After fitting an earpiece to a 7-year-old rhesus macaque, Yerkes psychologist Kim Wallen watched the computer monitor to determine whether the instrument was picking up impulses from the monkey’s ear.

“We’re still out of range,” he told his colleague, and carefully repositioned the earpiece. After a few more tries, he succeeded in calibrating the equipment.

“I think that does it,” Wallen said. “We’re ready to start the testing.”

Such ordinary scenes play out every day in labs at Yerkes. In this case, however, Wallen was collaborating in real time over hundreds of miles with another research psychologist at the University of Texas in Austin, in what may be one of the first long-distance research projects involving experimental animals in which a collaborator actively conducts protocols from a remote location.

Wallen is working with UT’s Dennis McFadden and research associate Edward Pasanen to examine how differences in sound processing between male and female monkeys may be indicative of gender-based differences in brain function.

Ordinarily, sound waves cause the tympanic membrane (eardrum) to vibrate, which produces actions in the inner ear, or cochlea, resulting in the experience of hearing. Sounds, however, also can propagate back out to make the eardrum vibrate like a miniature speaker. These cochlear-driven sounds are called otoacoustic emissions.

In studies of humans, McFadden and Pasanen have found that women produce much stronger emissions than do men—a difference that some scientists believe reflects gender differences in brain function.

“The cochlear amplifier, which produces these emissions, is directly controlled by the brain,” Wallen said. “Differences in acoustical output reflect the fundamental differences between the male and female brain. This project gives us one more way to look at this phenomenon.”

Wallen began his collaboration in 2001 after learning about McFadden’s human research at a conference.

“It was a good fit for us to work on this project together,” said Wallen, Dobbs Professor of Psychology and a core faculty member of the Yerkes Division of Psychobiology. “Dennis wanted to know whether his human findings could be confirmed in a monkey model, but he didn’t have the expertise in primate research or the animal resources to conduct the tests. Fortunately, we had a special population of monkeys that we offered to help him answer his questions.”

That “special population” is a group of 60 7-year-old rhesus macaque monkeys that are the focus of the behavioral and neuroendocrinology research program at the Yerkes Field Station in Lawrenceville. While in utero, the macaques were exposed to varying levels of sex hormones. As the monkeys have grown, Wallen has conducted various minimally invasive cognitive tests to identify any correlation with in utero hormonal exposure and gender differences in cognitive function.

In their study, Wallen, McFadden and Pasanen are attempting to correlate measures of otoacoustic emissions and prenatal hormone levels in both male and female monkeys. The researchers also have been assessing the monkeys at different points during the breeding season to observe any impact on fluctuating hormone levels on acoustical output.

At the Field Station, Wallen oversees the handling of the monkey subjects and the setup of the testing apparatus. Once everything is in place, Pasanen takes control via a real-time computer link and sends a series of clicking and popping sounds to the monkey’s ear. The equipment then captures and measures the resulting otoacoustic emissions. During the process, labs in Lawrenceville and Austin communicate over an Internet audio feed.

The use of network technology permits research projects that would be prohibitively expensive if they required repeated visits by outside investigators from other institutions.

“It simply would have been too expensive,” Wallen said, “for McFadden and Pasanen to fly up here to conduct these tests in person.”

Final results of the study, whose findings should complement Wallen’s own behavioral and neuroendocrine studies of hormonal influences on cognitive function, are expected this spring.