This review examines brain sites involved in sexual stimulation. New data on brain
activation sites in individuals having erections concomitant with visual erotic stimulation
were documented. The activation was chiefly at the midbrain around the cerebral peduncle,
and in the pons centering on the tegmentum, they are indicated by blood oxygenation level
dependent (BOLD) images captured by functional magnetic resonance imaging (fMRI). The
cerebellum and inferior temporal lobe were activated more extensively in individuals viewing
pornographic movie with a concomitant erection than those without. Similarly, individuals
with erection had activations in the midbrain and pons, while drug addicts had neither erections
nor any of these brainstem active sites. From our observation in the new data, we deduced
three possible transmitters might be involved in erection: i) cholinergic neurons forming
descending pathways and associated with motor activity ii) gamma-aminobutyric acid
(GABA), directly or indirectly via decreasing pathways, modulating autonomic vascular responses
in the penile vasculature causing the filling of blood iii) GABA decreases to stimulate
dopamine increase in ventral tegmentum of the brain, leading to euphoric responses.
Keywords: Penile erection, fMRI, visual sex stimulation, brain activation, neurotransmitters, drug addicts.
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