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Tag: neuron

The biology of how the brain forgets

Our brain tends to forget things that we wish we would always remember. And yet, it cannot forget certain things we wish never occurred and existed. How does your brain forget? And, can your brain forget on purpose? By nature, the human brain forgets. Inopportunely, the biological mechanism underlying this brain process is poorly understood. Only few studies shed light on this aspect. In May 2012, scientists attempted to explain the molecular biology of active elimination of memories on their report. In September 2018, another team of researchers identified the parts of the brain associated with forgetting. Based on brain frequencies, they analyzed how the human brain voluntarily forgets.

 

 

 

Molecular biology of forgetting

In 2012, an independent research team from the Scripps Research Department of Neuroscience attempted to understand the molecular biology of active forgetting.1 To do so, they used fruit flies (Drosophila) as key model since this species is often used for studying memory. Accordingly, they found that a small subset of dopamine neurons regulated the acquisition as well as the forgetting of memories. In other words, they saw that the neurons that acquired memory on one hand also eliminated the memory on the other hand. Notably, they identified the two dopamine receptors involved, i.e. dDA1 and DAMB.

 

In this case, dopamine, a neurotransmitter, seemingly performs dual, yet opposing, roles. At first, the dopamine activates the dDA1 receptor of a neuron. In effect, the neuron begins forming memories. However, the same neuron sends out signal via another dopamine receptor, DAMB. As dopamine binds to the DAMB receptor, it activates the receptor. As a result, it triggers events that lead to the forgetting of the recently acquired memory (provided that the memory has not been consolidated yet). A process, called consolidation, protects important memories from being forgotten. In essence, while memory actively forms, a dopamine-based forgetting mechanism works as well. Unless the brain reckoned the memory as important, it erases the forming memory.

 

 

 

Forgetting on purpose

In September 2018, researchers from Ruhr-Universität Bochum and the University Hospital of Gießen and Marburg collaborated with researchers from Bonn, the Netherlands, and the UK.2  In brief, they identified the parts of the brain involved in the process of voluntary forgetting. In particular, these brain areas include the prefrontal cortex and the hippocampus, the brain region associated with memories.

 

In this recent study,  the researchers found that the prefrontal cortex regulates the activity in the hippocampus. One of the leaders of the team, Carina Oehrn, explicated that the prefrontal cortex suppressed hippocampus activity. Further, she noted that the frequency changed. Accordingly, the difference in frequency caused the currently processed information to cease from being encoded. They referred to this frequency as the forgetting frequency.2

 

 

 

Forgetting – crucial to health

biology of forgetting - post-traumatic stress disorder
A Marine attended art therapy to relieve post-traumatic stress disorder painted this mask. Credit: Work by Cpl. Andrew Johnston, and released by the United States Marine Corps.

 

As much as recalling is important, forgetting certain things is pivotal to mental and emotional well being. We inherently forget on purpose. Imagine remembering all – both good and bad. Not only we would have to deal with information overload but we would also be long exposed to feelings associated with those memories.

 

Post-traumatic stress disorder, regarded as a mental disorder, develops when a person has gone through a traumatic event. People with this condition face higher risks of inflicting self-harm, or worse, committing suicide.3 Hyperthymesia, a condition wherein an individual can extraordinarily recall much of one’s life in vivid and perfect detail, can be off-putting and distressing to the affected individual. Based on one such case, the patient recounted how the ability to remember constant, uncontrollable chain of memories could be exhausting and a burden.4

 

 

More research

The metaphorical inability to forget hinders a person to move on and focus on the tasks at hand. Traumatic events seem to be ingrained deeply in mind and soul. For instance, loss of a loved one, warfare, and sexual assaults prove to be difficult to ignore. Thus, we need more insights on the neuro- and molecular biology of forgetting. More studies could help shape up future therapeutic intervention. It may not necessarily lead to the absolute incapacity to recall. But, hopefully, it can help set aside spiteful memories. In that way, affected individuals could be freed from the traps of the past, and help them live life with a sanguine hope for a future.

