Rhythms – always rhythms

Why do we learn trigonometry in our school days and not get past the triangles and on to the waves? Who knows. But waves, rhythms and sine functions are such a constant part of this world. They are certainly important in biology.

We have seasonal rhythms, some of us have monthly rhythms, and we have circadian daily rhythms. Then we have heart rhythms, breathing rhythms, peristaltic gut waves and we have automatic muscle rhythms for walking and eye movements. We use rhythms in our speech, music, and dancing. Then there are the many brain wave patterns that we are only beginning to understand. The brain seems to function using rhythmic waves, waves of many frequencies, overlapping, synchronized and nested.

I noted a few things lately on this subject.

A paper in Cell, Descending Command Neurons in the Brainstem that Halt Locomotion, by J Bouvier and others (here), looks at the control of the start and stop of walking. The walking rhythm comes from an automatic network in the spinal cord but the commands to start and stop walking come from the brain stem. The question was about this signaling. There might be one signal with walking when it was present and not walking when it was absent. Or there could be two signals and this is what they found, separate on and off signals. The interesting thing from the stand point of rhythms is that a ‘stop’ signal was needed. Stopping a rhythm is not simple. The rhythmic dynamic of walking cannot be stop instantaneously to any point. There is no point that it can be just frozen that would leave a stable position with all feet on the ground and the center of gravity not off center. It takes a special functional network to stop the rhythm without stumbling, tripping or falling. Of course the rhythm could be just slowed until it stopped but most animals want to stop ‘on a dime’ rather than after some time.

In a release from UoW Madison (here) there is an outline of the work of J Samaha. He has found that our sight is controlled by the alpha rhythm in the back of the brain. We do not process the information that arrives from the eyes during the trough in the alpha rhythm but only during the peaks. The faster a persons alpha frequency, the more often they sample the world and the better they can distinguish close flashes of light as separate.

ScienceDaily has an item (here) about a paper by R Cho and others about the strengthening of synapses as we form associations during learning, memory and development.

Over the past 30 years, scientists have found that strong input to a postsynaptic cell causes it to traffic more receptors for neurotransmitters to its surface, amplifying the signal it receives from the presynaptic cell. This phenomenon, known as long-term potentiation (LTP), occurs following persistent, high-frequency stimulation of the synapse. Long-term depression (LTD), a weakening of the postsynaptic response caused by very low-frequency stimulation…Scientists have focused less on the presynaptic neuron’s role in plasticity, in part because it is more difficult to study”

Presynaptic cells occasionally release transmitters into the synapse when there is no activity in the cell as a whole and this was thought of as noise. They are called minis. Cho found that minis were not just random noise but they could also strengthen a synapse if they were delivered with a high frequency. “When we gave a strong activity pulse to these neurons, these mini events, which are normally very low-frequency, suddenly ramped up and they stayed elevated for several minutes before going down.” After a signal was transmitted, activity resembling an action potential continued without an actual signal. High frequency minis causes the synapse to strengthen, but low frequency ones do not.

One thought on “Rhythms – always rhythms

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