Summary: A new study questions traditional views of how memories are formed and stored in the brain. Additionally, researchers propose a new mechanism for learning.
Researchers now report a new learning mechanism in the brain that calls into question the widely accepted view of how memories are formed and stored. Their findings could lend insight into the process underlying how humans are able to remember new places and the events that take place there.
Previous work suggested that the development of memory is the result of strengthened neural networks stemming from closely linked nerve cell activities. This principle is referred to as the Hebbian learning rule which postulates that “neurons wire together, if they fire together.” Short bursts (tens of milliseconds) of interconnected neuron stimulation improve signal transmission (called long-term potentiation, or LTP).
In contrast, Katie Bittner and colleagues identified another type of learning rule called behavioral time scale synaptic plasticity (BTSP), which spans a considerably longer time period (seconds).
The result implies that no causal relationship of interconnected neurons is required to form long-lasting associations between them. The authors say that this lengthier time scale allows for the storage of an entire sequence of events (such as places traversed) and leads to an overrepresentation of behaviorally important places, such as reward locations.
A related Perspective by Julija Krupic discusses the study in greater detail, and offers additional insight into the potential uses of BTSP learning.
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Original Research: Abstract for “Behavioral time scale synaptic plasticity underlies CA1 place fields” by Katie C. Bittner, Aaron D. Milstein, Christine Grienberger, Sandro Romani, and Jeffrey C. Magee in Science. Published online September 7 2017 doi:10.1126/science.aan3846
Behavioral time scale synaptic plasticity underlies CA1 place fields
Learning is primarily mediated by activity-dependent modifications of synaptic strength within neuronal circuits. We discovered that place fields in hippocampal area CA1 are produced by a synaptic potentiation notably different from Hebbian plasticity. Place fields could be produced in vivo in a single trial by potentiation of input that arrived seconds before and after complex spiking. The potentiated synaptic input was not initially coincident with action potentials or depolarization. This rule, named behavioral time scale synaptic plasticity, abruptly modifies inputs that were neither causal nor close in time to postsynaptic activation. In slices, five pairings of subthreshold presynaptic activity and calcium (Ca2+) plateau potentials produced a large potentiation with an asymmetric seconds-long time course. This plasticity efficiently stores entire behavioral sequences within synaptic weights to produce predictive place cell activity.
“Behavioral time scale synaptic plasticity underlies CA1 place fields” by Katie C. Bittner, Aaron D. Milstein, Christine Grienberger, Sandro Romani, and Jeffrey C. Magee in Science. Published online September 7 2017 doi:10.1126/science.aan3846