Abstract

Women diagnosed with complete spinal cord injury (SCI) at T10 or above report vaginal-cervical perceptual awareness. To test whether the Vagus nerves, which bypass the spinal cord, provide the afferent pathway for this response, we hypothesized that the Nucleus Tractus Solitarii (NTS) region of the medulla oblongata, to which the Vagus nerves project, is activated by vaginal-cervical self-stimulation (CSS) in such women, as visualized by functional magnetic resonance imaging (fMRI). Regional blood oxygen level-dependent (BOLD) signal intensity was imaged during CSS and other motor and sensory procedures, using statistical parametric mapping (SPM) analysis with head motion artifact correction. Physiatric examination and MRI established the location and extent of spinal cord injury. In order to demarcate the NTS, a gustatory stimulus and hand movement were used to activate the superior region of the NTS and the Nucleus Cuneatus adjacent to the inferior region of the NTS, respectively. Each of four women with interruption, or “complete” injury, of the spinal cord (ASIA criteria), and one woman with significant, but “incomplete” SCI, all at or above T10, showed activation of the inferior region of the NTS during CSS. Each woman showed analgesia, measured at the fingers, during CSS, confirming previous findings. Three women experienced orgasm during the CSS. The brain regions that showed activation during the orgasms included hypothalamic paraventricular nucleus, medial amygdala, anterior cingulate, frontal, parietal, and insular cortices, and cerebellum. We conclude that the Vagus nerves provide a spinal cord-bypass pathway for vaginal-cervical sensibility in women with complete spinal cord injury above the level of entry into spinal cord of the known genitospinal nerves (Fig 8).

Figure 8: Another example of activation of the region of the paraventricular nucleus of the hypothalamus at orgasm. This nucleus is localized in relation to the anterior commissure, as shown in the slightly modified schematic diagram of Netter [18]. The MRI (upper left) shows the midline sagittal anatomical view, the two lower images are “raw” fMRI images showing the activity during cervical self-stimulation (CSS) prior to orgasm (bottom left) and then at orgasm (bottom right). The fMRI activity at orgasm is superimposed on the anatomical MRI image (upper right). The crosshairs are situated at the anterior commissure. Note that the activated pixels (highlighted) are located slightly inferior and posterior to the anterior commissure. (Courtesy of Komisaruk BR, Whipple B, Crawford A, et al: Brain activation during vaginocervical self-stimulation and orgasm in women with complete spinal cord injury: fMRI evidence of mediation by the vagus nerves. Brain Res 1024:77-88. Copyright 2004 by Elsevier Science.)