New devices to deliver somatosensory stimuli during functional MRI

Abstract

A new class of devices are described for improving investigation of somatosensory neuronal activation using fMRI. Dubbed magnetomechanical vibrotactile devices (MVDs), the principle of operation involves driving wire coils with small oscillatory currents in the large static magnetic field inherent to MRI scanners. The resulting Lorentz forces can be oriented to generate large vibrations that are easily converted to translational motions as large as several centimeters. Representative data demonstrate the flexibility of MVDs to generate different well-controlled vibratory and tactile stimuli to activate special proprioceptive and cutaneous somatosensory afferent pathways. Functional MRI (fMRI) is an excellent experimental tool for probing the neural pathways associated with skin sensation-the somatosensory system. In particular, numerous studies have been performed that demonstrate the somatotopic organization of the primary somatosensory cortex (1-7). Somatotopic mapping at higher spatial resolution is facilitated by using scanners with larger magnetic fields, such as 4T, with which the different locations of finger digits within primary somatosensory cortex can be identified (8). Such work may ultimately have practical medical application in surgical planning to resect tumors or epileptic foci while minimizing somatosensory loss and paralysis (9,10).Beyond somatotopic mapping, however, additional fMRI investigation is required to improve scientific understanding of the human somatosensory system. A central, broad issue is to understand quantitatively the factors which modulate somatosensory activation. This includes investigating the relationship between parameters associated with stimulus delivery (e.g., rubbing force and frequency, or vibration frequency and amplitude), the specific peripheral receptors excited, and the activation signals observed using fMRI. In addition to these direct relationships, other functionally connected brain regions such as those involved in attention (11-15), as well as short-term and long-term neuroplasticity associated with learning (16) or recovery from injury to the nervous system (17), can act as strong modulatory factors affecting somatosensory activation.Investigating these factors clearly requires the capability to deliver well-controlled, reproducible somatosensory stimuli. Compared with sensory fMRI experiments involving vision and audition, however, careful somatosensory stimulus delivery is more challenging. Much of the somatosensory fMRI literature involves manual rubbing or brushing, or electrical stimulation of the appropriate sensory nerves. Manual brushing depends completely on the ability of an experimenter to apply tactile stimuli consistently, which is extremely difficult, whereas electrical stimuli are not a natural input to the central nervous system and appear to produce mixed results (6,18). This has prompted design of other somatosensory devices for specific experimental purposes, such as piezoelectric vibration (19) or compressed air (4,20,21), each with ...

Dodecapus: An MR-compatible system for somatosensory stimulation

“…That device does not use any metallic component inside the scanner, and produces precise vibrating frequencies and amplitudes. Magnetomechanical vibrotactile devices (MVDs) are made of MR-compatible coils, but are sensitive to placement and orientation inside the scanner (Graham et al, 2001). A piezoceramic vibrotactile stimulator generates 1-300 Hz vibrations, but requires high voltage to produce relatively small displacements (Harrington et al, 2000;Harrington and Downs, 2001;Francis et al, 2000;Gizewski et al, 2005;McGlone et al, 2002).…”

“…Most of the aforementioned MRcompatible devices have been used mainly for stimulation on the fingers. For instance, MVDs (Graham et al, 2001) were not tested for face stimulation inside the head coil. In addition, multiple stimulators are required to cover the whole face during the same scanning session.…”

Development of a simple MR-compatible vibrotactile stimulator using a planar-coil-type actuator

“…First, intensity can be changed with the position and direction of the planarcoil-type actuator (Graham et al, 2001). However, human subjects usually do not move during tactile fMRI studies, and the position of the planar-coil-type actuator can be fixed to provide a consistent stimulation intensity.…”

“…For vibrotactile stimulation in MR fields, pneumatic (Briggs et al, 2004;Chakravarty et al, 2009;Gallasch et al, 2010;Montant, Romaiquere, & Roll, 2009;Wienbruch, Candia, Svensson, Kleiser, & Kollias, 2006), piezoelectric-element (Gizewski et al, 2005;Harrington, Wright, & Downs, 2000), shaft (Golaszewski et al, 2002), and electromagnetic (Graham, Staines, Nelson, Plewes, & McIlroy, 2001) methods have been used.…”

“…The conventional system has limited stimulation frequency, intensity, and time, with inconsistent stimulation intensity that varies according to the position and orientation of the actuator. Since this method is used with a winding coil, the actuator is large and not expandable to multichannel stimuli (Graham et al, 2001). However, as compared to other methods of vibrotactile stimulation in MR field, this method uses low voltage, and the system is simple and small, with low cost.…”