Scientists have found the long sought-after link between gamma oscillations and memory formation. Gamma oscillations are electrical waves that reflect through your brain following an expectation or a memory trigger. Disruptions in these waves have previously been implicated in higher-level brain function disorders such as schizophrenia, Alzheimer's and autism.
Until now, no one knew the exact connection between the gamma waves and memory impairment and, as a result, the knowledge was not entirely useful in the treatment of disorders.
Scientists at the Salk Institute for Biological Sciences have found that the "smoking gun", or at least a major player, in controlling the gamma waves is astrocytes, supportive cells in the brain that are not neurons.
Salk professors Terrence Sejnowski, Inder Verma and Stephen Heinemann inhibited the release of chemicals from astrocytes in mice. Then the scientists induced gamma waves. The regions of the brain with the inhibited astrocyte activity resulted in shorter gamma waves. They followed up this experiment with a genetic block of astrocyte signaling to its neighbor cells and also found reduced gamma waves as a result.
Additionally, the mutant mice were unable to perform a cognitive test called novel object recognition, in which they are presented with new and familiar objects and are expected to behave differently with each. The mice with the astrocyte activity blocked spent the same amount of time and displayed the same behaviors with both old and new objects.
As per Sejnowski, novel object recognition in the mutant mice was not simply reduced--it was entirely removed, "as if we were deleting this one form of memory, leaving others intact."
Removing the signal block, however, both returned the gamma waves to their normal levels and restored novel object recognition.
The scientists were surprised by this result, as astrocytes usually act slower than neurons, so their involvement in high-speed brain activity was unanticipated.
"There are hundreds of papers linking gamma oscillations with attention and memory, but they are all correlational. This is the first time we have been able to do a causal experiment, where we selectively block gamma oscillations and show that it has a highly specific impact on how the brain interacts with the world," said Sejnowski.
The study, which was published in the Proceedings of the National Academy of Sciences, does not suggest that astrocytes act more quickly than previously thought, but rather that signaling by astrocytes creates the necessary environment for gamma waves to spread. This piece of information is "hugely important", says Sejnowski, and has implications for recognition memory and attention.
