Does Neuronal Morphology Predict Connectivity?

This piece, by Onno Berkan, was published on 12/03/24. The original text, by Rees et al., was published by Trends in Neurosciences on 02/2017.

This Kransnow Institute study looked at Peters' rule, an important concept in neuroscience that helps scientists understand how neurons connect with each other. The rule suggests that when axons and dendrites are physically close to each other in the brain, they are likely to form connections.

The concept was first introduced over 40 years ago by Peters and Feldman, who studied connections in the visual part of rat brains and was later expanded by other scientists. However, as the rule gained popularity, there has been some confusion and debate about its exact meaning and application.

Recent research has shown that Peters' rule is remarkably accurate, especially in the hippocampus. The rule correctly predicts about 75% of neural connections, and when accounting for some well-known exceptions, its accuracy increases to an impressive 99%.

The main exceptions to the rule involve two specific types of brain cells: axo-axonic cells, which only connect to specific parts of other neurons, and a specific kind of interneuron.

Scientists are using Peters' rule in different ways: to understand connections between types of neurons, to study connections between individual neurons, and to estimate the number of connections between pairs of neurons. These applications have led to some disagreement in the scientific community about how the rule should be used.

The rule is particularly valuable because it bridges a gap between two approaches to studying brain connectivity. One approach examines large-scale connections between brain regions, while the other examines tiny individual connections between neurons. Peters' rule helps connect these two levels of study.

Looking to the future, researchers are working on developing more sophisticated versions of Peters' rule that could help predict neural connections in different brain regions and species.

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