Memory study justifies need for witness cross-examination

In depictions of criminal trials on television and in the movies, the most suspenseful moments often involve an eyewitness testifying against the accused. Sometimes a jury may wholeheartedly believe a witness’ testimony, and the damage to the defense might seem permanent. In other cases, a criminal defense attorney might be able to expose inconsistencies in that testimony during the cross-examination.

Yet a cross-examination can quickly backfire -- as many attorneys might agree. Instead of revealing the witness’ fallibility or potentially flawed memory, a jury might view the cross-examination tactics as bullying, resulting in them giving even more weight to the original testimony elicited by prosecutors on direct examination.

Science, it turns out, may have provided extra validation for criminal defense attorneys. A recent experiment by researchers suggests that memories may mutate or become altered when combined with subsequent emotional associations. Researchers chemically tagged a region of the brain related to memory formation, called the hippocampus in half of a group of lab mice, leaving the other half unaffected.

All of the mice were then exposed to an electrical shock on a particular section of a maze floor, but those with the chemical marker were also stimulated in their hippocampus. When the mice were free and allowed to roam freely, those with the chemical marker avoided the spot, while the control group did not.

Researchers theorize that this behavior suggests the chemically marked mice made a false memory. The stimulation of the chemically marked brain region caused the mice to associate that maze area with at least one, if not multiple shocks. Typically, mice will learn this behavior after only repeated shocks -- not a single shock. The emotion-memory link apparently affected their memory-making process.

Source:, “Memories can't always be trusted, neuroscience experiment shows,” Melissa Healy, July 25, 2013


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