Scientists have long assumed that the neocortex makes top-down predictions about future stimuli by learning patterns in sensory data. According to this hypothesis, differential responses in both spiking and somatic calcium imaging data correspond to those that deviate from the patterns in response to visual stimuli.
However, whether these pattern-violation signals differ between somata, where bottom-up information is mainly incorporated, and distal apical dendrites, which are strongly targeted by top-down signals, is still unknown. Furthermore, it is not known how animals’ responses to norm-violating stimuli become habituated over time.
A long-standing theory holds that the brain learns a predictive model of the world, and updates its internal predictions when incoming sensory data proves wrong, however, what the researchers found surprised them.
To measure brain activity in the visual cortex, which processes visual information from the retina, the scientists used a mouse model that showed them graphic patterns for several days, followed by images that deviated from the patterns. The plan was to see how neurons responded to novel sensory data that differed from the norm.
The distal apical dendrites of neurons that receive signals from above and their cell bodies, which receive stimuli from below, are the sites of measurements in the visual cortex. They wanted to determine whether distal apical dendrites processed visual stimuli differently from their cell bodies when symptoms deviated from matched and expected patterns.
In contrast to pattern-matching images, the brain’s response to image patterns that defy expectations changes over time.
Associate Professor Joel Silberberg of the York Faculty of Science said, „Surprisingly, the responses of distal apical dendrites grew significantly over time, becoming more sensitive to inputs that violated patterns, while cell bodies initially lost strong sensitivity. This finding may provide important insight into emotional computation and predictive learning in the brain.”
The results indicated that pattern-violating stimuli caused changes, and that stimuli that violated different patterns could unexpectedly cause a variety of prediction errors. This suggests a hitherto unknown brain region that may play a unique and significant role in emotional learning.
Journal Note:
- Colin J. Gillen, Jason E. Bina, Jerome Lecoq, Ruwaida Ahmed, Yasan N. Bille, Sheila Caldejon, et al. In somata and distal apical dendrites, responses to pattern-violating visual stimuli develop differently over days. Journal of Neuroscience. DOI: 10.1523/JNEUROSCI.1009-23.2023
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