discovery of the original instrument as well as Mosso’s reports by Stefano Sandrone and colleagues (Sandrone S, et al., 2014). In 1890, Charles Roy and Charles Sherrington first experimentally linked brain function to its blood flow at Cambridge University (Raichle, M. E, et al., 2000). In 1936, Linus Pauling and Charles Coryell discovered solutions to measure blood flow to the brain. They found that oxygen-depleted blood with dHb was attracted to a magnetic field, although less so than ferromagnetic elements, such as iron, whereas oxygen-rich blood with Hb was weakly repelled by magnetic fields. As Seiji Ogawaat At&T Ball labs recognized, this could be used to augment MRI, which merely evaluates the static structure of the brain, because the different magnetic properties of Hb and dHb that are caused by blood flow to the activated brain regions would cause measurable changes in the MRI signal (Huettel, S. A, et al., 2009). In 1990, Ogawa discovered BOLD, which is the MRI contrast of dHb. Ogawa, Thulborn et al. and colleagues scanned rodents in a strong magnetic field(7.0T) in a seminal 1990 study.
They changed the proportion of oxygen that the animals breathed to manipulate the blood oxygen level. As this proportion fell, a map of blood flow in the brain was observed via MRI. They verified this by placing test tubes with deoxygenated or oxygenated blood and creating separate images. Belliveau and others used the contrast agent Magnevist, a ferromagnetic substance remaining in the bloodstream after intravenous injection, to detect the regional activity in the brain at Harvard University. Although the agent remains in the blood for only a short time, it was not acceptable for human fMRI because any medically unnecessary injection is to some extent uncomfortable and unsafe (Huettel, S. A, et al.,2009).In 1992, three studies first evaluated fMRI using BOLD contrast in humans. Kenneth Kwong and colleagues studied activation in the visual cortex by using a gradient-echo Echo planar Imaging(EPI) sequence at a magnetic field strength of 1.5T. Ogawa and others used a higher field(4.0 T) to conduct their study and showed that the BOLD signal depended on T2* loss of magnetization. Bandettini and colleagues used EPI at 1.5 T to show activation in the primary motor cortex, a brain region that in humans is located in the dorsal portion of the frontal lobe (Huettel, S. A, et al., 2009).