As we go about our day, our eyes are taking in a lot of images and our brain is processing them all. The images range from the familiar to the novel. Once these images come into the brain, how are they processed so that we know what familiar and what is novel. Two research projects, one at the Massachusetts Institute of Technology (MIT) and the other at the University of Pennsylvania looked into that question.
Starting with the study at MIT, researchers wanted to see how the brain’s visual recognition memory works so that it focuses on what’s new and ignores what isn’t. This is an important skill in that it allows mammals to recognize what is new and assess whether or not it needs to attend to it as a threat or resource.
“If you learn that this once-novel stimulus isn’t anything of significance, it is super adaptive to no longer pay attention to it,” said Mark Bear, Picower Professor in the Department of Brain and Cognitive Sciences and senior author of the study. “It’s absolutely essential for normal brain function that we’re able to make a quick determination of whether a stimulus is novel or not.” Bear also noted that those who have schizophrenia and have autism spectrum disorders have trouble in this area.
In 2006, Bear’s lab found signs of visual recognition memory when they detected patterns of increasing electrical activity in the visual cortex of mice as they became familiar with an image. Later research showed that this kind of response, called stimulus selective response plasticity, is correlation with the loss of interest that comes with seeing a familiar image.
Since then, the lab has been studying mice to understand how this happens. Their work has shown that a mechanism of learning and memory, known as LTP, which is a strengthening of neural connections during frequent activity, is involved. Yet that mechanism alone can’t produce visual recognition memory. Neurons known as parvalbumin (PV) expressing neurons are a part of this process. These neurons produce high frequency gamma rhythms in the cortex.
In a new study, Bear’s lab shows that as the visual patterns become familiar, the change is noted by a change in the visual cortex. Namely, the gamma rhythms give way to lower frequency beta rhythms. In addition, the activity of the PV neurons diminishes as the inhibitory somatostatin (SOM) expressing neurons increase in activity. This shows a measurable indicator of the brain’s transition from the new to the familiar.
Interesting, isn’t it? Part two will cover how the brain what it does with a familiar image.