Focus on chemical processes at the synapses:New findings on the lifelong learning brain

Neuroscientists investigate plasticity in the hippocampus

As part of the DFG funded Collaborative Research Centre 874, neuroscientists are investigating the plasticity of the brain. Plasticity describes the ability of the brain to learn and adapt throughout a lifetime, depending on how it is used. On a cellular level this is called synaptic plasticity. The signal strength between two nerve cells increases, when these connections are used often and it decreases when they are used rarely. Scientists at the Ruhr University Bochum have used animal models to find out which chemical processes influence plasticity at certain synapses in the hippocampus. Their results are published in a special issue of “Neuroscience”.

Hippocampus has a high degree of plasticity

As a hub for learning and memory, the hippocampus, an area in the temporal lobe of the brain, has a high degree of plasticity. Therefore, this particular area of the brain is of much interest to neuroscientists. Like in a chain reaction, signals pass through the different areas of the hippocampus: from the so called entorhinal cortex (EC), via the dentate gyrus (DG) to the corno ammonis (CA) regions 1 and 3. Some stimuli also reach the CA1 region directly from EC. This second pathway is of interest to Dr. Ayla Aksoy-Aksel and Prof. Dr. Denise Manahan-Vaughan. They examined the synapses in this particular pathway. Synapses are the small gaps between two nerve cells. Using laboratory rats, they measured which factors lead to a long-term strengthening of transmission at the synapses – neuroscientists call this effect long-term potentiation (LTP).

Synapses exhibit distinct characteristics

A special procedure allowed the scientists to isolate the signals from EC-CA1 synapses, so that important insights into their signal transmission could be gained. Measurements show that the EC-CA1 synapses are quite distinct from others in the hippocampus. The induction threshold of LTP is much lower. Furthermore, the dependency on particular glutamate receptors and voltage-gated calcium channels is unique in the hippocampus. Both are important components in the transmission of stimuli from one nerve cell to the next.

Cellular chemistry indicates special role in information processing

The scientists assume that the EC-CA1 synapse’s particular chemical profile is associated with a special role in the processing of information, distinguishing it from other synapses in the hippocampus. It is possible that the low LTP threshold serves to create a carbon copy of information that is stored elsewhere in the hippocampus.