Activation of sensory cortex by imagined genital stimulation: an fMRI analysis

Abstract

Background: During the course of a previous study, our laboratory made a serendipitous finding that just thinking about genital stimulation resulted in brain activations that overlapped with, and differed from, those generated by physical genital stimulation.

Objective: This study extends our previous findings by further characterizing how the brain differentially processes physical 'touch' stimulation and 'imagined' stimulation.

Design: Eleven healthy women (age range 29-74) participated in an fMRI study of the brain response to imagined or actual tactile stimulation of the nipple and clitoris. Two additional conditions - imagined dildo self-stimulation and imagined speculum stimulation - were included to characterize the effects of erotic versus non-erotic imagery.

Results: Imagined and tactile self-stimulation of the nipple and clitoris each activated the paracentral lobule (the genital region of the primary sensory cortex) and the secondary somatosensory cortex. Imagined self-stimulation of the clitoris and nipple resulted in greater activation of the frontal pole and orbital frontal cortex compared to tactile self-stimulation of these two bodily regions. Tactile self-stimulation of the clitoris and nipple activated the cerebellum, primary somatosensory cortex (hand region), and premotor cortex more than the imagined stimulation of these body regions. Imagining dildo stimulation generated extensive brain activation in the genital sensory cortex, secondary somatosensory cortex, hippocampus, amygdala, insula, nucleus accumbens, and medial prefrontal cortex, whereas imagining speculum stimulation generated only minimal activation.

Conclusion: The present findings provide evidence of the potency of imagined stimulation of the genitals and that the following brain regions may participate in erogenous experience: primary and secondary sensory cortices, sensory-motor integration areas, limbic structures, and components of the 'reward system'. In addition, these results suggest a mechanism by which some individuals may be able to generate orgasm by imagery in the absence of physical stimulation.

Keywords: clitoris; genitalia; homunculus; human female; nipple; primary somatosensory cortex; secondary somatosensory cortex; self-stimulation; sexual arousal; tactile imagery.

Fig. 1

Paracentral lobule ‘genital sensory’ cortical activations in physical self-stimulation and imagined tactile stimulation of the clitoris and nipple, indicated by location of the crosshairs (cluster z=1.0, p<0.01, N=11). In this and subsequent figures, the following convention was used: the MNI_152 slice coordinates, (y=coronal, z=axial) are specified clockwise, starting from upper left. In this figure, y=−32/−28/−24/−40. The contrasts shown above, and in Figs. 2 and 3, clockwise from upper left are CTS>CTM, CIS>CIM, NIS>NIM, and NTS>NTM, respectively. Abbreviations and analysis are specified in Methods section.

Fig. 2

Secondary somatosensory cortical activations in physical and imagined stimulation of the clitoris and nipple, (cluster z=1.0, p<0.01, N=11). Top left: clitoris, physical stimulation (OP1 right side of brain); top right: clitoris, imagined stimulation (OP4 left). Bottom left: nipple, physical stimulation (OP4 right); bottom right: nipple, imagined stimulation (OP4 left). OP1, parietal operculum 1; OP4, parietal operculum 4; MNI_152 coordinates: y=−26/−10/−2−2.

Fig. 3

Frontal cortical activations in physical and imagined self-stimulation of the clitoris and nipple (cluster z=1.0, p<0.01, N=11; MNI_152 coordinate: z=−12/−12/−12/−12).

Fig. 4

Regions activated by tactile self-stimulation of the clitoris>imagined self-stimulation of the clitoris. Top left: premotor cortex BA6 left side of brain. Top right: primary somatosensory cortex BA3a left. Bottom left: secondary somatosensory cortex OP1 right. Bottom right: cerebellum right. (Cluster z=1.0, p<0.01, N=11; MNI_152 coordinate: z=56/48/−42/22). The above contrast is CTS>CIS.

Fig. 5

Imagined stimulation by dildo>speculum (ID>IS) (cluster z=1.65, p<0.01, N=11).Mpfc, medial prefrontal cortex; Bilat Op4, bilateral parietal operculum 4; MNI_152 coordinate: y=62/10/−4/−6/−30/−24/−10.

Fig. 6

Participants’ reported mean levels of sexual arousal for tactile and imagined tactile stimulation on scale of 1 (no arousal) to 7 (high arousal). N=11; error bars ±2 SEM.CTS, clitoral touch stimulation; CIS, clitoral imagined stimulation; NTS, nipple touch stimulation; NIS, nipple imagined stimulation; ID, imagined dildo stimulation condition; IS, imagined speculum stimulation condition.