Elsevier

Magnetic Resonance Imaging

Volume 22, Issue 2, February 2004, Pages 205-209
Magnetic Resonance Imaging

Original contribution
Event-related fMRI with painful electrical stimulation of the trigeminal nerve

https://doi.org/10.1016/j.mri.2003.08.031Get rights and content

Abstract

Several functional brain imaging studies of pain using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have shown that painful stimulation causes activation of different brain areas. The aim of the present study was to develop and implement painful stimulation of the trigeminal nerve, which can be applied with event-related paradigms by using MRI. Twelve healthy, right-handed volunteers were examined. Painful electrical stimulation of the first trigeminal branch was performed. In an event-related setting with a 1.5 T clinical scanner with EPI capability, the following fMRI parameters were used: 20 slices, 3 mm thickness, isotropic voxel, 306 measurements with 54 randomized events. Statistical postprocessing was performed with SPM99. Activation of the ipsi- and contralateral secondary somatosensory cortex (SII), and the contralateral insular cortex was observed as well as a contralateral thalamic activation (T = 4.45, extension 15 voxels). Six of the 12 volunteers revealed also activation of the cingulate cortex. The investigation demonstrates that painful stimulation of the trigeminal nerve activates the contralateral insular cortex, SII, and thalamus, as well as the ipsilateral SII. In contrast to other studies, the cingulate cortex was only activated inconsistently.

Introduction

Anatomic and physiological studies in animals, as well as functional imaging studies in humans, have shown that besides the thalamus, multiple cortical areas are activated by painful stimuli: the primary somatosensory cortex, the secondary somatosensory cortex, the parietal operculum, the insula, the anterior cingulate cortex, and the prefrontal cortex [1], [2], [3]. These areas process most likely different aspects of pain [4]. The cerebral network activated by painful stimuli has been investigated with positron emission tomography (PET) as well as with functional magnetic resonance tomography (fMRI) by using block designs (for review, see [4]). For inducing pain, thermal, chemical, and electrical stimulations were applied [5]. One disadvantage of PET and fMRI studies with block design is the inferior temporal resolution. Higher temporal resolution can be achieved with magnetoencephalography (MEG) or electroencephalogramm (EEG). However, these techniques suffer from restricted spatial resolution [6], [7]. Event-related fMRI, on the other hand, may overcome these limitations due to the superior spatial resolution and its ability to use designs with fast adaptation (as expected in pain), which makes it possible to observe the propagation of excitation [8], [9]. Recent fMRI studies investigating somatosensory activation by using an event-related design were able to disentangle neuronal subprocessing within the nociceptive system [1], [9], [10].

The aim of the present study was to implement an event-related fMRI pain paradigm by applying electrical stimulation of the cranial nerve. One further aim of special interest was to investigate whether brain stem activations could be detected with this technique.

Section snippets

Subjects

The investigation was approved by the local ethics committee, and informed consent was obtained from all volunteers. Twelve healthy, right handed volunteers (8 men and 4 women, age range 26-42 years) participated in the study. The subjective individual pain threshold was tested by using an analog scale immediately before fMRI.

Imaging

Imaging was performed on a 1.5 T clinical scanner with a standard head coil (Magnetom Vision plus, Siemens Medical Systems, Erlangen). Functional images were acquired

Results

The electrical pulses caused painful stimulation of the first branch of the trigeminal nerve, which was associated with bilateral eye blinking for each stimulation due to an evoked brain stem blink reflex. The volunteers showed no adaptation to the randomized stimulation. The stimulation was perceived equally painful during the whole course of the experiment.

In all volunteers, electrically induced pain stimulation in the face and simultaneous fMRI examination was feasible. Only minor signal

Discussion

The present study demonstrates that event-related fMRI with electrical stimulation of cranial nerves is feasible. Painful stimulation of the trigeminal nerve can be used to visualize pain-related cortical activations in ipsi- and contralateral SII, contralateral insula, and thalamus. These results are consistent with activations observed with other pain paradigms (for a review, see [2]). Activation of the contralateral thalamus is known from experimental animal studies and PET and fMRI studies

Conclusion

These findings demonstrate that it is possible to perform event-related fMRI studies using short, painful electrical stimulation of cranial nerves, which appears promising for further investigations of cranial nerve pathologies, central post-stroke pain after brain stem or thalamic lesions, using adapted paradigm and postprocessing techniques.

References (20)

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