Controversial pesticides linked to declines in bee populations may harm the developing brains of unborn babies, experts at the European Food Safety Authority ruled on Tuesday. They want maximum exposure limits to the chemicals cut while more research is carried out.

The experts found the chemicals "may adversely affect the development of neurons and brain structures associated with functions such as learning and memory," an EFSA statement said. "Some current guidance levels for acceptable exposure may not be protective enough to safeguard against developmental neurotoxicity and should be reduced."

The move stems from research on rats which concluded "neonicotinoids may adversely affect human health, especially the developing brain". The newborn rats studied in the experiments found those exposed to one of the pesticides, called imidacloprid, suffered brain shrinkage, reduced activity of the nerve signals controlling movement, and weight loss. Another rat study found that exposure to the other pesticide, acetamiprid, led to reduced weight, survival and response to startling sounds.

EFSA said that for acetamiprid, the acceptable daily intake – the amount in food or drinks that can be ingested daily over a lifetime without an appreciable health risk – and the acceptable operator exposure level – the maximum exposure for workers – should be cut by two-thirds. The acute reference dose – the amount of a substance that can be ingested over a day without an appreciable health risk – should be cut by three-quarters, EFSA said.

For imidacloprid, the current acceptable daily intake was judged adequate, but the other two limits should be cut by a quarter, EFSA said.

The two pesticides are neonicotinoids, which attack the nervous system of insects and as a class are the most widely used insecticides in the world. Both imidacloprid and acetamiprid are produced by Bayer Cropscience, whose spokesman said the reduced exposure limits were "small changes".

"We are surprised that EFSA has taken a decision to recommend changes to the regulatory assessment of imidacloprid based on a set of simple cell culture experiments, when they had previously informed their views on this compound based on more realistic and comprehensive studies that had been submitted and accepted by EFSA," a Bayer spokesman said.

Imidacloprid was banned in the EU from many agricultural uses from 1 December, after EFSA ruled it posed an unnacceptable risk to bees. Pollinators are crucial in fertilising three-quarters of the world's food crops.

A key study that led to the ban found in 2012 that neonicotinoid exposure seriously harmed bees by damaging their renowned ability to navigate home. Another study, from March 2013, showed that neonicotinoids blocked a part of the brain that bees use for learning, rendering some of them unable to perform the essential task of associating scents with food. That research showed that within 20 minutes of exposure to neonicotinoids the neurons in the major learning centre of the bee brain stopped firing.

Bayer and Syngenta, which produce another neonicotinoid affected by the two-year EU ban, are taking legal action to try to overturn the moratorium. The crop protection industry has warned that yields may drop without neonicotinoids and that older chemicals could be more damaging to wildlife if used as replacements. The UK's National Farmers Union supports the legal action.

The UK was one of the 8 EU member states that fought against the neonicotinoid ban, arguing the scientific evidence was insufficient, but was outvoted by other nations. A UK study of neonicotinoids and bees, which ministers said showed no evidence of harm, was said by EFSA to have "several weaknesses".