This image shows a neuron in which the axon originates at a dendrite. Signals arriving at this dendrites become more efficiently forwarded than signals input elsewhere. Copyright: Alexei V. Egorov, 2014
The human brain is continually changing and evolving, and some believe it has even been steadily growing smaller since the stone age, while our intelligence has increased. With the rapidly advancing pace of science, our understanding of how the brain works is also evolving, and becoming more mysterious as we explore the frontiers of science and human consciousness.
A new, and unusual, type of neuron has been identified in the brain that appears to be more effective in transmitting information than a regular brain cell.
Neurons are nerve cells that rapidly transmit messages in the brain and throughout the human body by firing electrical signals between one another. These cells vary in size and shape, although they share similar characteristics in how they function. Each nerve cell has finger-like receivers called dendrites, messages are transmitted through the cell’s round body, and then a thin, long axon passes the message to another cell.
Now, researchers in Germany’s Heidelberg University have discovered a new type of neuron in the pyramidal cells of the hippocampus in brains of mice. In these new cells, the axon originates directly from a dendrite, bypassing the cell body. This structure allows for, what appears to be, an improved transmission of information when compared to a regular neuron.
“We found that in more than half of the cells, the axon does not emerge from the cell body, but arises from a lower dendrite,” Christian Thome of the Bernstein Center Heidelberg-Mannheim and Heidelberg University, one of the two first authors of the study.“Input signals at this dendrite do not need to be propagated across the cell body,” Thome explains.
The hippocampus is the region of the brain that is involved in the memory process and is known to be important for spatial navigation. This part of the brain has also been shown to consolidate information throughout the day and replay the same thought patterns at a quickened pace during sleep.
Once the researchers identified the new cell type, they studied the effects of signals received by the axon-carrying dendrites. For this, they injected a special neural transmitter substance glutamate into mice’s brain tissues. This messenger substance was activated using light pulses, which were beamed directly to specific dendrites and studied under a high-resolution microscope.
“Our measurements indicate that dendrites that are directly connected to the axon, actively propagate even small input stimuli and activate the neuron,” says second first author Tony Kelly, a member of the Sonderforschungsbereich (SFB) 1089 at the University of Bonn. A computer simulation of the scientists predicts that this effect is particularly pronounced when the information flow from other dendrites to the axon is suppressed by inhibitory input signals at the cell body. “That way, information transmitted by this special dendrite influences the behavior of the nerve cell more than input from any other dendrite,” Kelly says.
The next step for the research team is to identify which biological function is actually strengthened through this specific axon-carrying dendrite. The answers to this question will help us to further unravel the mysteries of the link between the human brain and human consciousness.
Click here to view a short video from the researchers explaining their research and discovery.
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