UMN Experimenter Who Drilled Into Monkeys’ Skulls Sidelined After PETA Push

For Immediate Release:
September 1, 2026

Contact:
Tasgola Bruner 202-483-7382

In a significant victory for animals used in experimentation, the University of Minnesota (UMN) has confirmed that the experimenter PETA exposed for having inflicted severe suffering on rhesus macaques is no longer allowed to experiment on primates.

Geoffrey Ghose “no longer works with nonhuman primates,” the university confirmed to PETA. PETA met with local law enforcement officials last year, presenting evidence of apparent animal welfare violations in UMN laboratories. Federal inspectors then visited Ghose’s laboratory on April 30. The U.S. Department of Agriculture found numerous violations of even the minimal care required under federal animal welfare laws, involving surgical duration, dosing and timing of pain relief, record-keeping, and maintenance of skull implants. On May 22, the university suspended Ghose’s experiments on animals.

“When Ghose was confronted with evidence that he’s crudely cut open monkeys’ skulls in botched experiments, he refused to accept responsibility, portraying himself as the victim rather than having one iota of remorse or compassion for the monkeys he tormented and killed,” says PETA Vice President Dr. Alka Chandna. “Similar atrocities are happening in other UMN experimenters’ laboratories, including those of Jan Zimmermann and Matt Johnson, and PETA calls on the university to shut them down too, and send all surviving monkeys to reputable sanctuaries.”

At the University of Minnesota, monkeys endure prolonged restraint in stereotaxic frames like these, which immobilize their heads for invasive brain experiments, despite serious ethical and scientific concerns. For illustrative purposes only.

Ghose carved into the heads of rhesus macaques, cut into their scalps, removed portions of their skulls, attached metal headposts, and implanted recording chambers over openings in their skulls. The devices failed repeatedly.

Last year, a monkey named Bilbo endured surgery to implant a headpost and chamber. Screws went missing, a metal stabilizing ring fell off inside his cage, his headpost had to be removed, and the chamber later sheared off his head, leaving his brain exposed for days.

The headpost of another monkey named Samwise detached during a behavioral experiment, leaving an approximately two-thirds–inch opening in his skull and requiring emergency attention.

According to university documents, Jan Zimmermann, while implanting a metal post into a monkey’s skull, drilled 20 screws so deep they pierced his brain tissue. Records show that after the surgery, the monkey was lethargic, vomited, and showed arm weakness, abnormal eye movements, and signs of a severe headache. He suffered for months before he was killed. In Johnson’s laboratory, a monkey named Ponyo reportedly suffered for weeks, with blood leaking from one of her screw holes. While Ponyo’s headpost was being affixed to the hardware of the restraint chair, the device reportedly detached from her skull, likely because the infection had weakened the underlying bone.

The university has a long history of animal welfare violations. In 2023, it was ranked the nation’s fifth-worst violator of federal animal welfare laws among schools with taxpayer-funded laboratories, according to a study by PETA scientists.

In nature, macaques live in large, tight-knit groups, travel several miles each day exploring diverse habitats, and cuddle together in their favorite “sleeping trees” at night.

PETA—whose motto reads, in part, that “animals are not ours to experiment on”—points out that Every Animal Is Someone and offers free Empathy Kits for people who need a lesson in kindness. For more information, please visit PETA.org or follow PETA on X, Facebook, or Instagram.