The National Institutes of Health (NIH) has responded to allegations made by People for the Ethical Treatment of Animals (PETA) about controversial psychological experiments conducted on baby macaque monkeys in a federal laboratory.

On Friday, NIH Director Francis Collins released a letter detailing the results of an NIH investigation of the experiments. The lab will stop using procedures that “previously yielded important data, but are not currently needed to achieve the research goals,” Collins wrote. The newly barred procedures include neonatal brain recordings and spinal taps. The researchers will also perform fewer blood draws on the infant animals, the letter said.

The experiments in question were led by Stephen Suomi, a psychologist at the U.S. National Institute of Child Health and Human Development in Poolesville, Maryland. For roughly 30 years, Suomi has studied the physical and psychological effects of separating baby monkeys from their mothers at birth. This research aims to better understand the development of mental disorders, such as depression and alcoholism, in people.

Suomi’s supporters argue that his work has been crucial to understanding how genes and environmental factors interact in early child development. Over the past seven years, his lab has received $10 million in federal funding. Suomi’s office declined to comment for BuzzFeed News.

Last fall, PETA, an animal rights advocacy group, launched a public campaign against Suomi’s maternal deprivation research. Through Freedom of Information Act requests the organization gained access to over 550 hours of video footage and 100 photos. Some are emotional images of baby monkeys that appear to be in distress.

In December, four members of Congress — Lucille Roybal-Allard, Dina Titus, Eliot L. Engel, and Sam Farr — sent Collins a letter requesting that the agency conduct a bioethical review of the experiments by February 2015.

PETA says the review didn’t go far enough: It asked whether the experiments complied with existing animal welfare regulations, rather than questioning their ethical merit. “What the NIH is trying to do is desperately avoid any type of meaningful discussion or accountability,” Justin Goodman, PETA’s director of laboratory investigations, told BuzzFeed News. “They’re insistent on defending the status quo.”

Many scientists, however, contend that Suomi’s research is crucial for understanding the developing brain.

“Monkeys are the ideal model for the work that Dr. Suomi does, because they share approximately 93% of human DNA, they live in social groups with similar mother infant dynamics as humans,” Howard Kurtzman, the American Psychological Association’s Executive Director for Science, wrote in a statement. “There are, in fact, no viable non-animal alternatives.”

Suomi’s work fills in crucial gaps in what we can study in human children, according to Charles Nelson, a professor of pediatrics and neuroscience at Harvard Medical School who has studied maternal deprivation by observing Romanian orphans over many years. “If we want to understand the mechanisms that underpin why deprivation is so horrible for kids, we need to do these studies in primates,” Nelson told BuzzFeed News.

But what’s less clear, Nelson added, is when we can collectively decide we’ve learned enough. “One could say that we’ve been doing these studies for 50 years now, and how much new information are we really generating? That’s a question I don’t know the answer to.”