For generations, scientists believed that nerve cells share information via a one-way street, where electrochemical signals flow from one neuron's axon to a receiving dendrite. However, recent breakthroughs suggest that there are instances where nerve cells send information in the wrong direction.
For the first time, scientists show that information flows in the opposite direction at the neural intersection known as synapses.
Peter Jonas, co-author, and neuroscientists from the Institute of Science and Technology, Austria says that the team observed that exact measurements prove that reality is much more complex than simplified models.
Understanding the Brain's Neural Network
According to the University of Queensland's Brain Institute, neurons are the brain's fundamental units responsible for receiving various sensory inputs from the external world and sending motor commands to the body's muscles, relaying electrical signals, and more.
There are about 100 billion neurons interacting closely with different cell types in the body.
The neuron has 3 main parts known as axon, soma, and dendrites. The dendrites are the receivers of the neurons. While the axon is the neuron's output structure and is used by the neuron when it wants to talk to another neuron by sending electrical messages known as action potential throughout the entirety of the axon.
Neural Messages Sent in the Wrong Direction
The study published in the journal Nature Communications, entitled "Transsynaptic modulation of presynaptic short-term plasticity in hippocampal mossy fiber synapses" explains that in the brain's hippocampus, the mossy fiber pathway in human brains involved in learning and memory. The network of neurons is key for storing short-term memory and spatial learning as seen in mice.
Naturally, networked cells within the rat's brains were used by IST neuroscientists like David Vandal and his colleagues to record the interactions between the mossy neurons in the hippocampus sending axons and receiving dendrites. The setup allowed researchers to simulate a single message for each cell to pass on.
As expected and predicted, mossy neurons influenced the signaling. However, they were stunned to observe that the reverse was true as well. Jonas explains that the pre-synaptic fibers detect when post-synaptic neurons are unable to take the information. When activities in the neurons increase the pre-synaptic neurons reduce their plasticity.
This proves that there is reverse-traveling of signals from the dendrites in a complex way that can modify the signal strength sent by the neuron's axons. This challenges long-standing assumptions about the process of the neural networks confirming that the firing of synapses depends on both pre and post-synaptic activity.
Jonas equates the scenario to a "smart teacher" who quickly adapts the lessons when students are bombarded and overloaded with information. On the other hand, researchers are unsure how pyramidal neurons send messages that they are overloaded to the pre-synaptic neuron or update the mossy neuron.
Researchers admit that there are many questions left unsolved such as whether or not glutamate is released from the neuron's dendrites to modify the axon's signals and why glutamates released by the signaling neurons have the same effect.
At this time, the research is a puzzle piece into the larger mystery that is the human brain.
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