Your brain knows more than you think - India, UK, USA

Neurobiologists at California's Salk Institute for Biological Studies have carried out experiments that prove for the first time that the brain remembers, even if we don't and the umbrella stays behind. They report their findings in the Oct 20 issue of Neuron.

"For the first time, we can look at the brain activity of a rhesus monkey and infer what the animal knows," lead investigator Thomas D. Albright, director of the Vision Center Laboratory, was quoted as saying in a Salk Institute release.

First author Adam Messinger compares it to subliminal knowledge: It is there, even if it doesn't enter our consciousness.

"You know you've met the wife of your colleague but you can't recall her face," he said, giving an example.

Human memory relies mostly on association; when we try to retrieve information, one thing reminds us of another, which reminds us of yet another and so on. Neurobiologists are trying to understand how associative memory works.

One way to study associative memory is to train rhesus monkeys to remember arbitrary pairs of symbols. After being shown the first symbol dark clouds, for example, they are presented with two symbols, from which they have to pick the one that has been associated with the initial cue, that is, an umbrella. The reward is a sip of their favourite fruit juice.

"We want the monkeys to behave perfectly on these tests, but one of them made a lot of errors," Albright said.

"We wondered what happened in the brain when the monkeys made the wrong choice, although they had apparently learned the right pairing of the symbols."

So, while the monkeys tried to remember the associations and made their error-prone choices, the scientists observed signals from the nerve cells in a special area of the brain called the inferior temporal cortex (ITC), which is known to be critical for visual pattern recognition and for storage of this type of memory.

When the team analysed the activity patterns of brain cells in the ITC, they could trace about a quarter of the activity to the monkey's behavioural choice.

But more than 50 percent of active nerve cells belonged to a novel class of nerve cells or neurons, which the researchers believe represents the memory of the correct pairing of cue and associated symbol. Surprisingly, these brain cells kept firing even when the monkeys picked the wrong symbol.

"In this sense, the cells 'knew' more than the monkeys let on in their behaviour," Albright said.

Although behavioural performance is generally accepted to reliably reflect knowledge, in fact, behaviour is heavily influenced - in the laboratory and in the real world - by other factors, such as motivation, attention and environmental distractions.

"Thus behaviour may vary, but knowledge endures," concluded the team in its paper.