The federal government has spent almost $100 million on monkey brain studies since 2007, including $16 million on tests in which scientists tried to scare the monkeys with rubber snakes and spiders — and lawmakers are demanding to know why.

“We have serious concerns about whether this questionable research deserves continued support from Congress and taxpayers,” a bipartisan group of lawmakers led by Reps. Brendan Boyle, D-Pa., and Brian Mast, R-Fla., say in a letter to the director of the National Institutes of Health, which was obtained by NBC News.

Videos of the bizarre tests by the National Institute of Mental Health, some of which were performed on monkeys whose brains had been intentionally damaged beforehand, were obtained by the White Coat Waste Project after it filed a Freedom of Information Act lawsuit in Washington, D.C., federal court.

The watchdog group shared the videos with NBC News. Some of them show macaques cowering in the corners of their cages as a panel is opened revealing a rubber snake or what a researcher described as “hairy rubber spiders.” The government has spent $16.3 million on the studies since 2007, records show.

Some of the total of $95 million in government funding also went to other studies monitoring how the monkeys react to nature documentaries and how they can tell faces apart from fruit, records show. The scientists damaged various parts of the monkeys’ brains to gauge what effect the damage had on their responses, the studies say. Some had parts of their brains removed surgically, while others had parts of their brains damaged with acid injections.

Download the NBC News app for breaking news and politics

In the nature documentary experiments, which have cost over $10 million since 2007, some of the rhesus monkeys also had “custom-designed fiberglass headposts” implanted on their skulls to immobilize their heads while scientists tracked their eyes, the study says.

Congress has been urging the Department of Health and Human Services, which oversees the NIH and the NIMH, to reduce testing on primates, and lawmakers say the videos have only heightened their sense of urgency.

“New reports about disturbing taxpayer-funded experiments on monkeys at the National Institute of Mental Health in Bethesda, Maryland, demonstrate why more Congressional oversight of NIH primate research is urgently needed,” Boyle and Mast say in a letter to NIH Director Francis Collins, which was also signed by Reps. Lucille Roybal-Allard, D-Calif., Matt Gaetz, R-Fla., and Dina Titus, D-Nev.

Roybal-Allard questioned the scientific need for the experiments and called for “more efficient and humane non-animal research alternatives.”

“We’ve made progress, but these disturbing psychological tests on monkeys that have gone on for decades highlight the need for greater oversight of NIH efforts to reduce primate testing,” Roybal-Allard said.

The experiments looking into how the macaques react to the rubber snakes and spiders is aimed at providing “insights into the neural regulation of defensive responses to threat and inform the etiology and treatment of anxiety disorders in humans,” the study says.

Asked about the lawmakers’ criticisms, the NIH defended primate testing, saying it has helped scientists understand how the brain copes with conditions like post-traumatic stress disorder, schizophrenia and obsessive-compulsive disorder.

“Monkeys are used in research because of their marked similarities to humans with respect to anatomy, physiology, and behavior,” the agency said in a statement to NBC News.

“Testing procedures produce a range of animal responses, mirroring human traits and attributes, ranging from no response to momentary and transient anxiety. Each animal’s well-being was closely monitored during and after testing by experienced and trained animal care staff and veterinarians. The procedures under question resulted in no harm to any of the animals tested.”

The letter from lawmakers asks Collins to answer several questions about how long the experiments have been funded and for “specific examples of when and where the research has had successful direct clinical applications in humans.”

Under language that was inserted in the agency’s spending bill for the first time in 2020, the NIH has to report to Congress on its efforts to reduce primate research in favor of alternatives by December.

Anthony Bellotti, president and founder of the White Coat Waste Project, said, “Taxpayers should not be forced to foot the bill to fulfill the morbid curiosities of some out-of-touch NIH bureaucrats who want to destroy monkeys’ brains with toxic acid and torment them with fake snakes and spiders.”

“This is government waste, fraud and abuse at its lowest, and it needs to stop,” Bellotti said.