Contemporary biological investigators have noted an association between temporal lobe disorders and variant sexuality in males, including hypersexuality, hyposexuality and altered sexual preference (Langevin 1990). The temporal lobe, an integral component of the limbic system of the mammalian brain, appears critical to the regulation of mood, the modulation of anxiety, the integration of the appetitive drives (sex, appetite, and sleep), and the modulation of aggression. Unfortunately, the specific lesions involving temporal lobe epilepsy or temporal lobe damage cited in case examples of PAs do not predominate in larger samples.

Neuroanatomic and neuropsychological examination of the sexually aggressive paraphilic offender, with specific attention to temporal lobe and limbic structures, has been undertaken by Langevin et al. (1990). Because sex offenders are a heterogeneous group with a diversity of paraphilic and nonparaphilic sexual behaviors, it would at first appear unlikely that a specific neuropsychological profile or neuroanatomic lesion would be uncovered. It is possible, however, that specific subgroups of sexually aggressive paraphilic individuals might have deficits that distinguish their violent or sadistic propensities (Hucker et al. 1988).

Another line of biological investigation exploring the etiology of PAs has focused on testosterone, the sex hormone that influences both sexual and aggressive male behavior (Rubinow and Schmidt 1996). Testosterone, the principal androgen (sex hormone) produced by the testes in response to hormonal mediators synthesized and released from the hypothalamus and pituitary gland, is the most important androgen affecting male sexual behavior. The role of testosterone as a primary etiological factor in physical (Archer 1991) and sexual (Bradford and Maclean 1981; Knussmann et al. 1986; Langevin et al. 1985; Raboch et al. 1987; Rada et al. 1983) aggression in men, however, remains ambiguous. Although some studies have suggested a correlation between elevated serum testosterone and violent sexual aggression (Rada et al. 1976, 1983), the majority of studies reveal that serum total testosterone (i.e., protein-bound and -unbound) is within normal limits in all but a subgroup of the most violent paraphilic individuals (Hucker and Bain 1990). Several prominent contemporary investigators have failed to find any distinctive hormonal profile in either violent or nonviolent paraphilic males (Berlin 1983; Hucker and Bain 1990; Lang et al. 1989). In addition to the aforementioned studies that did not confirm a relationship between sexual aggression and serum testosterone, there have been additional reports of men with PAs and low baseline serum testosterone (Gurani and Dwyer 1986; Kravitz et al. 1996; Langevin et al. 1979). No published studies exist of testosterone serum levels in men with nonviolent PAs or PRDs.