 

 

 

— written by Maria Victoria Gonzaga

 

 

 

References:
1 Sauter, E. (2012, May 14). “Team Identifies Neurotransmitters that Lead to Forgetting”. The Scripps Research Institute. Retrieved from https://www.scripps.edu/newsandviews/e_20120514/davis.html
2 Ruhr-University Bochum. (2018, September 7). This is how the brain forgets on purpose: Two brain regions apparently play a pivotal role in forgetting. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2018/09/180907110501.htm
3 Bisson, JI; Cosgrove, S; Lewis, C; Robert, NP (2015, November 26). “Post-traumatic stress disorder”. BMJ (Clinical research ed.). 351: h6161. doi:10.1136/bmj.h6161. PMC 4663500
4 Parker ES, Cahill L, McGaugh JL (2006, February). “A case of unusual autobiographical remembering”. Neurocase. 12 (1): 35–49. doi:10.1080/13554790500473680.

Newly identified human brain neuron may have unique genetic signature

Dubbed as rosehip neuron, a new brain neuron recently discovered is unique based on its morphology and the set of genes it activates. Neuroscientists recently uncovered this new type of neuron from postmortem human brain samples. They presumed that this rosehip neuron occurs in the brain of humans but not in rodents.

 

Rosehip neurons found in human brains

What makes human brain special? What sets it apart from other animal brains? Humans have this sort of consciousness and intelligence that make them different from other species.  Apart from the complexity and the size of the human brain, its cellular components seem to be different from that of the other animals. Neuroscientists found rosehip neurons in human brain. These cells have not yet been observed in the brains of mice and other well-studied laboratory animals. Researchers reported this recent discovery in Nature Neuroscience.1 Nevertheless, they were fast to warn not to make haste assumptions. The rosehip neurons may not be unique to humans. More studies are on the way to confirm it.

 

What their findings implicate is the suitability of rodent brains as experimental models. Rodent brains lack such neurons. Thus, they may not be fit as laboratory models, especially when one tries to understand human neurologic diseases and how the brain works.

 

 

 

Current info on human rosehip neurons

rosehip neuron
A reconstruction of a newly discovered type of human neuron. Image credit: U.S. Army graphic (human brain) and Boldog, et al. & Nature Neuroscience (rosehip neuron)

 

Since rosehip neurons are a recent discovery, there is currently little information about them. What the neuroscientists know is they appear bushy. In fact, their bushy appearance accounts for their name “rosehip“. Rosehip originally refers to the accessory fruit of the rose plant. The rosehip neuron looks like the accessory fruit of the rose after petals are shed.

 

Researchers discovered the rosehip neurons from the top layer of the cortex of the brain from the postmortem brains of two men in their 50s. The rosehip neuron belongs to a group of inhibitory neurons. This means that it works by inhibiting other neuronal activity in the brain.

 

Researchers from the Allen Institute collaborated with the J. Craig Venter Institute. They found that the rosehip neurons seemed to have a different genetic signature. The rosehip neurons turned on a unique set of genes. They also formed synapses with pyramidal neurons. Pyramidal neurons are a different type of brain cells named after their shape.

 

 

Future research on rosehip neurons

Researchers have yet to fully recognize the purpose and importance of rosehip neurons in the human brain. In doing so, they may gain a significant insight regarding their role in neurologic function and diseases. They also aim to check the presence of rosehip neurons in other human brain parts as well as in the brains of other animals. Details on their recent work on rosehip neurons is published in Nature Neuroscience.2

 

 

 

written by Maria Victoria Gonzaga based on the news release and materials from the Allen Institute website

 

 

 

Reference:

1 Allen Institute. (27 Aug. 2018). Scientists identify a new kind of human brain cell. Retrieved from http://www.alleninstitute.org/what-we-do/brain-science/news-press/articles/scientists-identify-new-kind-human-brain-cell

2 Boldog, E. et al. (2018). Transcriptomic and morphophysiological evidence for a specialized human cortical GABAergic cell type. Nature Neuroscience. DOI: 10.1038/s41593-018-0205-2