A graduate student of famed neuroscientist Vilayanur S. Ramachandran has found a group of men and women who report that their sexual identity can switch involuntarily to that of the opposite sex and back again. The transgender metamorphosis, these people assert, can occur several times a day and at inopportune moments. It is also accompanied by the sensation of phantom breasts or genitalia of the non-biological sex.

The research grows out of Ramachandran’s long-standing fascination with the study of body image and how it contributes to a basic sense of the self, work that has included investigations into the phantom limbs of amputees.

The preliminary study by Laura Case, Ramachandran’s student, raises the prospect of a new category of transgenderism. “Alternating gender incongruity (AGI),” the neuropsychiatric term the researchers have tentatively proposed, describes the involuntary change of gender identity, along with perceived phantom sex characteristics, a tendency toward ambidexterity and bipolar disorder, all signs that suggest a biological basis for AGI. (A related term, bigender, defined as blending or alternating gender states, precedes AGI.)

A paper published in the April issue of the journal Medical Hypotheses—“Alternating gender incongruity: A new neuropsychiatric syndrome providing insight into the dynamic plasticity of brain-sex”—found 32 respondents (11 anatomically female) on an online bigender forum that hosts about 600. Average age was 29. About a third of the respondents said that gender switching was predictable. A majority said they switched weekly and 14 said the transformation occurred once or more a day.

Some quotes from the paper:

—“I still have the same values and beliefs, but a change in gender is really a change in the filter through which I interact with the world and through which it interacts with me.”

—“If I’m in male mode and I see someone crying, I’ll think more along the lines of ‘Man up… while if I’m in girl mode I’ll think more long the lines of ‘Oh sweety!’”

—“I sometimes wake up thinking I have a penis,” says one female respondent, “or that I have no breasts…I usually end up in tears and I can’t get out of bed because once I get up I’ll know for sure it’s not really true and it’s just my mind playing tricks on me, so I just lie there and cry. It’s strange though because I normally don’t even want to have a penis.”

Medical Hypotheses is a controversial journal—it once published an article on the nature of navel lint—and only adopted a peer review system in 2010. Yet, Ramachandran, Nobelist Arvid Carlsson and other science luminaries have served on its editorial board because of its stated goal of foraging for “radical new ideas and speculations.” Ramachandran published previously in the journal on phantom genitalia after sex-change surgery.

The “more research needed” refrain certainly applies to the AGI work, a concession the investigators themselves make. “These results are suggestive but not conclusive,” Ramachandran says. “We need to rule out the possibility that this is just a variant of dissociative identity disorder (multiple personality disorder) or the subjects are simply “role–playing.” Without the “smoking gun”- physical evidence in the form of fluctuating hormone levels or brain imaging data – we don’t know what we are dealing with. Its something we are currently working on.”

At the Cognitive Neuroscience Society meeting in early April, Case presented preliminary research that one nominal AGI subject who was anatomically male performed differently on cognitive tests depending on his gender state: when male, he did better at a targeting task (throwing darts) and he had a superior score on a verbal fluency test after a switch to the female state. It was inconclusive whether testosterone levels fluctuated with the change in sexual identity.

Case is now preparing to move ahead with a larger study of forum members in which she will conduct neuropsychological testing by telephone and examine hormone levels with saliva samples sent through the mail. The researchers are not ready yet to do brain imaging studies on the group, which is scattered throughout the country. Ultimately, that line of research would examine patterns of activity within each brain hemisphere that differ between sexes.

If the researchers’ hypothesis holds, it would furnish an increasingly nuanced definition of sexuality. The Neuroskeptic blog, which wrote about the study, wondered what would have happened to the little-known bigenders before the advent of the term. The anonymous blogger wrote: “Would they have been identified as transgender? Maybe… but maybe not. Would they have had any label at all?”

The scientists expect that AGI could eventually be classified as a neuropsychiatric condition, which would point immediately to the deeper question of “the extent to which each of us is a multiplicity of genders, or even persons, co-existing in harmony.” If this research succeeds, AGI could ultimately help provide a biological rationale for the protean nature of the self.