Long hypothesized, elusive neuron finally discovered.

It is known that the brain measures time continuously, with the person aware of how long they have performed a certain task, such as eating or sleeping. This exact measurement of time allows humans to make complex movements requiring muscle coordination within a microsecond of sensitivity, or decode complex auditory signals in the form of speech or music. The brain’s timing abilities are impressive, however, it is still unclear how it can keep time without external signals or cues. Now, a study from Brown University identifies a previously unknown brain cell that acts as the brain’s long-hypothesized clock or metronome. The team states the neuron spikes in a rhythmically and synchronized manner independent of external sensations. The study is published in the journal Neuron.

Previous studies show a gamma wave is a pattern of neural oscillation in the human brain with a frequency between 25 and 100 Hz. Gamma rhythms have been a huge topic of debate, with researchers hypothesizing the existence of a metronome-like function of the gamma rhythm, however, this has been largely disputed because gamma rhythms change in response to sensations. Recent studies from the lab showed that boosting rodents’ natural gamma rhythms helped the animals detect fainter whisker sensations. The current study identifies gamma regular nonsensory fast-spiking interneurons, or ‘metronome’ neurons, which spike or ‘tick’ regularly at gamma range intervals independent of external influences.

The current study utilizes a very precise machine to move the whiskers of rodents slightly, just at the edge of the animal’s ability to detect movement while recording neuron activity in the whisker-sensation part of the brain. The study concentrates on a subtype of inhibitory interneurons whose main function is to inhibit spikes or ticking from other cells. Results show that about one-third of these fast-spiking interneurons were ‘ticking’ very regularly, meaning the rodent was better able to perceive subtle sensations.

Data findings show the metronome neurons were identified in the touch region of the brain and were ‘ticking’ in synch with one another, independent of sensory interaction. The team states that even though metronome neurons are newly discovered, disruptions within the broader group of fast-spiking interneurons have been implicated in several neurological disorders including autism, schizophrenia, and ADHD. They go on to add that some of these conditions could be caused by disturbances of the metronome neuron subtype with more research needed into its function and neuroanatomy.

The team surmises they have identified a previously unknown type of brain cell which acts as the brain’s metronome. For the future, the researchers state as a next step they want to determine if these metronome neurons exist in primates and humans.

Source: Brown University

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