Learning requires rhythmical activity of neurons

September 26, 2012
Learning requires rhythmical activity of neurons
Schematic diagram of the trisynaptic circuit of the hippocampus (red) and the position of the stimulation electrode (Stim). Neuronal activity was measured using fluorescent dyes that react to changes in voltage and a fluorescence microscope (VSDI). Microelectrodes in the CA1 and CA3 region record the electrical signals. Credit: MPI of Psychiatry

The hippocampus represents an important brain structure for learning. Scientists at the Max Planck Institute of Psychiatry in Munich discovered how it filters electrical neuronal signals through an input and output control, thus regulating learning and memory processes. Accordingly, effective signal transmission needs so-called theta-frequency impulses of the cerebral cortex. With a frequency of three to eight hertz, these impulses generate waves of electrical activity that propagate through the hippocampus. Impulses of a different frequency evoke no transmission, or only a much weaker one. Moreover, signal transmission in other areas of the brain through long-term potentiation (LTP), which is essential for learning, occurs only when the activity waves take place for a certain while. The scientists even have an explanation for why we are mentally more productive after drinking a cup of coffee or in an acute stress situation: in their experiments, caffeine and the stress hormone corticosterone boosted the activity flow.

When we learn and recall something, we have to concentrate on the relevant information and experience it again and again. Electrophysiological experiments in mice now show why this is the case. Scientists belonging to Matthias Eder´s Research Group measured the transmission of between neurons in the mouse hippocampus. Under the fluorescence microscope, they were able to observe in real time how the neurons forward signals.

Jens Stepan, a junior scientist at the Institute of Psychiatry in Munich, stimulated the input region of the hippocampus the first time that specifically theta-frequency stimulations produce an effective impulse transmission across the hippocampal CA3/CA1 region. This finding is very important, as it is known from previous studies that theta-rhythmical neuronal activity in the always occurs when new information is taken up in a focused manner. With this finding, the researchers demonstrate that the hippocampus highly selectively reacts to the entorhinal signals. Obviously, it can distinguish important and, thus, potentially recollection-worth information from unimportant one and process it in a physiologically specific manner.

Learning requires rhythmical activity of neurons
Filmstrip of an activity wave through the hippocampus. The activity wave is triggered by stimulating the input region with a microelectrode (black arrow) and recorded using voltage-sensitive dyes. Warmer colors represent stronger neuronal activity. Credit: MPI of Psychiatry

One possible reaction is the formation of the so-called long-term potentiation (LTP) of signal transmission at CA3-CA1 synapses, which is often essential for learning and memory. The present study documents that this CA1-LTP occurs only when the activity waves through the hippocampus take place for a certain time. Translating this to our learning behavior, to commit for instance an image to memory, we should intently view it for a while, as only then we produce the activity waves described long enough to store the image in our brain.

With this study, Matthias Eder and colleagues succeeded in closing a knowledge gap. "Our investigation on neuronal communication via the hippocampal trisynaptic circuit provides us with a new understanding of learning in the living organism. We are the first to show that long-term potentiation depends on the frequency and persistency of incoming sensory signals in the hippocampus," says Matthias Eder.

Explore further: A brain filter for clear information transmission

More information: Jens Stepan, Julien Dine, Thomas Fenzl, Stephanie A. Polta, Gregor von Wolff, Carsten T. Wotjak and Matthias Eder (2012) Entorhinal theta-frequency input to the dentate gyrus trisynaptically evokes hippocampal CA1 LTP, Frontiers in Neural Circuits, Volume 6, Article 64, 1-13.

Related Stories

A brain filter for clear information transmission

September 6, 2012
Every activity in the brain involves the transfer of signals between neurons. Frequently, as many as one thousand signals rain down on a single neuron simultaneously. To ensure that precise signals are delivered, the brain ...

The hippocampus as a decision-maker

July 19, 2012
(Medical Xpress) -- Synapses are modified through learning. Up until now, scientists believed that a particular form of synaptic plasticity in the brain’s hippocampus was responsible for learning spatial relations. This ...

Recommended for you

Brain activity buffers against worsening anxiety

November 17, 2017
Boosting activity in brain areas related to thinking and problem-solving may also buffer against worsening anxiety, suggests a new study by Duke University researchers.

Study may point to new treatment approach for ASD

November 17, 2017
Using sophisticated genome mining and gene manipulation techniques, researchers at Vanderbilt University Medical Center (VUMC) have solved a mystery that could lead to a new treatment approach for autism spectrum disorder ...

Neuroscience research provides evidence the brain is strobing, not constant

November 17, 2017
It's not just our eyes that play tricks on us, but our ears. That's the finding of a landmark Australian-Italian collaboration that provides new evidence that oscillations, or 'strobes', are a general feature of human perception.

Paraplegic rats walk and regain feeling after stem cell treatment

November 16, 2017
Engineered tissue containing human stem cells has allowed paraplegic rats to walk independently and regain sensory perception. The implanted rats also show some degree of healing in their spinal cords. The research, published ...

Neuroscientists find chronic stress skews decisions toward higher-risk options

November 16, 2017
Making decisions is not always easy, especially when choosing between two options that have both positive and negative elements, such as deciding between a job with a high salary but long hours, and a lower-paying job that ...

Brain implant tested in human patients found to improve memory recall

November 15, 2017
(Medical Xpress)—A team of researchers with the University of Southern California and the Wake Forest School of Medicine has conducted experiments involving implanting electrodes into the brains of human volunteers to see ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Mike_Massen
3 / 5 (2) Sep 26, 2012
Caffeine, a natural pesticide which is a stimulant for humans, aint nature interesting, thanks
A_Paradox
not rated yet Sep 27, 2012
Interesting indeed! Nicotine also. What occurs to me is that maybe the simple fact that in insect brains, just bundles of ganglia really and being very much smaller than mamalian brains, will still utilise occillations of circuits to stabilise useful patterns. That being so the small size means signals travel much less distance so the occillations are probably much higher frerquencies.

It may be that the extra stimulation provided by these neuron stimulating and/or neurotransmitter mimicing molecules simply overloads the insect brain circuitry.

Mind you the effect of pyrethrins and so forth in the concentrations of pressure can sprays gets to be rather permanent doesn't it. That would seem to point to action as a catalyst rather than just over-supply of a neurotransmitter.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.